Author: Huang, X.
Paper Title Page
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.