B-1 Light Sources and FELs
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SAPAG03 Mode-Analysis Methods for the Study of Collective Instabilities in Electron-Storage Rings 30
 
  • M. Venturini
    LBNL, Berkeley, California, USA
  
  We re­port on re­cent progress on the ap­pli­ca­tion of mode analy­sis to the study of col­lec­tive in­sta­bil­i­ties in elec­tron stor­age rings in­clud­ing Higher Har­monic RF Cav­i­ties (HHCs). The focus is on trans­verse in­sta­bil­i­ties in the pres­ence of a dom­i­nant re­sis­tive-wall im­ped­ance, a prob­lem of par­tic­u­lar rel­e­vance to the new gen­er­a­tion of dif­frac­tion-lim­ited light sources. The sec­u­lar equa­tion for the sys­tem eigen­val­ues is solved after ap­ply­ing a reg­u­lar­iz­ing trans­for­ma­tion, a key step to ob­tain­ing nu­mer­i­cally ac­cu­rate so­lu­tions. We pro­vide a demon­stra­tion that for van­ish­ing chro­matic­ity and in the ab­sence of ra­di­a­tion damp­ing the beam mo­tion is al­ways un­sta­ble. This is in con­trast to the more con­ven­tional Trans­verse-Mode-Cou­pling In­sta­bil­ity (TMCI) with­out HHCs, which is known to ex­hibit a well de­fined in­sta­bil­ity thresh­old.  
slides icon Slides SAPAG03 [2.261 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAG03  
About • paper received ※ 18 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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SUPAG08
 Machine Learning for X-Ray Free-Electron Lasers  
 
  • D.F. Ratner
    SLAC, Menlo Park, California, USA
  
  X-ray Free Elec­tron Lasers (XFELs) are among the most com­plex ac­cel­er­a­tor pro­jects in the world today. With large pa­ra­me­ter spaces, sen­si­tive de­pen­dence on beam qual­ity, huge data rates, and chal­leng­ing ma­chine pro­tec­tion, there are ex­pand­ing op­por­tu­ni­ties to apply ma­chine learn­ing (ML) to XFEL op­er­a­tion. In this talk I will sum­ma­rize some promis­ing ML meth­ods for XFELs, and high­light re­cent ex­am­ples of suc­cess­ful ap­pli­ca­tions.  
slides icon Slides SUPAG08 [2.695 MB]  
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SUPAG12
 Quantum Statistical Properties of Free Electron Laser With a Planar Wiggler and Ion-Channel Guiding  
 
  • M. Alimohamadi
    Farhangian University, Tehran, Iran
  
  Funding: [4] A. Bambini and A. Renieri. Lett. Nuovo Cimento 21, 399 (1978). [5] F. Ciocci, G. Dattoli, A. Renieri and A. Torre, Physics Reports, 141(1), 1-50(1986).
An analy­sis of the free-elec­tron lasers (FELs) with a pla­nar wig­gler and in the pres­ence of ion-chan­nel guid­ing, has been car­ried out using a Hamil­ton­ian quan­tum field the­ory. The quan­tum Hamil­ton­ian of sin­gle a par­ti­cle has been de­rived in the Bam­bini-Re­nieri (BR) frame [1-5]. The equa­tions are valid in a ref­er­ence frame, mov­ing with a rel­a­tivis­tic ve­loc­ity with re­spect to the lab­o­ra­tory frame, cho­sen in such a way that the car­rier fre­quency of the pulse equals the pseudo­ra­di­a­tion (wig­gler) field fre­quency. In this ref­er­ence frame, the equa­tions as­sume a sim­ple non-rel­a­tivis­tic form. Time-de­pen­dent wave func­tion and three con­stants of mo­tion are ob­tained. The Wei-Nor­man [2] Lie al­ge­braic ap­proach has been em­ployed to solve ex­actly the spher­i­cal Ra­man-Nath equa­tion (SRNE) [3-5]. A quan­tum ap­proach has been used to get pho­ton gain, pho­ton sta­tis­tics and squeez­ing prop­er­ties of a FEL. The quan­tum sta­tis­ti­cal prop­er­ties have also been stud­ied nu­mer­i­cally.
[1]H. Mehdian, M. Alimohamadi, etal, J.Plasma. Phys. 78 (5), 537-544(2012). [2] J. Wei, E. Norman, J. Math. Phys. A 4,575 (1963).[3] M. Alimohamadi, et al, J. Fus. Energy 31 (5), 463-466(2012). 		 
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TUPAF16 Analysis of the Beam Loss Mechanism During the Energy Ramp-Up at the SAGA-LS 227
 
  • Y. Iwasaki
    SAGA, Tosu, Japan
  
  The ac­cel­er­a­tor of the SAGA Light Source con­sists of 255 MeV in­jec­tor linac　and 1.4 GeV stor­age ring. The ac­cu­mu­lated elec­tron beam cur­rent of the　stor­age ring is about 300 mA. The en­ergy of　the elec­trons are raised up to 1.4 GeV in 4 min­utes in the stor­age ring. At the mo­ment of the　beam ac­cel­er­a­tion (the beam en­ergy is lower than 300 MeV), the elec­tron　beam is lost like the step func­tion. The lost beam cur­rent is nor­mally　about 5 mA to 30 mA. The beam loss at the en­ergy ramp-up is not ob­served, when the beam cur­rent is lower than 200 mA. To un­der­stand the beam loss mech­a­nism, which de­pend on the beam cur­rent, we de­vel­oped high-speed log­ging sys­tem of 100 kHz for mon­i­tor­ing the beam cur­rent and the mag­nets power sup­plies using Na­tional In­stru­ments PXI. We in­ves­ti­gated the re­la­tion­ship be­tween the beam loss and the be­ta­tron tune shifts. The tune shifts dur­ing the beam ac­cel­er­a­tion were an­a­lyzed from the mea­sured data of the out­put cur­rent of the mag­nets power sup­plies by using beam track­ing code of TRA­CY2. By adopt­ing the new high-speed log­ging sys­tem, the time struc­ture of the beam loss process was clearly ob­served. We will pre­sent the high-speed log­ging sys­tem de­vel­oped for mon­i­tor­ing the beam cur­rent and the power sup­plies at this meet­ing. The re­sults of the in­ves­ti­ga­tion to find the re­la­tion­ship of the beam loss and the tune shifts will be also shown.  
slides icon Slides TUPAF16 [1.286 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF16  
About • paper received ※ 19 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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TUPAF22 FEL Simulation Using the Lie Method 240
 
  • K. Hwang, J. Qiang
    LBNL, Berkeley, California, USA
  
  Funding: U.S. Department of Energy under Contract No. DE-AC02-05CH11231
Ad­vances in nu­mer­i­cal meth­ods for free-elec­tron-laser~(FEL) sim­u­la­tion under wig­gler pe­riod av­er­ag­ing~(WPA) are pre­sented. First, WPA is gen­er­al­ized using per­tur­ba­tion Lie map method. The con­ven­tional WPA is iden­ti­fied as the lead­ing order con­tri­bu­tion. Next, a widely used shot-noise mod­el­ing method is im­proved along with a par­ti­cle mi­gra­tion scheme across the nu­mer­i­cal mesh. The ar­ti­fi­cial shot noise aris­ing from par­ti­cle mi­gra­tion is sup­pressed. The im­proved model also al­lows using ar­bi­trary mesh size, slip­page res­o­lu­tion, and in­te­gra­tion step size. These ad­vances will im­prove mod­el­ing of lon­gi­tu­di­nal beam pro­file evo­lu­tion for fast FEL sim­u­la­tion. 		 
slides icon Slides TUPAF22 [2.245 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF22  
About • paper received ※ 17 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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TUPAF24
 Numerical Simulations for Generating Fully Coherent Soft X-Ray Free Electron Lasers With Ultra-Short Wavelength  
 
  • K.S. Zhou
    SINAP, Shanghai, People’s Republic of China
  
  Funding: Shanghai Institute of Applied Physics, Chinese Academy of Sciences
For the fully co­her­ent, ul­tra-short and high power soft x-rays are be­com­ing key in­stru­ments in dif­fer­ent re­search fields, such as bi­ol­ogy, chem­istry or physics. How­ever it’s not easy to gen­er­ate this kind of ad­van­taged light source by con­ven­tional lasers, es­pe­cially for the soft x-rays with ul­tra-short wave­length. The ex­ter­nal seeded free elec­tron laser (FEL) is con­sid­ered as one fea­si­ble method. Here, we give an ex­am­ple to gen­er­ate fully co­her­ent soft x-rays with the wave­length 1nm by the two-stage cas­caded FELs. The EEHG scheme is used in the first-stage while the HGHG scheme is used in the sec­ond-stage. 		 
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TUPAG17 Beamline Map Computation for Paraxial Optics 297
 
  • B. Nash, J.P. Edelen, N.B. Goldring, S.D. Webb
    RadiaSoft LLC, Boulder, Colorado, USA
  
  Funding: Department of Energy office of Basic energy sciences, DE-SC0018571
Mod­el­ing of ra­di­a­tion trans­port is an im­por­tant topic tightly cou­pled to many charged par­ti­cle dy­nam­ics sim­u­la­tions for syn­chro­tron light sources and FEL fa­cil­i­ties. The ra­di­a­tion is de­ter­mined by the elec­tron beam and mag­netic field source, and then passes through beam­lines with fo­cus­ing el­e­ments, aper­tures and mono­chro­ma­tors, in which one may typ­i­cally apply the parax­ial ap­prox­i­ma­tion of small an­gu­lar de­vi­a­tions from the op­ti­cal axis. The ra­di­a­tion is then used in a wide range of spec­tro­scopic ex­per­i­ments, or else may be re­cir­cu­lated back to the elec­tron beam source, in the case of an FEL os­cil­la­tor. The Wigner func­tion rep­re­sen­ta­tion of elec­tro­mag­netic wave­fronts has been de­scribed in the lit­er­a­ture and al­lows a phase space de­scrip­tion of the ra­di­a­tion, sim­i­lar to that used in charged par­ti­cle dy­nam­ics. It can en­com­pass both fully and par­tially co­her­ent cases, as well as po­lar­iza­tion. Here, we de­scribe the cal­cu­la­tion of a beam­line map that can be ap­plied to the ra­di­a­tion Wigner func­tion, re­duc­ing the com­pu­ta­tion time. We dis­cuss the use of ray trac­ing and wave op­tics codes for the map com­pu­ta­tion and bench­mark­ing. We con­struct a four crys­tal 1:1 imag­ing beam­line that could be used for re­cir­cu­la­tion in an XFEL os­cil­la­tor, and bench­mark the map based re­sults with SRW wave­front sim­u­la­tions. 		 
slides icon Slides TUPAG17 [2.289 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG17  
About • paper received ※ 19 October 2018       paper accepted ※ 18 December 2018       issue date ※ 26 January 2019  
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TUPAG19
 Bragg Diffraction Modeling Between X-Ray Free-Electron Laser and Crystals  
 
  • H.X. Deng, N. S. Huang, K. Li
    SINAP, Shanghai, People’s Republic of China
  
  In pur­suit of fully co­her­ent X-ray free-elec­tron laser (FEL), high re­flec­tive Bragg crys­tals have being and will be used as high se­lec­tive spec­tral fil­ter in the hard X-ray self-seed­ing FELs and X-ray FEL os­cil­la­tors (XFELO), re­spec­tively. How­ever, cur­rently in the self-seed­ing FEL and XFELO sim­u­la­tions, the three-di­men­sional ef­fect of Bragg dif­frac­tion is not fully con­sid­ered. In this paper, we de­rive com­pre­hen­sive so­lu­tion for the re­sponse func­tion of crys­tal in Bragg dif­frac­tion. And a three-di­men­sional X-ray crys­tal Bragg dif­frac­tion code named BRIGHT is in­tro­duced, which could col­lab­o­rate closely with other FEL re­lated code, e.g., GEN­E­SIS and OPC. The per­for­mance and fea­si­bil­ity are eval­u­ated by two nu­mer­i­cal ex­am­ples, i.e., self-seed­ing ex­per­i­ment for LCLS and XFELO op­tions for Shang­hai high rep­e­ti­tion rate XFEL and ex­treme light fa­cil­ity (SHINE). The re­sults in­di­cate BRIGHT pro­vides a new and use­ful tool for three-di­men­sional FEL sim­u­la­tion.  
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TUPAG21 Novel, Fast, Open-Source Code for Synchrotron Radiation Computation on Arbitrary 3D Geometries 309
 
  • D.A. Hidas
    BNL, Upton, Long Island, New York, USA
  
  Open Source Code for Ad­vanced Ra­di­a­tion Sim­u­la­tion (OS­CARS) is an open-source pro­ject (https://​oscars.​bnl.​gov) de­vel­oped at Brookhaven Na­tional Lab­o­ra­tory for the com­pu­ta­tion of syn­chro­tron ra­di­a­tion from ar­bi­trary charged par­ti­cle beams in ar­bi­trary and time-de­pen­dent mag- netic and elec­tric fields on ar­bi­trary geome­tries in 3D. Com­pu­ta­tional speed is sig­nif­i­cantly in­creased with the use of built-in multi-GPU and multi-threaded tech­niques which are suit­able for both small scale and large scale com­put­ing in­fra­struc­tures. OS­CARS is ca­pa­ble of com­put­ing spec­tra, flux, and power den­si­ties on sim­ple sur­faces as well as on ob­jects im­ported from com­mon CAD soft­ware. It is ad­di­tion­ally ap­plic­a­ble in the regime of high-field ac­cel­er­a­tion. The method­ol­ogy be­hind OS­CARS cal- cu­la­tions will be dis­cussed along with prac­ti­cal ex­am­ples and ap­pli­ca­tions to mod­ern ac­cel­er­a­tors and light sources.  
slides icon Slides TUPAG21 [1.712 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG21  
About • paper received ※ 20 October 2018       paper accepted ※ 18 December 2018       issue date ※ 26 January 2019  
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