Keyword: space-charge
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MOPMB032 A New Fault Recovery Mechanism for Superconducting Cavity Failure in C-ADS FPGA, cavity, hardware, linac 158
 
  • Z. Xue, J.P. Dai, C. Meng
    IHEP, Beijing, People's Republic of China
  
  For proton linear accelerators used in applications such as C-ADS, due to the nature of the operation, it is essential to have beam failures at the rate several orders of magnitude lower than usual performance of similar accelerators. A fault-tolerant mechanism should be mandatorily imposed in order to maintain short recovery time, high uptime and extremely low frequency of beam loss. This paper proposes an innovative and challenging way for compensation and rematch of cavity failure using fast electronic devices and Field Programmable Gate Array (FPGA) instead of embedded computers to complete the computation of beam dynamics. Due to the high arithmetic-computing-speed, good portability and repeatability, it is possible to realize calculation and re-adjustment online. In order to achieve the goal of instantaneous compensation and rematch, an advanced hardware design methodology including high-level synthesis and an improved genetic algorithm will be used.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMB032  
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MOPMR039 Review of Emittance Diagnostics for Space Charge Dominated Beams for AWAKE e- Injector emittance, quadrupole, focusing, radiation 337
 
  • O. Mete Apsimon, G.X. Xia
    UMAN, Manchester, United Kingdom
  • S. Döbert
    CERN, Geneva, Switzerland
  • C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
  
  Funding: This work is supported by the Cockcroft Institute Core Grant and STFC.
For a low energy, high intensity beam, total beam emittance is dominated by defocusing space charge force. This is most commonly observed in photo-injectors. In this low energy regime, emittance measurement techniques such as quadrupole scans fail as they consider the beam size only depends on optical functions. The pepper-pot method is used for 2D emittance measurements in a single shot manner. In order to measure the beam emittance in space charge dominated regime by quadrupole scans, space charge term should be carefully incorporated into the transfer matrices. On the other hand, methods such as divergence interferometry via optical transition radiation (OTRI), phase space tomography using 1D projections of quadrupole scans can be suitably applied for such conditions. In this paper, the design of a versatile pepper-pot system for AWAKE experiment at CERN is presented for a wide range of bunch charges from 0.1 to 1nC where the space charge force increases significantly. In addition, other aforementioned methods and respective algorithms are introduced as alternative methods. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMR039  
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MOPMW042 Multi-Dimensional RF Sources Design klystron, electron, cavity, gun 501
 
  • M. Dal Forno, A. Jensen, R.D. Ruth, S.G. Tantawi
    SLAC, Menlo Park, California, USA
  
  Funding: Work supported by the US DOE under contract DE-AC02-76SF00515.
Vacuum electronic devices, such as rf sources for accelerator applications, must provide high rf power with high efficiency. To achieve these requirements, multi-beam klystron and sheet-beam klystron devices have been developed. Multi-beam klystrons, at high frequency employ separate output cavities; hence they have the disadvantage that combining all the rf pulses, generated by all the beams, is challenging. Sheet-beam klystrons have problems with instabilities and with space charge forces that makes the beam not naturally confined. We are proposing an alternative approach that reduces space charge problems, by adopting geometries in which the space charge forces are naturally balanced. An example is when the electron beam is generated by a central source (well) and the electron motion corresponds to the natural expansion of the electron cloud (three-dimensional device). In this paper we will present the design and challenges of a bi-dimensional rf source, a cylindrical klystron, composed by concentric pancake resonant cavities. In this case, space charge forces are naturally balanced in the azimuthal direction. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMW042  
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MOPMY035 Theoretical Analysis and Simulation of a Compact Frequency Multiplier for High Power Millimeter and Terahertz Sources cavity, electron, cathode, coupling 576
 
  • A.R. Vrielink, S.G. Tantawi, F. Toufexis
    SLAC, Menlo Park, California, USA
  
  As the demands on accelerating gradients and the temporal resolution of beam diagnostics and manipulation schemes grow, millimeter-wave and terahertz (THz) accelerator structures may present a natural solution. The recent advent of a radiofrequency undulator and the development of a 0.45 THz accelerator demonstrate growing interest in this frequency regime; however, growth in this area is limited by the lack of efficient, compact high power sources. We present a novel vacuum electronic device featuring an interaction between a radially bunched electron beam and azimuthally traveling waves. The use of an inward traveling radial sheet beam mitigates space charge effects at the low operating energy of 10-30 keV and allows for a high input beam current of approximately 0.5-10 A. Based on preliminary calculations, these devices could operate from 50 GHz to 250 GHz with tens of kiloWatts of output power, while the expected efficiency would scale from 60% at 80 GHz to 15% at 230 GHz. Here we present the underlying theory, possible structure design, and preliminary results from analytical calculations and simulation.
Tantawi, S. et al. Phys. Rev. Lett. 112, 164802 (April, 2014)
Nanni, E. et al. Nat. Commun. 6, 8486 (October, 2015) 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPMY035  
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MOPOR019 Beta Function Measurement and Resonances Induced by Space Charge Force and Lattice Magnets resonance, lattice, emittance, simulation 641
 
  • K. Ohmi, K.G. Sonnad
    KEK, Ibaraki, Japan
  
  J-PARC MR has been operated at tune (νx,νy)=(22.40,20.75). A new operating point around (21.4,21.4) has been proposed by simulation studies on space charge effect since 2013. Machine experiments at the operating point has been performed since 2014 and many encouraging results are being obtained. We discuss why new operating point is better than present one from view point of space charge effects.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR019  
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MOPOR021 Space Charge Studies with High Intensity Single Bunch Beams in the CERN SPS emittance, injection, brightness, resonance 644
 
  • H. Bartosik, F. Schmidt
    CERN, Geneva, Switzerland
  • A. Oeftiger
    EPFL, Lausanne, Switzerland
  • M. Titze
    HZB, Berlin, Germany
  
  In order to reach the target beam parameters of the LHC injectors upgrade (LIU) project the beam degradation due to losses and emittance growth on the long injection plateau of the SPS needs to be minimized. A detailed study of the dependence of losses, transverse emittance blow-up and transverse beam tail creation as function of the working point is presented here for a high brightness single bunch beam with a vertical space charge tune spread of about 0.2 on the 26 GeV injection plateau. The beam behaviour close to important betatron resonances is characterised and a region in the tune diagram with minimal beam degradation is identified. Implications about the performance for LIU beams are discussed.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR021  
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MOPOR023 Flat Bunches with a Hollow Distribution for Space Charge Mitigation synchrotron, emittance, resonance, injection 652
 
  • A. Oeftiger, H. Bartosik, A. Findlay, S. Hancock, G. Rumolo
    CERN, Geneva, Switzerland
  • A. Oeftiger
    EPFL, Lausanne, Switzerland
  
  Funding: CERN, Doctoral Studentship EPFL, Doctorate
Longitudinally hollow bunches provide one means to mitigate the impact of transverse space charge. The hollow distributions are created via dipolar parametric excitation during acceleration in CERN's Proton Synchrotron Booster. We present simulation work and beam measurements. Particular emphasis is given to the alleviation of space charge effects on the long injection plateau of the downstream Proton Synchrotron machine, which is the main goal of this study. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR023  
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MOPOR024 Evolution of High Intensity Beams in the CERN PS Booster after H− Injection and Phase Space Painting emittance, injection, booster, lattice 656
 
  • M. Cieslak-Kowalska, J.L. Abelleira, E. Benedetto, C. Bracco
    CERN, Geneva, Switzerland
  
  With the LHC Injector Upgrade (LIU) project, the injection energy of PS Booster (PSB) ' first circular accelerator in the LHC injector chain ' will be raised from 50 MeV to 160 MeV and the present multiturn injection will be upgraded to H− injection with transverse and longitudinal painting. In the scope of this project, it is planned to double the beam intensities, profiting from the fact that the βγ2 factor will be two times larger (0.35 at 50 MeV and 0.71 at 160 MeV), so the resulting tune spread driven by a direct space charge should remain similar. This paper describes the feasibility to double the intensity of high intensity and large emittance beams, looking into the evolution under space charge and taking into account losses constrains in the ring and in the extraction lines.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR024  
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MOPOR034 Numerical Space-Charge Compensation Studies and Comparison of Different Models electron, simulation, proton, ion 674
 
  • D. Noll, M. Droba, O. Meusel, U. Ratzinger, K. Schulte, C. Wiesner
    IAP, Frankfurt am Main, Germany
  
  The design of many Low-Energy Beam Transport sections relies on the presence of space-charge compensation by particles of opposing charge. To improve understanding of the processes involved in the built-up and steady-state, simulations using the Particle-in-Cell code bender were made. We will present the influence of various system parameters on the results. Furthermore, the electron velocity distribution was found to be approximately thermal. The spatial distribution can then be found by solving the Poisson-Boltzmann equation. Such a model for the electron distribution was implemented in a 2D PIC code and applied to typical beam transport situations. We will present results in comparison to the 3D simulations.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR034  
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MOPOR035 Space Charge Neutralization Studies with H− Beam in Low Energy Beam Transport Test Stand emittance, ion, ion-source, rfq 677
 
  • S. Artikova
    Private Address, Tsukuba, Japan
  • K. Ikegami
    J-PARC, KEK & JAEA, Ibaraki-ken, Japan
  • T. Shibata, A. Takagi
    KEK, Tokai, Ibaraki, Japan
  
  J-PARC is intensity-upgraded up to pulse current of 50 mA of H− beam. Two-solenoid based LEBT test stand is being built to support the operation of J-PARC linac. It imitates the actual LEBT of linac, yet contains the diagnostics chamber composed of horizontal and vertical beam emittance-meters and Faraday-cup for the current measurement. Vacuum composition of LEBT is predominantly H2 gas. The pressure inside the LEBT can be varied by the differential pumps allowing us to study the beam phase space evolution under space charge effects. The measurements of the beam phase space emittance were made as a function of the residual gas pressure. This paper presents the results and discussion on beam space charge neutralization and its effect on the beam phase space emittance.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR035  
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MOPOR047 Numerical and Experimental Substantiation of the Ion Density Beam Transfer Function Measurements ion, electron, betatron, accumulation 698
 
  • D. Sauerland, W. Hillert
    ELSA, Bonn, Germany
  
  Funding: Funded by the BMBF, Germany under grant 05K13PDA
In the ELSA stretcher ring electrons are accelerated to a beam energy of 3.2 GeV utilizing a fast energy ramp of 6 GeV/s. Ions being generated by collision with the residual gas molecules accumulate inside the beam potential, causing incoherent tune shifts and coherent beam instabilities. Since the ion induced incoherent tune shift rises linearly with the beam neutralisation, it offers a suitable approach for evaluating the efficiency of several ion clearing measures. It was indirectly measured using a new experimental approach: By measuring the beam transfer function using a broadband transversal kicker, one was able to perceive a shift and broadening of the tune peak. Both effects could be adequately parameterized providing a quantity proportional to the incoherent tune shift and thus the average neutralisation. The impact of incoherent effects to the coherent electron beam response during the measurement has not been subject to intensive theoretical attention yet. This leaves the obtained quantity unscaled. Here new numerical simulations and experimental investigations will be presented in order to further substantiate the results of this new method. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR047  
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MOPOW037 Developments in the CLARA FEL Test Facility Accelerator Design and Simulations linac, FEL, undulator, simulation 797
 
  • P.H. Williams, D. Angal-Kalinin, A.D. Brynes, J.A. Clarke, F. Jackson, J.K. Jones, J.W. McKenzie, B.L. Militsyn, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • R.B. Appleby
    UMAN, Manchester, United Kingdom
  • B. Kyle
    University of Manchester, Manchester, United Kingdom
  
  We present recent developments in the accelerator design of CLARA (Compact Linear Accelerator for Research and Applications), the proposed UK FEL test facility at Daresbury Laboratory. In order to prioritise FEL schemes requiring the shortest electron bunches, the layout has changed significantly to enable compression at higher energy. Four proposed modes of operation are defined and tracked from cathode to FEL using ASTRA. Supplementing these baseline mode definitions with CSR-enabled codes (such as CSRTRACK) where appropriate is in progress. The FEL layout is re-optimised to include shorter undulators with delay chicanes between each radiator.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOW037  
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MOPOY003 Study of Achieving Low Energy Beam by Energy Degradation and Direct Resonance Extraction in a Compact Ring extraction, resonance, synchrotron, simulation 850
 
  • G.R. Li, X.W. Wang, Z. Yang, H.J. Yao, Q. Zhang, S.X. Zheng
    TUB, Beijing, People's Republic of China
  • X. Guan
    Tsinghua University, Beijing, People's Republic of China
  
  We have designed a compact proton synchrotron(7~230 MeV) for applications like proton therapy and space environment study. These applications may require slow extraction from 10~230 MeV. Traditionally, the low energy beam(10~70 MeV) is achieved by energy degradation from high energy beam which may cause beam lose and energy spread increase, because the beam quality may suffer from magnetic remanence, power ripple and strong space charge effects in low energy stage. To achieve high quality beam directly from resonance extraction, we study these effects by performing multi-particle simulation. Methods of improving beam quality are discussed.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOY003  
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MOPOY010 Simulations and Measurements of Stopbands in the Fermilab Recycler simulation, resonance, proton, operation 864
 
  • R. Ainsworth, P. Adamson, K.J. Hazelwood, I. Kourbanis, E.G. Stern
    Fermilab, Batavia, Illinois, USA
  
  Fermilab has recently completed an upgrade to the complex with the goal of delivering 700 kW of beam power as 120 GeV protons to the NuMI target. A major part of boosting beam power is to use the Fermilab Recycler to stack protons. Simulations focusing on the betatron resonance stopbands are presented taking into account different effects such as intensity and chromaticity. Simulations are compared with measurements.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOY010  
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MOPOY012 Space Charge Simulations in the Fermilab Recycler for PIP-II simulation, proton, booster, experiment 870
 
  • R. Ainsworth, P. Adamson, I. Kourbanis, E.G. Stern
    Fermilab, Batavia, Illinois, USA
  
  Proton Improvement Plan-II (PIP-II) is Fermilab's plan for providing powerful, high-intensity proton beams to the laboratory's experiments. Upgrades are foreseen for the recycler which will cope with bunches containing fifty percent more beam. Of particular concern is large space charge tune shifts caused by the intensity increase. Simulations performed using Synergia are detailed focusing on the space charge footprint.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOY012  
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MOPOY029 Transverse Emittance Measurements in CSNS Linac emittance, focusing, quadrupole, linac 916
 
  • Z.P. Li, Y. Li, J. Peng, S. Wang
    IHEP, Beijing, People's Republic of China
  
  Commissioning of the front-end of the linac at CSNS has been accomplished. Double scanning slit system and wire-scanners were employed to carry out the transverse emittance measurements in both low energy beam transport (LEBT) and medium energy beam transport (MEBT). Different results of different measurement methods are presented and compared. Corresponding codes were developed for each of the emittance measurement methods.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOY029  
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MOPOY032 Beam Twiss Measurement With Ws Including Space Charge Effect experiment, lattice, simulation, rfq 925
 
  • Y.L. Zhao, H. Geng, C. Meng, F. Yan
    IHEP, Beijing, People's Republic of China
  
  Wire Scanners (WS) are used to measure beam profile and calculate the transverse Twiss parameters at the entrance of MEBT1 in the CADS injector I test stand. As to data process, the traditional method with transfer map doesn't consider the space charge effect. But, as we know, space charge effect can't be neglected for high intensity accelerators. In this paper, optimization algorithm is used in beam emittance measurement.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOY032  
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TUOCA02 APEX Phase-II Commissioning Results at the Lawrence Berkeley National Laboratory gun, electron, cavity, linac 1041
 
  • F. Sannibale, J.A. Doyle, J. Feng, D. Filippetto, G.L. Harris, M.J. Johnson, T.D. Kramasz, D. Leitner, C.E. Mitchell, J.R. Nasiatka, H.A. Padmore, H.J. Qian, H. Rasool, J.W. Staples, S.P. Virostek, R.P. Wells, M.S. Zolotorev
    LBNL, Berkeley, California, USA
  • S.M. Gierman, R.K. Li, J.F. Schmerge, T. Vecchione, F. Zhou
    SLAC, Menlo Park, California, USA
  • C. Pagani, D. Sertore
    INFN/LASA, Segrate (MI), Italy
  
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
Science needs in the last decade have been pushing the accelerator community to the development of high repetition rates (MHz/GHz-class) linac-based schemes capable of generating high brightness electron beams. Examples include X-ray FELs; ERLs for light source, electron cooling and IR to EUV FEL applications; inverse Compton scattering X-ray or gamma sources; and ultrafast electron diffraction and microscopy. The high repetition rate requirement has profound implications on the technology choice for most of the accelerator parts, and in particular for the electron gun. The successful performance of the GHz room-temperature RF photo-injectors running at rates <~ 100 Hz, cannot be scaled up to higher rates because of the excessive heat load that those regimes would impose on the gun cavity. In response to this gun need, we have developed at Berkeley the VHF-Gun, a lower-frequency room-temperature RF photo-gun capable of CW operation and optimized for the performance required by MHz-class X-ray FELs. The Advanced Photo-injector EXperiment (APEX) was funded and built for demonstrating the VHF gun performance, and the results of its last phase of commissioning are presented. 		 
slides icon Slides TUOCA02 [12.015 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUOCA02  
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TUPMR020 In-depth Analysis and Optimization of the European Spallation Source Front End Lattice rfq, solenoid, simulation, emittance 1274
 
  • Y.I. Levinsen, M. Eshraqi
    ESS, Lund, Sweden
  • L. Celona, L. Neri
    INFN/LNS, Catania, Italy
  
  The European Spallation Source front end will deliver a 62.5 mA beam current of 2.8 ms duration at 352 MHz to the downstream linac, which in turn will produce a 5 MW proton beam onto the target. Such unprecedented beam power requires a high quality beam with accurate and stable beam parameters in order to assure low beam losses and safe transport through the linac. In this paper we present advanced tuning methods for the low energy beam transport and the radio frequency quadrupole.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMR020  
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TUPMR032 Initial Commissioning of the Rutherford Appleton Laboratory (RAL) Scaled Negative Penning Ion Source interface, plasma, cathode, operation 1314
 
  • D.C. Faircloth, S.R. Lawrie, T. Rutter, M. Whitehead, T. Wood
    STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
  
  A new high duty factor, scaled Penning surface plasma source is being developed at RAL. This paper provides initial commissioning results. A stable high-current (up to 100 A) pulsed discharge is obtained, but the anode overheats, caused by poor thermal contact at elevated temperatures. The overheating anode yields a noisy discharge, with low output current, and makes high duty factor operation impossible. The performance of a thermal interface material for aperture plate (plasma electrode) cooling is detailed. An update on the cathode heaters is provided. The anode to source-body fit is analysed at different temperatures for different combinations of mechanical tolerances. This offers insights when compared to ISIS operational sources. A new anode with modified tolerance dimensions for improved fit is being manufactured and will be tested in June 2016.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMR032  
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TUPMY013 Progress on Beam-Plasma Effect Simulations in Muon Ionization Cooling Lattices plasma, simulation, scattering, emittance 1571
 
  • J.S. Ellison
    IIT, Chicago, Illinois, USA
  • P. Snopok
    Illinois Institute of Technology, Chicago, Illlinois, USA
  
  Funding: Work supported by the U.S. Department of Energy.
New computational tools are essential for accurate modeling and simulation of the next generation of muon based accelerator experiments. One of the crucial physics processes specific to muon accelerators that has not yet been implemented in any current simulation code is beam induced plasma effect in liquid, solid, and gaseous absorbers. We report here on the progress of developing the required simulation tools and applying them to study the properties of plasma and its effects on the beam in muon ionization cooling channels. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMY013  
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TUPMY031 Estimation and Suppression of Aberrations in Emittance Exchange based Current Profile Shaping collective-effects, emittance, acceleration, FEL 1615
 
  • G. Ha, M.-H. Cho, W. Namkung
    POSTECH, Pohang, Kyungbuk, Republic of Korea
  • W. Gai, G. Ha, K.-J. Kim, J.G. Power
    ANL, Argonne, Illinois, USA
  
  The longitudinal current profile manipulation has been explored for many applications including THz radiation, FEL and advanced acceleration schemes. Especially, collinear dielectric wakefield accelerations require a microbunch shaping for a high transformer ratio. We have studied aberrations from the emittance exchange based current profile shaping to preserve the high transformer ratio. All second order aberration terms in the double dog-leg emittance exchange beam line are discovered. Aberration patterns from each aberration sources like second order terms, space-charge, and CSR and their effect on the transformer ratio are estimated analytically. These aberration sources and corresponding patterns are confirmed using a particle tracking code GPT. Simple methods to suppress each aberration will be presented too. All calculation in this work is done with a double dog-leg emittance exchange beam line.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPMY031  
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TUPOR018 Design Optimization of Compensation Chicanes in the LCLS-II Transport Lines simulation, FEL, electron, undulator 1695
 
  • J. Qiang, C.E. Mitchell, M. Venturini
    LBNL, Berkeley, California, USA
  • Y. Ding, P. Emma, Z. Huang, G. Marcus, Y. Nosochkov, T.O. Raubenheimer, L. Wang, M. Woodley
    SLAC, Menlo Park, California, USA
  
  LCLS-II is a 4th-generation high-repetition rate Free Electron Laser (FEL) based x-ray light source to be built at the SLAC National Accelerator Laboratory. To mitigate the microbunching instability, the transport lines from the exit of the Linac to the undulators will include a number of weak compensation chicanes with the purpose of cancelling the momentum compaction generated by the main bend magnets of the transport lines. In this paper, we will report on our design optimization study of these compensation chicanes in the presence of both longitudinal and transverse space-charge effects.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOR018  
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TUPOW018 Tunable High-Intensity Electron Bunch Train Production Based on Nonlinear Longitudinal Space Charge Oscillation radiation, electron, experiment, gun 1782
 
  • Z. Zhang, H.B. Chen, Y.-C. Du, W.-H. Huang, J. Shi, X.L. Su, C.-X. Tang, Q.L. Tian, D. Wang, W. Wang, L.X. Yan, L.M. Zheng, Z. Zhou
    TUB, Beijing, People's Republic of China
  • W. Gai
    ANL, Argonne, Illinois, USA
  
  High peak current electron bunch trains with tunable terahertz (THz) spacing are produced and measured experimentally. An initial picosecond periodic modulation in the temporal profile of a relativistic electron beam is magnified by the longitudinal space charge forces. As opposed to trying to reduce its smearing effect for large beam current, we take advantages of the nonlinear space charge oscillation through controlling the plasma phase advance. The spacing of the bunch train can be varied continuously either by tuning the velocity bunching of a radio-frequency gun or by tuning the compression of a downstream magnetic chicane. The narrow-band μJ-level THz radiation from the bunch train are also measured with tunable central frequency of the spectral from ~0.5 THz to 1.6 THz. The bunch train measurements are consistent with the particle tracking simulations.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOW018  
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TUPOW032 Modelling of the Short Bunch Optics for BERLinPro linac, emittance, simulation, booster 1820
 
  • A. Ginter, A.N. Matveenko
    HZB, Berlin, Germany
  
  The Energy Recovery Linac principle allows compressing electron bunches to lengths at least two orders of magnitude shorter compared to storage rings. At BERLinPro bunch compression and decompression can be done in two stages in the injector and main arcs. Starting with different bunch lengths from the gun the distribution of compression between these two stages is subject to optimization. Simulations show that the length and shape of the bunch in the injector and before the linac are the limiting factors for minimal bunch length. Injector simulations have to consider space charge effects, whereas CSR effects are limiting compression in the arcs. The strength of these effects and optimal compression ratios changes with different bunch charges. Optimization and simulation tools have to be chosen according to the energy regime and dominant collective effects. Current status of injector optimization and effect on the compressed bunch are presented.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOW032  
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TUPOY002 AOC, A Beam Dynamics Design Code for Medical and Industrial Accelerators at IBA cyclotron, extraction, simulation, synchro-cyclotron 1902
 
  • W.J.G.M. Kleeven, M. Abs, E. Forton, V. Nuttens, E.E. Pearson, J. Walle, S. Zaremba
    IBA, Louvain-la-Neuve, Belgium
  
  The Advanced Orbit Code (AOC) facilitates design studies of critical systems and processes in medical and industrial accelerators. Examples include: i) injection into and extraction from cyclotrons, ii) central region, beam-capture and longitudinal beam dynamics studies in synchro-cyclotrons, iii) studies of resonance crossings, iv) stripping extraction, v) beam simulation from the ion source to the extraction, vi) space charge effects, vii) beam transmission studies in gantries or viii) calculation of Twiss-functions. The main features of the code and some applications are discussed.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOY002  
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TUPOY023 A Compact and High Current FFAG for the Production of Radioisotopes for Medical Applications target, proton, injection, simulation 1957
 
  • D. Bruton, R.J. Barlow, T.R. Edgecock, R. Seviour
    University of Huddersfield, Huddersfield, United Kingdom
  • C. Johnstone
    PAC, Batavia, Illinois, USA
  
  A low energy Fixed Field Alternating Gradient (FFAG) accelerator has been designed for the production of radioisotopes. Tracking studies have been conducted using the OPAL code, including the effects of space charge. Radioisotopes have a wide range of uses in medicine, and recent disruption to the supply chain has seen a renewed effort to find alternative isotopes and production methods. The design features separate sector magnets with non-scaling, non-linear field gradients but without the counter bends commonly found in FFAG's. The machine is isochronous at the level of 0.3% up to at least 28 MeV and hence able to operate in Continuous Wave (CW) mode. Both protons and helium ions can be used with this design and it has been demonstrated that proton beams with currents of up to 20 mA can be accelerated. An interesting option for the production of radioisotopes is the use of a thin internal target. We have shown that this design has large acceptance, ideal for allowing the beam to be recirculated through the target many times, the lost energy being restored on each cycle. In this way, the production of Technetium-99m, for example, can take place at the optimum energy.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOY023  
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TUPOY032 Design and Simulation of a Thermionic Electron Gun for a 1 MeV Parallel Feed Cockcroft-Walton Industrial Accelerator electron, gun, cathode, simulation 1976
 
  • M. Nazari, F. Abbasi
    Shahid Beheshti University, Tehran, Iran
  • F. Ghasemi
    NSTRI, Tehran, Iran
  • M. Jafarzadeh
    ILSF, Tehran, Iran
  
  Electron accelerators are made of different parts and one of the main part of every electron accelerator is its electron gun. In this article a diode electron gun is designed and simulated for a 1MeV parallel feed Cockcroft-Walton accelerator for industrial applications. The pierce configuration is selected for focusing electrode. Simulations are carried out using CST Particle Studio. The gun is thermionic with indirect heating of spherical dispenser cathode that is made from porous tungsten which is impregnated with barium compounds. The gun maximum achievable current is 200 mA at 10 kV and required current in our accelerator is about 100 mA.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUPOY032  
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WEPMY023 Self-focusing and Wakefield-focusing of Relativistic Electron Bunches in Plasma focusing, wakefield, plasma, electron 2602
 
  • V.I. Maslov, I.P. Levchuk (Yarovaya), I.N. Onishchenko
    NSC/KIPT, Kharkov, Ukraine
  
  It was shown that at the wakefield excitation by electron bunch, the length of which is equal to half of the wavelength, the ratio of wakefield focusing to self-focusing is large at the end of the bunch, the shape of which is such that it falls from the current maximum value in the head of the bunch to zero at the end of the bunch. However, the ratio of wakefield focusing to self-focusing tends to zero at the end of the bunch, if the current increases along the bunch from zero in the head of the bunch to a maximum value at the end of the bunch. In the case of homogeneous bunch with sharp edges, the length of which is several plasma wavelength, the self-focusing force Fs is constant along the bunch, and wakefield force of focusing changes from -Fs to Fs. In the case of homogeneous bunch with precursor of half current and length, equal to half of wavelength, focusing of bunch is determined by the homogeneous self-focusing force and wakefield focusing force equals zero. Cases of rectangular and Gaussian bunches, the length of which is equal to half of wavelength, also were considered.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMY023  
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WEPOY009 Simulation Study of Emittance Growth from Coulomb Explosion in a Charge Separator System After Stripping emittance, electron, simulation, ion 3005
 
  • M. Droba, O. Meusel, U. Ratzinger
    IAP, Frankfurt am Main, Germany
  
  Funding: BMBF-05P15RFRBA
A computer 3D particle-in-cell (PIC) simulation is used to examine the emittance growth of an intense heavy ion beam after a charge stripper. Multi-species dynamics of the bunched uranium beam with various charge states and including compensation electrons will be presented. The rms-emittance growth shows different behaviour in the horizontal, vertical and longitudinal planes, dependent on initial conditions, like a bunch size, beam current and phase space ellipse orientation. An optimization of initial parameters is therefore crucial for a successful and efficient post-acceleration. The role of the separation system and of co-moving electrons will be discussed for the example of the GSI-Unilac. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY009  
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WEPOY015 Longitudinal Bram Dynamics at Rf-Compressor gun, simulation, electron, brightness 3011
 
  • A.V. Andrianov
    BINP SB RAS, Novosibirsk, Russia
  
  Nowadays the usage of charged particle beams for study of nature became widespread. Modern experiments are require particle beams with duration around hundreds femtosecond. Relatively simple and cheap method of production such pulses is using RF-gun with photocathode and then the special insertion device which compress the beam. The paper described the RF-compressor for the electron beam. In result of work was obtained a device configuration. Electromagnetic field configuration and distribution were simulated for the configuration. Beam dynamics was computed in this field distribution. Incoming beam parameters are following: beam length is 1-5ps, beam charge is 0.1-2pC and energy is 3MeV. Output beam duration was compressed to less than 150fs. Influence of RF-compressor at beam parameters was estimated.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY015  
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WEPOY033 Space Charge Compensation in Low Energy Beam Lines simulation, proton, electron, solenoid 3055
 
  • F. Gérardin, N. Chauvin, D. Uriot
    CEA/IRFU, Gif-sur-Yvette, France
  • M.A. Baylac, D. Bondoux, F. Bouly
    LPSC, Grenoble Cedex, France
  • A. Chancé, O. Napoly, N. Pichoff
    CEA/DSM/IRFU, France
  
  The dynamics of a high intensity beam with low energy is governed by its space-charge forces which may be responsible of emittance growth and halo formation due to their non-linearity. In a low energy beam transport (LEBT) line of a linear accelerator, the propagation of a charged beam with low energy causes the production of secondary particles created by the interaction between the beam and the background gas present in the accelerator tube. This phenomenon called space-charge compensation is difficult to characterize analitically. In order to obtain some quantitative to characterize the space-charge compensation (or neutralization), numerical simulations using a 3D PIC code have been implemented.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY033  
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WEPOY034 Latest Improvements of OPAL dipole, electromagnetic-fields, simulation, linac 3058
 
  • C.J. Metzger-Kraus, M. Abo-Bakr, B.C. Kuske
    HZB, Berlin, Germany
  • A. Adelmann
    PSI, Villigen PSI, Switzerland
  
  OPAL (Object Oriented Parallel Accelerator Library) is an open source, C++ based tool for charged particle tracking in large accelerator structures and beam lines including 3D space charge, particle matter interaction and FFAG capabilities. The careful parallel design makes it possible to tackle large and complex problems, in a reasonable time frame. The current code status and latest program improvements and upgrades are introduced. One of the provided flavors, OPAL-T, was, so-far, used for relatively simple lattices and was not well suited for more complicated arrangements of elements. One of the major upgrades is the possibility to place elements in 3D space, giving the user a better control in absolute element positioning. The old input format with relative positioning is still supported. We show results of the BERLinPro lattice and compare it with results obtained with elegant.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY034  
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WEPOY039 GIOTTO: A Genetic Code for Demanding Beam-dynamics Optimizations electron, software, gun, interface 3073
 
  • A. Bacci
    Istituto Nazionale di Fisica Nucleare, Milano, Italy
  • V. Petrillo
    Universita' degli Studi di Milano, Milano, Italy
  • M. Rossetti Conti
    Universita' degli Studi di Milano & INFN, Milano, Italy
  
  GIOTTO is a software based on a Genetic Algorithm (GA). Its development started in 2007 with a work published on NIMB (263, 2007, 488-496) and presented at PAC07 (THPAN031). When the parameters, defining an acceleration machine beam line, are strongly correlated in nonlinear way, the GAs are a powerful tool to coup with these difficulties. These conditions are typically generated by space-charge, as in the high brightness e-beam photo-injectors or when the Velocity Bunching compression technique (VB) is used. The power of GIOTTO is the adaptability to different cases, given by its own structure that permits to drive different external codes in series, the possibility to define a user dependent multi objective fitness function and function constraints on the beam dynamics, as well as the possibility to turn off the genetic optimization to perform statistical analysis (machine jitters). Up today it has been used in Thomson/Compton sources, ultra-short e-bunches generation by VB, focusing channel and dog-leg lines optimizations.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY039  
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WEPOY041 Fast Tracking of Nonlinear Dynamics in the ESS Linac Simulator via Particle-Count Invariance sextupole, proton, framework, multipole 3080
 
  • B.T. Folsom, E. Laface
    ESS, Lund, Sweden
  
  Real-time beam modeling has been used in accelerator diagnostics for several decades. Along the way, the theory for matrix calculations of linear forces has matured, allowing for fast calculations of a beam's momentum and position distributions. This formalism becomes complicated and ultimately breaks down with high-order beam elements like sextupoles. Such elements can be accurately modeled with a Lie-algebra approach, but these techniques are generally implemented in slower, offline multiparticle tracking software. Here, we demonstrate an adaptation of the conventional Lie techniques for rapid first-order tracking of position, which is accomplished by treating a bunch's particle count as an invariant.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY041  
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WEPOY044 Review of CPU and GPU Faddeeva Implementations timing, GPU, interface, simulation 3090
 
  • A. Oeftiger, R. De Maria, L. Deniau, K.S.B. Li, E. McIntosh, L. Moneta
    CERN, Geneva, Switzerland
  • A. Aviral
    BITS Pilani, Pilani, India
  • S. Hegglin
    ETH, Zurich, Switzerland
  • A. Oeftiger
    EPFL, Lausanne, Switzerland
  
  Funding: CERN, Doctoral Studentship EPFL, Doctorate
The Faddeeva error function is frequently used when computing electric fields generated by two-dimensional Gaussian charge distributions. Numeric evaluation of the Faddeeva function is particularly challenging since there is no single expansion that converges rapidly over the whole complex domain. Various algorithms exist, even in the recent literature there have been new proposals. The many different implementations in computer codes offer different trade-offs between speed and accuracy. We present an extensive benchmark of selected algorithms and implementations for accuracy, speed and memory footprint, both for CPU and GPU architectures. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY044  
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WEPOY050 A Differential Algebraic Framework for the Fast Indirect Boundary Element Method multipole, simulation, framework, controls 3107
 
  • A.J. Gee, B. Erdelyi
    Northern Illinois University, DeKalb, Illinois, USA
  • B. Erdelyi
    ANL, Argonne, USA
  
  Beam physics at the intensity frontier must account for the beams' realistic surroundings on their dynamics in an accurate and efficient manner. Mathematically, the problem can be expressed as a Poisson PDE with given boundary conditions. Commonly, the Poisson boundary value problem is solved locally within many volume elements. However, it is known the PDE may be re-expressed as indirect bound- ary integral equations (BIE) which give a global solution*. By solving the BIEs on M surface elements, we arrive at the indirect boundary element method (iBEM). Iteratively solving this dense linear system of form Ax = b scales like (miterations M2 ). Accelerating with the fast multipole method (FMM) can reduce this to O(M) if miterations << M. For N evaluation points, the total complexity would be O(M) + O(N) or O(N) with N = M. We have implemented a constant element version of this fast iBEM based on our previous work with the FMM in the differential algebraic (DA) framework**. This implementation is to illustrate the flexibility and accuracy of our method. A future version will focus on allowing for higher order elements.
* Sauter, S. and C. Schwab. Boundary Element Methods (2011)
** Abeyratne, S., S. Manikonda, and B. Erdelyi. "A novel differential algebraic adaptive fast multipole method." IPAC 2013: 1055-1057. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY050  
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WEPOY054 A Matlab Interface Package for Elegant Simulation Code lattice, booster, quadrupole, betatron 3117
 
  • V.V. Smaluk, T.V. Shaftan, G.M. Wang
    BNL, Upton, Long Island, New York, USA
  
  Funding: Work supported by DOE contract DE-AC02-98CH10886
A Matlab interface package for Elegant simulation code is under development. This package combines advantages of Elegant, which is one of the most advanced codes for accelerator simulations, with advantages of useful and effective Matlab functions for data processing, analysis, optimization, and real-time machine control using Maltab Middle Layer. A number of functions have been already developed: calculation of lattice parameters and Twiss functions, linear and high-order chromaticity, amplitude-dependent tune shifts, modification of lattice elements, correction of betatron tunes and chromaticity, a set of functions for graphic representation. These functions have been successfully used at NSLS-II for tracking and turn-by-turn simulations near the half-integer resonance, for maximizing tunability and dynamic aperture of NSLS-II Booster, and for calculating limits of top-up Booster energy interlock. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPOY054  
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THYA01 Advanced Concepts and Methods for Very High Intensity Linacs emittance, diagnostics, focusing, simulation 3155
 
  • P.A.P. Nghiem, N. Chauvin, D. Uriot
    CEA/DSM/IRFU, France
  • M. Comunian
    INFN/LNL, Legnaro (PD), Italy
  • C. Oliver
    CIEMAT, Madrid, Spain
  • W. Simeoni
    IF-UFRGS, Porto Alegre, Brazil
  • M. Valette
    CERN, Geneva, Switzerland
  
  For very high intensity linacs, both beam power and space charge should be taken into consideration for any analysis of accelerators aiming at comparing their performances and pointing out the challenging sections. As high beam power is an issue from the lowest energy, careful and exhaustive beam loss predictions have to be done. High space charge implies lattice compactness making the implementation of beam diagnostics very problematic, so a clear strategy for beam diagnostic has to be defined. Beam halo becomes no longer negligible, and it plays a significant role in the particle loss process. Therefore, beam optimization must take the halo into account and beam characterization must be able to describe the halo part in addition to the core one. This presentation discusses advanced concepts and methods for beam analysis, beam loss prediction, beam optimization, beam diagnostic and beam characterization especially dedicated to very high intensity accelerators.  
slides icon Slides THYA01 [6.177 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THYA01  
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THOBA02 Space Charge Induced Collective Modes and Beam Halo in Periodic Channels focusing, resonance, emittance, simulation 3165
 
  • C. Li, Zh.C. Liu, Q. Qin, Y.L. Zhao
    IHEP, Beijing, People's Republic of China
  
  Funding: This work is supported by the Ministry of Science and Technology of China under Grant No. 2014CB845501.
The collective mode instabilities of periodically focused high intensity beams based on the Vlasov-Poisson equation are investigated both analytically and numerically. It is found that the broadened collective stop bands resulting from space charge induced structure resonance in long periodic channels predict well the areas where the rms emittance growth accompanied with n-fold phase space structure (beam halo) would take place. We believe that the formed beam halo, which is depicted in action-angle frame, could be understood as a side-effect of the collective beam mode. 		 
slides icon Slides THOBA02 [4.704 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THOBA02  
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THOBA03 Start-to-end Calculations and Trajectory Correction for BERLinPro laser, linac, simulation, timing 3167
 
  • B.C. Kuske, C.J. Metzger-Kraus
    HZB, Berlin, Germany
  
  Funding: Work funded by the Bundesministerium für Bildung und Forschung, Land Berlin and grants of the Helmholtz Association
BERLinPro is an ERL project under construction at the Helmholtz-Zentrum Berlin, with the goal to illuminate the challenges and promises of a high brightness 100 mA superconducting RF gun in combination with a 50 MeV return loop and energy recovery. Latest changes to the optics code OPAL allow for the first time to perform start-to-end tracking studies including space charge in a single run, without switching between codes. This opens the way to apply correction schemes to displaced trajectories in the complete machine and to study the effect of jitter sources, including the space charge dominated injector, on the machine performance parameters. Trajectory correction is discussed. Jitter is studied with respect to its potential impact on the recovery process and parameter changes before the dump.

 
slides icon Slides THOBA03 [5.903 MB]  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THOBA03  
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THPMB037 Comparing the Transverse Dynamics of the ESS Linac Simulator and the Spallation Neutron Source Linac linac, kicker, neutron, controls 3314
 
  • E. Laface, Y.I. Levinsen
    ESS, Lund, Sweden
  • T.A. Pelaia II
    ORNL, Oak Ridge, Tennessee, USA
  
  The ESS Linac Simulator (ELS) is the model that will be used at the European Spallation Source ERIC in Lund, Sweden, to simulate the transport of the beam envelope during operations. On August 12th 2015, we had the opportunity to use two hours of beam time in the linac of the Spallation Neutron Source in Oak Ridge to benchmark ELS. In this paper we present the results of the transverse dynamics measurements. Such measurements are obtained upon kicking the beam in the medium-energy beam transport (MEBT) and measuring the effect of the oscillation of the beam centroid in 58 beam position monitors (BPMs). The ELS model and these measurements are in agreement with an average discrepancy of 4% in the superconducting section of the accelerator.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMB037  
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THPMR014 Core-halo Limits and Beam Halo-formation Dynamic emittance, focusing, resonance, plasma 3417
 
  • M. Valette, P.A.P. Nghiem
    CEA/IRFU, Gif-sur-Yvette, France
  • N. Pichoff
    CEA/DSM/IRFU, France
  
  In high intensity linear accelerators, space charge related instabilities and effects are the cause of emittance increase and beam losses. The mechanism of halo formation due to a mismatched beam causing parametric resonances and energy transfer between phase-spaces is one of them. The previously defined one dimensional core-halo limit [1][2] was extended to two dimensional distributions [3][4]. This halo characterization method is applied to a classical case of transport for halo formation studies: the transport of a mismatched beam. Our method provides a core-halo limit that matches the expected halo formation mechanism with a very good precision.
* Appl. Phys. Lett. 104, 074109 (2014)
** Phys. Plasmas, 22, 083115, (2015)
*** IPAC (2015) MOPWA010
**** TBP 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMR014  
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THPOW018 Simulations of Field Emitted Dark Current Dynamics in DC Photoinjectors simulation, gun, electron, cavity 3971
 
  • P.J. Tipping, J.W. McKenzie, B.L. Militsyn
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  Field emission is a concern in injectors with DC photoelectron guns because of the constant generation of dark current, which is accelerated down the beam line and can deteriorate the photoemitted bunch quality and lead to hardware damage. Simulations were carried out on the co-propagation of a field emitted, dark current halo and a photoemitted bunch in a typical 350 kV gun as used in an ERL or FEL injector, followed by a single cell buncher cavity. The photoemitted bunch repelled the halo longitudinally, leaving the area in the centre of the bunch with very low dark current, surrounded by two peaks of relatively high current at the front and back of the bunch. The peaks in current occur at all levels of dark current and were about 3.5 times the amplitude of the undisturbed dark current. The buncher caused the dark current to overcompress, forming a 'ghost' pulse an order of magnitude larger than the initial level of dark current, in front of the photoemitted bunch.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOW018  
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THPOW019 Beam Characterisation and Machine Developments at VELA experiment, gun, cathode, electron 3975
 
  • D. Angal-Kalinin, A.D. Brynes, F. Jackson, S.P. Jamison, J.K. Jones, J.W. McKenzie, B.L. Militsyn, B.D. Muratori, T.C.Q. Noakes, M.D. Roper, Y.M. Saveliev, D.J. Scott, R.J. Smith, E.W. Snedden, P.H. Williams
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • S.D. Barrett, C.P. Topping, A. Wolski
    The University of Liverpool, Liverpool, United Kingdom
  • C.S. Edmonds, F. Jackson, S.P. Jamison, J.K. Jones, J.W. McKenzie, B.D. Muratori, Y.M. Saveliev, D.J. Scott, C.P. Topping, P.H. Williams, A. Wolski
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  
  An overview is presented of developments on VELA (Versatile Electron Linear Accelerator), an RF photo-injector with two user stations at Daresbury Laboratory. Numerous commissioning, machine development, beam characterisation and user experiments have been completed in the past year. A new beamline and a dedicated multiuser station have been commissioned and the first experiments performed. A number of measures have been taken to improve the stability of machine by mitigating a phase drift, laser beam transport drift and a coherent ~1 Hz beam oscillation. The 6D phase space of the electron beam has been characterised through quad scans, transverse tomography and with a transverse deflecting cavity.  
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOW019  
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THPOY060 Four Beam Generation for Simultaneous Four-Hall Operation at CEBAF laser, timing, electron, gun 4240
 
  • R. Kazimi, J.M. Grames, J. Hansknecht, A.S. Hofler, G.E. Lahti, T. E. Plawski, M. Poelker, R. Suleiman, Y.W. Wang
    JLab, Newport News, Virginia, USA
  
  Funding: Authored by JSA, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. The U.S. Gov't retains a non-exclusive, paidup, irrevocable, worldwide license to publish or reproduce this for U.S. Gov't purposes.
As part of the CEBAF 12 GeV upgrade at Jefferson Lab, a new experimental hall was added to the existing three halls. To deliver beam to all four halls simultaneous-ly, a new timing pattern for electron bunches is needed at the injector. This pattern change has consequences for the frequency of the lasers at the photogun, beam behavior in the chopping system, beam optics due to space charge, and setup procedures. We have successfully demonstrated this new pattern using the three existing drive lasers. The implementation of the full system will occur when the fourth laser is added and upgrades to the Low Level RF (LLRF) are complete. In this paper we explain the new bunch pattern, the challenges for setting and measuring the pattern such as 180° RF phase ambiguity, addition of the fourth laser to the laser table and LLRF upgrade. 		 
DOI • reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPOY060  
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