Author: Reiche, S.
Paper Title Page
MOP052 Update on FEL Performance for SwissFEL 140
 
  • E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  
  The Swiss­FEL pro­ject under con­struc­tion at the Paul Scher­rer In­sti­tute fore­sees for 2017 the re­al­iza­tion of an X-ray FEL with a pho­ton wave­length down to 1 Å. In this paper we pre­sent the ex­pected SASE per­for­mance for Swiss­FEL based on input dis­tri­b­u­tions ob­tained from de­tailed start-to-end sim­u­la­tion re­sults. The ef­fects of the lon­gi­tu­di­nal wake­fields due to re­sis­tive wall and sur­face rough­ness in the un­du­la­tor beam­line have been taken into ac­count. We have stud­ied and op­ti­mized the im­pact on the FEL per­for­mance of dif­fer­ent fac­tors like the elec­tron fo­cus­ing or the un­du­la­tor ta­per­ing. Re­sults for the stan­dard cases with 200 pC and 10 pC elec­tron bunch charge are shown.  
 
MOP053 SASE FEL Performance at the SwissFEL Injector Test Facility 144
 
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  
  A 4 m long pro­to­type of the Swiss­FEL un­du­la­tor mod­ule with an un­du­la­tor pe­riod length of 15 mm was in­stalled at the Swiss­FEL In­jec­tor Test Fa­cil­ity and tested with a 200 MeV elec­tron beam in the be­gin­ning of 2014. We ob­served FEL las­ing in SASE mode in the wave­length range from 70 to 800 nm, tun­ing the wave­length by en­ergy and gap. The mea­sure­ments of the FEL per­for­mance are re­ported.
on behalf of the SwissFEL Team 		 
 
MOP061 Electron Beam Delays for Improved Temporal Coherence and Short Pulse Generation at SwissFEL 181
 
  • N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  
  Pro­pos­als have been made for the in­tro­duc­tion of mag­netic elec­tron beam de­lays in be­tween the un­du­la­tor mod­ules of a long sec­tional FEL un­du­la­tor - these can be used for the gen­er­a­tion of trains of FEL pulses which can in­di­vid­u­ally be shorter than the FEL co­op­er­a­tion time [*] or to greatly im­prove the tem­po­ral co­her­ence of the FEL out­put com­pared to the nom­i­nal SASE con­fig­u­ra­tion [**,***,***]. This paper com­prises a fea­si­bil­ity study of the ap­pli­ca­tion of these tech­niques to the Swiss­FEL hard X-Ray beam­line. Three-di­men­sional sim­u­la­tions are used to in­ves­ti­gate the po­ten­tial pho­ton out­put.
[*] N.R. Thompson and B.W.J. McNeil, PRL 100:203901, 2008.
[**] N.R. Thompson et al. In Proc IPAC2010, pages 2257–2259, 2010
[***] J. Wu, A. Marinelli, and C. Pellegrini. Proc FEL2012, 2012. 		 
 
TUP019 Update on the FEL Code Genesis 1.3 403
 
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  
  The widely used time-de­pen­dent code Gen­e­sis 1.3 has been mod­i­fied to ad­dress new needs of users world­wide. The ex­ist­ing lim­i­ta­tion of track­ing iso­lated slices of the FEL beam has been over­come by keep­ing the en­tire elec­tron beam in mem­ory, which is tracked as a whole through the un­du­la­tor. This mod­i­fi­ca­tion al­lows for ad­di­tional fea­tures such as al­low­ing par­ti­cles to mi­grate into other slices or ap­ply­ing self-con­sis­tent wake­field and space charge mod­els.  
 
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.  
 
TUP031 FEL Code Comparison for the Production of Harmonics via Harmonic Lasing 451
 
  • G. Marcus, W.M. Fawley
    SLAC, Menlo Park, California, USA
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  • E. Schneidmiller, M.V. Yurkov
    DESY, Hamburg, Germany
  
  Har­monic las­ing of­fers an at­trac­tive op­tion to sig­nif­i­cantly ex­tend the pho­ton en­ergy range of FEL beam­lines. Here, the fun­da­men­tal FEL ra­di­a­tion is sup­pressed by var­i­ous com­bi­na­tions of phase shifters, at­ten­u­a­tors, and de­tuned un­du­la­tors while the ra­di­a­tion at a de­sired har­monic is al­lowed to grow lin­early. The sup­port of nu­mer­i­cal sim­u­la­tions is ex­ten­sively used in eval­u­at­ing the per­for­mance of this scheme. This paper com­pares the re­sults of har­monic growth in the har­monic las­ing scheme using three FEL codes: FAST, GEN­E­SIS, and GIN­GER.  
 
THP016 Optimization of FEL Performanceby Dispersion-based Beam-tilt Correction 714
 
  • M.W. Guetg, S. Reiche
    PSI, Villigen PSI, Switzerland
  
  In Free Elec­tron Lasers (FEL) the beam qual­ity is of cru­cial im­por­tance for the ra­di­a­tion power. A trans­verse cen­troid mis­align­ment of lon­gi­tu­di­nal slices in an elec­tron bunch re­duces the ef­fec­tive over­lap be­tween ra­di­a­tion field and elec­tron bunch. This leads to a re­duced bunch­ing and de­creased FEL per­for­mance. The dom­i­nant sources of slice mis­align­ments in FELs are the co­her­ent syn­chro­tron ra­di­a­tion within bunch com­pres­sors as well as trans­verse wake fields in the ac­cel­er­at­ing cav­i­ties. This is of par­tic­u­lar im­por­tance for over-com­pres­sion, which is re­quired for one of the key op­er­a­tion modes for the Swiss­FEL under con­struc­tion at the Paul Scher­rer In­sti­tute in Switzer­land. The slice cen­troid shift can be cor­rected using multi-pole mag­nets in dis­per­sive sec­tions, e.g. the bunch com­pres­sors. First and sec­ond order cor­rec­tions are achieved by pairs of sex­tu­pole and quadru­pole mag­nets in the hor­i­zon­tal plane while skew quadrupoles cor­rect to first order in the ver­ti­cal plane.  
 
THP059 The Laser Heater System of SwissFEL 871
 
  • M. Pedrozzi, M. Calvi, R. Ischebeck, S. Reiche, C. Vicario
    PSI, Villigen PSI, Switzerland
  • B.D. Fell, N. Thompson
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  
  Short wave­length FELs are gen­er­ally dri­ven by high-bril­liance photo-cath­ode RF-guns which gen­er­ate elec­tron beams with an un­cor­re­lated en­ergy spread on the order of 1 keV or less. These ex­tremely cold beams can eas­ily de­velop mi­cro-bunch­ing in­sta­bil­i­ties caused by lon­gi­tu­di­nal space charge forces after the com­pres­sion process. This can re­sult in a blow up of the en­ergy spread and emit­tance be­yond the tol­er­a­ble level for SASE emis­sion. It has been demon­strated the­o­ret­i­cally and ex­per­i­men­tally [1] that a con­trolled in­crease of the un­cor­re­lated en­ergy spread to typ­i­cally a few keV is suf­fi­cient to strongly re­duce the in­sta­bil­ity growth. In the laser heater sys­tem, one achieves a con­trolled in­crease of the beam en­ergy spread by a res­o­nant in­ter­ac­tion of the elec­tron beam with a trans­ver­sally po­lar­ized laser beam in­side of an un­du­la­tor mag­net. The mo­men­tum mod­u­la­tion re­sult­ing from the en­ergy ex­change within the un­du­la­tor is con­se­quently smeared out in the trans­mis­sion line down­stream of the laser heater sys­tem. In Swiss­FEL, the laser heater sys­tem is lo­cated after the first two S-band ac­cel­er­at­ing struc­tures at a beam en­ergy of 150 MeV. This paper de­scribes the lay­out and the sub-com­po­nents of this sys­tem.
[1] Z. Huang, et al, Phys. Rev. Special Topics – Accelerator and beams 13, 020703 (2010)