MC5: Beam Dynamics and EM Fields
D08 High Intensity in Linear Accelerators - Space Charge, Halos
Paper Title Page
WEPTS007 Short Bunch Experiment at EXALT Facility 3100
 
  • C. Bruni, J-N. Cayla, S. Chancé, V. Chaumat, N. Delerue, N. ElKamchi, P. Lepercq, H. Purwar
    LAL, Orsay, France
  • E. Baynard, M. Pittman
    CLUPS, Orsay, France
  • B. Lucas, O. Neveu
    CNRS LPGP Univ Paris Sud, Orsay, France
  • T. Vinatier
    DESY, Hamburg, Germany
 
  Nowdays, different applications required short bunches, with low energy spread and low emittances. On EXALT facility, we perform an experiment with a short (few100 femtosecond) laser pulse on a photocathode in a 3 GHz RF gun. We perform the measurement of the single photon emission process with a copper cathode. We show that the longitudinal photoinjector model via transfer matrix is suitable for the reconstruction of the bunch duration even in short pulse mode with an increased accurracy charge below 20 pC. We clearly measure the parabolic profile in the energy spectrum resulting from blow out phenomena at the cathode due to strong space charge forces. Measurements are also compared with the Astra simulations.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS007  
About • paper received ※ 21 May 2019       paper accepted ※ 23 May 2019       issue date ※ 21 June 2019  
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WEPTS010 Beam Dynamics Errors Studies for the IFMIF-DONES SRF-LINAC 3103
 
  • N. Chauvin, N. Bazin, J. Plouin
    CEA-DRF-IRFU, France
  • S. Chel, L. Du
    CEA-IRFU, Gif-sur-Yvette, France
 
  The goal of the IFMIF-DONES (International Fusion Materials Irradiation Facility-DEMO Oriented Neutron Source) project is to build an irradiation facility that will provide a sufficient neutron flux to study and characterize structure materials foreseen for future fusion power plant. In order to accelerate the required 125mA/40 MeV continuous deuteron beam from 5 MeV to 40 MeV, a superconducting radio-frequency (SRF) linac, housed in five cryomodules, is proposed. The design is based on two beta families (β=0.11 and β=0.17) of half-wave resonators (HWR) at 175MHz. The transverse focusing is achieved using one solenoid coil per focusing period. This paper presents the extensive multiparticle beam dynamics simulations that have been performed to adapt the beam along the SRF-linac in such a high space charge regime. As one of the constraints of the IFMIF linac is a low level of beam losses, specific optimizations have been done to minimize the beam occupancy in the line (halo). A Monte Carlo error analysis has also been carried out to study the effects of misalignments or field imperfections (static errors) and also vibrations or power supplies ripple (dynamic errors). The results of these errors studies are presented and discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS010  
About • paper received ※ 21 May 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019  
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WEPTS013 The Cooling Effect of Beam Self-Fields on the Photocathode Surface in High Gradient RF Injectors 3112
 
  • Y. Chen, M. Krasilnikov, F. Stephan
    DESY Zeuthen, Zeuthen, Germany
 
  The intrinsic slice emittance of the emitted electrons on the photocathode surface at each moment during the transient photoemission process depends on the transverse size of the slice and the mean kinetic energy of the electrons within the slice. The latter relies on the surface barrier potentials of the cathode material at a fixed wavelength of the incident light, and is thus significantly influenced by the presence of strong rf and beam self-fields at / close to the cathode surface. This is, in particular, the case in high brightness injectors for modern free electron lasers. In this article, the beam self-fields are determined in a self-consistent approach, based on which improved transverse and temporal emission distributions are obtained. The nonlinear correlations of the intrinsic surface slice emittance within the bunch are shown for multiple bunch charges. A peak to peak variation of the intrinsic surface emittance is estimated as 30\% for the highest charge-density case considered in this paper. An overall reduction of the average intrinsic emittance is computed as 10\% accordingly. The cooling effect on the cathode surface is enhanced as the local space-charge density rises. Furthermore, the impacts of the cooling effect on downstream beam qualities are demonstrated through particle tracking simulations based on the injector setup at the Photo Injector Test Facility at DESY in Zeuthen (PITZ).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS013  
About • paper received ※ 27 April 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019  
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WEPTS019 Accumulating Laser-Coolable Ions in a Linear Paul Trap for Ultrahigh-Density Beam Dynamics Experiment 3134
 
  • K. Ito, H. Higaki, T. Masuda, H. Okamoto
    HU/AdSM, Higashi-Hiroshima, Japan
 
  An ion plasma confined in a linear Paul trap (LPT) exhibits the dynamic behavior physically equivalent to that of a charged-particle beam in an alternating-gradient transport channel. The Simulator of Particle Orbit Dynamics (S-POD) is a compact apparatus designed on the basis of this fact for diverse beam-physics experiments. We have so far employed Ar+ ions that can readily be produced from neutral Ar gas atoms through the electron bombardment process. A space-charge-induced tune shift of up to about 20% of the bare tune can be achieved in Ar+ plasmas [*]. We are now preparing for future S-POD experiment to explore even higher beam-density regions. For this purpose, a large number of Ca+ ions need to be stored in the LPT. Since S-POD is equipped with a powerful laser cooler for Ca+, the use of this ion species vastly expands the density range we can survey. The production of an intense bunch of Ca+ ions is, however, not so easy because of some technical reasons. By optimizing the operating condition of a multi-sectioned LPT, we succeeded in increasing the number of accumulated Ca+ ions to the level comparable to Ar+ ion plasmas. This paper reports on updated results of the experiment.
* K. Ito et al., Phys. Rev. Accel. Beams Vol. 20, 064201 (2017).
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS019  
About • paper received ※ 26 April 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019  
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WEPTS023 Hamiltonian Formalism of Intense Beams in Drift-Tube Linear Accelerators 3145
 
  • H. Okamoto
    HU/AdSM, Higashi-Hiroshima, Japan
 
  Starting from the principle of least action, we construct a general Hamiltonian formalism for beam dynamics in drift-tube linear accelerators (DTLs). The Alvarez-type structure is considered here as an example, but the present theory can readily be extended to other types of conventional linacs. The three-dimensional Hamiltonian derived includes the third-order chromatic term as well as the effects from acceleration and space charge. A clear dynamical analogy between the DTL system and compact Paul ion-trap system is pointed out, which indicates that we can conduct a fundamental design study of high-intensity hadron linacs experimentally in a local tabletop environment instead of relying on large-scale machines.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS023  
About • paper received ※ 09 May 2019       paper accepted ※ 20 May 2019       issue date ※ 21 June 2019  
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WEPTS031 The Beam Dynamics Design of the Proton Synchrotron Linear Injector for Proton Therapy 3167
SUSPFO067   use link to see paper's listing under its alternate paper code  
 
  • J. Qiao, Y.H. Pu, X.C. Xie
    SINAP, Shanghai, People’s Republic of China
 
  A compact room-temperature injector is designed to accelerate 20 mA proton beam from 30 keV to 7.0 MeV for the purpose of Proton Synchrotron Linear Injector for Proton Therapy. The main feature of this linac injector is that the 4-vane Radio Frequency Quadrupole (RFQ) and the Drift Tube Linac (DTL) section are matched by one triplet and powered by one RF power source. The beam is matched from the first RFQ section to the second DTL section in traverse and longitudinal directions. The overall accelerating gradient of this design has reached up to 1.6 MV/m with transmission efficiency of 96%.This injector combines a 3 m long 4-vane RFQ from 30 keV to 3.0 MeV with a 0.8 m long H-type DTL section to 7.0 MeV. In general, the design meets the requirements of the Pro-ton Synchrotron and the Terminal treatment.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS031  
About • paper received ※ 15 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019  
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WEPTS069 The Effects of Stochastic Space Charge in High Brightness Photolectron Beamlines for Ultrafast Electron Diffraction 3283
SUSPFO124   use link to see paper's listing under its alternate paper code  
 
  • M.A. Gordon, Y.K. Kim
    University of Chicago, Chicago, Illinois, USA
  • J.M. Maxson
    Cornell University, Ithaca, New York, USA
  • J.M. Maxson
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: This work was supported by the U.S. National Science Foundation under award PHY-1549132, the Center for Bright Beams.
As we move to ultra-high brightness photocathodes and ultra-cold beams, we may become more sensitive to stochastic, point-to point effects such as disorder induced heating and the Boersch effect, given the failure of Debye screening.  In this study, we explore the effects of stochastic scattering. Modern beam dynamics codes often approximate point to point interactions with a potential created by smoothing the charge over space, removing sensitivity to stochastic effects. This approximation is often used in beamline optimization, because it is much faster. We study the limits of validity of this approximation. In particular, we will simulate effects of stochastic space charge on a high brightness photoemission beamline, an ultrafast electron diffraction beamline with a photocathode temperature of 5 meV with a final beam energy of 225 keV. Emittance dilution in the transverse plane and transverse beam size relative to smooth space charge simulations will be presented.
 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS069  
About • paper received ※ 13 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019  
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