Author: Wu, J.
Paper Title Page
MOP045 Phase Shifter Design for iSASE 123
 
  • S.D. Chen, K. Fang, H.-D. Nuhn, C. Pellegrini, J. Wu, L. Zhu
    SLAC, Menlo Park, California, USA
  • S.D. Chen, C.-S. Hwang
    NCTU, Hsinchu, Taiwan
  • K. Fang
    Indiana University, Bloomington, Indiana, USA
  • C.-S. Hwang
    NSRRC, Hsinchu, Taiwan
  
  A phase shifter to gen­er­ate an ad­di­tional phase ad­vance of the spon­ta­neous light ver­sus the elec­tron beam was de- signed for the iSASE scheme. The iSASE mech­a­nism is for re­duc­ing the band­width fur­ther from SASE FEL process. A large phase ad­vance about 1600*2Pi as the FEL op­er­at­ing at wave­length 0.8 nm was needed ac­cord­ing to the sim­u­la­tion of iSASE process. Since the iSASE is thought to im­ple­ment into LCLS II pro­ject, the space lim­i­ta­tion caus­ing by LCLS II should be con­sid­ered when de­sign­ing the phase shifter. An op­ti­mized three-pole elec­tric phase shifter with 7.3 mm gap has the cen­ter field of 1.8 T . The vana­dium steel was con­sid­ered as pole ma­te­r­ial and the mag­net phys­i­cal length is 260 mm, mean­while the wa­ter-cool­ing type cop­per coil was adopted. The tem­per­a­ture in­cre­ment, force analy­sis, low field op­er­a­tion mode con­cept, and pre­lim­i­nary tol­er­ance study were dis­cussed.  
 
MOC03 Radiation Properties of Tapered Hard X-ray Free Electron Lasers 300
 
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, California, USA
  • S.D. Chen
    NCTU, Hsinchu, Taiwan
  • K. Fang, C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  • S. Serkez
    DESY, Hamburg, Germany
  
  We per­form an analy­sis of the trans­verse co­her­ence of the ra­di­a­tion from a TW level ta­pered hard X-ray Free Elec­tron Laser (FEL). The ra­di­a­tion prop­er­ties of the FEL are stud­ied for a Gauss­ian, par­a­bolic and uni­form trans­verse elec­tron beam den­sity pro­file in a 200-m un­du­la­tor at a res­o­nant wave­length of 1.5 Angstrom. Sim­u­la­tions per­formed using the 3-D FEL par­ti­cle code GEN­E­SIS show that dif­frac­tion of the ra­di­a­tion oc­curs due to a re­duc­tion in op­ti­cal guid­ing in the ta­pered sec­tion of the un­du­la­tor. This re­sults in an in­creas­ing trans­verse co­her­ence for all three trans­verse elec­tron beam pro­files. We de­ter­mine that for each case con­sid­ered the ra­di­a­tion co­her­ence area is much larger than the elec­tron beam spot size, mak­ing X-ray dif­frac­tion ex­per­i­ments pos­si­ble for TW X-ray FELs.  
slides icon Slides MOC03 [3.797 MB]  
 
TUP025 TW X-ray Free Electron Laser Optimisation by Transverse Pulse Shaping 425
 
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, California, USA
  • C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  
  We study the de­pen­dence of the peak power of a 1.5 Angstrom TW, ta­pered X-ray free-elec­tron laser on the trans­verse elec­tron den­sity dis­tri­b­u­tion. Mul­ti­di­men­sional op­ti­miza­tion schemes for TW hard X-Ray free elec­tron lasers are ap­plied to the cases of trans­versely uni­form and par­a­bolic elec­tron beam dis­tri­b­u­tions and com­pared to a Gauss­ian dis­tri­b­u­tion. The op­ti­miza­tions are per­formed for a 200 m un­du­la­tor and a res­o­nant wave­length of 1.5 Angstrom using the fully 3-di­men­sional FEL par­ti­cle code GEN­E­SIS. The study shows that the flat­ter trans­verse elec­tron dis­tri­b­u­tions en­hance op­ti­cal guid­ing in the ta­pered sec­tion of the un­du­la­tor and in­crease the max­i­mum ra­di­a­tion power from a max­i­mum of 1.56 TW for a trans­versely Gauss­ian beam to 2.26 TW for the par­a­bolic case and 2.63 TW for the uni­form case. Spec­tral data also shows a 30-70 % re­duc­tion in en­ergy de­posited in the side­bands for the uni­form and par­a­bolic beams com­pared with a Gauss­ian.  
 
TUP028 Mode Contents Analysis of a Tapered Free Electron Laser 437
 
  • S.D. Chen, K. Fang, X. Huang, C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  • S.D. Chen, C.-S. Hwang
    NCTU, Hsinchu, Taiwan
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, California, USA
  • K. Fang, S.-Y. Lee
    Indiana University, Bloomington, Indiana, USA
  • C.-S. Hwang
    NSRRC, Hsinchu, Taiwan
  • S. Serkez
    DESY, Hamburg, Germany
  
  For the ul­ti­mate use for the sci­en­tific ex­per­i­ments, the free elec­tron laser (FEL) will prop­a­gate for long dis­tance, much longer than the Rayleigh range, after ex­it­ing the undu- lator. To char­ac­ter­ize the FEL for this pur­pose, we study the elec­tro­mag­netic field mode com­po­nents of the FEL pho­ton beam. With the mode de­com­po­si­tion, the trans­verse co­her- ence can be an­a­lyzed all along. The FEL here in this paper is a highly ta­pered one evolv­ing through the ex­po­nen­tial growth and then the post-sat­u­ra­tion taper. Modes con­tents are an­a­lyzed for elec­tron bunch with three dif­fer­ent types of trans­verse dis­tri­b­u­tion: flat­top, Gauss­ian, and par­a­bolic. The ta­pered FEL sim­u­la­tion is per­formed with Gen­e­sis code. The FEL pho­ton beam trans­verse elec­tric field is de­com- posed with Gauss­ian-La­guerre poly­no­mi­als. The evo­lu­tions of spot size, source lo­ca­tion, and the por­tion of the power in the fun­da­men­tal mode are dis­cussed here. The ap­proach can be ap­plic­a­ble to var­i­ous kind scheme of FEL.  
 
TUP029 iSASE Study 442
 
  • K. Fang
    Indiana University, Bloomington, Indiana, USA
  • S.D. Chen
    NCTU, Hsinchu, Taiwan
  • S.D. Chen, K. Fang, X. Huang, C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, California, USA
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  
  Im­proved Self Am­pli­fied Spon­ta­neous Emis­sion (iSASE) is a scheme that re­duces FEL band­width by in­creas­ing phase slip­page be­tween the elec­tron bunch and ra­di­a­tion field. This is achieved by re­peat­edly de­lay­ing elec­trons using phase shifters be­tween un­du­la­tor sec­tions. Gen­e­sis code is mod­i­fied to fa­cil­i­tate this sim­u­la­tion. With this sim­u­la­tion code, the iSASE band­width re­duc­tion mech­a­nism is stud­ied in de­tail. A Tem­po­ral cor­re­la­tion func­tion is in­tro­duced to de­scribe the sim­i­lar­ity be­tween the new grown field from bunch­ing fac­tor and the am­pli­fied shifted field. This cor­re­la­tion func­tion in­di­cates the ef­fi­ciency of iSASE process.  
 
TUP030 Mode Component Evolution and Coherence Analysis in Terawatt Tapered FEL 446
 
  • K. Fang, S.D. Chen, X. Huang, C. Pellegrini, J. Wu
    SLAC, Menlo Park, California, USA
  • S.D. Chen
    NCTU, Hsinchu, Taiwan
  • C. Emma, C. Pellegrini
    UCLA, Los Angeles, California, USA
  • K. Fang
    Indiana University, Bloomington, Indiana, USA
  • C.-S. Hwang
    NSRRC, Hsinchu, Taiwan
  • S. Serkez
    DESY, Hamburg, Germany
  
  A fast and ro­bust al­go­rithm is de­vel­oped to de­com­pose FEL ra­di­a­tion field trans­verse dis­tri­b­u­tion into a set of or­tho­nor­mal basis. La­guerre Gauss­ian and Her­mite Gauss­ian can be used in the analy­sis. The in­for­ma­tion of mode com­po­nents strength and Gauss­ian beam pa­ra­me­ters al­lows users in down­stream bet­ter uti­lize FEL. With this method, physics of mode com­po­nents evo­lu­tion from start­ing stage, to lin­ear regime and post sat­u­ra­tion are stud­ied with de­tail. With these de­com­posed modes, cor­re­la­tion func­tion can be com­puted with less com­plex­ity. Eigen­modes of the FEL sys­tem can be solved using this method.  
 
TUP032 FEL Simulation and Performance Studies for LCLS-II 456
 
  • G. Marcus, Y. Ding, P. Emma, Z. Huang, T.O. Raubenheimer, L. Wang, J. Wu
    SLAC, Menlo Park, California, USA
  
  The de­sign and per­for­mance of the LCLS-II free-elec­tron laser beam­lines are pre­sented using start-to-end nu­mer­i­cal par­ti­cle sim­u­la­tions. The par­tic­u­lar beam­line geome­tries were cho­sen to cover a large pho­ton en­ergy tun­ing range with x-ray pulse length and band­width flex­i­bil­ity. Re­sults for self-am­pli­fied spon­ta­neous emis­sion and self-seeded op­er­a­tional modes are de­scribed in de­tail for both hard and soft x-ray beam­lines in the base­line de­sign.  
 
TUP047 Chirped Pulse Superradiant Free-electron Laser 489
 
  • Y.-C. Huang, C.H. Chen
    NTHU, Hsinchu, Taiwan
  • J. Wu, Z. Zhang
    SLAC, Menlo Park, California, USA
  
  Funding: This work is supported by Ministry of Science and Technology under Contract NSC 102-2112-M-007-002-MY3
When a short elec­tron bunch tra­verses an un­du­la­tor and ra­di­ates a wave­length sig­nif­i­cantly longer than the bunch length, the elec­trons quickly loses en­ergy through so-called su­per­ra­di­ance and gen­er­ate a neg­a­tively chirped ra­di­a­tion fre­quency at the out­put. In this paper, we de­velop a the­ory to de­scribe this chirped-pulse ra­di­a­tion and nu­mer­i­cally demon­strate pulse com­pres­sion by using a qua­dratic phase fil­ter. As a de­sign ex­am­ple at THz, a pho­toin­jec­tor/linac sys­tem gen­er­ates a 15 MeV elec­tron bunch con­tain­ing 15-pC charge in a 60-fs du­ra­tion. The elec­trons ra­di­ate a chirped pulse at 2.5 THz from a 1.5 m long un­du­la­tor with a pe­riod of 5.6 cm and un­du­la­tor pa­ra­me­ter of 1.7. By using a grat­ing pair, the out­put THz field can be com­pressed from 27 to 3 cy­cles. As an­other ex­am­ple at EUV, a fu­ture di­elec­tric laser ac­cel­er­a­tor [1] is as­sumed to gen­er­ate a 100 MeV elec­tron bunch con­tain­ing 75-fC charge in 1-nm long length. The elec­trons ra­di­ate a chirped EUV pulse at 13.5 nm from a 15.8 cm long di­elec­tric laser un­du­la­tor [2] with a pe­riod of 1.05 mm and un­du­la­tor field of 3.3 T. By using a qua­dratic phase fil­ter as a pulse com­pres­sor, the peak power of the EUV ra­di­a­tion is in­creased from 0.7 to 10 kW.
*Y.C. Huang and R.L. Byer, Appl. Phys. Lett. 69 (15), (1996) 2185-2177.
**T. Plettner, R. L. Byer., Phys. Rev. ST Accel. Beams 11, (2008) 030704. 		 
 
TUC02
 Soft X-ray Self-seeding Setup and Results at LCLS  
 
  • D.F. Ratner, J.W. Amann, D.K. Bohler, M. Boyes, D. Cocco, F.-J. Decker, Y. Ding, D. Fairley, Y. Feng, J.B. Hastings, P.A. Heimann, Z. Huang, J. Krzywinski, H. Loos, A.A. Lutman, G. Marcus, A. Marinelli, T.J. Maxwell, S.P. Moeller, P.A. Montanez, D.S. Morton, H.-D. Nuhn, D.R. Walz, J.J. Welch, J. Wu
    SLAC, Menlo Park, California, USA
  • K. Chow, L.N. Rodes
    LBNL, Berkeley, California, USA
  • U. Flechsig
    PSI, Villigen PSI, Switzerland
  • S. Serkez
    DESY, Hamburg, Germany
  
  The soft X-ray self seed­ing pro­gram was de­signed to pro­vide near trans­form-lim­ited pulses in the range of 500 eV to 1000 eV. The pro­ject was a three-way col­lab­o­ra­tion be­tween SLAC, Lawrence Berke­ley Na­tional Lab, and the Paul Scher­rer In­sti­tute in Switzer­land. In­stal­la­tion fin­ished in the Fall of 2013, and after the early stages of com­mis­sion­ing we have mea­sured up to 0.5mJ pulse en­ergy and re­solv­ing pow­ers of up to 5000 across the de­sign wave­length range, rep­re­sent­ing a sev­eral-fold in­crease in the bright­ness com­pared to the nor­mal LCLS op­er­at­ing mode. Fu­ture work will aim to in­crease the total pulse en­ergy and es­tab­lish self-seed­ing as a ro­bust user op­er­a­tion mode.  
slides icon Slides TUC02 [10.464 MB]