MC3 - Novel Particle Sources, Acceleration Techniques, and their Applications
SUP019
A W-band corrugated waveguide for high-efficiency high-gradient wakefield acceleration
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Compact RF structures in the sub-terahertz regime are promising for structure wakefield acceleration due to their ability in achieving high gradients in a reduced footprint. We report on the design, fabrication, and testing of a metallic corrugated waveguide operating at 110 GHz, tailored to the 42 MeV electron beam parameters at the Argonne Wakefield Accelerator (AWA). The experiment utilized the emittance exchange (EEX) beamline at AWA for longitudinal bunch shaping in two configurations: (1) a single short drive bunch to study high decelerating gradients, and (2) a two-bunch scheme featuring a triangularly shaped drive bunch followed by a long witness bunch to probe the wakefield and achieve a high transformer ratio. We will present the experimental design and results, which show good agreement with simulation predictions.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP008
About: Received: 07 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 13 Aug 2025 — Issue date: 28 Jan 2026
SUP020
Design and cold test of a novel waveguide power splitter for distributed power coupling in short-pulse acceleration
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RF breakdown is the major limitation to achieving higher accelerating gradients. Recent experimental evidence shows that this limitation can be mitigated by reducing the RF pulse length to a few nanoseconds. One key challenge in designing an accelerator operating in the short-pulse regime is achieving the required short filling time. In this work, we designed a novel waveguide power splitter to independently feed an array of accelerating cells. A prototype X-band waveguide array for a one-to-four power splitter has been developed to drive standing-wave cavities operating in the short-pulse regime. The power is designed to be equally split and fed into four cavities, with the desired phase advance per cavity. A 3D-printed prototype has been used for low-power microwave measurements ("cold" tests). The results, including measurements with a vector network analyzer and time-domain measurements, show good agreement with simulations. Ongoing work includes designing a multi-cell accelerator based on this concept for two-beam acceleration with few-nanosecond RF pulses.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP017
About: Received: 07 Aug 2025 — Revised: 11 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
SUP021
Design of an optical amplifier for amplified OSC in IOTA facility at Fermilab
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Optical stochastic cooling (OSC) is a cutting-edge beam cooling technology to reduce, control the 3 dimensional spread and the motion of particle beams. It has recently been successfully, experimentally, demonstrated in Fermilab's IOTA storage ring, marking a major step forward in beam cooling. OSC has the potential to significantly improve both the performance and flexibility as a beam cooling system. One promising way to boost OSC performance is by adding a high-gain optical amplifier. However, this amplifier must be carefully designed to meet the specific constraints of the OSC system. A major challenge lies in the limited optical delay, which is just 6 mm for the case of IOTA, set by the beam bypass, restricts us to use a short-length gain medium. This, along with IOTA’s high repetition rate and the relatively long duration of the optical pulses, limits the peak power available for the pump laser without damaging the crystal, which is crucial for achieving strong nonlinear gain. Additionally, it's essential to preserve the phase coherence of the undulator radiation during amplification, which further complicates the amplifier design. This report details a specialized amplifier setup that addresses these challenges, includes simulations of the integrated system, and summarizes the latest experimental progress and results.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP021
About: Received: 12 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
SUP022
Developments in Lume-ACE3P including S-parameter optimization for S3P
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We present here the introduction of optimization to LUME-ACE3P (LUME: Lightsource Unified Modeling Environment; ACE3P: Advanced Computational Electromagnetics 3D Parallel). LUME-ACE3P is a Python wrapper that streamlines workflows for ACE3P, a suite of finite element solvers for electromagnetic fields in complex geometries. LUME-ACE3P offers parameter sweep capabilities, which was previously the only means to perform optimization with this code. In the integration of LUME-ACE3P with the optimization package Xopt, we facilitate efficient and easy to use optimization for accelerator component design. We present the LUME-ACE3P-Xopt workflow with an example problem.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP029
About: Received: 07 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
SUP023
Flat beam PWFA theory and experiment at AWA
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A wakefield experiment at the Argonne Wakefield Accelerator (AWA) facility utilizes flat electron beams with highly asymmetric transverse emittances to drive plasma wakefields in the underdense regime. These beams create elliptical blowout structures, producing asymmetric transverse focusing forces. The experiment utilizes a compact 4-cm-long capillary discharge plasma source developed at UCLA. Analytic models of blowout ellipticity and matching conditions, supported by particle-in-cell simulations, guide the experiment's design. Engineering preparations including the use of windows for vacuum-gas separation, beam transport and diagnostics are discussed along with the first beam runs which involve flat beam generation and transport. The theory of flat beam plasma wakefield interaction will also be discussed
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUBN01
About: Received: 09 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
SUP024
Investigating Dirac semimetal cadmium arsenide as a potential low-MTE photocathode
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We report on the quantum efficiency (QE) and mean transverse energy (MTE) of photoemitted electrons from cadmium arsenide(Cd₃As₂), a three-dimensional Dirac semimetal (3D DSM) of interest for photocathode applications due to its unique electronic band structure, characterized by a 3D linear dispersion relation at the Fermi energy. Samples were synthesized at the National Renewable Energy Laboratory (NREL) and transferred under ultra-high vacuum to Arizona State University (ASU) for measurement using a photoemission electron microscope (PEEM). The maximum QE was measured to be 3.37 × 10⁻⁴ at 230 nm, and the minimum MTE was 55.8 meV at 250 nm. These findings represent the first reported QE and MTE measurements of Cd₃As₂ and are an important step in evaluating the viability of 3D DSMs as low-MTE photocathodes. Such photocathodes, constrained to lower MTEs by the electronic band structure, may prove effective in advancing beam brightness in next-generation instruments and techniques.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP047
About: Received: 01 Aug 2025 — Revised: 10 Aug 2025 — Accepted: 10 Aug 2025 — Issue date: 28 Jan 2026
SUP025
Investigation of wakefields in dielectric structures with different cross sections
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Dielectric-lined waveguides are a promising platform for high-gradient beam-driven dielectric wakefield acceleration (DWFA). We present experimental results from a recent study at the Argonne Wakefield Accelerator (AWA), focusing on the performance of three copper-coated dielectric structures with distinct cross-sections: circular, rectangular, and square. These geometries enable a comparative evaluation of the accelerating gradients and wakefield characteristics supported by each configuration. A key feature of this experiment is the use of a "loading bunch" to suppress the wakefield, demonstrating active control of energy transfer along the beam path. To directly measure wakefield suppression, a circular structure with an angled downstream cut was used to redirect coherent Cherenkov radiation into an autocorrelator for temporal diagnostics. Accelerating gradients were measured using a single-shot longitudinal phase space diagnostic, providing insight into geometry-dependent wakefield behavior. These results support future structure optimization efforts and advance experimental techniques for wakefield control in dielectric-based acceleration.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP049
About: Received: 15 Aug 2025 — Revised: 18 Aug 2025 — Accepted: 19 Aug 2025 — Issue date: 28 Jan 2026
Laser-ionized plasma sources for plasma wakefield accelerators: Alignment technique, tolerance, and applications
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Plasma wakefield accelerators (PWFA) are promising candidates for next-generation colliders due to their ability to sustain extremely high acceleration gradients. Laser-ionized plasma sources offer key advantages for PWFA, including precise control over the transverse and longitudinal plasma density profiles for emittance preservation, tunable plasma column widths suited for positron acceleration, and resilience to heat deposition. A critical experimental challenge, however, is the precise alignment of the plasma source to the electron beam and maintaining that alignment over time. We report on a novel alignment technique developed at the Facility for Advanced Accelerator Experimental Tests II (FACET-II), enabling high-precision alignment of a 1-meter-long laser-ionized plasma source to a 10 GeV, 1.6 nC electron beam with a transverse accuracy better than 10 µm, limited primarily by laser pointing jitter. We present our methodology, discuss the alignment tolerances between the drive beam and the laser-ionized plasma, and explore future opportunities for using narrow plasma columns for positron acceleration.
SUP027
Light-induced enhancement of quantum efficiency in III-nitride photocathodes
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High quantum efficiency (QE) semiconductor photocathodes are essential for generating high average beam current and brightness. One class of semiconductor photocathodes considered for use in photoinjectors for unpolarized and polarized electron beams are III-nitride heterostructures. These materials can exhibit negative electron affinity at the surface, utilizing intrinsic polarization fields to engineer the band structure without the need for additional surface treatments. In this study, we investigate the effects of light exposure on the surface of III-nitride photocathodes and the resulting changes in QE and photoemission, using photoemission electron microscopy (PEEM) for characterization. We demonstrate that exposing a GaN photocathode to a 240 nm wavelength laser at 870 µW for 15 minutes increases the QE by two orders of magnitude, with a maximum QE of 2.34 × 10⁻⁴ observed. Although III-nitride photocathodes are known for their robustness, our findings indicate that laser exposure can significantly alter their QE. Our observations reveal the need for a detailed investigation of photo-induced effects on QE in III-Nitride photocathodes."
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP055
About: Received: 08 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
SUP028
Passive plasma lens experiments at FACET-II
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The beam-driven, passive plasma lens can provide axisymmetric focusing with strengths orders of magnitude greater than conventional quadrupole magnets, while remaining ultra-compact. These characteristics make it attractive for beam matching into a plasma wakefield accelerator and for controlling beam divergence downstream of plasma stages. Optimal performance can be achieved in the underdense regime, resulting in a linear focusing force and emittance preservation of the focused beam. We report progress on experimental results from SLAC’s FACET-II facility, where we utilized a fs Ti:Sapphire laser pulse to ionize hydrogen gas from a supersonic gas jet to focus several hundred pCs of charge of a 10 GeV electron beam.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP064
About: Received: 11 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
SUP029
Picometer-scale emittance and space charge effects in nanostructured photocathodes.
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Generation of ultralow-emittance electron beams with high brightness is critical for several applications such as ultrafast electron diffraction, microscopy, and advanced accelerator techniques. By leveraging the differences in work function and electronic structure between different materials, we enabled spatially localized photoemission, resulting in picometer-scale emittance from a flat photocathode. We also investigated space charge effects by measuring how the emission spot size, as measured in a photoemission electron microscope, changes with the number of electrons emitted per laser pulse. When more than one electron is emitted simultaneously, Coulomb repulsion causes a substantial broadening of the observed source size, enabling us to investigate the limitations imposed by vacuum space charge forces during pulsed photoemission. Our results highlight the potential of nanoscale photoemitters as high-brightness electron sources and offer new insights into electron correlations that emerge after ultrafast photoemission.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUBN03
About: Received: 03 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
SUP030
Preliminary computational study on minimizing longitudinal emittance in photoinjector
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Recently, we proposed a novel photoinjector that incorporates an emittance exchange (EEX) beamline. Previous studies demonstrated promising 4D emittance performance of an EEX-based injector, but the beam’s longitudinal emittance at the linac exit still limits the final transverse emittance downstream of the EEX stage. We performed a comprehensive scan of injector parameters—including gun phase, laser spot size and pulse length, and solenoid strengths—to (1) estimate the minimum achievable longitudinal emittance, (2) identify sources of emittance growth, and (3) explore mitigation strategies. Here, we present the status of this study. Simulations were carried out using General Particle Tracer (GPT) including space-charge effects.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP069
About: Received: 08 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
SUP031
RF breakdown and dark current studies in short-pulse acceleration
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Recent experimental studies at the Argonne Wakefield Accelerator (AWA) have shown that operating RF cavities with short pulses, only a few nanoseconds in duration, can raise the accelerating gradient to nearly 400 MV/m in a series of X-band structure tests. These results motivate further investigation into the breakdown physics underlying the short-pulse acceleration regime. In this work, we present analytical models and numerical simulations of dark current dynamics in X-band cavities driven by short RF pulses. These studies explore key phenomena associated with RF breakdown across various time scales, including field emission, secondary electron emission, and plasma formation, with particular focus on their dependence on RF pulse length. Building on these insights, we describe the design and experimental plan for a single-cell X-band RF cavity operating at 11.7 GHz, optimized for high-gradient operation with 6~ns long RF pulses and integrated with RF breakdown diagnostics. This work aims to deepen the understanding of RF breakdown physics in the short-pulse regime and support the development of compact linear accelerators for future applications.
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP079
About: Received: 08 Aug 2025 — Revised: 10 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
THz detection and investigation of vacuum-compatible optical components
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Detecting terahertz (THz) radiation in ultra-high vacuum (UHV) environments presents notable challenges due to the limited availability of commercially compatible components. In preparation for upcoming THz measurements at the Argonne Wakefield Accelerator (AWA) facility, we investigated two critical aspects: (1) the THz transmission characteristics of fused silica windows, and (2) the suitability of commercial off-axis parabolic mirrors (OAPs) for use in UHV conditions. While fused silica is widely used in optical systems, its performance in the THz regime is rarely documented. We present transmission measurements and assess its viability for THz diagnostics. Additionally, we address the incompatibility of anodized, off-the-shelf OAPs with UHV by developing and testing both mechanical and chemical de-anodization techniques. These methods aim to maintain surface integrity and optical quality. This work provides practical guidelines and compatibility benchmarks for implementing THz diagnostics in UHV environments and serves as a reference for future experiments at AWA and other accelerator facilities.
MOZN01
Exploration of ultra-high dose rate radiobiology with laser-driven protons at BELLA
30
Laser-driven (LD) proton sources are of interest for various applications due to their ability to produce short proton bunches with high charge and low emittance. These sources can be used in biological studies investigating improvements to radiation cancer therapy. Recently, the differential sparing effect on normal tissues versus tumors using the delivery of high radiation doses >10 Gy at extremely high dose rates (DR), called FLASH effect, has received increasing attention. However, the molecular and cellular mechanisms underlying the sparing effect are not yet fully understood. To explore these mechanisms, we have implemented a beamline at the BELLA PW that delivers LD proton bunches at ultra-high instantaneous DR (UHIDR) up to 10^8 Gy/s. This allowed us to investigate in vivo the acute skin damage and late radiation-induced fibrosis in mouse ears after UHIDR with 10 MeV LD protons and prescribed doses of several 10 Gy. We observe sparing of healthy mouse ear tissue after irradiations with LD proton bunches at UHIDR compared to irradiations with 300 kV x-rays at clinical dose rates and similar total dose. Recent improvements to the LD proton source, delivery beamline, and diagnostic suite have also enabled first peptide sample irradiations to explore the sparing effect on the molecular level. This talk will provide a summary of radiobiology research activities at the BELLA PW.
Paper: MOZN01
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-MOZN01
About: Received: 07 Aug 2025 — Revised: 10 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
Bright bunch generation in a short pulse high gradient RF gun operating in the transient regime
Normal-conducting accelerating structures capable of supporting GV/m-scale electric fields offer a promising pathway to compact accelerators. Similarly, achieving such high fields in photocathode guns is critical for the generation of bright electron bunches. Our group has demonstrated the generation of ~0.4 GV/m electric fields on a photocathode surface in an X-band (11.7 GHz) photoemission gun (Xgun) powered by short RF pulses (~9 ns). In this work, we investigate the RF characteristics and beam dynamics evolution in the transient field regime. Accurately accounting for the transient nature of the RF field is essential for optimizing the beam dynamics and ensuring the production of high-quality electron bunches.
Testing photocathodes in extreme conditions
Photocathodes are the electron sources of choice for accelerator applications that rely on bright and ultrashort electron bunches, including next-generation light sources and electron microscopes. These applications benefit significantly from photocathodes with low mean transverse energy (MTE), which directly contributes to higher beam brightness and better transverse coherence. However, the need for high charge densities, combined with the disordered structure of many photocathode materials, surface roughness, and spatial work function variations, limits the achievable MTE from conventional photocathodes to several hundred meV, which is nearly two orders of magnitude above the theoretical minimum. Additionally, most commonly used photocathodes degrade under high electric fields or intense laser fluences, posing challenges for reliable operation in advanced accelerator environments. Robust photocathodes capable of sustaining these extreme conditions while delivering bright electron beams with significantly reduced MTE are thus critical for enabling next-generation accelerator performance. In this talk, we will highlight recent advances in photocathode development and testing under extreme conditions, including high fields and cryogenic temperatures, conducted by the Center for Bright Beams (CBB, https://cbb.cornell.edu) and beyond toward brighter, more resilient electron sources.
Design of plasma-based colliders
This presentation covers the design of plasma and wakefield-based particle colliders. It will briefly review the development of wakefield collider concepts over the past decades and then focus on the HALHF Higgs Factory and 10 TeV pCM Wakefield Collider design studies, discuss commonalities between these efforts and highlight their unique aspects.
TUBN01
Flat beam PWFA theory and experiment at AWA
314
A wakefield experiment at the Argonne Wakefield Accelerator (AWA) facility utilizes flat electron beams with highly asymmetric transverse emittances to drive plasma wakefields in the underdense regime. These beams create elliptical blowout structures, producing asymmetric transverse focusing forces. The experiment utilizes a compact 4-cm-long capillary discharge plasma source developed at UCLA. Analytic models of blowout ellipticity and matching conditions, supported by particle-in-cell simulations, guide the experiment's design. Engineering preparations including the use of windows for vacuum-gas separation, beam transport and diagnostics are discussed along with the first beam runs which involve flat beam generation and transport. The theory of flat beam plasma wakefield interaction will also be discussed
Paper: TUBN01
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUBN01
About: Received: 09 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
Advanced THz deflectors for attosecond MeV-UED timing
Timestamping electron pulses is a promising strategy for improving the overall temporal resolution of the MeV UED beamline. Timestamping can be achieved with a time-varying deflection of the beam: the deflection angle records the time of arrival of the pulse, from which it is possible to accurately read back the pump-probe delay shot-by-shot. This proposal targets the demonstration of ultrastrong deflection from an optimized, precision machined copper horn structure excited by a tilted pulse front THz source. The tapered horn structure provides an extremely high deflecting field. We show results of a recent experiment aims to go beyond earlier successful proof-of-concept results by determining optimal design parameters for UED. One important parameter is the diameter of the exit aperture in the horn (through which the electron beam must pass before being collected on the detector). The choice of aperture diameter involves a trade-off between (a) field enhancement from a small aperture diameter, delivering a larger kick for a given THz pulse energy, and (b) higher electron beam transmission from a larger aperture, providing better statistics for measuring the beam centroid and finer substructure.
TUBN03
Picometer-scale emittance and space charge effects in nanostructured photocathodes
317
Generation of ultralow-emittance electron beams with high brightness is critical for several applications such as ultrafast electron diffraction, microscopy, and advanced accelerator techniques. By leveraging the differences in work function and electronic structure between different materials, we enabled spatially localized photoemission, resulting in picometer-scale emittance from a flat photocathode. We also investigated space charge effects by measuring how the emission spot size, as measured in a photoemission electron microscope, changes with the number of electrons emitted per laser pulse. When more than one electron is emitted simultaneously, Coulomb repulsion causes a substantial broadening of the observed source size, enabling us to investigate the limitations imposed by vacuum space charge forces during pulsed photoemission. Our results highlight the potential of nanoscale photoemitters as high-brightness electron sources and offer new insights into electron correlations that emerge after ultrafast photoemission.
Paper: TUBN03
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-TUBN03
About: Received: 03 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
WEP008
A W-band corrugated waveguide for high-efficiency high-gradient wakefield acceleration
701
Compact RF structures in the sub-terahertz regime are promising for structure wakefield acceleration due to their ability in achieving high gradients in a reduced footprint. We report on the design, fabrication, and testing of a metallic corrugated waveguide operating at 110 GHz, tailored to the 42 MeV electron beam parameters at the Argonne Wakefield Accelerator (AWA). The experiment utilized the emittance exchange (EEX) beamline at AWA for longitudinal bunch shaping in two configurations: (1) a single short drive bunch to study high decelerating gradients, and (2) a two-bunch scheme featuring a triangularly shaped drive bunch followed by a long witness bunch to probe the wakefield and achieve a high transformer ratio. We will present the experimental design and results, which show good agreement with simulation predictions.
Paper: WEP008
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP008
About: Received: 07 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 13 Aug 2025 — Issue date: 28 Jan 2026
Collider-quality electron bunches from an all-optical plasma photoinjector
In recent years, plasma accelerators have advanced significantly toward producing beams suitable for colliders, aiming to replace conventional MV/m RF fields with GV/m fields of nonlinear plasma waves. Realizing a plasma-based collider requires electron bunches with high charge (hundreds of pC), low normalized emittance (~100 nm), and energy spread below 1%. Minimizing energy spread during acceleration involves flattening the accelerating field, which is achievable with a trapezoidal charge distribution. We present a plasma photoinjector concept that enables collider-quality electron bunch generation using two-color ionization injection. The spatiotemporal control over the ionizing laser creates a moving ionization front inside a nonlinear plasma wave, generating an electron bunch with a current profile that flattens the accelerating field. Particle-in-cell (PIC) simulations of the ionization stage show the formation of an electron bunch with 220 pC charge and low emittance (ϵ_x = 171 nm-rad, ϵ_y = 76 nm-rad). Quasistatic PIC simulations of the acceleration stage show that this bunch is efficiently accelerated to 20 GeV over 2-meters with an energy spread below 1% and emittances of ϵ_x = 177 nm-rad and ϵ_y = 82 nm-rad. This high-quality electron bunch meets Snowmass collider requirements and establishes the feasibility of plasma photoinjectors for future collider applications.
WEP013
Compact electron buncher with tunable permanent magnet focusing
709
We present a compact electron buncher that uses a permanent magnet setup for beam focusing. The buncher modulates the input direct-current beam into 5.7-GHz bunch train. The buncher consists of two radiofrequency (RF) cavities. Immediately downstream of each RF cavity, there is an electrostatic potential depression (EPD) section. An EPD section in an electrically insulated beam pipe biased with a negative high voltage. The EPD method remarkably shortens the buncher structure by rapidly forming the bunch train. Each of the RF cavities and the EPD sections uses an individual set of rectangular permanent magnets, arranged in a circular array, which provide a solenoid-like focusing field. The polarity of the magnets is configured to form an alternating on-axis magnetic field orientation for minimizing the total weight. Coarse adjustment of the magnetic field is achieved by adding or removing permanent magnet rectangles. For fine adjustments, the rectangles are moved evenly in the radial direction. We show simulation results of the buncher performance and the tunable magnetic focusing. Initial experimental results are also reported.
Paper: WEP013
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP013
About: Received: 09 Aug 2025 — Revised: 11 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
WEP016
Demonstration of a sheet electron beam production from a UNCD field emitter array
719
Ultra nanocrystalline diamond (UNCD) is a promising material for field emitters because of its mechanical and chemical stability, high thermal conductivity, and low electrical resistivity. We proposed to demonstrate fabrication of a special shape field emitter array to produce a sheet electron beam for high frequency vacuum tubes. At Los Alamos, we established a Field Emitter Array Test Stand (FEATS) where we can apply voltages up to 40 kV to test field emitter arrays in a vacuum level of 10^-7 Torr or lower. At this test stand, we can take beam images, measure beam current and study beam divergence. We fabricated diamond cathodes in form of arrays of 1 by 81 pyramids and used them to demonstrate production of a sheet electron beam. This talk will present details of the emission tests and analyses of the produced sheet beam.
Paper: WEP016
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP016
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 13 Aug 2025 — Issue date: 28 Jan 2026
WEP017
Design and cold test of a novel waveguide power splitter for distributed power coupling in short-pulse acceleration
722
RF breakdown is the major limitation to achieving higher accelerating gradients. Recent experimental evidence shows that this limitation can be mitigated by reducing the RF pulse length to a few nanoseconds. One key challenge in designing an accelerator operating in the short-pulse regime is achieving the required short filling time. In this work, we designed a novel waveguide power splitter to independently feed an array of accelerating cells. A prototype X-band waveguide array for a one-to-four power splitter has been developed to drive standing-wave cavities operating in the short-pulse regime. The power is designed to be equally split and fed into four cavities, with the desired phase advance per cavity. A 3D-printed prototype has been used for low-power microwave measurements ("cold" tests). The results, including measurements with a vector network analyzer and time-domain measurements, show good agreement with simulations. Ongoing work includes designing a multi-cell accelerator based on this concept for two-beam acceleration with few-nanosecond RF pulses.
Paper: WEP017
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP017
About: Received: 07 Aug 2025 — Revised: 11 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
Design guidelines and longitudinal dynamics for plasma-based, extreme compression
High-brightness, ultra-high peak current electron beams are of great interest for a range of applications, including high-energy colliders, strong field quantum electrodynamics, and laboratory astrophysics. However, the task of compressing electron beams to attosecond pulse durations and mega-amp peak currents while maintaining beam quality continues to pose a significant challenge. We explore, with start-to-end simulations, the feasibility of using plasma-based compression to generate ultra-short, high-peak current electron beams. By taking advantage of the large longitudinal electric fields present in a plasma wakefield, we demonstrate that large chirps can be imparted onto an electron beam, allowing it to be compressed to ultrashort durations in a magnetic chicane. We investigate the viability and limitations of this technique, and establish how the compressed beam properties depend on both accelerator and plasma parameters. Using these relationships, we find the optimal beam and plasma conditions for different applications, looking towards demonstrating plasma-based compression at the FACET-II facility at SLAC National Accelerator Laboratory.
Design of a high-power X-band load with circular waveguide TE01 mode input
RF loads are critical components in any high-power rf system. There are two types of commonly used rf loads in multi-megawatt systems: water loads and dry loads. Water loads have a ceramic window separating vacuum from the water. Use of water loads in large scale rf systems is risky because of the possibility of water leaking into vacuum. At SLAC multi-megawatt dry loads were developed and used in S-band and X-Band applications. For example, a compact X-band load based on a tapered WR90 and circularly polarized TE11 mode has been in use for decades. To increase high power performance of a load beyond the state-of-the art, we designed an 11.424 GHz load fed by the TE01 circular waveguide mode. The load is of disk-loaded-waveguide type, built out of a set of cells. The cells are made of magnetic stainless-steel with bulk conductivity is 160000 S/m. The passband of the load is about 180 MHz. The load utilizes axially symmetric TE mode which has minimal surface electric fields. We show the design of the load and results of X-band resonant measurements of the load’s cells. The measurements allow us to determine conductivity of the 430 stainless steels after multiple brazing cycles.
WEP021
Design of an optical amplifier for amplified OSC in IOTA facility at Fermilab
729
Optical stochastic cooling (OSC) is a cutting-edge beam cooling technology to reduce, control the 3 dimensional spread and the motion of particle beams. It has recently been successfully, experimentally, demonstrated in Fermilab's IOTA storage ring, marking a major step forward in beam cooling. OSC has the potential to significantly improve both the performance and flexibility as a beam cooling system. One promising way to boost OSC performance is by adding a high-gain optical amplifier. However, this amplifier must be carefully designed to meet the specific constraints of the OSC system. A major challenge lies in the limited optical delay, which is just 6 mm for the case of IOTA, set by the beam bypass, restricts us to use a short-length gain medium. This, along with IOTA’s high repetition rate and the relatively long duration of the optical pulses, limits the peak power available for the pump laser without damaging the crystal, which is crucial for achieving strong nonlinear gain. Additionally, it's essential to preserve the phase coherence of the undulator radiation during amplification, which further complicates the amplifier design. This report details a specialized amplifier setup that addresses these challenges, includes simulations of the integrated system, and summarizes the latest experimental progress and results.
Paper: WEP021
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP021
About: Received: 12 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
WEP024
Design study of novel deuteron cyclotron auto-resonance accelerator
741
A novel deuteron cyclotron auto-resonance accelerator (dCARA) is described here. It is predicted to produce a 40-MeV, 125 mA CW deuteron beam, with notable features including continuous acceleration without bunching for good beam stability, high efficiency, wide beam aperture, and an exceptionally short length of 1.6 meters. Such an accelerated beam can be used to produce the intense neutron flux via breakup of deuterons on a low-Z target. It is estimated that 5-10 small dCARA-based modules could provide the same level of transmutation as one acceleration driven system (ADS) employing a GeV-level 25-MW linac. Other applications of dCARA include medical isotope production system, or fusion prototypic neutron source for testing inner-wall materials for a future fusion power reactor.
Paper: WEP024
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP024
About: Received: 08 Aug 2025 — Revised: 15 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
Developing a hybrid accelerating structure based on short-pulse Structure Wakefield Acceleration
Structure Wakefield Acceleration (SWFA) powered by -short RF pulses (~10 ns) generated by Two-Beam Acceleration (TBA) at the Argonne Wakefield Accelerator (AWA) has demonstrated effective suppression of RF breakdowns and achieved gradients exceeding 400 MV/m at X-band (11.7 GHz) frequencies. To fully exploit the benefits of this short RF pulse operation, an accelerating structure must simultaneously achieve two goals: high group velocity (Vg) to ensure rapid RF filling (need for high efficiency), and simultaneously maintain high shunt impedance (R) (need for high accelerating gradient). Conventional accelerating structures involve inherent tradeoffs between these parameters, limiting their effectiveness in the short-pulse regime. To this end, we developed a hybrid structure composed of two co-optimized sub-structures fed by one coupler at the middle: one backward wave (BW) filling and one forward wave (FW) filling sub-sections.This design not only preserves the short-pulse advantage, it also simplifies the setup (one input coupler for two structures) and enhances the beam’s energy gain by doubling the acceleration length without requiring extended RF pulse duration. In this work, we present the detailed RF design with preliminary beam dynamics simulations demonstrating efficient energy gain within a compact acceleration length.
WEP029
Developments in LUME-ACE3P including S-parameter optimization for S3P
748
We present here the introduction of optimization to LUME-ACE3P (LUME: Lightsource Unified Modeling Environment; ACE3P: Advanced Computational Electromagnetics 3D Parallel). LUME-ACE3P is a Python wrapper that streamlines workflows for ACE3P, a suite of finite element solvers for electromagnetic fields in complex geometries. LUME-ACE3P offers parameter sweep capabilities, which was previously the only means to perform optimization with this code. In the integration of LUME-ACE3P with the optimization package Xopt, we facilitate efficient and easy to use optimization for accelerator component design. We present the LUME-ACE3P-Xopt workflow with an example problem.
Paper: WEP029
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP029
About: Received: 07 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
Experimental generation of petawatt peak power, extreme electron beams for advanced accelerator applications
In this contribution we report on the experimental generation of high energy (10 GeV), ultra-short (fs-duration), ultra-high current (∼ 0.1 MA), petawatt peak power electron beams at the FACET-II National User Facility at SLAC National Accelerator Laboratory. These extreme beams enable the exploration of a new frontier of high intensity beam-light and beam-matter interactions broadly relevant across fields ranging from high-field plasma wakefield acceleration to laboratory astrophysics and strong field quantum electrodynamics. We demonstrate our ability to generate and control the properties of these electron beams by means of a laser-electron beam shaping technique. This experimental demonstration opens the door to on-the-fly customization of extreme beam current profiles for desired experiments and is poised to benefit a broad swathe of cross-cutting applications of relativistic electron beams including optimization of advanced accelerator applications.
Experimental progress of PWFA in a laser-ionized plasma source FACET-II
To compete with conventional accelerators, collider and light source applications based on plasma wakefield acceleration need to be able to handle 10s of Joules of energy transfer between the drive beam, plasma, and witness beam at repetition rates exceeding 100 Hz. Scaling up to these parameters is challenging due to the large amount of heat deposited in the plasma source. To begin approaching this regime, we developed a laser ionized plasma source using a pair of diffractive optics to produce a meter-scale Bessel focus with a tailored axial intensity profile. Using this source, we demonstrate multi-Joule energy transfer in the plasma accelerator at SLAC’s FACET-II facility with strong deceleration of the drive bunch and acceleration of a witness bunch.
Fast and efficient modeling of structure-based wakefield accelerators
Structure-based wakefield accelerators (SWFA) have been identified as a candidate technology for future applications ranging from free electron lasers to colliders. However, achieving the desired beam energy and quality requires meter-scale structures with tight tolerances, placing constraints on structure and beam characteristics to minimize emittance growth and combat transverse instabilities. High fidelity and self-consistent simulations over these lengths necessitate enormous computational resources, making parametric studies of novel structures or instability-mitigation schemes unfeasible with standard practices. We present a technique for decomposing high dimensional wakefield systems into a set of lower dimensional components, capable of accurately reconstructing the structure response in a fraction of the time. We discuss the approach and implementation of this technique using Green’s Functions for common structure geometries. We demonstrate the potential for significant reduction in computation times and memory footprint using such representations. Finally, we discuss the application of machine learning in generating these representations for novel structure geometries.
WEP042
Heavy ion implantation analysis in graphite for the FRIB charge selector
769
An advanced charge selector is currently under development at the Facility for Rare Isotope Beams (FRIB) to intercept unwanted charge states of stripped heavy ion beams. Rotating graphite wheels are employed to absorb beams with a power up to 5 kW and a size as small as an rms width of 0.7 mm × 1.25 mm. The implantation of beam ions and accumulated radiation damage affect the material properties, potentially leading to its structural failure. Determining the foreign ion accumulation behavior is one critical aspect for predicting the operational lifetime of the graphite wheels. In this study, ion implantation distribution was first characterized using SRIM simulations, then coupled with Monte Carlo analysis to account for wheel geometry and rotational dynamics. The evolution of the ion concentration profiles was subsequently determined considering the diffusion effects. The analysis reveals that strategic beam positioning optimization, combined with diffusion effects, substantially reduces peak ion concentrations and implantation rates, providing essential data for graphite wheel lifetime assessment.
Paper: WEP042
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP042
About: Received: 10 Aug 2025 — Revised: 13 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
WEP047
Investigating Dirac semimetal cadmium arsenide as a potential low-MTE photocathode
773
We report on the quantum efficiency (QE) and mean transverse energy (MTE) of photoemitted electrons from cadmium arsenide (Cd₃As₂), a three-dimensional Dirac semimetal (3D DSM) of interest for photocathode applications due to its unique electronic band structure, characterized by a 3D linear dispersion relation at the Fermi energy. Samples were synthesized at the National Renewable Energy Laboratory (NREL) and transferred under ultra-high vacuum to Arizona State University (ASU) for measurement using a photoemission electron microscope (PEEM). The maximum QE was measured to be 3.37 × 10⁻⁴ at 230 nm, and the minimum MTE was 55.8 meV at 250 nm. These findings represent the first reported QE and MTE measurements of Cd₃As₂ and are an important step in evaluating the viability of 3D DSMs as low-MTE photocathodes. Such photocathodes, constrained to lower MTEs by the electronic band structure, may prove effective in advancing beam brightness in next-generation instruments and techniques.
Paper: WEP047
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP047
About: Received: 01 Aug 2025 — Revised: 10 Aug 2025 — Accepted: 10 Aug 2025 — Issue date: 28 Jan 2026
Investigation of transverse instability in efficient plasma-based accelerators
Plasma-based accelerators offer a promising route to compact high-energy particle sources. However, recent theoretical work* has suggested that accelerating a low-energy-spread electron beam may not be feasible at high efficiency because of the excitation of transverse beam break up (BBU) instability. This instability, which leads to a growing spatio-temporal oscillations of the beam centroid, is a consequence of a significant misalignment or loss of symmetry between the beam and the accelerating structure (ion cavity) and arises because of the coupling between the accelerating beam electrons and the plasma sheath electrons surrounding the ion cavity. The instability deteriorates the electron beam parameters (notably, the beam emittance) and hinders the usefulness of the plasma-based accelerators for some potential applications like, particle colliders. Here, using particle-in-cell simulations and analytical modelling, we evaluate the centroid evolution of a partially misaligned trailing electron bunch coupled with a plasma accelerator and provide novel solutions for its suppression. We also present preparation status of an experiment designed to characterize the transverse instability on a well-defined externally injected electron beam from a conventional linac in a CO2 pulse driven LWFA at Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL).
WEP049
Progress report on two-bunch excitation of wakefield in dielectric structures
777
Wakefield accelerators have the potential to achieve accelerating fields in the GV/m range, offering a promising path to more compact and cost-effective acceleration compared to conventional methods. Structure-based wakefield accelerator (SWFA) technology provides a viable approach to implementing beam-driven wakefield acceleration. An experiment at the Argonne Wakefield Accelerator (AWA) will utilize dielectric-lined structures to explore multi-beam excitation of wakefields for wakefield-pulse shortening and mapping of the transverse wakefield topology. These structures were commercially sourced and require a thin metallic film deposited on their outer surface. The first part of this paper summarizes the preparation of these structures. In parallel, a two-bunch beam configuration is required to support the experimental investigation, where one bunch excites the wakefield and the second serves as a loading or probe bunch. The experimental generation and testing of this two-bunch scheme at AWA are presented in this work.
Paper: WEP049
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP049
About: Received: 15 Aug 2025 — Revised: 18 Aug 2025 — Accepted: 19 Aug 2025 — Issue date: 28 Jan 2026
Laser-ionized plasma sources for plasma wakefield accelerators: Alignment technique, tolerance, and applications
Plasma wakefield accelerators (PWFA) are promising candidates for next-generation colliders due to their ability to sustain extremely high acceleration gradients. Laser-ionized plasma sources offer key advantages for PWFA, including precise control over the transverse and longitudinal plasma density profiles for emittance preservation, tunable plasma column widths suited for positron acceleration, and resilience to heat deposition. A critical experimental challenge, however, is the precise alignment of the plasma source to the electron beam and maintaining that alignment over time. We report on a novel alignment technique developed at the Facility for Advanced Accelerator Experimental Tests II (FACET-II), enabling high-precision alignment of a 1-meter-long laser-ionized plasma source to a 10 GeV, 1.6 nC electron beam with a transverse accuracy better than 10 µm, limited primarily by laser pointing jitter. We present our methodology, discuss the alignment tolerances between the drive beam and the laser-ionized plasma, and explore future opportunities for using narrow plasma columns for positron acceleration.
Latest progress on Plasma Wakefield Acceleration at FACET-II
Plasma Wakefield Acceleration (PWFA) can provide 10’s of GeV/m acceleration gradients, providing a novel path towards efficient and compact future colliders and high brightness free electron lasers. At the Facility for Advanced Accelerator Experimental Tests II (FACET-II) at SLAC, we are undertaking experiments in PWFA using a 10 GeV electron beam configured as a drive and witness pair. We will share our progress towards the ultimate goal of doubling the energy of the 10 GeV witness bunch by PWFA, with high efficiency and while preserving beam quality. Our latest results demonstrate multi-GeV acceleration of the witness bunch, with energy gains exceeding 5 GeV and sub-percent energy spread, using a 40 cm long lithium vapor plasma source. Additionally, we have achieved near-complete charge capture of the witness bunch and are actively working to minimize emittance growth through careful control of the transverse properties of the bunches.
WEP055
Light-induced enhancement of quantum efficiency in III-nitride photocathodes
786
High quantum efficiency (QE) semiconductor photocathodes are essential for generating high average beam current and brightness. One class of semiconductor photocathodes considered for use in photoinjectors for unpolarized and polarized electron beams are III-nitride heterostructures. These materials can exhibit negative electron affinity at the surface, utilizing intrinsic polarization fields to engineer the band structure without the need for additional surface treatments. In this study, we investigate the effects of light exposure on the surface of III-nitride photocathodes and the resulting changes in QE and photoemission, using photoemission electron microscopy (PEEM) for characterization. We demonstrate that exposing a GaN photocathode to a 240 nm wavelength laser at 870 µW for 15 minutes increases the QE by two orders of magnitude, with a maximum QE of 2.34 × 10⁻⁴ observed. Although III-nitride photocathodes are known for their robustness, our findings indicate that laser exposure can significantly alter their QE. Our observations reveal the need for a detailed investigation of photo-induced effects on QE in III-Nitride photocathodes.
Paper: WEP055
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP055
About: Received: 08 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
Modeling of plasma channels for laser plasma accelerators
Structured plasma channels are an essential technology for driving high-gradient, plasma-based acceleration and control of electron and positron beams for advanced concepts accelerators. Laser and gas technologies can permit the generation of long plasma columns known as hydrodynamic, optically-field-ionized (HOFI) channels, which feature low on-axis densities and steep walls. By carefully selecting the background gas and laser properties, one can generate narrow, tunable plasma channels for guiding high intensity laser pulses. We present on the development of 1D and 2D simulations of HOFI channels using the FLASH code, a publicly available radiation hydrodynamics code. We explore sensitivities of the channel evolution to laser profile, intensity, and background gas conditions. We examine experimental measurements of plasma channels and their comparison to model predictions. Lastly, we discuss ongoing work to couple these tools to community PIC models to capture variations in initial conditions and channel influence on wakefield accelerator applications.
Overview of the FACET-II facility at SLAC
FACET-II is a National User Facility offering unique capabilities for the advancement of accelerator science. Utilizing high-energy electron beams, it enables state-of-the-art research in advanced acceleration methods, ultra-high-brightness beam generation, and novel radiation sources. Here, we provide an overview of the FACET-II facility and highlight its experimental infrastructure, which is accessible to the scientific community through a competitive user program.
WEP064
Passive plasma lens experiments at FACET-II
808
The beam-driven, passive plasma lens can provide axisymmetric focusing with strengths orders of magnitude greater than conventional quadrupole magnets, while remaining ultra-compact. These characteristics make it attractive for beam matching into a plasma wakefield accelerator and for controlling beam divergence downstream of plasma stages. Optimal performance can be achieved in the underdense regime, resulting in a linear focusing force and emittance preservation of the focused beam. We report progress on experimental results from SLAC’s FACET-II facility, where we utilized a fs Ti:Sapphire laser pulse to ionize hydrogen gas from a supersonic gas jet to focus several hundred pCs of charge of a 10 GeV electron beam.
Paper: WEP064
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP064
About: Received: 11 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
WEP069
Preliminary computational study on minimizing longitudinal emittance in photoinjector
824
Recently, we proposed a novel photoinjector that incorporates an emittance exchange (EEX) beamline. Previous studies demonstrated promising 4D emittance performance of an EEX-based injector, but the beam’s longitudinal emittance at the linac exit still limits the final transverse emittance downstream of the EEX stage. We performed a comprehensive scan of injector parameters—including gun phase, laser spot size and pulse length, and solenoid strengths—to (1) estimate the minimum achievable longitudinal emittance, (2) identify sources of emittance growth, and (3) explore mitigation strategies. Here, we present the status of this study. Simulations were carried out using General Particle Tracer (GPT) including space-charge effects.
Paper: WEP069
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP069
About: Received: 08 Aug 2025 — Revised: 14 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
WEP070
Progress of polarized ion sources at BNL
828
The OPPIS has undergone multiple upgrades since 2000, with the most recent completed in 2022. Improvements to the Rb and Na cells have reduced vapor dispersion in the beamline, significantly lowering consumption and improving source stability. Plasmatron modifications extended component lifetimes. These upgrades enabled reliable Run-24 operation, with a mean current of 350 μA, 300 μs pulse width, and ~80% polarization delivered at the 200 MeV linac exit. Development is also underway for a high-intensity (2×10¹¹ ions/pulse) polarized ³He⁺⁺ source for the future EIC. The approach uses metastability-exchange optical pumping of high-purity ³He gas in a strong magnetic field, followed by ionization in EBIS. In tests with an “open” cell, 80–85% polarization has been achieved. The final gas cell configuration is now being tested with a 5 T EBIS solenoid magnet.
Paper: WEP070
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP070
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 13 Aug 2025 — Issue date: 28 Jan 2026
Progress of the plasma acceleration research platform at IHEP
Plasma acceleration is an innovative principle characterized by high acceleration gradients, which has attracted significant interest from major accelerator laboratories worldwide, because of its potential to increase accelerator energy and reduce size. One promising approach involves using existing conventional accelerators as external injectors for plasma-based accelerators, a topic of considerable interest within the research community. At IHEP, we propose utilizing the BEPCII Linac in conjunction with a new linac based on a photocathode RF gun to develop a new plasma acceleration research platform. This manuscript presents recent progress in the development of this platform.
Progress on commissioning of the CARIE facility at LANL
The cathodes and RF interaction at extremes (CARIE) is a project in Los Alamos National Laboratory (LANL) that aims for generating a high-brightness electron beam from a high-gradient photocathode. The commissioning of the CARIE facility started in 2022. A 50 MW C-band klystron was conditioned in 2023. A waveguide line including a high-power circulator was constructed and conditioned up to 12 MW in 2024. The facility has new control and logging systems currently being in implementation. An RF injector without a cathode plug was successfully tuned and is ready for installation. This talk will present the progress on commissioning and outlook of the project.
WEP073
Progress update on compressed ultrashort pulse injector demonstrator
832
Stable high gradient operation of a photoinjector is important for generating high brightness electron beams. The Argonne Wakefield Accelerator (AWA) facility recently commissioned an X-band photoinjector at 400 MV/m cathode field without significant breakdown rates using nanosecond RF pulses generated from a wakefield accelerator. We propose to develop an X-band photoinjector at 500 MV/m cathode field fed by ultrashort RF pulses generated by RF pulse compression technology developed at SLAC National Accelerator Laboratory, named as Compressed Ultrashort Pulse Injector Demonstrator (CUPID). The klystron based pulse compression is more stable and allows higher repetition rate. Here we provides the progress update of CUPID project, in particular on the mechanical design of the electron gun, solenoid's requirement and design constraints.
Paper: WEP073
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP073
About: Received: 07 Aug 2025 — Revised: 08 Aug 2025 — Accepted: 10 Aug 2025 — Issue date: 28 Jan 2026
WEP076
R&D progress of electron cyclotron resonance accelerator
840
Several attractive features of a novel electron Cyclotron Resonance Accelerator (eCRA) include: a compact robust room-temperature single-cell RF cavity as the accelerator structure; continuous ampere-level high current output without bunching; and a self-scanning accelerated energetic e-beam, obviating need for a separate beam scanner. Hence an eCRA can be highly compact and efficient to produce high power electron beams and x-ray beams. The applications of the eCRA includes the replacement of Cs-137 based dosimeter calibration system, and the replacement of Co-60 based sterilization system. The R&D progress of eCRA is reported here. A 2 MeV eCRA Demonstrator is under construction at BNL to validate the eCRA acceleration mechanism experimentally. A 5 MeV eCRA Upgrade with high beam power is in the design phase.
Paper: WEP076
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP076
About: Received: 08 Aug 2025 — Revised: 15 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
WEP079
RF breakdown and dark current studies in short-pulse acceleration
847
Recent experimental studies at the Argonne Wakefield Accelerator (AWA) have shown that operating RF cavities with short pulses, only a few nanoseconds in duration, can raise the accelerating gradient to nearly 400 MV/m in a series of X-band structure tests. These results motivate further investigation into the breakdown physics underlying the short-pulse acceleration regime. In this work, we present analytical models and numerical simulations of dark current dynamics in X-band cavities driven by short RF pulses. These studies explore key phenomena associated with RF breakdown across various time scales, including field emission, secondary electron emission, and plasma formation, with particular focus on their dependence on RF pulse length. Building on these insights, we describe the design and experimental plan for a single-cell X-band RF cavity operating at 11.7 GHz, optimized for high-gradient operation with 6~ns long RF pulses and integrated with RF breakdown diagnostics. This work aims to deepen the understanding of RF breakdown physics in the short-pulse regime and support the development of compact linear accelerators for future applications.
Paper: WEP079
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP079
About: Received: 08 Aug 2025 — Revised: 10 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
Science enabled by the the FACET-II low-energy laser arm
The FACET-II 10 TW laser system enables a variety of studies ranging from plasma wakefield acceleration over laboratory astrophysics to strong-field QED. While we successfully improved the performance of the high-energy laser-arm has, the much more versatile low-energy arm has yet to keep up. We report on the currently ongoing efforts to improve the performance of the low-energy laser-arm performance. The improvements are expected to enable studies, such as ultra-low emittance electron beams from plasma accelerators, plasma lenses, and novel ultrafast beam diagnostics.
Simulating dielectric wakefield acceleration of positrons from a solid target converter
Positrons and electrons can be generated by impinging a relativistic electron beam onto a solid converter, sometimes referred to as a non-neutral fireball beam. Depending on the scenario, a substantial fraction of the incoming driver bunch may still have sufficient quality to drive high gradient (~GV/m) accelerating wakefields in a dielectric structure. Here we consider the design of a dielectric loaded waveguide, positron converter, and electron driver bunch structure to realize capture and GV/m dielectric wakefield acceleration of positrons at SLAC FACET-II.
WEP083
Status of the experimental demonstration of GW power generation from THz-TBA
855
We present the current status of preparations for the experimental demonstration of GW power generation from THz-TBA. The presentation will cover the status of structure fabrication, RF power extraction and absolute power measurement, and THz drive beam preparation. Currently, 0.4 THz structures are being fabricated using two improved methods over previous fabrication techniques. RF power extraction will be achieved using an on-axis elliptical horn antenna and off-axis parabolic mirrors. The RF power will be detected with a bolometer and calibrated based on the total beam energy loss measured by a spectrometer. In recent machine studies, we successfully generated a high-charge bunch train (1 nC/bunch) compatible with 0.4 THz structure.
Paper: WEP083
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP083
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026
WEP085
Start-to-end simulations of a compact, linac-based positron source
862
Slow positrons are increasingly important to the study of material surfaces. For these kinds of studies, the positrons must have low emittance and relatively high brightness. Unfortunately, fast positron sources like radioactive capsules or linac driven sources have broad energy and angular spread, which make them difficult to capture and use. Moderators are materials that produce slow, mono-energetic positrons from a fast positron beam. Since their efficiencies are typically less than 10^-3 slow e+ per fast e+, research into how to maximize efficiency is of great interest. Previous work has shown that using a linac, one can decelerate the fast positron beam in order to greatly increase moderation efficiency. We present here start-to-end simulations using G4beamline to model a 100~MeV electron beam incident upon a Tungsten target, focused by an adiabatic matching device, and decelerated by a 1.3~GHz, 5-cell pillbox cavity. We show that by decelerating the positrons after their creation we can increase the number of positrons under 500~keV by 15 times, translating to a 16.3 times improvement in moderation efficiency, and therefore leading to a brighter positron source.
Paper: WEP085
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP085
About: Received: 08 Aug 2025 — Revised: 08 Aug 2025 — Accepted: 10 Aug 2025 — Issue date: 28 Jan 2026
THz detection and investigation of vacuum-compatible optical components
Detecting terahertz (THz) radiation in ultra-high vacuum (UHV) environments presents notable challenges due to the limited availability of commercially compatible components. In preparation for upcoming THz measurements at the Argonne Wakefield Accelerator (AWA) facility, we investigated two critical aspects: (1) the THz transmission characteristics of fused silica windows, and (2) the suitability of commercial off-axis parabolic mirrors (OAPs) for use in UHV conditions. While fused silica is widely used in optical systems, its performance in the THz regime is rarely documented. We present transmission measurements and assess its viability for THz diagnostics. Additionally, we address the incompatibility of anodized, off-the-shelf OAPs with UHV by developing and testing both mechanical and chemical de-anodization techniques. These methods aim to maintain surface integrity and optical quality. This work provides practical guidelines and compatibility benchmarks for implementing THz diagnostics in UHV environments and serves as a reference for future experiments at AWA and other accelerator facilities.
WEP091
Transverse deflecting cavity optimization for active control of electron beam energy chirp
873
The Transverse Deflecting Cavity Based Chirper (TCBC) is a novel concept of imposing and removing a significant energy chirp of an ultra-relativistic electron beam. The TCBC method requires much less footprint, compared to the conventional chirping and dechirping method involving operating a linear accelerator off-crest. When the compressed bunch is very short, the dechirping has to rely on the wakefields. We present our updated design of the L-band traverse deflecting cavity (TDC) for demonstrating the TCBC concept at the Argonne Wakefield Accelerator (AWA) facility. Our TDC design update is based on the original design provided by Tsinghua University. The TDC design update focused on ensuring improved performance under more intense electromagnetic fields, reducing the peak pulsed temperature rise. The tuners of the TDC were meanwhile reworked to allow greater adjustability of the resonant frequency and of the electromagnetic field balance among the cells. We also report the tolerance study of the TDC. Two copies of the TDC with the updated design are currently under fabrication with Dymenso, LLC.
Paper: WEP091
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP091
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 15 Aug 2025 — Issue date: 28 Jan 2026
WEP092
Ultra-violet laser transverse shaping with phase plates
876
Shaping ultraviolet (UV) laser beams is critical for optimizing photoinjector performance for applications in free-electron lasers (FELs). It has been shown that a 50% truncated Gaussian beam can achieve the lowest emittance via space charge compensation at LCLS-I. However, conventional shaping techniques to prepare this beam are limited by significant power losses or are not adapted for UV light. Here we report a high-precision transverse-shaping technique based on custom fused-silica phase plates with >99 % transmission at 253 nm. This approach enables spatial beam profile tailoring and significantly enhances beam stability at the photocathode. Using IMPACT-T simulations, we predict a 33% (from 0.67um to 0.45um) reduction in normalized emittance for a 250 pC bunch at LCLS-I. Experimental implementation at FACET-II demonstrated a 37% emittance reduction (from 5.4um to 3.4um) at 1.6 nC. These results establish phase-plate beam shaping as a high-fidelity, low-loss approach for high-brightness photoinjectors. Implementation at LCLS-II which will enable stable operation at megahertz repetition rates is underway.
Paper: WEP092
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP092
About: Received: 10 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 12 Aug 2025 — Issue date: 28 Jan 2026
Monte-Carlo modeling and experimental investigation of photoemission from CsTe semiconductor photocathode under high fields
Beam brightness can be enhanced with high gradient operation in photocathode guns. Such high gradient guns, such as the L-band gun at the Argonne Wakefield Accelerator (AWA) facility and the C-band high gradient gun being commissioned in the CARIE project at Los Alamos National Laboratory, are also typically equipped with semiconductor photocathodes due to their high quantum efficiency. To investigate the photoemission process in semiconductor thin-film photocathode under such conditions, we developed Monte-Carlo transport and photoemission models employing electronic, phonon, dielectric and optical properties directly from Density Functional Theory (DFT) calculation, as well as the photo excitation model based on the light interference effect in thin films. This photoemission model is further employed in photocathode gun simulation and used to investigate a recent high-gradient experiment conducted at the AWA photo injector. We will discuss the effects of the high field gradient on photoemission through a comparison of the measurement and the simulated beam dynamics.
Recent LANSCE efforts on improving H+ duoplasmatron capabilities
LANSCE uses a duoplasmatron ion source to produce H+ ion beams for the Isotope Production Facility, which uses 100 MeV proton beams to produce a variety of therapeutic and diagnostic isotopes for research purposes and also supports a variety of other experiments for materials and nuclear physics. We have recently begun work to improve the reliability, peak current, and lifetime of the ion source, while restoring existing capabilities to build new ion sources and filaments. This poster will cover these efforts, with a particular focus on the work to re-establish and improve the filament production capability and production of higher peak current beams.
WEP100
Upgraded photoinjector laser pulse train generator at the Argonne Wakefield Accelerator
888
The Argonne Wakefield Accelerator (AWA) facility operates a high-charge (100s of nC) electron beam in a bunch train, with eight electron bunches at a 769 ps spacing matching the linac operating frequency of 1.3 GHz. AWA’s electron beam is optimized for producing large wakefields in resonant structures to study structure wakefield acceleration. This is achieved by maximizing total beam charge, and by correct bunch train timing to enhance the wakefield via inter-bunch coherence. The properties of the bunch train are determined by a “multisplitter” in the photoinjector laser system, in which a series of beamsplitters splits one laser source into eight - ideally equal - pulses. However, AWA’s previous system did not split pulses evenly, with up to a 2:1 ratio between pulse energies within a train. Damaging electrical breakdown events within the electron gun, driven by high single bunch charge, occurred at lower total charge in this non-uniform set-up, limiting maximum charge. Thus, a new multisplitter using polarizing beamsplitters and half-wave plates (HWPs) was implemented. Unlike the previous fixed-ratio beam-splitter design, the new system enables tuning the splitting ratio for each beamsplitter, resulting in a more uniform pulse train. Large 2” optics and uncoated HWPs are also used to increase the laser intensity damage threshold (LIDT). This paper presents the design, characterization and lessons learned in early commissioning of AWA's upgraded laser pulse train generator.
Paper: WEP100
DOI: reference for this paper: 10.18429/JACoW-NAPAC2025-WEP100
About: Received: 08 Aug 2025 — Revised: 12 Aug 2025 — Accepted: 14 Aug 2025 — Issue date: 28 Jan 2026