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. 		 
poster icon Poster MOPAB056 [0.366 MB]  
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.  
poster icon Poster MOPAB372 [0.694 MB]  
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.  
poster icon Poster TUPAB082 [1.825 MB]  
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.  
poster icon Poster TUPAB220 [1.082 MB]  
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. 		 
poster icon Poster WEPAB077 [1.332 MB]  
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. 		 
poster icon Poster WEPAB083 [1.129 MB]  
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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