TY - CONF AU - Li, F.Y. AU - Carlsten, B.E. AU - Garimella, R. AU - Huang, C. AU - Kwan, T.J. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Validation of a Novel Method for the Calculation of Near-Field Synchrotron Radiation J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - The phenomenon of synchrotron radiation (SR) from electrons is at the core of modern accelerator based light sources. While SR in the far field has been well characterized, the near-field SR and its impacts on self-consistent electron beam dynamics remain an ongoing topic. Since it is difficult to experimentally characterize the near fields, it is desirable to develop accurate and efficient numerical methods for the design of these light sources. Here, we investigate a novel method, originally proposed by Shintake and which potentially has both high efficiency and accuracy. We focus on the field calculation of this method and show that the original idea has missed the important terms of fields due to electron acceleration and therefore only applies to a linear motion. To correct this limitation we developed a modified algorithm that gives consistent fields with direct calculations using the Liénard-Wiechert equation. Some basic signatures of the near-field SR fields are also drawn for a cyclotron motion by using this modified approach. PB - JACoW Publishing CP - Geneva, Switzerland SP - 397 EP - 399 KW - electron KW - acceleration KW - radiation KW - cyclotron KW - synchrotron DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-MOPGW116 UR - http://jacow.org/ipac2019/papers/mopgw116.pdf ER - TY - CONF AU - Smith, S.J. AU - Biedron, S. AU - Bolin, T.B. AU - Carlsten, B.E. AU - Cary, J.R. AU - Cheatham, D.M. AU - Krawczyk, F.L. AU - Sosa Guitron, S.I. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Exploration of High-Gradient Structures for 4th Generation Light Sources J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - As the energy, scale and therefore the cost of large-scale accelerator projects, such as X-ray free-electron lasers (XFELs) increases, new technologies must be developed in order to minimize costs and maximize efficiency wherever possible. One obvious way to reduce costs is to reduce the length of accelerating sections by utilizing higher accelerating gradients. Here we present the results of a study into the various structure options for FEL linacs, contrasting different frequencies, geometries and operating modes. An investigation into the possibility of using cryo-cooled travelling wave (TW) electron structures which allow for higher gradient operation by exploiting the anomalous skin effect is also detailed. Finally, we give simulation results from a number of commercial codes including VSim 9, for a hypothetical TW high gradient C-band structure design employing cryo-cooled technology. Breakdown effects, pulsed heating, tolerances, efficiencies and potential rf sources are also explored, all within the framework of typical FELs and their requirements. PB - JACoW Publishing CP - Geneva, Switzerland SP - 1155 EP - 1157 KW - cavity KW - FEL KW - linac KW - cryogenics KW - electron DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-MOPTS117 UR - http://jacow.org/ipac2019/papers/mopts117.pdf ER - TY - CONF AU - Bradley III, J.T. AU - Merrill, L.N. AU - Rouleau, G. AU - Roybal, W. AU - Sanchez, G. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Test Results of the Low-Stored-Energy -80 kV Regulator for Ion Sources at LANSCE J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - The H⁻ ion source at the LANSCE accelerator facility uses an 80 kV accelerating column to produce an H⁻ ion beam. A regulated power supply maintains the source and support equipment racks at -80kV with respect to local ground. As the facility’s H⁻ beam currents have been increased, voltage droop on the regulated -80 kV power supply has become one of the limiting factors on beam current. The previous regulator used a standard 120kV DC HV supply and a high power planar triode in series to regulate the voltage down to 80 kV and to stop the flow of current during an arcdown of the -80 kV accelerating column. In 2018 we devised a method of using a pair of standard, 50 kV capacitor charging supplies to produce the required 80 kV with minimal stored energy and significantly better voltage regulation over the beam pulse. This configuration has been tested on the Ion Source Test Stand and is being considered for installation on the main LANSCE linac. We will present the design, modeling and measured results of the new system as compared with the performance of the previous system. PB - JACoW Publishing CP - Geneva, Switzerland SP - 1369 EP - 1371 KW - linac KW - power-supply KW - ion-source KW - controls KW - flattop DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPMP053 UR - http://jacow.org/ipac2019/papers/tupmp053.pdf ER - TY - CONF AU - Tajima, T. AU - Bernal, J.E. AU - Borden, M.J. AU - Chamberlin, J.P. AU - Martinez, F.A. AU - O'Hara, J.F. AU - Poudel, A. AU - Stephens, K.A. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - LANSCE Vacuum System Improvements in the Last ~10 Years J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - The Los Alamos Neutron Science Center (LANSCE) accelerator started its operation in 1972. To mitigate the vulnerability due to old equipment and to restore the 120 Hz operation capability we lost a while ago, we have gone through a refurbishment / risk mitigation project since 2007. This paper summarizes the improvements in the vacuum systems in the last ~10 years and shows some data on the downtimes caused by vacuum failures. The refurbished equipment is significantly more maintainable and will contribute to extend the life of this old accelerator, but it has been a challenge to reduce the downtime. Some examples that caused a long downtime will be described. PB - JACoW Publishing CP - Geneva, Switzerland SP - 1375 EP - 1377 KW - vacuum KW - operation KW - neutron KW - linac KW - status DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPMP056 UR - http://jacow.org/ipac2019/papers/tupmp056.pdf ER - TY - CONF AU - Stockli, M.P. AU - Clemmer, M.E. AU - Cousineau, S.M. AU - Draganic, I.N. AU - Dudnikov, V.G. AU - Garnett, R.W. AU - Han, B. AU - Justice, T.A. AU - Kang, Y.W. AU - Kleinjan, D. AU - Murray, S.N. AU - Pennisi, T.R. AU - Piller, C. AU - Rouleau, G. AU - Stinson, C. AU - Welton, R.F. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Operating the SNS RF H⁻ Ion Source with a 10% Duty Factor J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - The SNS (Spallation Neutron Source) (radio-frequency) RF-driven, H⁻ ion source injects ~50 mA of H⁻ beam into the SNS accelerator at 60 Hz with a 6% duty factor. It injects up to 7 A·hrs of H⁻ ions during its ~14-week service cycles, which is an unprecedented lifetime for small-emittance, high-current pulsed H⁻ ion sources. The SNS source also features unprecedented low cesium consumption and can be installed and started up in <10 h. Presently, the LANSCE (Los Alamos Neutron Science CEnter) accelerator complex in Los Alamos is fed by a filament-driven, biased converter-type H⁻ source that operates with a high plasma duty factor of 10%. It needs to be replaced every 4 weeks with a ~4 day startup phase. The measured negative beam current of 16-18 mA falls below the desired 21 mA acceptance of LANSCE’s accelerator especially since the beam contains several mA of electrons. LANSCE and SNS are exploring the possibility of using the SNS RF H⁻ source at LANSCE to increase the H⁻ beam current and the ion source lifetime while decreasing the startup time. For this purpose, the SNS H⁻ source has been tested at a 10% duty factor by operating it at 120 Hz with 840 µs plasma pulses generated with ~30 kW of 2 MHz RF power, and extracting ~25 mA around-the-clock for 28 days. This, and additional tests and other considerations are discussed in this paper. PB - JACoW Publishing CP - Geneva, Switzerland SP - 1951 EP - 1953 KW - ion-source KW - plasma KW - electron KW - neutron KW - LEBT DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS009 UR - http://jacow.org/ipac2019/papers/tupts009.pdf ER - TY - CONF AU - Kleinjan, D. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Arc and Convertor Current Transient Studies for Multi-cusp Cesiated Surface Conversion H⁻ Source at Lansce J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - The Multi-cusp Cesiated Surface Conversion H⁻ Ion Source at the Los Alamos Neutron Science Center (LANSCE) has provided beam at ~14 mA, 120 Hz, and 10% D.F. for many years of neutron science research. Recently, random high current transients were discovered in the arc current used to ionize hydrogen in the LANSCE H⁻ ion source, and in the convertor current used to convert protons to H⁻ ions. Most have no effect, but more severe transients can cripple beam output. Hypothesized causes are related to cesiation effects, plasma potential changes, tungsten filament vaporation/sputtering, or from the pulsed power system. A dedicated study was recently done on the LANSCE H⁻ Ion source test stand to determine the cause of these transients. Current understanding indicates that the more severe transients come from a combination of cesiation effects and plasma potential changes. The status of these current transient studies on the LANSCE H⁻ ion source will be discussed. PB - JACoW Publishing CP - Geneva, Switzerland SP - 1983 EP - 1985 KW - ion-source KW - operation KW - plasma KW - extraction KW - electron DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS025 UR - http://jacow.org/ipac2019/papers/tupts025.pdf ER - TY - CONF AU - Draganic, I.N. AU - Kleinjan, D. AU - Rouleau, G. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - H⁺ and H⁻ Ion Beam Injectors at LANSCE: Beam Production Status and Planned Injector Upgrades J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - The Los Alamos Neutron Science Center operates with two 750 keV Cockcroft-Walton accelerators for simultaneous injection of H⁺ and H⁻ ion beams into a 800 MeV linear accelerator. The proton ion beam is produced using a duoplasmatron source and the H⁻ ion beam is formed with a cesiated, multi-cusp-field, surface converter ion source. An overview of ion injector status, recent low energy beam transport line optimizations and ion source performance improvements will be presented. To reduce long term operational risks and to improve existing LANSCE beam production for all facility users, new injector upgrades are underway: 1) replacing the H⁺ CW injector with a Radio-Frequency Quadruple accelerator and 2) increasing H⁻ ion beam brightness and extending source lifetime using the novel SNS RF negative ion source. The status of upgrade projects will be discussed. PB - JACoW Publishing CP - Geneva, Switzerland SP - 2087 EP - 2089 KW - ion-source KW - plasma KW - cathode KW - proton KW - LEBT DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS071 UR - http://jacow.org/ipac2019/papers/tupts071.pdf ER - TY - CONF AU - Kim, D. AU - Andrews, H.L. AU - Choi, B.K. AU - Fleming, R.L. AU - Huang, C. AU - Lewellen, J.W. AU - Nichols, K.E. AU - Pavlenko, V.N. AU - Simakov, E.I. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Analysis of Electron Beam Divergence in Diamond Field Emitter Array Cathodes J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - At Los Alamos National Laboratory (LANL), we have recently established a capability to fabricate diamond array cathodes for electron beam sources. Our fabricated diamond field emitter arrays (DFEAs) are the arrays of micrometer-scale diamond pyramids with nanometer-scale sharp tips and produce high per-tip current (> 15 μA per-tip) in DC testing. For the beam divergence measurements, we designed and assembled a test stand consisting of a DFEA cathode, a mesh aperture of 0.375-inch for an anode, and AZO (ZnO:Al2O3) screen coated on a sapphire substrate for beam visualization. A negative voltage of about 40 kV is applied to the cathode, and the mesh and the screen are kept at ground. We measure a size of the electron beam on the AZO screen at different mesh to screen distances at a fixed cathode-mesh gap in order to calculate the beam divergence angles. We also perform the beam dynamics simulations with Computer Simulation Technology (CST) Studio and General Particle Tracer (GPT) using a single pyramidal shape with a nanowire tip model. In this presentation, the measured experimental results of the beam divergences will be compared to the beam dynamic simulations. PB - JACoW Publishing CP - Geneva, Switzerland SP - 2090 EP - 2093 KW - cathode KW - focusing KW - experiment KW - simulation KW - electron DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS073 UR - http://jacow.org/ipac2019/papers/tupts073.pdf ER - TY - CONF AU - Lewis, S.M. AU - Dolgashev, V.A. AU - Haase, A.A. AU - Kim, D. AU - Nanni, E.A. AU - Othman, M.A.K. AU - Simakov, E.I. AU - Sy, A.V. AU - Tantawi, S.G. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Design of a High Gradient THz-Driven Electron Gun J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - We present the design of a high-gradient electron gun. The goal of this gun is to generate relativistic electrons using GV/m accelerating fields. The initial design is a standing-wave field-emission gun operating in the pi-mode with a cavity frequency of 110.08 GHz. A pulsed 110 GHz gyrotron oscillator will be used to drive the structure with power coupled in through a TM01 circular waveguide mode. The gun is machined in two halves which are bonded. This prototype will be used to characterize the electron beam and study RF breakdown at 110 GHz. PB - JACoW Publishing CP - Geneva, Switzerland SP - 2098 EP - 2100 KW - electron KW - gun KW - acceleration KW - experiment KW - FEL DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS077 UR - http://jacow.org/ipac2019/papers/tupts077.pdf ER - TY - CONF AU - Simakov, E.I. AU - Andrews, H.L. AU - Black, D.S. AU - Fleming, R.L. AU - Kim, D. AU - Leedle, K.J. AU - Pavlenko, V.N. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Observations of the Femtosecond Laser-Induced Emission From the Diamond Field Emitter Tips J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - We present the results of experimental observation of emission from single diamond field emitter tips when triggered by an ultra-short laser pulse. Diamond field emitter array (DFEA) cathodes were originally proposed for applications that require large current densities. DFEAs represent periodic arrays of diamond pyramids with micron-size dimensions and tips with diameters of the order of tens of nanometers. DFEAs are known to produce significant currents in field emission regime under direct current (DC) fields and in radio-frequency (RF) guns. It has been proposed that single diamond tip emitters can be employed for production of small tightly focused electron beams for dielectric laser accelerators (DLAs) that accelerate particles using the energy of light produced by infrared lasers. To generate short electron bunches required by DLAs diamond pyramids may be triggered with a laser. We have recently observed emission produced by a single diamond pyramid when triggered by a laser at different wavelengths from 256 nm to 2020 nm. We have conducted studies with the goal to understand mechanism of the emission. We clearly observed the change in emission mechanism when the wavelength changed from 256 nm to 512 nm. We believe that while the emission at 256 nm is a clear photoemission, the emission at longer wavelengths is likely the field emission caused by intense electric fields of the laser. PB - JACoW Publishing CP - Geneva, Switzerland SP - 2130 EP - 2133 KW - laser KW - electron KW - cathode KW - photon KW - experiment DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS089 UR - http://jacow.org/ipac2019/papers/tupts089.pdf ER - TY - CONF AU - Nichols, K.E. AU - Andrews, H.L. AU - Antipov, S.P. AU - Chen, G. AU - Conde, M.E. AU - Doran, D.S. AU - Ha, G. AU - Kim, D. AU - Liu, W. AU - Power, J.F. AU - Shao, J.H. AU - Simakov, E.I. AU - Whiteford, C. AU - Wisniewski, E.E. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Experimental Results of Dense Array Diamond Field Emitters in RF Gun J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - We present experimental emission results from arrays of diamond field emitter tips operating in an RF gun at the Argonne Cathode Test-stand. Results from various arrays will be presented with different spacing between array elements. Very high charge densities were produced at various field gradients. The maximum field gradient for a particular geometry was discovered and break-down effects will be presented. Cathode lifetime was preliminarily studied. Further experiments are being planned and work on the cathode design optimization to produce higher quality beams will be discussed. PB - JACoW Publishing CP - Geneva, Switzerland SP - 2134 EP - 2136 KW - cathode KW - gun KW - experiment KW - solenoid KW - wakefield DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS090 UR - http://jacow.org/ipac2019/papers/tupts090.pdf ER - TY - CONF AU - Huang, C. AU - Andrews, H.L. AU - Baker, R.C. AU - Fleming, R.L. AU - Kim, D. AU - Kwan, T.J. AU - Pavlenko, V.N. AU - Piryatinski, A. AU - Simakov, E.I. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - Physics of Electron Beam Generation and Dynamics From Diamond Field Emitter Arrays J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - Many applications such as compact accelerators and electron microscopy demand high brightness electron beams with small beam size and low emittance. Electric-field-assisted diamond emitters manufactured from semiconductor processes are strong candidates for cathodes in such sources. The micro-scale pyramid structure of the emitter has the desirable attribute of significant field enhancement at the sharp interfaces (apex and edges) to facilitate electron emission. We use the LSP particle-in-cell code to simulate the diamond emitter in a diode setup and obtain the beam size and divergence. An empirical fit of the fields around the apex is extracted for detail study. The trend of the beam divergence observed in the simulation is further corroborated using electron’s trajectory in the empirical field model. PB - JACoW Publishing CP - Geneva, Switzerland SP - 2137 EP - 2139 KW - electron KW - simulation KW - cathode KW - ECR KW - experiment DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-TUPTS091 UR - http://jacow.org/ipac2019/papers/tupts091.pdf ER - TY - CONF AU - Barkley, W.C. AU - Borden, M.J. AU - Garnett, R.W. AU - Gulley, M.S. AU - Kerstiens, E.L. AU - Pieck, M. AU - Rees, D. AU - Shelley, F.E. AU - Smith, B.G. ED - Boland, Mark ED - Tanaka, Hitoshi ED - Button, David ED - Dowd, Rohan ED - Schaa, Volker RW ED - Tan, Eugene TI - First Results of the Analytical Method Used to Reduce Downtime Risk at an Accelerator Facility J2 - Proc. of IPAC2019, Melbourne, Australia, 19-24 May 2019 CY - Melbourne, Australia T2 - International Particle Accelerator Conference T3 - 10 LA - english AB - The Los Alamos Neutron Science Center (LANSCE), like many other accelerator facilities, was built decades ago and has been repurposed when new missions were adopted. With an ongoing beam availability expectation of at least 80% delivered to the Experimental Areas (EAs), a balance between cost of spare equipment and budget has always been a challenge. Beam availability data has been meticulously captured and binned over the years to completely characterize the Structures, Systems and Components (SSCs) and other factors that have caused or contributed to accelerator downtime. Over these years, a critical spares list prioritized the spare equipment purchases that were deemed most critical by the management team. In the span of the years 2013 ’ 2015, significant accelerator upgrades and equipment replacements were performed in a set of activities known as LANSCE-RM. Last year, a new risk-based approach was developed by the management team that included an analytical assessment and a quantitative evaluation of probability and consequence. The resulting risk register (risk-based equipment list) is being used to guide decisions on funding requests and provide justification to mitigate operational risks. A paper by the same authors was published at LINAC 2018 describing this risk-based approach that serves to reformulate the critical spares list. This paper, in the sections that follow, expands on the approach by detailing the specific results of the analyses that led to the first risk register. Additionally, it evaluates the historical beam downtime at LANSCE compared to the current funding allocation choices made to increase the reliability. PB - JACoW Publishing CP - Geneva, Switzerland SP - 4349 EP - 4351 KW - target KW - linac KW - operation KW - DTL KW - vacuum DA - 2019/06 PY - 2019 SN - 978-3-95450-208-0 DO - DOI: 10.18429/JACoW-IPAC2019-THPTS103 UR - http://jacow.org/ipac2019/papers/thpts103.pdf ER -