Keyword: emittance
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TUCOXBS01 Beam Halo in Energy Recovery Linacs operation, linac, collimation, electron 23
 
  • O.A. Tanaka
    KEK, Ibaraki, Japan
 
  The beam halo mitigation is a very important challenge for reliable and safe operation of a high energy machine. Since Energy Recovery Linacs (ERLs) are known to produce high energy electron beams of high virtual power and high density, the beam halo and related beam losses should be properly mitigated to avoid a direct damage of the equipment, an unacceptable increase in the vacuum pressure, a radiation activation of the accelerator components etc. To keep the operation stable, one needs to address all possible beam halo formation mechanisms, including those unique to each machine that can generate beam halo. Present report is dedicated to the beam halo related activities at the Compact ERL at KEK, and our operational experience with respect to the beam halo.  
slides icon Slides TUCOXBS01 [4.480 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-TUCOXBS01  
About • paper received ※ 16 September 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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TUCOXBS04 The LHeC ERL - Optics and Performance Optimizations linac, optics, cavity, lattice 34
 
  • S.A. Bogacz
    JLab, Newport News, Virginia, USA
 
  Funding: Work has been authored by Jefferson Science Associates, LLC under Contract No. DE-AC05-06OR23177 with the U.S. Department of Energy.
The LHeC 60 GeV ERL baseline design features a racetrack composed of two linacs, completed with 6 return arcs, including vertical spreaders and recombines at the arcs ends. Here, we consider a design strategy aiming at ’downsizing’ the ERL e.g. to 50 GeV, while preserving its performance in terms of synchrotron radiation effects. This results in a significant reduction of accelerator components. The optimization explores tuning of each arc, which takes into account the impact of synchrotron radiation at different energies. At the highest energy, it is crucial to minimize the emittance dilution; therefore, the cells are tuned to minimize the dispersion in the bending sections, as in a theoretical minimum emittance lattice. At the lowest energy, one compensates for the bunch elongation with a negative momentum compaction setup which, additionally, contains the beam size. The intermediate energy arcs are tuned to a double bend achromat lattice, offering a compromise between isochronicity and emittance dilution. Finally, a feasibility of a ’dogbone’ ERL is discussed.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-TUCOXBS04  
About • paper received ※ 16 September 2019       paper accepted ※ 07 November 2019       issue date ※ 24 June 2020  
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WEPNEC10 Investigation on the Ion Clearing of Multi-Purpose Electrodes of BERLinPro simulation, electron, brightness, linac 80
 
  • G. Pöplau
    COMPAEC e.G., Rostock, Germany
  • A. Meseck
    KPH, Mainz, Germany
  • A. Meseck
    HZB, Berlin, Germany
 
  High-brightness electron beams provided by modern accelerators require several measures to preserve their high quality and to avoid instabilities. The mitigation of the impact of residual ions is one of these measures. It is particularly important if high bunch charges in combination with high repetition rates are aimed for. This is because ions can be trapped in the strong negative electrical potential of the electron beam causing emittance blow-up, increased beam halo and longitudinal and transverse instabilities. One ion-clearing strategy is the installation of clearing electrodes. Of particular interest in this context is the performance of multi-purpose electrodes, which are designed such that they allow for a simultaneous ion-clearing and beam-position monitoring. Such electrodes will be installed in the BERLinPro facility. In this contribution, we present numerical studies of the performance of multi-purpose clearing-electrodes planned for BERLinPro, i.e. we investigate the behavior of ions generated by electron bunches while passing through the field of the electrodes. Hereby, several ion species and configurations of electrodes are considered.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-WEPNEC10  
About • paper received ※ 11 October 2019       paper accepted ※ 06 November 2019       issue date ※ 24 June 2020  
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WEPNEC17 Developments in Photocathode R&D at STFC Daresbury Laboratory: New Transverse Energy Spread Measurements and the Development of a Multi-Alkali Photocathode Preparation Facility cathode, vacuum, electron, laser 103
 
  • L.B. Jones, B.L. Militsyn, T.C.Q. Noakes
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • L.B. Jones, D.P. Juarez-Lopez, B.L. Militsyn, T.C.Q. Noakes, L.A.J. Soomary, C.P. Welsch
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • D.P. Juarez-Lopez, L.A.J. Soomary, C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
 
  Photocathode R&D activity within ASTeC is focussed on further development of the tools required for the preparation and characterisation of high performance photocathodes for X-FELs. Our Transverse Energy Spread Spectrometer (TESS)* experimental facility can be used with III-V semiconductor, multi-alkali and metal photocathodes to measure transverse and longitudinal energy distributions of the emitted electrons. Recently TESS has been upgraded to increase the instrument sensitivity for operation with low QE materials under UV illumination. Our R&D facilities also include in-vacuum quantum efficiency measurement, XPS, STM, plus ex-vacuum optical and STM microscopy for surface metrology. Intrinsic photocathode emittance is affected by many factors including illumination wavelength and surface roughness. We present energy distribution measurements for electrons emitted from copper, niobium and zirconium photocathode samples with measured levels of surface roughness under illumination by wavelengths between 256 and 291 nm. We also present an update on progress to establish a multi-alkali photocathode preparation facility to support the CLARA** linear accelerator.
* Proc. FEL’13, TUPPS033, 290-293
** CLARA Conceptual Design Report J. Inst. 9 T05001
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-WEPNEC17  
About • paper received ※ 04 October 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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WEPNEC19 Optimisation of the PERLE Injector booster, gun, electron, cavity 107
 
  • B. Hounsell, M. Klein, C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
  • B. Hounsell, B.L. Militsyn, C.P. Welsch
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  • B. Hounsell, W. Kaabi
    Université Paris-Saclay, CNRS/IN2P3, IJCLab, Orsay, France
  • B.L. Militsyn
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
 
  The injector for PERLE, a proposed electron Energy Recovery Linac (ERL) test facility for the LHeC and FCC-eh projects, is intended to deliver 500 pC bunches at a repetition rate of 40.1 MHz for a total beam current of 20 mA. These bunches must have a bunch length of 3 mm rms and an energy of 7 MeV at the entrance to the first linac pass while simultaneously achieving a transverse emittance of less than 6 mm mrad. The injector is based around a DC photocathode electron gun, followed by a focusing and normal conducting bunching section, a booster with 5 independently controllable SRF cavities and a merger into the main ERL. A design for this injector from the photocathode to the exit of the booster is presented. This design was simulated using ASTRA for the beam dynamics simulations and optimized using the many objective optimization algorithm NSGAIII. The use of NSGAIII allows more than three beam parameters to be optimised simultaneously and the trade-offs between them to be explored.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-WEPNEC19  
About • paper received ※ 01 October 2019       paper accepted ※ 11 November 2019       issue date ※ 24 June 2020  
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WEPNEC21 Decoupling Cathode and Lattice Emittance Contributions from a 100 pC, 100 MeV Electron Injector System cathode, electron, cavity, FEL 112
 
  • N.P. Norvell
    SLAC, Menlo Park, California, USA
  • M.B. Andorf, I.V. Bazarov, C.M. Gulliford, J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  We present simulation results to decouple the emittance contributions that are intrinsic from the injector lattice versus emittance contributions due to the quality of the cathode out of a 100 MeV electron injector system. Using ASTRA driven by the NSGA-II genetic algorithm, we optimized the LCLS-II injector system with a zero emittance cathode. We then imposed FEL specific energy constraints and show how the Pareto Front solution shifts. Lastly, we reoptimized at various cathode emittances to map out the dependence of cathode emittance versus final emittance out of the injector system. We then determined the cathode quality needed to hit a 0.1 mm mrad 95% rms transverse emittance specification out of the current LCLS-II injector system.  
poster icon Poster WEPNEC21 [3.227 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-WEPNEC21  
About • paper received ※ 01 October 2019       paper accepted ※ 07 November 2019       issue date ※ 24 June 2020  
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WEPNEC25 Research on Alkali Antimonide Photocathode Fabrication Recipe at PKU cathode, laser, vacuum, electron 120
 
  • D.M. Ouyang, L.W. Feng, S. Huang, K.X. Liu, S.W. Quan, H.M. Xie, X.K. Zhang, S. Zhao
    PKU, Beijing, People’s Republic of China
 
  Low emittance, high QE and long lifetime photocathode is widely studied for X-ray Free Electron Laser (XFEL)and Energy Recovery Linacs (ERL) applications. A deposition system for alkali antimonide photocathode (K2CsSb, Cs3Sb etc.) is being commissioned at Peking University. In this paper, we present our experimental results on alkali antimonide photocathode with this deposition system. We successfully fabricated Cs3Sb photocathode on oxygen free copper, p-type Si (100) and Mo substrates with QE of 1.4%, 2.6% and 2.6% respectively.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2019-WEPNEC25  
About • paper received ※ 27 September 2019       paper accepted ※ 01 November 2019       issue date ※ 24 June 2020  
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