Keyword: bunching
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MOPAB054 Start-to-End Simulation of a Free-Electron Laser Driven by a Laser-Plasma Wakefield Accelerator plasma, laser, electron, radiation 233
 
  • W. Liu, Y. Jiao, S. Wang
    IHEP, Beijing, People’s Republic of China
  
  The rapid development of laser-plasma wakefield accelerator (LPA) has opened up a new possible way to achieve ultra-compact free-electron laser (FEL). To this end, LPA experts have made many efforts to generate electron beams with sub-micrometer emittance and low energy spread. Recently, a new laser modulation method was proposed for generating EUV coherent pulse in an LPA-driven FEL. The simulation demonstration of this scheme is based on the Gaussian beam. However, the distribution of the LPA beam is not Gaussian. To further verify the feasibility of the method mentioned above, a start-to-end simulation is required.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB054  
About • paper received ※ 18 May 2021       paper accepted ※ 27 May 2021       issue date ※ 22 August 2021  
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MOPAB056 Optimization of a TBA with Stable Optics and Minimal Longitudinal Dispersion and CSR-Induced Emittance Growth emittance, synchrotron, quadrupole, FEL 241
 
  • C. Zhang, Y. Jiao
    IHEP, Beijing, People’s Republic of China
  • C.-Y. Tsai
    HUST, Wuhan, People’s Republic of China
  
  Funding: National Natural Science Foundation of China (No. 11922512), Youth Innovation Promotion Association of Chinese Academy of Sciences (No. Y201904), National Key R&D Program of China (No. 2016YFA0401900)
In the beam transfer line which often consists of dipoles to deflect the beam trajectory, longitudinal dispersion effect and emission of coherent synchrotron radiation (CSR) will lead to beam phase space distortion, thus degrading the machine performance. In this study, optimizations of a triple-bend achromat (TBA) cell are conducted using the multi-objective particle swarm optimization (MOPSO) method to suppress the CSR-induced emittance growth and minimize the longitudinal dispersion functions up to high orders, simultaneously. For the longitudinal dispersion function, results of three optimization settings are reported, which makes the TBA design first-order, second-order, and higher-order isochronous. Furthermore, we study the shortest possible beamline length of the higher-order isochronous TBA design, which may pave the way to designing a more compact beam transfer line. 		 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB056  
About • paper received ※ 12 May 2021       paper accepted ※ 28 May 2021       issue date ※ 15 August 2021  
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MOPAB270 Beam Dynamics Studies in a Standing Wave Ka-band Linearizer electron, emittance, operation, simulation 857
 
  • J. Scifo, M. Behtouei, L. Faillace, M. Ferrario, A. Giribono, B. Spataro, C. Vaccarezza
    INFN/LNF, Frascati, Italy
  • M. Migliorati
    INFN-Roma1, Rome, Italy
  • M. Migliorati
    Sapienza University of Rome, Rome, Italy
  • G. Torrisi
    INFN/LNS, Catania, Italy
  
  Next-generation FEL user facilities require high-quality electron beams with kA peak current. The combination of a high brightness RF injector and a magnetic compression stage represents a very performant solution in terms of electron beam emittance and peak current. One of the important issues is the design of a proper device that acts as a linearizer for the beam longitudinal phase space. Recently, the design of a SW Ka band RF accelerating structure has been proposed with promising results. The paper reports on electron beam dynamics studies in the described RF structure.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB270  
About • paper received ※ 19 May 2021       paper accepted ※ 29 August 2021       issue date ※ 26 August 2021  
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MOPAB337 Design Study of the Spiral Buncher Cavities for the High Current Injector at IUAC cavity, linac, impedance, rfq 1048
 
  • S. Kedia, R. Ahuja, R. Mehta, C.P. Safvan
    IUAC, New Delhi, India
  
  Two high energy beam transport (HEBT) cavities have been designed to provide the longitudinal beam bunching between drift tube linac and superconducting super-buncher of the superconducting linear (SC-LINAC) accelerator. The spiral type cavities were chosen over standard quarter wave-type geometry due to its higher shunt impedance. The TRACE-3D ion-optical codes have been used to determine the bunching voltage and physical location of the cavities. The two-gap RF cavity requires 80 kV/gap to provide the longitudinal beam bunching at the entrance of the superconducting buncher. The CST-MWS simulations were performed to design the spiral type bunching cavities. The various parameters including shunt impedance, quality factor, average accelerating field, and total power loss were determined using CST-MWS simulations. The ratio of drift tube radius to the gap was optimized to achieve the maximum effective electric field with minimum field penetration within the gap. The SolidWorks software has been used to prepare a mechanical model for the fabrication.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB337  
About • paper received ※ 15 May 2021       paper accepted ※ 26 May 2021       issue date ※ 26 August 2021  
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MOPAB339 Design Of An X-band 3MeV Standing-wave Accelerating Structure with Nose-cone Structure Made From Two Halves coupling, impedance, cavity, electron 1051
 
  • F. Liu, H.B. Chen, J. Shi, C.-X. Tang, H. Zha
    TUB, Beijing, People’s Republic of China
  
  This work presents an X-band 3MeV standing-wave accelerating structure with nose cones made from two halves. Milling two longitudinally split halves is one economic method to manufacture accelerating structure for decrease of welding, with increasing the difficulty in machining. This linear accelerator includes 4 buncher cavities and 4 accelerating cavities, and nose cone is applied to achieve high shunt impedance. A technical prototype is under fabrication to bring two milled halves manufacture way into practical application.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB339  
About • paper received ※ 19 May 2021       paper accepted ※ 26 May 2021       issue date ※ 15 August 2021  
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MOPAB372 KARVE: A Nanoparticle Accelerator for Space Thruster Applications acceleration, ECR, radio-frequency, simulation 1151
 
  • J.W. Lewellen, L.R. Danielson, A. Essunfeld, J.A. Hollingsworth, M.A. Holloway
    LANL, Los Alamos, New Mexico, USA
  • E.K. Lewis
    NASA Johnson Space Center, Houston, Texas, USA
  
  We present a concept for using RF-based acceleration of nanoparticles (NPs) as a means of generating thrust for future space missions: the Kinetic Acceleration & Resource Vector Engine (KARVE) thruster. Acceleration of nanoparticles (NPs) via DC accelerators has been shown to be feasible in dust accelerator labs such as the Heidelberg dust accelerator and the 3 MV hypervelocity dust accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies. In contrast, KARVE uses RF-driven acceleration of nanoparticles as the basis of a thruster design lying between chemical and ion engines in performance: more efficient than chemical engines in terms of specific impulse; and higher thrust than ion engines. The properties of multi-gap RF accelerators also allow an on-the-fly tradeoff between specific impulse and thrust.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB372  
About • paper received ※ 19 May 2021       paper accepted ※ 27 May 2021       issue date ※ 10 August 2021  
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TUPAB045 The Low Energy Injector Design for the Southern Advanced Photon Source electron, linac, cavity, gun 1450
 
  • Y. Han
    IHEP CSNS, Guangdong Province, People’s Republic of China
  • Y. Jiao, B. Li, X. Liu, S. Wang
    IHEP, Beijing, People’s Republic of China
  
  The Southern Advanced Photon Source (SAPS) is a project under design, which aims at constructing a 4th generation storage ring with emittance below 100 pm.rad at the electron beam energy of around 3.5 GeV. At present, two injector options are under consideration. One is a full energy booster plus a low energy injector, and another is a full energy linac injector. In this paper, a preliminary design of the low energy injector is presented, which consists of an DC thermionic electron gun, a bunching section and an accelerating section. The beam energy at the end of the injector is about 150 MeV.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB045  
About • paper received ※ 17 May 2021       paper accepted ※ 09 June 2021       issue date ※ 18 August 2021  
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TUPAB047 Bunch Compressor Design in the Full Energy Linac Injector for the Southern Advanced Photon Source linac, electron, simulation, laser 1458
 
  • B. Li
    IHEP CSNS, Guangdong Province, People’s Republic of China
  • Y. Jiao, X. Liu, S. Wang
    IHEP, Beijing, People’s Republic of China
  
  A mid-energy fourth-generation storage ring light source named the Southern Advanced Photon Source (SAPS), has been considered to be built neighboring the China Spallation Neutron Source (CSNS). A full energy linac has been proposed as an injector to the storage ring, with the capability to generate high brightness electron beams to feed a Free Electron Laser (FEL) at a later stage. To achieve the high peak current in FELs, space charge, RF structure wakefield, coherent synchrotron radiation (CSR), RF curvature, and the second-order momentum compaction factor should be carefully considered and optimized during the bunch compression processes. In this paper, physic design and simulation results of the bunch compressors are described.  
poster icon Poster TUPAB047 [1.918 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB047  
About • paper received ※ 15 May 2021       paper accepted ※ 09 June 2021       issue date ※ 28 August 2021  
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TUPAB066 Status of the Short-Pulse Source at DELTA laser, electron, undulator, simulation 1518
 
  • A. Held, B. Büsing, H. Kaiser, S. Khan, D. Krieg, A.R. Krishnan, C. Mai
    DELTA, Dortmund, Germany
  
  Funding: Work supported by BMBF (05K19PEB).
At the synchrotron light source DELTA operated by the TU Dortmund University, the short-pulse source employs the seeding scheme coherent harmonic generation (CHG) and provides ultrashort pulses in the vacuum ultraviolet and terahertz regime. Here, the interaction of laser pulses with the stored electron bunches result in a modulation of the longitudinal electron density which gives rise to coherent emission at harmonics of the laser wavelength. Recently, investigations of the influence of the Gouy phase shift at the focal point of the laser pulses on the laser-electron interaction have been performed. For the planned upgrade towards the more sophisticated seeding scheme echo-enabled harmonic generation (EEHG) featuring a twofold laser-electron interaction, simulations of the ideal parameters of the laser beams have been carried out. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB066  
About • paper received ※ 19 May 2021       paper accepted ※ 22 July 2021       issue date ※ 28 August 2021  
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TUPAB082 Analysis of the Effect of Energy Chirp in Implementing EEHG at SXL electron, simulation, FEL, linac 1566
 
  • M.A. Pop, F. Curbis, B.S. Kyle, S.P. Pirani, W. Qin, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
  • F. Curbis, S. Werin
    Lund University, Lund, Sweden
  • W. Qin
    DESY, Hamburg, Germany
  
  As a part of the efforts to improve the longitudinal coherence in the design of the Soft X-ray FEL (the SXL) at MAX IV, we present a possible implementation of the EEHG harmonic seeding scheme partly integrated into the second bunch compressor of the existing LINAC. A special focus is given to the effect of CSR on the resulting EEHG bunching and on how this unwanted effect might be controlled.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB082  
About • paper received ※ 15 May 2021       paper accepted ※ 28 July 2021       issue date ※ 17 August 2021  
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TUPAB103 Discussion on CSR instability in EEHG Simulation electron, laser, FEL, simulation 1622
 
  • D. Samoilenko, W. Hillert
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • F. Curbis, M.A. Pop, S. Werin
    MAX IV Laboratory, Lund University, Lund, Sweden
  • P. Niknejadi, G. Paraskaki
    DESY, Hamburg, Germany
  • F. Pannek
    University of Hamburg, Hamburg, Germany
  
  Echo-Enabled Harmonic Generation (EEHG) is an external seeding technique for XUV and soft X-ray Free Electron Lasers (FEL). It has recently been experimentally demonstrated and currently many facilities worldwide intend to incorporate it in user operation. The EEHG process relies on very accurate and complex transformations of electron beam phase space by means of a series of undulators coupled to lasers and dispersive chicanes. As a result of the phase space manipulation, electrons are bunched at a high harmonic of the seed laser wavelength allowing coherent emission at few nm wavelength. Dispersion occurring in strong chicanes is imperative for implementation of this scheme and effective electron bunching generation. However, strong chicanes at the same time can be source of beam instability effects, such as Coherent Synchrotron Radiation (CSR), that can significantly grow in these conditions and suppress the bunching process. Therefore, there is a common need to investigate such effects in detail. Here, we discuss their treatment with simulation codes applied to a typical EEHG setup.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB103  
About • paper received ※ 19 May 2021       paper accepted ※ 17 June 2021       issue date ※ 12 August 2021  
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TUPAB116 Toward THz Coherent Undulator Radiation Experiment with a Combination of Velocity Bunchings radiation, undulator, electron, acceleration 1663
 
  • Y. Sumitomo, K. Hayakawa, Y. Hayakawa, K. Nogami, T. Sakai, T. Tanaka
    LEBRA, Funabashi, Japan
  
  Funding: Japan Society for the Promotion of Science (JSPS), Grant-in-Aid for Scientific Research (KAKENHI), Grant Number JP19K12631.
We have launched a research program to generate the THz coherent undulator radiations, following the proposal of the combination of velocity bunchings * at Nihon University. The combination of velocity bunchings is an efficient way of bunch compression allowing a range of energy choices, in other words, a range of quasi-monochromatic radiation wavelengths generated at the undulator. In addition to the existing wideband THz light sources (0.1 - 2 THz) by the coherent edge and transition radiations currently available at Nihon Univ., the development of a high peak-power and quasi-monochromatic coherent radiation should accelerate the activities including the material science related to the THz bandwidths. In this presentation, we illustrate the program and report the current status of the experiment.
* Y. Sumitomo et al., J. Phys. Conf. Ser., vol. 1067, p. 032017, 2018. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB116  
About • paper received ※ 19 May 2021       paper accepted ※ 15 June 2021       issue date ※ 15 August 2021  
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TUPAB131 Measurement of Coherent Smith-Purcell Radiation Using Ultra-Short Electron Bunch at T-Acts radiation, electron, experiment, background 1696
 
  • H. Yamada, H. Hama, F. Hinode, K. Kanomata, S. Kashiwagi, S. Miura, T. Muto, I. Nagasawa, K. Nanbu, H. Saito, K. Shibata, K. Takahashi
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  
  The coherent Smith-Purcell radiation (SPR) emitted as a short electron bunch passes over a periodic metal surface is expected to be applied as a non-destructive beam diagnostic tool. The longitudinal profile of the electron bunch can be deduced by the measured spectrum of the coherent SPR, which is compared with the theoretical one for single electron. There are several theoretical models that explain the SPR mechanism, such as the surface current (SC) model and the van den Berg model. But the difference of estimation in radiation intensity between different models is not trivial, and also the experimental data to evaluate those validity is not enough. At test accelerator, t-ACTS, in Tohoku University we are conducting experimental research on coherent SPR in the terahertz frequency region using an ultra-short electron bunch of about 100 fs. The status and results of the experiment will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB131  
About • paper received ※ 19 May 2021       paper accepted ※ 27 July 2021       issue date ※ 13 August 2021  
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TUPAB186 Longitudinal Dynamics in the Prototype vFFA Ring for ISIS2 acceleration, extraction, injection, neutron 1834
 
  • D.J. Kelliher, J.-B. Lagrange, S. Machida, C.R. Prior, C.T. Rogers
    STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
  • A.P. Letchford, J. Pasternak
    STFC/RAL, Chilton, Didcot, Oxon, United Kingdom
  • J. Pasternak
    Imperial College of Science and Technology, Department of Physics, London, United Kingdom
  • E. Yamakawa
    JAI, Egham, Surrey, United Kingdom
  
  A vertical Fixed Field Accelerator (vFFA) is a candidate for a future high-power (MW-class) spallation source at ISIS. In order to assess the feasibility of this novel ring, a prototype is currently being designed. Here we consider the longitudinal dynamics in the prototype ring. A key requirement of future neutron spallation sources is flexibility of operation to best serve multiple target stations. Beam stacking allows a rapid cycling, high intensity machine to operate at lower repetition rates but with higher peak output. Here we show how beam stacking can be realised in the vFFA while minimising the peak RF voltage required.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB186  
About • paper received ※ 19 May 2021       paper accepted ※ 17 June 2021       issue date ※ 23 August 2021  
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TUPAB192 Studies on Momentum Collimation for CSNS-RCS Upgrades collimation, betatron, space-charge, emittance 1855
 
  • Y.W. An, J. Chen, S.Y. Xu, Y. Yuan
    IHEP, Beijing, People’s Republic of China
  • X.H. Lu, J.B. Yu
    IHEP CSNS, Guangdong Province, People’s Republic of China
  
  The CSNS project was a high intensity pulsed facility, and achieved the the design goal of 100kW in 2020. The upgrades of the CSNS are proposed, and the momentum collimator is a component of the upgrades. This paper will show the design scheme of the momentum collimator and the simulation results are also presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB192  
About • paper received ※ 18 May 2021       paper accepted ※ 15 June 2021       issue date ※ 28 August 2021  
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TUPAB196 Achievement of 100-kW Beam Operation in CSNS/RCS injection, MMI, acceleration, space-charge 1869
 
  • S.Y. Xu, Y.W. An, J. Chen, L. Huang, M.Y. Huang, Y. Li, S. Wang
    IHEP, Beijing, People’s Republic of China
  • H.Y. Liu, X.H. Lu
    IHEP CSNS, Guangdong Province, People’s Republic of China
  
  The China Spallation Neutron Source (CSNS) is an accelerator-based science facility. CSNS is designed to accelerate proton beam pulses to 1.6 GeV kinetic energy, striking a solid metal target to produce spallation neutrons. CSNS has two major accelerator systems, a linear accelerator (80 MeV Linac) and a 1.6 GeV rapid cycling synchrotron(RCS). The RCS accumulates and accelerates the proton beam to 1.6 GeV and then extracts the beam to the target at the repetition rate of 25 Hz. The Beam commissioning of CSNS/RCS had been started since April 2017. The most important issue in high-power beam commissioning is the beam loss control, as well as the control of induced activities, to meet the requirement of manual maintenance. A series of beam loss optimization work had been done to reduce the uncontrolled beam loss. At the end of February 2020, the CSNS reached the design beam power of 100 kW with very low uncontrolled beam loss.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB196  
About • paper received ※ 19 May 2021       paper accepted ※ 31 May 2021       issue date ※ 28 August 2021  
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TUPAB220 Longitudinal Dynamics with Harmonic Cavities under the Over-stretching Conditions cavity, detector, beam-loading, longitudinal-dynamics 1939
 
  • J.Y. Xu, H.S. Xu
    IHEP, Beijing, People’s Republic of China
  
  Higher harmonic cavities (HHCs) are often used to lengthen the bunches, mainly for increasing the Touschek lifetime or for suppressing the coupled-bunch instabilities in electron storage rings. There have been quite many studies on the beam dynamics with the consideration of HHCs. We revisited the basic longitudinal dynamics with HHCs. The derivation of the longitudinal equations of motion with HHCs will be presented in this paper. The difference in the number of fixed points at different HHC settings (mainly under the over-stretching conditions) is also discussed.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB220  
About • paper received ※ 19 May 2021       paper accepted ※ 02 August 2021       issue date ※ 29 August 2021  
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TUPAB275 Enhanced Orthogonal Polarization Component Treatment in COTRI Model for Microbunched Beam Diagnostics radiation, diagnostics, polarization, laser 2113
 
  • D.W. Rule
    Private Address, Silver Spring, USA
  • A.H. Lumpkin
    ANL, Lemont, Illinois, USA
  
  Funding: Work supported by U.S. Department of Energy, Office of Science, under Contract No. DE-AC02-06CH11357.
We present the results of modifying our coherent optical transition radiation interferometry (COTRI) model’s treatment of the perpendicular polarization of OTR, Iperp. Our previous analytic approximation for Iperp was for beam divergences, sy << 1/g, where g is the Lorentz factor and sy is the rms y-component of the beam divergence. We have replaced our analytical form with a Gaussian quadrature for the convolution of Iperp with the divergence in theta-y. This extends the range of divergences we reliably model to sy > 1/g. Ipar, the parallel polarization in the model, is unchanged. Iperp is polarized along the y-axis and is proportional to the square of the y-component of the beam’s velocity distribution. We illustrate our results with two cases: 1) beam energy E=1 GeV, OTR wavelength 633 nm, Q=235 pC, microbunching fraction, bf=1%, divergences of 0.1-0.7 mrad, and rms beam sizes 2,10, and 30 microns; 2) E=375 MeV, wavelength 266 nm, Q=300 pC, bf=10%, divergences of 0.1-0,7 mrad, and rms beam sizes of 10,25,50, and 100 microns. We will present two cases that would be of interest for the diagnostics of laser-plasma accelerator beams* and pre-bunched FELs**, respectively.
* A. H. Lumpkin et al., Phys. Rev. Lett. 125, 014801 (2020).
** A. H. Lumpkin and D. W. Rule, in Proc., 39th International FEL Conference, FEL 2019 (JACoW Pub., Hamburg, Germany, 2019), pp. 408-411. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB275  
About • paper received ※ 22 May 2021       paper accepted ※ 10 June 2021       issue date ※ 20 August 2021  
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WEPAB077 High Power Terahertz Cherenkov Free Electron Laser from a Waveguide with a Thin Dielectric Layer by a Near-Relativistic Electron Beam electron, GUI, radiation, wakefield 2769
 
  • W.W. Li, T.L. He, Z.G. He, R. Huang, Q.K. Jia, S.M. Jiang, L. Wang
    USTC/NSRL, Hefei, Anhui, People’s Republic of China
  
  Funding: National Natural Science Foundation of China (11705198, 11775216, 11805200) Fundamental Research Funds for the Central Universities (No. WK2310000082 and No. WK2310000090)
Corrugated and dielectric structures have been widely used for producing accelerator based terahertz radiation source. Recently, the novel schemes of the sub-terahertz free electron laser (FEL) from a metallic waveguide with corrugated walls and a normal dielectric loaded waveguide driven by a near-relativistic (beam energy of a few MeV) picosecond electron beam were studied respectively. Such a beam is used for driving resonant modes in the waveguide, and if the pipe is long enough, the interaction of these modes with the co-propagating electron beam will result in micro-bunching and the coherent enhancement of the wakefield radiation. It offers a promising candidate for compact accelerator-based high power terahertz source which can be realized with relatively low energy and low peak-current electron beams. However the choices of the waveguide above is less effective in order to obtain high power with frequency around 1THz. In this paper, we propose to use the waveguide with a thin dielectric layer instead, and high power radiation (>~10 MW) around 1 THz is expected to obtain in the proposed structure according to the simulation results. 		 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB077  
About • paper received ※ 12 May 2021       paper accepted ※ 23 June 2021       issue date ※ 22 August 2021  
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WEPAB083 Effect of Negative Momentum Compaction Operation on the Current-Dependent Bunch Length operation, simulation, synchrotron, storage-ring 2786
 
  • P. Schreiber, T. Boltz, M. Brosi, B. Härer, A. Mochihashi, A.-S. Müller, A.I. Papash, R. Ruprecht, M. Schuh
    KIT, Karlsruhe, Germany
  
  Funding: Funded by the European Union’s Horizon 2020 Research and Innovation programme, Grant Agreement No 730871. P.S, T.B are supported by DFG-funded Karlsruhe School of Elementary and Astroparticle Physics.
New operation modes are often considered during the development of new synchrotron light sources. An understanding of the effects involved is inevitable for a successful operation of these schemes. At the KIT storage ring KARA (Karlsruhe Research Accelerator), new modes can be implemented and tested at various energies, employing a variety of performant beam diagnostics devices. Negative momentum compaction optics at various energies have been established. Also, the influence of a negative momentum compaction factor on different effects has been investigated. This contribution comprises a short report on the status of the implementation of a negative momentum compaction optics at KARA. Additionally, first measurements of the changes to the current-dependent bunch length will be presented. 		 
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB083  
About • paper received ※ 19 May 2021       paper accepted ※ 01 July 2021       issue date ※ 26 August 2021  
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WEPAB177 Consideration of Triple-Harmonic Operation for the J-PARC RCS operation, injection, simulation, cavity 3020
 
  • H. Okita
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
  • M. Furusawa, Y. Sugiyama
    KEK, Tokai, Ibaraki, Japan
  • K. Hara, K. Hasegawa, M. Nomura, C. Ohmori, T. Shimada, F. Tamura, M. Yamamoto, M. Yoshii
    KEK/JAEA, Ibaraki-Ken, Japan
  
  The wideband magnetic alloy (MA) cavities are employed in the J-PARC RCS. The dual-harmonic operation, in which each MA cavity is driven by superposition of the fundamental accelerating voltage and the second harmonic voltage, significantly improves the bunching factor and is indispensable for acceleration of the high intensity beams. The original LLRF control system was replaced with the new system in 2019, which can control the amplitudes of the higher harmonics as well as the fundamental and second harmonics. Therefore we consider to use additionally the third harmonic voltage for further improvement of the bunching factor during acceleration. By the triple-harmonic operation, the flat RF bucket can be realized with a higher synchronous phase and improvement of the bunching factor is expected. In this presentation, we describe the longitudinal simulation studies of the triple-harmonic operation. Also the preliminary test results are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB177  
About • paper received ※ 18 May 2021       paper accepted ※ 25 June 2021       issue date ※ 19 August 2021  
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WEPAB178 Non-Adiabatic Longitudinal Bunch Manipulation at Flattop of the J-PARC MR extraction, kicker, experiment, flattop 3023
 
  • F. Tamura
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
  • C. Ohmori, Y. Sugiyama, M. Yoshii
    KEK, Tokai, Ibaraki, Japan
  
  The J-PARC MR delivers the high-intensity proton beams for the neutrino experiment. Eight bunches of high peak current are extracted by the extraction kickers, therefore the neutrino beam has a similar time structure. The new Intermediate Water Cherenkov Detector (IWCD) will be constructed for the future neutrino experiment and a low peak time structure is desired by the IWCD. Thus, we consider bunch manipulation at flattop of the MR for reducing the peak current. The manipulation requires a longer repetition period to extend the flattop. This reduces the output beam power. The manipulation should be quickly done to minimize the loss of the beam power. Also, the beam gap must be kept for the rise time of the extraction kicker. We propose a non-adiabatic bunch manipulation using the multiharmonic rf voltage. By using the neighbor harmonic of the accelerating harmonic, the first and eighth bunches can be decelerated and accelerated, respectively. After a certain period, the rf phase is flipped to pi for debunching. Thanks to the initial deceleration and acceleration, the beam gap for the kickers is kept. We present the concept and the longitudinal simulation result.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB178  
About • paper received ※ 17 May 2021       paper accepted ※ 25 June 2021       issue date ※ 28 August 2021  
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WEPAB213 Optimization of Antiproton-Atom Collision Studies Using GEANT4 proton, antiproton, experiment, simulation 3126
 
  • V. Rodin, A. Farricker, N. Kumar, C.P. Welsch
    The University of Liverpool, Liverpool, United Kingdom
  • N. Kumar, V. Rodin, C.P. Welsch
    Cockcroft Institute, Warrington, Cheshire, United Kingdom
  
  Funding: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 721559.
The interaction between antiprotons and hydrogen or helium atoms is a fundamental problem in many-particle atomic physics, attracting strong interest from both theory and experiments. Atomic collisions are ideal to study the three and four-body Coulomb problem as the number of possible reaction channels is limited. Currently, only the total cross-sections of such interactions have been measured in an energy range between keV and a few MeV. This contribution investigates the discrepancies between different theories and available experimental data. It also describes a pathway for obtaining differential cross-sections. A purpose-designed experimental setup is presented and detailed Geant4 simulations provide an insight into the interaction between short (ns) antiproton bunches and a dense gas-jet target. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB213  
About • paper received ※ 23 May 2021       paper accepted ※ 30 June 2021       issue date ※ 24 August 2021  
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WEPAB226 Investigation of Vlasov Systems with a Certain Class of Linearly-Collective Hamiltonians simulation, collective-effects, linear-dynamics, distributed 3157
 
  • Ph. Amstutz, M. Vogt
    DESY, Hamburg, Germany
  
  In many cases the Vlasov equation cannot be solved exactly due its inherent non-linearity arising from collective terms in the Hamiltonian. Based on the analysis of the Hamiltonian’s dependence on the phase-space density and the requirement for self-consistency in this contribution a class of Hamiltonians is defined and characterized. For members of this class the corresponding expansion of the Vlasov equation terminates. The new, potentially non-autonomous, Hamiltonian of the resulting Liouville equation depends only on the initial condition of the phase-space density. Prominent members of this class are Poisson-type kick-Hamiltonians, which we show as an example. We expect these investigations to be a potential starting point for the analysis and conception of operator-splitting schemes or splitting-free methods for beam-dynamics simulation codes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB226  
About • paper received ※ 18 May 2021       paper accepted ※ 01 July 2021       issue date ※ 17 August 2021  
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WEPAB228 Modelling and Counteracting Microbunching Instability in Spreader Lines of Radiofrequency and Plasma-Based Accelerators for Free-Electron Lasers electron, laser, free-electron-laser, scattering 3165
 
  • G. Perosa
    Università degli Studi di Trieste, Trieste, Italy
  • S. Di Mitri
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  
  High energy radiofrequency and plasma-driven accelerators target electron beam brightness suitable for x-ray free-electron lasers. Microbunching instability can be enhanced during beam transport through the spreader line from the accelerator to the undulator, degrading the brightness of the accelerated beam and therefore reducing the lasing efficiency. We present a semi-analytical model of the instability, benchmarked with experimental data at the FERMI free-electron laser, in the presence of intrabeam scattering and beam heating. Strategies for minimization of the instability both in conventional and plasma-based accelerators are discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB228  
About • paper received ※ 19 May 2021       paper accepted ※ 08 July 2021       issue date ※ 02 September 2021  
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WEPAB233 Excitation of Micro-Bunching in Short Electron Bunches Using RF Amplitude Modulation synchrotron, electron, radiation, experiment 3173
 
  • T. Boltz, E. Blomley, M. Brosi, E. Bründermann, B. Härer, A. Mochihashi, A.-S. Müller, P. Schreiber, M. Schuh, M. Yan
    KIT, Karlsruhe, Germany
  
  In its short-bunch operation mode, the KIT storage ring KARA provides picosecond-long electron bunches, which emit coherent synchrotron radiation (CSR) up to the terahertz frequency range. Due to the high spatial compression under these conditions, the self-interaction of the bunch with its own emitted CSR induces a wake-field, which significantly influences the longitudinal charge distribution. Above a given threshold current, this leads to the formation of dynamically evolving micro-structures within the bunch and is thus called micro-bunching instability. As CSR is emitted at wavelengths corresponding to the spatial dimension of the emitter, these small structures lead to an increased emission of CSR at higher frequencies. The instability is therefore deliberately induced at KARA to provide intense THz radiation to dedicated experiments. To further increase the emitted power in the desired frequency range, we consider the potential of RF amplitude modulations to intentionally excite this form of micro-bunching in short electron bunches. This work is supported by the BMBF project 05K19VKC TiMo (Federal Ministry of Education and Research).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB233  
About • paper received ※ 19 May 2021       paper accepted ※ 01 July 2021       issue date ※ 17 August 2021  
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WEPAB246 Influence of Different Beam Energies on the Micro-Bunching Instability damping, synchrotron, radiation, operation 3209
 
  • M. Brosi, A.-S. Müller, P. Schreiber, M. Schuh
    KIT, Karlsruhe, Germany
  
  During the operation of an electron synchrotron with short electron bunches, the beam dynamics are influenced by the occurrence of the micro-bunching instability. This collective instability is caused by the self-interaction of a short electron bunch with its own emitted coherent synchrotron radiation (CSR). Above a certain threshold bunch current dynamic micro-structures start to occur on the longitudinal phase space density. The resulting dynamics depend on various parameters and were previously investigated in relation to, amongst others, the momentum compaction factor and the acceleration voltage. In this contribution, the influence of the energy of the electrons on the dynamics of the micro-bunching instability is studied based on measurements at the KIT storage ring KARA (Karlsruhe Research Accelerator).  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB246  
About • paper received ※ 19 May 2021       paper accepted ※ 08 July 2021       issue date ※ 11 August 2021  
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THXA02 Overview of the Micro-Bunching Instability in Electron Storage Rings and Evolving Diagnostics operation, electron, simulation, diagnostics 3686
 
  • M. Brosi
    KIT, Karlsruhe, Germany
  
  The micro-bunching instability is a longitudinal instability that leads to dynamical deformations of the charge distribution in the longitudinal phase space. It affects the longitudinal charge distribution, and thus the emitted coherent synchrotron radiation spectra, as well as the energy distribution of the electron bunch. Not only the threshold in the bunch current above which the instability occurs, but also the dynamics above the instability threshold strongly depends on machine parameters, e.g., natural bunch length, accelerating voltage, momentum compaction factor, and beam energy. All this makes the understanding and potential mitigation or control of the micro-bunching instability an important topic for the next generation of light sources and circular e+/e− colliders. This presentation will give a review on the micro-bunching instability and discuss how technological advances in the turn-by-turn and bunch-by-bunch diagnostics are leading to a deeper understanding of this intriguing phenomenon.  
slides icon Slides THXA02 [23.626 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXA02  
About • paper received ※ 19 May 2021       paper accepted ※ 23 July 2021       issue date ※ 31 August 2021  
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THXA04 Microbunching Instability in the Presence of Intrabeam Scattering for Single-Pass Accelerators electron, scattering, FEL, simulation 3692
 
  • C.-Y. Tsai
    HUST, Wuhan, People’s Republic of China
  • W. Qin
    Lund University, Lund, Sweden
  
  Funding: This work is supported by the Fundamental Research Funds for the Central Universities under Project No. 5003131049 and National Natural Science Foundation of China under project No. 11905073.
Intrabeam scattering (IBS) has long been studied in lepton or hadron storage rings as a slow diffusion process, while the effects of IBS on single-pass or recirculating electron accelerators have drawn attention only in the recent two decades due to the emergence of linac-based or ERL-based 4th-generation light sources, which require high-quality electron beams during the beam transport. Recent experimental measurements indicate that in some parameter regimes, IBS can have a significant influence on microbunched beam dynamics. Here we develop a theoretical formulation* of microbunching instability (MBI) in the presence of IBS for single-pass accelerators. We start from the Vlasov-Fokker-Planck (VFP) equation, combining both collective longitudinal space charge and incoherent IBS effects. The linearized VFP equation with the corresponding coefficients is derived. The evolutions of the phase space density and energy modulations are formulated as a set of coupled integral equations. The formulation** is then applied to a simplified single-pass transport line. The results from the semi-analytical calculation are compared and show good agreement with particle tracking simulations.
* C.-Y. Tsai et al., Phys. Rev. Accel. Beams 23, 124401 (2020)
** C.-Y. Tsai and W. Q, Phys. Plasmas (2021), accepted for publication 		 
slides icon Slides THXA04 [2.699 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXA04  
About • paper received ※ 13 May 2021       paper accepted ※ 19 July 2021       issue date ※ 13 August 2021  
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THXC06 Design and Measurements of an X-Band 8 MeV Standing-Wave Electron Accelerator electron, gun, experiment, linac 3744
 
  • F. Liu, H.B. Chen, J. Shi, C.-X. Tang, H. Zha
    TUB, Beijing, People’s Republic of China
  
  X-band low-energy electron linear accelerators are attractive to industrial and medical applications due to the compact size. In this work we present tests of an 8 MeV X-band accelerator for industrial use. It adopts the coaxial coupling standing wave structure working at 9300 MHz. The accelerator length is 50 cm including the cavity, thermal gun, and electron window. Dedicated bunching cells are designed to reduce the energy spread. In the high power tests, the accelerator was able to generate the electron beam with RMS energy spread less than 1% (beam energy: 8.1 MeV, peak current: 45 mA). Combining features of compact size and the low energy spread, this X-band accelerator design is valuable for various applications.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THXC06  
About • paper received ※ 19 May 2021       paper accepted ※ 01 July 2021       issue date ※ 02 September 2021  
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THPAB060 Dispersion Controlled Temporal Shaping of Photoinjector Laser Pulses for Electron Emittance Reduction in X-Ray Free Electron Lasers laser, electron, emittance, simulation 3886
 
  • R.A. Lemons, S. Carbajo, J.P. Duris, A. Marinelli, N.R. Neveu
    SLAC, Menlo Park, California, USA
  • C.G. Durfee
    Colorado School of Mines, Golden, USA
  
  Funding: Office of Science DE-SC0014664
Temporal shaping of photocathode excitation laser pulses is a long-sought-after challenge to tailor the phase-space of electrons. The temporal profile of lasers, typically up-converted from infrared to ultraviolet, have significant impact on the distribution and time-evolution of the collective electron bunches. Towards this end, we present a method combining efficient nonlinear up-conversion with simultaneous and adaptable temporal profile shaping through dispersion-controlled sum-frequency generation* resulting in temporal profiles with sharp rise-fall times and flat top profiles. Using the LCLS-II photoinjector as a case study, we demonstrate a reduction in generated electron transverse emittance by upwards of 30% over conventionally implemented temporal profiles. Additionally, we discuss the ongoing experimental implementation of this method and preliminary results.
* R. Lemons, et al. arXiv:2012.00957 [physics.optics] (2020) 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB060  
About • paper received ※ 17 May 2021       paper accepted ※ 08 July 2021       issue date ※ 26 August 2021  
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THPAB207 Beam Dynamics Simulation about the Dual Harmonic System by PyORBIT simulation, synchrotron, acceleration, space-charge 4194
 
  • H.Y. Liu, X.Y. Feng, L. Huang, M.T. Li, X.H. Lu
    IHEP CSNS, Guangdong Province, People’s Republic of China
  • S. Wang, S.Y. Xu
    IHEP, Beijing, People’s Republic of China
  
  The space charge effect is a strong limitation in high-intensity accelerators, especially for low- and medium-energy proton synchrotrons. And for CSNS-II, the number of particles in the RCS is 3.9·1013 ppp, which is five times of CSNS. To mitigate the effects of the strong space charge effect, CSNS-II/RCS (Rapid Cycling Synchrotron) will use a dual harmonic system to increase the bunching factor during the injection and the initial acceleration phase. For studying the beam dynamics involved in a dual harmonic RF system, PyORBIT is used as the major simulation code, which is developed at SNS to simulate beam dynamics in accumulation rings and synchrotrons. We modified parts of the code to make it applicable to the beam dynamic in RCS. This paper includes the major code modification of the Dual Harmonic RF system and some benchmark results. The preliminary simulation results of the dual-harmonic system in CSNS-II/RCS simulated by the particle tracking code PyORBIT will also be discussed.  
poster icon Poster THPAB207 [0.354 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB207  
About • paper received ※ 16 May 2021       paper accepted ※ 05 July 2021       issue date ※ 11 August 2021  
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THPAB228 Study on Laser Modulator for Electron Beam Density Modulation laser, electron, undulator, simulation 4241
 
  • K. Kan, M. Gohdo, J. Yang, Y. Yoshida
    ISIR, Osaka, Japan
  
  Ultrashort electron beams are essential for light sources and time-resolved measurements. Laser modulation using an undulator and pulsed near infrared light is expected for attosecond density modulation of electron beam. In this study, simulation of laser modulation using undulator with period length of 6.6 mm and optical pulse with a wavelength of 800 nm was performed by ELEGANT* code. Simulation results of laser modulation for electron beam with an energy of 32.5 MeV will be presented from a view point of the density modulation.
* M. Borland, elegant: A Flexible SDDS-Compliant Code for Accelerator Simulation, Advanced Photon Source LS-287, September 2000. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB228  
About • paper received ※ 19 May 2021       paper accepted ※ 28 July 2021       issue date ※ 16 August 2021  
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THPAB244 Design of Interdigital H-Mode Re-Buncher at KoBRA Beamline cavity, heavy-ion, impedance, simulation 4285
 
  • Y. Lee, E.-S. Kim
    KUS, Sejong, Republic of Korea
  
  KOrea Broad acceptance Recoil spectrometer & Apparatus (KOBRA) is an experimental facility for low energy nuclear physics in the heavy ion accelerator complex RAON. Two re-buncher systems at KOBRA beamline are required to longitudinally focus the 40Ar9+ with 27MeV/u. The normal conducting IH resonator with seven-gap as the re-buncher structure was chosen because of the reduction in the risk of particulate contamination and total power consumption. In this paper, the detailed design results of the 162.5 MHz IH re-buncher cavity will be presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-THPAB244  
About • paper received ※ 19 May 2021       paper accepted ※ 27 July 2021       issue date ※ 24 August 2021  
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FRXA06 Mitigation of Beam Instabilities in the Echo-Enabled Harmonic Generation Beamline for FLASH2020+ laser, electron, FEL, free-electron-laser 4514
 
  • F. Pannek, W. Hillert, D. Samoilenko
    University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
  • S. Ackermann, E. Allaria, P. Niknejadi, G. Paraskaki, L. Schaper
    DESY, Hamburg, Germany
  • M.A. Pop
    MAX IV Laboratory, Lund University, Lund, Sweden
  
  With the FLASH2020+ upgrade, one of the beamlines of the free-electron laser FLASH at DESY will be based on the Echo-Enabled Harmonic Generation (EEHG) seeding scheme and provide high-repetition-rate, coherent radiation down to 4 nm. To reach this wavelength, it is necessary to imprint intricate structures on the longitudinal phase space of the electron bunch at a very high harmonic of the seed laser wavelength, making the scheme potentially vulnerable to beam instabilities. Part of the beamline is a strong chicane, which is necessary to create the dispersion required by EEHG. Resulting effects such as Coherent Synchrotron Radiation (CSR) can be very detrimental for the bunching process and have to be taken into account already in the design of the beamline to ensure optimum FEL performance. We investigate and propose possible mitigation solutions to such instabilities in the FLASH2020+ parameter range.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-FRXA06  
About • paper received ※ 19 May 2021       paper accepted ※ 20 July 2021       issue date ※ 20 August 2021  
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