Keyword: space-charge
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MOPGW005 Space-Charge Potential for Elliptical Beams beam-beam-effects, focusing, proton 69

• S.R. Koscielniak

This work is motivated by the weak-strong beam-beam effect as occurs in colliding charged-particle beams. We consider beams with elliptical cross section and power law binomial forms for the density distribution. We demonstrate explicitly how to construct analytically the space-charge potential inside the ’strong’ beam. This is essential to the program of calculating beam-beam effects for non-gaussian beams.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW005
About • paper received ※ 19 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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MOPGW020 Numerical Calculation of Micro Bunching in BERLinPro Due to Space Charge and CSR Effects bunching, linac, emittance, optics 116

• B.C. Kuske, A. Meseck
HZB, Berlin, Germany

Funding: Work supported by the German Bundesministerium für Bildung und Forschung, Land Berlin and grants of the Helmholtz Association
BERLinPro is an Energy Recovery Linac Project, currently being set up at the Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany. BERLinPro is a small demonstrator for ERL technology and applications. Due to the low energy of 50, resp. 32MeV, space charge plays a dominant role in the beam dynamics. Micro-bunching, due to unavoidable shot noise from the cathode in combination with space charge, is seen in the merger as well as in the recirculator. Coherent synchrotron radiation (CSR) can amplify this bunching, as well as micro-bunching can enhance CSR losses. With the release of OPAL 2.0** in May 2018, for the first time, an open source, highly parallel tracking code is available, that is capable of numerically calculating both effects, space charge and CSR, simultaneously. The calculations are compared to earlier results*, that used analytical formulas on tracked, space charge dominated bunches.
* "On space charge driven microbunching instability in BERLinPro", PhD thesis, S.D.Rädel, Humboldt Universität zu Berlin, 2017
** http://amas.web.psi.ch/docs/opal/opaluserguide-2.0.0.pdf

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW020
About • paper received ※ 13 May 2019       paper accepted ※ 20 May 2019       issue date ※ 21 June 2019
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MOPGW036 Studies on Coherent Multi-Bunch Tune Shifts with Different Bunch Spacing at the J-PARC Main Ring proton, impedance, operation, injection 167

• A. Kobayashi, S. Igarashi, Y. Sato, T. Shimogawa, Y. Sugiyama, T. Toyama, M. Yoshii
KEK, Tokai, Ibaraki, Japan

At a high-power proton synchrotron, betatron tune shifts induced by space charge effects cause beam loss which limits the beam intensity. To achieve further high beam intensity at the main ring of the Japan Proton Accelerator Research Complex, precise control of the tune shift is indispensable. When carrying out multi-bunch measurements, we observed that the dependence of the tune shift intensity on the number of bunches follow opposite slope trends for the horizontal and vertical directions. The influence of the bunch spacing was also observed. We report on a simplified tune shift model reconstruction for understanding the origin of these phenomena and present a correction of the tune shifts for reducing beam loss up to 30 %.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW036
About • paper received ※ 01 May 2019       paper accepted ※ 20 May 2019       issue date ※ 21 June 2019
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MOPGW088 A Two-Mode Model to Study the Effect of Space Charge on TMCI in the "Long-Bunch" Regime coupling, impedance, optics, simulation 316

• E. Métral
CERN, Geneva, Switzerland

Using a two-mode approach for the Transverse Mode-Coupling Instability (TMCI) in the ’short-bunch’ regime (where the mode-coupling takes place between the modes 0 and -1, such as in the CERN LHC), both a reactive damper (ReaD) and Space Charge (SC) are expected to be beneficial: the ReaD would shift the mode 0 up while SC would shift the mode -1 down, but in both cases the coupling (and related instability) would occur at higher intensities. However, the situation is more involved in the ’long-bunch’ regime (where the mode-coupling takes place between higher-order modes, such as in the CERN SPS). As the ReaD modifies only the (main) mode 0 and not the others, it is expected to have no effect for the main mode-coupling. As concerns SC, it modifies all the modes except the mode 0, and the result has been a subject of discussion for two decades. A two-mode approach is discussed in detail in this contribution for the case of a single bunch interacting with a broad-band resonator impedance in the ’long-bunch’ regime. This model reveals in particular that in the presence of space charge, the intensity threshold can only be similar to or lower than that in the absence of space charge.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPGW088
About • paper received ※ 23 April 2019       paper accepted ※ 23 May 2019       issue date ※ 21 June 2019
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MOPMP044 Improving the Luminosity for Beam Energy Scan II at RHIC cavity, operation, electron, luminosity 540

• C. Liu, M. Blaskiewicz, K.A. Drees, A.V. Fedotov, W. Fischer, C.J. Gardner, H. Huang, D. Kayran, Y. Luo, G.J. Marr, A. Marusic, K. Mernick, M.G. Minty, C. Montag, I. Pinayev, S. Polizzo, V.H. Ranjbar, D. Raparia, G. Robert-Demolaize, T. Roser, J. Sandberg, V. Schoefer, T.C. Shrey, S. Tepikian, P. Thieberger, A. Zaltsman, K. Zeno, I.Y. Zhang, W. Zhang
BNL, Upton, Long Island, New York, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
The QCD (Quantum Chromodynamics) phase diagram has many uncharted territories, particularly the nature of the transformation from Quark-Gluon plasma (QGP) to the state of Hadronic gas. The Beam Energy Scan I (BES-I) at the Relativistic Heavy Ion Collider (RHIC) was completed but measurements had large statistical errors. To improve the statistical error and expand the search for first-order phase transition and location of the critical point, Beam Energy Scan II will commence in 2019 with a goal of improving the luminosity by a factor of 3-4. The beam lifetime at low energies was and will be limited by some physical effects of which the most significant are intrabeam scattering, space charge, beam-beam, persistent current effects. This article will review these potential limiting factors and introduce the countermeasures which will be in place to improve BES-II luminosity.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPMP044
About • paper received ※ 14 May 2019       paper accepted ※ 20 May 2019       issue date ※ 21 June 2019
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MOPRB046 Status of the ESSnuSB Accumulator Design linac, injection, simulation, target 666

• Y. Zou, T.J.C. Ekelöf, M. Olvegård, R.J.M.Y. Ruber
Uppsala University, Uppsala, Sweden
• E. Bouquerel, M. Dracos
IPHC, Strasbourg Cedex 2, France
• M. Eshraqi, B. Gålnander
ESS, Lund, Sweden
• H.O. Schönauer, E.H.M. Wildner
CERN, Geneva, Switzerland

Funding: This project is supported by the COST Action CA15139 EuroNuNet. It has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 777419.
The 2.0 GeV, 5 MW proton linac for the European Spallation Source, ESS, will have the capacity to accelerate additional pulses and send them to a neutrino target, providing an excellent opportunity to produce an unprecedented high performance neutrino beam, the ESS neutrino Super Beam, ESSnuSB, to measure, with precision, the CP violating phase at the 2nd oscillation maximum. In order to comply with the acceptance of the target and horn systems that will form the neutrino super beam, the long pulses from the linac must be compressed by about three orders of magnitude with minimal particle loss, something that will be achieved through multi-turn charge-exchange injection in an accumulator ring. This ring will accommodate over 2·1014 protons, which means that several design challenges are encountered. Strong space charge forces, low-loss injection with phase space painting, efficient collimation, a reliable charge stripping system, and e-p instabilities are some of the important aspects central to the design work. This paper presents the status of the accumulator ring design, with multi-particle simulations of the injections procedure.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPRB046
About • paper received ※ 14 May 2019       paper accepted ※ 20 May 2019       issue date ※ 21 June 2019
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MOPTS086 Identification and Compensation of Betatronic Resonances in the Proton Synchrotron Booster at 160 Mev resonance, injection, proton, emittance 1054

• A. Santamaría García, S.C.P. Albright, F. Antoniou, F. Asvesta, H. Bartosik, G.P. Di Giovanni, B. Mikulec
CERN, Geneva, Switzerland
• F. Asvesta
NTUA, Athens, Greece
• H. Rafique
University of Manchester, Manchester, United Kingdom

The Proton Synchrotron Booster (PSB) is the first circular accelerator in the injector chain to the Large Hadron Collider (LHC) and accelerates protons from 50 MeV to 1.4 GeV. The PSB will need to deliver two times the current brightness after the LHC Injectors Upgrade (LIU) in order to meet the High Luminosity LHC (HL-LHC) beam requirements. At the current injection energy a large incoherent space charge tune spread limits the brightness of the beams, which is one of the main motivations to increase the injection energy to 160 MeV with the injection provided by Linac4, a new H linear accelerator. The higher injection energy will allow doubling the beam intensity while maintaining a space charge tune spread similar to current values. The degradation of the beam brightness due to the tune spread can be minimized with a proper choice of working point and an efficient compensation of resonances. In this paper, we present the measurement of the betatronic resonances in the four rings of the PSB at 160 MeV before the Long Shutdown 2, as well as the results of a proposed compensation scheme.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-MOPTS086
About • paper received ※ 13 May 2019       paper accepted ※ 20 May 2019       issue date ※ 21 June 2019
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TUZZPLS3 New Method of Calculation of the Wake due to Radiation and Space Charge Forces in Relativistic Beams radiation, wakefield, electron, synchrotron-radiation 1223

• G. Stupakov
SLAC, Menlo Park, California, USA

Funding: This work was supported by the Department of Energy, Contract No. DE-AC02-76SF00515.
Radiation reaction force in a relativistic beam, also known as a CSR wakefield, is often computed using a 1D model of a line charge beam. While this model can serve as a useful tool for a quick calculation, in some cases, it may not be sufficiently accurate. In particular, this model misses the so-called compression effects associated with the change of the electromagnetic energy when the beam is compressed longitudinally or transversely. The existing 3D simulation codes that take this effect into account are often slow and are not easy to use. In this work, we propose a new approach to the calculations of radiation and space charge longitudinal forces based on the use of the integrals for the retarded potentials. Our main result expresses the rate of change of particles energy through 2D (in a 2D model) or 3D integrals for a given orbit of the beam. It generalizes the 1D model and includes the transient effects of at the entrance and the exit from the magnet. For a given beam line with known magnetic lattice, and a known distribution function of the beam, the calculation reduces to taking 2D or 3D integrals along the orbit.

Slides TUZZPLS3 [2.080 MB]
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUZZPLS3
About • paper received ※ 29 April 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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TUPTS015 Design Steps Towards an Electron Source for Ultrafast Electron Diffraction at DELTA electron, laser, cavity, gun 1968

• D. Krieg, S. Khan
DELTA, Dortmund, Germany
• T.J. Albert, K. Sokolowski-Tinten
Universität Duisburg-Essen, Duisburg, Germany

Funding: MERCUR Pr-2017-0002
Ultrafast electron diffraction (UED) is a pump-probe technique to explore the structural dynamics of matter, combining sub-angstrom De-Broglie wavelength of electrons with femtosecond time resolution. UED experiments require ultrashort laser pulses to pump a sample, electron bunches with small emittance and ultrashort length to analyze the state of the sample and excellent control of the delay between them. Electrons accelerated to a few MeV in a photocathode gun offer significant advantages compared to keV electrons from electrostatic electron sources regarding emittance, bunch length and, due to the reduction of space charge effects, bunch charge. Furthermore, thicker samples and hence a wider range of possible materials are enabled by the longer mean free path of MeV electrons. In this paper, design steps towards a university-based UED facility with ultrashort and low-emittance MeV electron bunches are presented, including the transverse and longitudinal focusing schemes, which minimize space charge effects and nonlinearities.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS015
About • paper received ※ 15 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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TUPTS099 Predicting the Performances of Coherent Electron Cooling with Plasma Cascade Amplifier electron, plasma, kicker, collider 2150

• G. Wang, V. Litvinenko, J. Ma
BNL, Upton, Long Island, New York, USA
• V. Litvinenko
Stony Brook University, Stony Brook, USA

Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Recently, we proposed a new type of instability, Plasma Cascade Instability (PCI), to be used as the amplification mechanism of a Coherent Electron Cooling (CeC) system, which we call Plasma Cascade Amplifier (PCA). In this work, we present our analytical estimate of the cooling force as expected from a PCA- based CeC system and compare it with the simulation results. As examples, we apply our analysis to a few possible CeC systems and investigate the evolution of the circulating ion beams in the presence of cooling.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS099
About • paper received ※ 15 May 2019       paper accepted ※ 23 May 2019       issue date ※ 21 June 2019
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WEPGW027 Evaluation and Reduction of Influence of Filling Pattern on X-Ray Beam Position Monitors for SPring-8 storage-ring, operation, electron, undulator 2526

• H. Aoyagi, Y. Furukawa, S. Takahashi
JASRI/SPring-8, Hyogo, Japan

SPring-8 constantly provides various several-bunch mode operations, which combine single bunches and train bunches. Recently, influence of filling pattern on the accuracy of the XBPMs became apparent, so that we started a systematic evaluation. It was found that the influence was caused by suppression of current signal due to space charge effect, which could be quantified by observing a behaviour of the current signal while changing the voltage of photoelectron collecting electrodes. In order to mitigate the space charge effect, we examined some methods, such as, changing operation parameters of the XBPMs and the undulators. As a result, we successfully reduced the influence of filling pattern.
* H. Aoyagi et al., Proc. of PASJ2018 WEOL06
http://www.pasj.jp/webpublish/pasj2018/proceedings/PDF/WEOL/WEOL06.pdf
http://www.pasj.jp/webpublish/pasj2018/proceedings/PDF/WEOL/WEOL06oral.pdf

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPGW027
About • paper received ※ 10 May 2019       paper accepted ※ 17 May 2019       issue date ※ 21 June 2019
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WEPGW051 Designing of a Solenoid Lens for the Application to a Compact Electron Beam Testing Bench solenoid, electron, gun, cathode 2591

• S.Y. Lu, G. Feng, T. Hu, X.D. Tu, Y.Q. Xiong, P. Yang
HUST, Wuhan, People’s Republic of China

To calculate beams transport is vital for designing vacuum pipe and arranging focusing elements for each electron beam line system. Space charge effects of a low-energy, high-intensity DC electron beam focused by a solenoid lens with bucking coil are investigated theoretically in this paper. A second-order equation is numerical solved for the beam envelope focused by a short solenoid lens. In addition, a conventional transfer matrix of solenoid is not applicable to low-energy, high-intensity electron beams because the strong space charge effects are ignored. By cutting a solenoid into several segments, we have derived a micro-transfer matrix which takes space charge fields into account, and a complete beam envelope for a transport system. A simulation is used to verify our theoretical calculation results, and corresponding discussions are given in detail.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPGW051
About • paper received ※ 13 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPGW059 A Preliminary Feasibility Study of Measurement of Quadrupolar Beam Oscillations at CSNS RCS quadrupole, pick-up, kicker, synchrotron 2611

• Y. Yuan, P. Li, S.Y. Xu
IHEP, Beijing, People’s Republic of China

In high intensity proton synchrotrons, linear and nonlinear betatron resonances cause beam loss. When the betatron tune spreads over a resonance line, the betatron oscillation amplitude will get larger, causing large beam loss. In the quadrupolar beam transfer function, the coherent space-charge tune shift of quadrupolar beam oscillations is used to determine the incoherent tune shift. China Spallation Neutron Source (CSNS) is a high intensity accelerator based facility consists of linear accelerator and the Rapid Cycle Synchrotron (RCS). A system of quadrupolar pick-up and kicker can be used for evaluating tune shifts and spreads. This paper will present already existing beam diagnostic instrumentation on CSNS/RCS, and discuss feasibility study of measurement of quadrupolar beam oscillations through adding a quadrupolar-type beam pick-up.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPGW059
About • paper received ※ 15 May 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPGW114 Interferometric Measurement of Bunch Length of a 3Mev Picocoulomb Electron Beam laser, electron, cathode, experiment 2766

• X. Yang, M. Babzien, B. Bacha, G.L. Carr, W.X. Cheng, L. Doom, M.G. Fedurin, B.N. Kosciuk, J.J. Li, D. Padrazo Jr, T.V. Shaftan, V.V. Smaluk, C. Swinson, L.-H. Yu, Y. Zhu
BNL, Upton, Long Island, New York, USA

Funding: BNL LDRD
We report the bunch length measurement of low-energy 3 MeV electron beams in picosecond regime with the charge from 1.0 to 14 pC. It is the first time that we demonstrate single-cycle nano-joule coherent terahertz (THz) radiation from 3MeV electron beam can be meas-ured via a far-infrared Michelson interferometer using a QOD. At this low energy range, when charge is about 1 pC, the signal from the conventional helium-cooled sili-con composite bolometer is too low. Compared to the bunch length measurement via the ultrafast-laser-pump and electron-beam-probe in the timescale 10-14 to 10-12 s which is determined by the phase-transition dynamics in solids, the advantages are: there are no needs of pump laser and probe sample, greatly simplifying the experi-ment; the timing jitter between laser and electron beams contributes no error to the bunch length measurement; furthermore, the method can be extended to sub-picosecond regime enabling bunch length measurement in a much broader timescale 10-14 to 10-11 s for low-energy electron beams. In the current experiment the bunch length is limited to 1 ps only because the setup of driving laser to cathode with a large 70° incident angle, effective-ly lengthening the laser pulse to ≥1 ps.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPGW114
About • paper received ※ 14 May 2019       paper accepted ※ 23 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 cathode, emittance, laser, electron 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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WEPTS014 Coherent vs Incoherent Effects and Debye Length plasma, focusing, lattice, vacuum 3116

• G. Franchetti

In this proceeding it is discussed the effect of coherent vs. incoherent effect and discussing the validity of frozen models of space charge according to the Debye length and beam radius. This in view of discussing the relation of IBS and space charge
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS014
About • paper received ※ 15 April 2019       paper accepted ※ 28 May 2019       issue date ※ 21 June 2019
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WEPTS022 Stability Tune Diagram of a High-Intensity Hadron Ring resonance, emittance, lattice, betatron 3141

• H. Okamoto, K. Kojima, Y. Tokashiki

To date, the optimum operating point of a high-intensity hadron ring has been determined on the basis of the conventional incoherent picture. It is generally chosen on the tune diagram such that the so-called "incoherent tune spread" of a stored beam does not overlap with low-order "single-particle resonance" lines. We here propose a new approach to construct the stability tune diagram on the basis of the self-consistent coherent picture. The betatron resonance condition recently conjectured from one-dimensional Vlasov predictions is employed for this purpose, which predicts the existence of twice as many resonance stop bands as expected from the well-known incoherent resonance condition at high beam density *,**. The proposed general rules for the stability-chart construction are very simple and free from any model-dependent unobservables like space-charge-depressed incoherent tunes. As an example, we apply the present rules to the lattice of the rapid cycling synchrotron at J-PARC and explain why the operating bare tunes of this machine have been chosen slightly below 6.5 in both transverse directions.
* K. Ito et al., Phys. Rev. Accel. Beams 20, 064201 (2017).
** H. Okamoto and K. Yokoya, Nucl. Instrum. Meth. A 482, 51 (2002).

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS022
About • paper received ※ 09 May 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 DTL, quadrupole, acceleration, focusing 3145

• H. Okamoto

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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WEPTS024 Tune Shifts and Optics Modulations in the High Intensity Operation at J-PARC MR simulation, betatron, sextupole, quadrupole 3148

• T.Y. Yasui
The University of Tokyo, Graduate School of Science, Tokyo, Japan
• S. Igarashi, T. Koseki, K. Ohmi, Y. Sato, K. Satou
KEK, Ibaraki, Japan

Funding: This study is supported by the MEXT program "Advanced Leading Graduate Course for Photon Science (ALPS)"
J-PARC Main Ring (MR) is the intensity-frontier proton accelerator. The beam intensity of 2.6×1014 protons per pulse has been achieved for the current user operation. In this high-intensity operation, the tune spread caused by the space-charge is one of the main reasons for beam loss. The modulation of the betatron function and the tune shift were simulated with a PIC algorithm calculation code*. The simulation results showed that the space-charge effects were dominant in small particle action, and the sextupole fields effects were dominant in large particle action. Because sextupole strength is large in MR, sextupole fields induce substantial tune shifts. At the benchmark of the space-charge simulation, the simulation results matched the analytical space-charge calculations performed without sextupoles. It was found that the betatron function was modulated at most 6% by the space-charge effects and at most 8% by the effects of sextupoles in J-PARC MR. These effects to the injection beam optics matching and to the beam aperture will be investigated.
* K. Ohmi et al., "Study of Halo Formation in J-PARC MR", Proceedings of the 22nd Particle Accelerator Conf. (PAC’07), Albuquerque, NM, USA, Jun. 2007, paper THPAN040, pp. 3318-3320.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS024
About • paper received ※ 15 May 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS034 Generation of Sub-Femtosecond Electron Beams and Electron Bunch Trains With High Form Factor Using Wake Field Structures electron, wakefield, bunching, simulation 3174

• Z. Dong, H. Chen, X.J. Deng, Y. C. Du, Z. Zhou
TUB, Beijing, People’s Republic of China

In this paper, we propose two beam manipulation methods with wakefield structures in a photo-injector. First, we propose a simple scheme to compensate non-linear effects during ballistic bunching by using a wakefield structure. Simulations have shown beams of 1 pC charge can be compressed to 1.56 fs rms, and even shorter beams (a few hundred attoseconds) can be obtained with bunch charge well below 1 pC. In the second part, a method of producing bunch trains with high form factor is proposed by using multiple wake-field structures. Simulation results have shown the production of a train with a form factor of 0.5 using a 1 nC beam at few-MeV energy.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS034
About • paper received ※ 11 May 2019       paper accepted ※ 23 May 2019       issue date ※ 21 June 2019
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WEPTS037 DC Beam Space-Charge Modeling for OpenXAL simulation, LEBT, solenoid, GUI 3177

• B.E. Bolling, N. Milas
ESS, Lund, Sweden

OpenXAL is an open source multi-purpose accelerator physics software platform based on a pure Java open source development environment used for creating accelerator physics applications, scripts and services. Currently, the software has been used with an ellipsoidal (bunched) beam to account for space-charge effects. Applications developed so far for ESS, such as the Virtual Machine for the ESS Low Energy Beam Transport (LEBT) section, would profit from a DC beam description. In this paper, the space-charge component for a continuous beam is derived taking into account beams with different transverse charge distributions (uniform, gaussian, etc). The implementation in OpenXAL and a comparison with other simulation codes is also presented.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS037
About • paper received ※ 14 May 2019       paper accepted ※ 20 May 2019       issue date ※ 21 June 2019
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WEPTS038 New RFQ and Field Map Model for the ESS Linac Simulator rfq, linac, cavity, simulation 3181

• J.F. Esteban Müller, E. Laface
ESS, Lund, Sweden

The Java ESS Linac Simulator (JELS) is an extension of the Open XAL online model that is a fundamental part of the accelerator control system. The model is used by high-level physics applications for commissioning, tuning, and machine development activities at the European Spallation Source (ESS). This paper summarizes the upgrades done to JELS during the last year. An RFQ model is under development. The RFQ was the only element of the linac missing in the online model. The electromagnetic field map model has been refactored to ease implementation of new elements (rf cavities and magnets), and to allow the superposition of more than one field map and other elements. Further improvements have also been done in the treatment of corrector magnets and space charge for continuous beam in the Low-Energy Beam Transport (LEBT). Finally, the machine description can now include arbitrary aperture definitions.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS038
About • paper received ※ 14 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS041 Coupling and Space Charge Studies at the CERN PSB resonance, optics, coupling, emittance 3192

• F. Asvesta
NTUA, Athens, Greece
• F. Antoniou, H. Bartosik, G.P. Di Giovanni, Y. Papaphilippou
CERN, Meyrin, Switzerland

In the nominal optics of the CERN PS-Booster (PSB), the fourth order coupling resonance is excited by space charge (Montague resonance) due to the same integer tune values. This resonance can be avoided by changing the tunes to different integers. A new PSB optics is presented and emittance measurements crossing the coupling resonance for the nominal and the new optics are shown.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS041
About • paper received ※ 17 April 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS047 Space Charge Driven Resonances in the CERN PS resonance, brightness, simulation, lattice 3216

• F. Asvesta
NTUA, Athens, Greece
• H. Bartosik, A. Huschauer, Y. Papaphilippou
CERN, Geneva, Switzerland

In the CERN Proton Synchrotron space charge driven resonances are excited around the operational working point due to the periodicity of the optics functions. In this paper, the resonances are studied using analytical methods, i.e. the evaluation of the resonance driving terms connected to the space charge potential of Gaussian distributions. Furthermore, the resonances are characterized in measurements and simulations for various beams. The beams considered are different in terms of brightness, in order to study the dependence of the resonance strength on the space charge force.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS047
About • paper received ※ 17 April 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS050 Multi-Species Electron-Ion Simulations and their Application to the LHC electron, simulation, operation, beam-losses 3228

• L. Mether, G. Iadarola, K.L. Poland, G. Rumolo, G. Skripka
CERN, Meyrin, Switzerland

During operation in 2017 and 2018, the LHC suffered from recurrent beam aborts associated with beam losses in one of its arc cells in correlation with quickly developing transverse coherent oscillations. The events are thought to have been caused by a localised high gas density resulting from the phase transition of a macro-particle that has entered the beam. In order to model the observed coherent effects through the interaction of the beam with the induced pressure bump, novel modelling capabilities have been implemented that allow for the simulation of multiple clouds of different particle species and their interaction with the beam. In this contribution the simulation model and its application are described.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS050
About • paper received ※ 13 May 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS057 Recent Studies of the Resonances at a Cell Tune of 0.25 Using the Ibex Paul Trap resonance, experiment, emittance, simulation 3255

• L. Martin, S.L. Sheehy
JAI, Oxford, United Kingdom
• D.J. Kelliher
STFC/RAL/ASTeC, Chilton, Didcot, Oxon, United Kingdom

We use the IBEX linear Paul trap to study the resonance at a cell tune of \frac{1}{4} with both equal and unequal transverse tunes, at a range on intensities. We compare this experimental result to simulation using the PIC code Warp. We find that the experimental result differs from the simulation, which may be explained by the ion loss in the IBEX experiment, which more closely replicates a real accelerator. Knowledge of the tune corresponding to greatest beam loss is important for the design of future high intensity machines.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS057
About • paper received ※ 30 April 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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WEPTS068 A Novel S-Based Symplectic Algorithm for Tracking With Space Charge simulation, resonance, optics, proton 3279

• J.P. Edelen, D.T. Abell, D.L. Bruhwiler, N.M. Cook, C.C. Hall, S.D. Webb

Funding: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of High Energy Physics under Award Number DE-SC0011340
Traditional finite-difference particle-in-cell methods for modeling self-consistent space charge introduce non-Hamiltonian effects that make long-term tracking in storage rings unreliable. Foremost of these is so-called grid heating. Particularly for studies where the Hamiltonian invariants are critical for understanding the beam dynamics, such as nonlinear integrable optics, these spurious effects make interpreting simulation results difficult. To remedy this, we present a novel symplectic spectral space charge algorithm that is free of non-Hamiltonian numerical effects and, therefore, suitable for long-term tracking studies. Results presented here include a detailed study of the solver’s performance under a range of conditions. First, we show benchmarking and convergence studies for different particle shapes and different particle distributions. Then we demonstrate the solver’s ability to preserve Hamiltonian structure by studying the formation of space-charge driven resonances using both our algorithm and traditional PIC.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS068
About • paper received ※ 14 May 2019       paper accepted ※ 23 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 simulation, electron, emittance, cathode 3283

• 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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WEPTS078 Chaos Indicators for Studying Dynamic Aperture in the IOTA Ring with Protons dynamic-aperture, lattice, simulation, betatron 3301

• K. Hwang, C.E. Mitchell, R.D. Ryne
LBNL, Berkeley, California, USA

The Integrable Optics Test Accelerator (IOTA) is a novel storage ring under commissioning at Fermi National Accelerator Laboratory designed (in part) to investigate the dynamics of beams in the presence of highly nonlinear transverse focusing fields that generate integrable single-particle motion. In this study, we explore the sensitivity of the lattice dynamic aperture to the presence of nonlinear space charge. For this purpose, two distinct chaos indicators are compared (frequency map analysis and forward-backward integration). Because the integrability of motion requires integer betatron tune advance between passes through the nonlinear magnetic element, a large role is played by space-charge-induced tune spread. As a result, these tools are also applied to a toy model of the IOTA lattice to investigate the sensitivity of dynamic aperture to violations of the integer tune advance condition.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS078
About • paper received ※ 14 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS079 Analysis of Particle Noise in a Gridless Spectral Poisson Solver for Symplectic Multiparticle Tracking focusing, emittance, plasma, simulation 3304

• C.E. Mitchell, J. Qiang
LBNL, Berkeley, California, USA

Funding: This work was was supported by the Director, Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Gridless symplectic methods for self-consistent modeling of space charge in intense beams possess several advantages over traditional momentum-conserving particle-in-cell methods, including the absence of numerical grid heating and the presence of an underlying multi-particle Hamiltonian. Despite these advantages, there remains evidence of irreversible emittance growth due to numerical particle noise. For a class of such algorithms, a first-principles kinetic model of the numerical particle noise is obtained and applied to gain insight into noise-induced entropy growth and thermal relaxation.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS079
About • paper received ※ 14 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS083 Multipass Simulations of Space Charge Compensation using Electron Columns at IOTA electron, simulation, cavity, proton 3313

• C.S. Park, E.G. Stern
Fermilab, Batavia, Illinois, USA
Northern Illinois University, DeKalb, Illinois, USA
• C.E. Mitchell, R.D. Ryne
LBNL, Berkeley, California, USA

Defocusing repulsive forces due to self space charge fields lead to degradation of high-intensity particle beams. Being of particular concern for low- and medium-energy proton beams, they result in emittance growth, beam halo formation, and beam loss. They set stringent limits on the intensity of frontier accelerators; therefore, the mitigation of space charge effects is a crucial challenge to improve proton beam intensity. The space charge effects in a positively charged proton beam can be effectively compensated using negatively charged electron columns. In this paper, we present the results of simulations using Synergia of the Electron Column lattice for IOTA. Beam loss due to space charge effects and aperture restrictions have been studied, as well as bunch formation and matching using an adiabatic ramp of the RF cavity. The results show the need for space charge compensation, and provide the basis for integration of the Synergia and Warp codes in order to form a complete simulation of space charge compensation using an Electron Column in IOTA.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS083
About • paper received ※ 16 May 2019       paper accepted ※ 22 May 2019       issue date ※ 21 June 2019
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WEPTS093 Emittance Preservation for LCLS-II-HE Project emittance, electron, lattice, laser 3333

• J. Wu, T.O. Raubenheimer, M.D. Woodley
SLAC, Menlo Park, California, USA
• J. Qiang
LBNL, Berkeley, California, USA

Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
A small transverse slice emittance at the undulator entrance is essential for high performance of the free electron laser. To achieve this, preservation of the phase space density of the electron bunch during acceleration and compression is absolutely necessary. The LCLS-II-HE is designed to transport a 100 pC bunch with an emittance of ~0.3 mm-mrad with minimal emittance dilution. However, in simulations starting from a normalized emittance on the order of 0.1 mm-mrad, the emittance growth is significant. In this paper, the sources of emittance growth are studied along the accelerator, in particular, around the laser-heater, the two bunch compressors. We have investigated mechanisms of emittance growth such as space charge, coherent synchrotron radiation, chromatic aberration, and spurious dispersion. Due to the extremely small emittance from the injector, 3-D space charge effect is important to determine the space charge dominated region and emittance dominated region. With this understanding, emittance preservation schemes are proposed. Studies are carried out with IMPACT simulation code, as well as ASTRA and ELEGANT.

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS093
About • paper received ※ 23 May 2019       paper accepted ※ 24 May 2019       issue date ※ 21 June 2019
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THPGW029 Crucial Transverse Beam Dynamics of the Racetrack-shape Fixed Field Induction Accelerator for Giant Cluster Ions acceleration, injection, induction, optics 3643

• T. Taufik
BATAN, Yogyakarta, Indonesia
• T. Adachi, K. Takayama, M. Wake
KEK, Ibaraki, Japan

A racetrack-shape fixed field induction accelerator (RAFFIA) for high energy giant cluster ion acceleration was proposed in 2015*. The RAFFIA employs 4 bending magnets with gradient in the main pole face and reverse field strip at its front side which generate strong focusing in both planes. Beam dynamics properties of the RAFFIA of 140 MeV for C-60 have been evaluated by linear optics. The result has been confirmed with a help of 3D macro-particle computer simulation**. It is identified that the issue of COD generated from field non-uniformity associated with a finite size of the bending magnet is inherent. The programmed COD correction by steering magnets are discussed as well as the importance of uniformity in the magnet field profile. So far it has been unknown what beam current is acceptable in the RAFFIA. In order to estimate space-charge effects in the RAFFIA under design, the 2D core (σ) evolution equation has been derived from the envelope equation perturbed by space-charge fields. Resonant structures and chaotic motion in the phase space of (σ,σ’) have been clarified as a function of beam current. Those results were justified by macro-particle tracking based on a renormalized transfer matrix approach***. As a result, it turns out that the 8+ C-60 beam of 200 uA is acceptable.
* K.Takayama, et. al, Phys. Rev. ST Accel. Beams 18, 050101 (2015).
** Taufik, et. al, sub. to Phys. Rev. AB (2018).
*** Taufik, K.Takayama, and T. Adachi, sub. Phys. Rev. AB (2019).

DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-THPGW029
About • paper received ※ 14 May 2019       paper accepted ※ 21 May 2019       issue date ※ 21 June 2019
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