FLASH is undergoing major modifications in the framework of the FLASH2020+ project. During the last upgrade phase in 2021/22 alterations to the superconducting linac have been the main priorty. Among other changes two accelerating modules were replaced by modern high gradient versions. This allows to operate FLASH routinely with electron beam energies exceeding 1.3 GeV and thus extends the photon wavelength range to below 4 nm in the fundamental. This presentation summarises the major facility modifications during the 2021/22 shutdown and will give an overview and outlook about the operation since then.

In order to develop a stable LWFA based accelerator and demonstrate FEL generation, the unique LWFA platform was constructed in the RIKEN SPring-8 center and systematic experiments have being conducted financially supported by ImPACT (2013-2018) and JST MIRAI (2018-) programs. Although undulator radiation in an XUV spectral range driven by LWFA electron beams was successfully demonstrated on the platform in 2019, the sufficient reproducibility was not obtained due to the poor electron pointing stability and large energy fluctuations. In order to solve the above problems, the accelerated electron beam quality has been improved by developing the Shock injection scheme enabling a precise injection control and a stable plasma condition. This development has dramatically improved the reproducibility and stability of the LWFA electron beam. The preliminary proof-of-concept experiment has recently demonstrated the clear amplification of the undulator radiation and the possibility of LWFA based FEL in XUV range. The talk will be presenting the outline of the LWFA platform, the setup of a proof-of-concept experiment focusing on key improvements and obtained results.

Wakefield structures are broadly employed in free electron laser (FEL) facilities for beam manipulation. Compared with cylindrical geometries, planar structures are typically preferred due to their increased flexibility, allowing for tunable wakefield strength through gap adjustment. However, these planar configurations can induce time-dependent quadrupole wakefields, which require careful compensation in various applications. To address this issue, we propose a novel structure design incorporating four identical corrugated elements which are independently controllable. By adjusting the gaps between orthogonal pairs, the quadrupole wakefield can be either fully compensated to avoid emittance growth or significantly amplified to enhance beam mismatch for slice lasing control. This manuscript presents both the physical and mechanical design of the proposed structure, as well as the planned proof-of-principle experiment.

Fermilab recently completed production and testing of 1.3 GHz cryomodules for the LCLS-II project. Each cryomodule consists of eight TESLA-shaped superconducting elliptical cavities equipped with two High Order Mode (HOM) coupler ports. Measurement of the HOM spectrum is part of the incoming quality control of cavities at room temperature and the final qualification cold test of cryomodules at the Cryomodule Test Facility (CMTF). In this paper we describe the procedure for measuring the HOM spectrum along with further data processing. Finally, we present accumulated statistics of individual HOM frequencies and quality factors related to various cavity vendors and discuss the possible contribution of HOMs to heat loads and beam dynamics.

The mid-Infrared region (2-5 um) is currently a frontier of laser science with short durations, where many molecular absorbing spectrums exist. The oscillator free electron lasers have advantages against solid-state laser systems, that include the fundamental generations of high-intensity mid-IR pulses with femto-seconds scale short duration, continuous variations of the central wavelength, and the high-repetitions of pulses due to RF accelerations of electron bunches. Especially, the coexistence of high-intensities and high-repetitions at GHz scales is important for the development of mid-IR frequency combs that may open up a new direction of molecule nonlinear reactions. In this presentation, we report on the importance of phase-locking between FEL pulses that grow up independently due to shot noises for the mid-IR frequency combs, and the states of development of a test phase-locking system, and introduce possible applications of the mid-IR frequency combs.

The Compact X-ray Light Source (CXLS) is a compact source of femtosecond pulses of x-rays that is now commissioning in the hard x-ray energy range 6-20 keV. It collides the electron beam from recently developed X-band distributed-coupling, room-temperature, standing-wave linacs and photoinjectors operating at 1 kHz repetition rates and 9300 MHz RF frequency with a Yb:YAG 1030 nm laser beam operating at high peak and average power at 1 kHz repetition rate with pulse energy up to 200 mJ. We present the performance of the CXLS accelerator, laser, and timing systems, and initial x-ray results.

Many years ago, the use of a corrugated dechirper for energy-chirp control in a relativistic electron beam was experimentally demonstrated at the Pohang Accelerator Laboratory (PAL). Since then, a lot of efforts have been made at the PAL-XFEL to utilize the dechirper for the electron beam diagnostics and the short pulse generation as well as the removal of energy correlation. Currently, the PAL-XFEL operates the two undulator sections: one for the hard x-ray (HX) and the other for the soft x-ray (SX), both of which employ the corrugated dechirper (vertical streaking at HX while horizontal streaking at SX). Using these dechirpers, we have conducted experiments to generate the short-pulse FEL down to a few femtoseconds via the fresh-slice technique at the hard x-ray regime and to measure the longitudinal phase space (LPS) of electron beam at the soft x-ray line of PAL-XFEL. The results of these experiments using the dechirper will be presented.

We will present the results of the commissioning program to establish x-ray lasing and operation of the LCLS-II facility, based on the 4 GeV superconducting accelerator. The commissioning scope included the cryogenic systems, SRF and cryomodules, beam transport and two undulator beamlines serving the hard and soft x-ray programs. The talk will include a discussion of achieved beam performance, both for electron and photon beam and our plans to ramp up to the final objectives. A report of operational issues will be included as well. Finally a brief summary of the status of LCLS-II-HE will be provided.

Free-electron lasers (FELs) send an accelerated electron beam through a magnetic undulator to provide a source of continuously tunable, short (10s of fs), high-peak power (GW-scale) radiation. FELs have found many applications, particularly in the infrared, extreme ultraviolet (EUV) and X-ray regimes. However, current EUV and X-ray FELs are large (100s of m) and expensive facilities, limiting the accessibility of these sources. In this work, we present FEL simulations driven by a compact accelerator combining high-gradient short pulse two-beam wakefield accelerators [1] and short-period superconducting undulators [2]. An FEL demo based on a GeV-scale accelerator is discussed as a driver for a water-window ( 2.3-4.4 nm) FEL with a ≈ 50 m length. Such a proof-of-principle integrated facility would serve the dual purpose of supporting user-based research in the water-window regime, and providing a proving ground for these new technologies to later be applied to shorter wavelength FELs. Here, we present early design and simulation efforts with a focus on FEL-process modeling.

The operation of hard X-ray FEL in a self-seeded mode requires much more precise control of electron phase space distribution compared to a SASE mode. In PAL-XFEL, we developed a unique RF feedback control based on high precision e-beam characterization (combined with ~1 fs RF timing distribution) to maintain the optimized self-seeded FEL without drift during the user run.

The PAL-XFEL accelerator is operating simultaneous operation of HX (10 GeV) and SX (3 GeV). To facilitate simultaneous operation, kicker MPS is necessary, requiring both AC mode and DC operation mode. AC mode operates with a square waveform at a repetition rate of 60 Hz. It operates as a bipolar type with an output voltage of 200 V and an output current of 45 A. The MPS is implemented using digital signal processing technology, employing DSP, FPGA, ADC, and others. The peak current stability of the kicker MPS showed approximately 50 ppm at a 45 A peak current. The long-term stability at 45 A in DC mode was measured to be 20 ppm peak-to-peak. These test results of kicker MPS indicate that it is sufficient for the stable simultaneous operation of PAL-XFEL.

The UK is conducting a multi-stage project to analyse the case for major investment into XFELs, through either developing its own facility or by investing at existing machines. The project’s 2020 Science Case identified a clear need for ‘next-generation’ XFEL capabilities including near-transform limited x-ray pulses across a wide range of photon energies and pulse durations; evenly spaced high-repetition rate pulses; and a high-efficiency facility with a step-change in the simultaneous operation of multiple end stations. The project is developing a conceptual design to meet these requirements, significantly aided by collaboration with international XFELs. It is also guided by an extensive ongoing user engagement programme of Townhall meetings and other activities. Both the science requirements and the emerging conceptual design are expected to be of general interest to the community.

Use of a cavity-based X-ray free electron laser (CBXFEL) is potentially a way to dramatically improve the stability and coherence of existing XFELs. A proof-of-principle project is underway as a collaboration between Argonne National Laboratory (ANL), The Institute of Physical and Chemical Research in Japan (RIKEN), and SLAC National Accelerator Laboratory. The CBXFEL is expected to operate using 9.831 keV photons from LCLS, using synthetic diamonds as cavity Bragg mirrors. The LCLS copper linac will deliver two electron bunches 624 RF buckets apart, resulting in a total X-ray cavity length of 65500.87 mm. The final X-ray cavity design, and installation and production status will be presented.