Author: Xiao, L.
Paper Title Page
MOPA85 Design of a 185.7 MHz Superconducting RF Photoinjector Quarter-Wave Resonator for the LCLS-II-HE Low Emittance Injector 245
 
  • S.H. Kim, W. Hartung, T. Konomi, S.J. Miller, M.S. Patil, J.T. Popielarski, K. Saito, T. Xu, T. Xu
    FRIB, East Lansing, Michigan, USA
  • C. Adolphsen, L. Ge, F. Ji, J.W. Lewellen, L. Xiao
    SLAC, Menlo Park, California, USA
  • M.P. Kelly, T.B. Petersen, P. Piot
    ANL, Lemont, Illinois, USA
  • P. Piot
    Northern Illinois University, DeKalb, Illinois, USA
  
  Funding: Work supported by the U.S. Department of Energy Contract DE-AC02-76SF00515.
A 185.7 MHz su­per­con­duct­ing quar­ter-wave res­onator (QWR) was de­signed for the low emit­tance in­jec­tor of the Linac Co­her­ent Light Source high en­ergy up­grade (LCLS-II-HE). The cav­ity was de­signed to min­i­mize the risk of cath­ode ef­fi­ciency degra­da­tion due to mul­ti­pact­ing or field emis­sion and to op­er­ate with a high RF elec­tric field at the cath­ode for low elec­tron-beam emit­tance. Cav­ity de­sign fea­tures in­clude: (1) shap­ing of the cav­ity wall to re­duce the strength of the low-field coax­ial mul­ti­pact­ing bar­rier; (2) four ports for elec­trop­o­l­ish­ing and high-pres­sure water rins­ing; and (3) a fun­da­men­tal power cou­pler (FPC) port lo­cated away from the ac­cel­er­at­ing gap. The de­sign is ori­ented to­ward min­i­miz­ing the risk of par­tic­u­late con­t­a­m­i­na­tion and avoid harm­ful di­pole com­po­nents in the RF field. The ANL 162 MHz FPC de­sign for PIP-II is being adapted for the gun cav­ity. We will pre­sent the RF de­sign of the cav­ity in­te­grated with the FPC. 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-MOPA85  
About • Received ※ 03 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 11 August 2022 — Issue date ※ 30 August 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA02 Beam Dynamics Studies on a Low Emittance Injector for LCLS-II-HE 619
 
  • F. Ji, C. Adolphsen, R. Coy, L. Ge, C.E. Mayes, T.O. Raubenheimer, L. Xiao
    SLAC, Menlo Park, California, USA
  • J. Qiang
    LBNL, Berkeley, California, USA
  
  The SLAC High En­ergy up­grade of LCLS-II (LCLS-II-HE) will dou­ble the beam en­ergy to 8 GeV, in­creas­ing the XFEL pho­ton en­ergy reach to about 13 keV. The en­ergy reach can be ex­tended to 20 keV if the beam emit­tance can be halved, which re­quires a higher gra­di­ent elec­tron gun with a lower in­trin­sic emit­tance pho­to­cath­ode. To this end, the Low Emit­tance In­jec­tor (LEI) will be built that will run par­al­lel to the ex­ist­ing LCLS-II In­jec­tor. The LEI de­sign will be based on a state-of-the-art SRF gun with a 30 MV/m cath­ode gra­di­ent. The main goal is to pro­duce trans­verse beam emit­tances of 0.1 mm-mrad for 100 pC bunch charges. This paper de­scribes the beam dy­nam­ics stud­ies on the de­sign of the LEI in­clud­ing the sim­u­la­tions and multi-ob­jec­tive ge­netic al­go­rithm (MOGA) op­ti­miza­tions. Per­for­mance with dif­fer­ent in­jec­tor lay­outs, cath­ode gra­di­ents, bunch charges and cath­ode mean trans­verse en­er­gies (MTEs) will be pre­sented.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA02  
About • Received ※ 02 August 2022 — Revised ※ 11 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 17 August 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA03 Status of the SLAC/MSU SRF Gun Development Project 623
 
  • J.W. Lewellen, C. Adolphsen, R. Coy, L. Ge, F. Ji, M.J. Murphy, L. Xiao
    SLAC, Menlo Park, California, USA
  • A. Arnold, S. Gatzmaga, P. Murcek, R. Xiang
    HZDR, Dresden, Germany
  • Y. Choi, C. Compton, X.-J. Du, D.B. Greene, W. Hartung, S.H. Kim, T. Konomi, S.J. Miller, D.G. Morris, M.S. Patil, J.T. Popielarski, L. Popielarski, K. Saito, T. Xu
    FRIB, East Lansing, Michigan, USA
  • M.P. Kelly, T.B. Petersen
    ANL, Lemont, Illinois, USA
  
  Funding: US Department of Energy.
The LCLS-II-HE pro­ject at SLAC is in­tended to in­crease the pho­ton en­ergy reach of the LCLS-II FEL to at least 20 keV. In ad­di­tion to up­grad­ing the un­du­la­tor sys­tem, and in­creas­ing the elec­tron beam en­ergy to 8 GeV, the pro­ject will also con­struct a low-emit­tance in­jec­tor (LEI) in a new tun­nel. To achieve the LEI emit­tance goals, a low-MTE pho­to­cath­ode will be re­quired, as will on-cath­ode elec­tric fields up to 50% higher than those achiev­able in the cur­rent LCLS-II pho­toin­jec­tor. The beam source for the LEI will be based around a su­per­con­duct­ing quar­ter­wave cav­ity res­o­nant at 185.7 MHz. A pro­to­type gun is cur­rently being de­signed and fab­ri­cated at the Fa­cil­ity for Rare Iso­tope Beams (FRIB) at Michi­gan State Uni­ver­sity. This paper pre­sents the per­for­mance goals for the new gun de­sign, an overview of the pro­to­type de­vel­op­ment ef­fort, cur­rent sta­tus, and fu­ture plans in­clud­ing fab­ri­ca­tion of a "pro­duc­tion" gun for the LEI. 		 
poster icon Poster WEPA03 [4.510 MB]  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA03  
About • Received ※ 21 July 2022 — Revised ※ 28 July 2022 — Accepted ※ 08 August 2022 — Issue date ※ 11 August 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA08 Design and Operation Experience of a Multi-Collimator/YAG Screen Device on LCLS II Low Energy Beamline 631
 
  • X. Liu, C. Adolphsen, M. Santana-Leitner, L. Xiao, F. Zhou
    SLAC, Menlo Park, California, USA
  
  Dur­ing the com­mis­sion­ing of the nor­mal con­duct­ing VHF RF gun of LCLS II, it was ob­served that field emis­sion (dark cur­rent) of roughly 2 µA level was pre­sent under nor­mal op­er­a­tion of the gun. While the dark cur­rent of this level is deemed man­age­able with ex­ist­ing beam­line con­fig­u­ra­tions, it is de­sired in pre­cau­tion to add a col­li­ma­tor on the low en­ergy beam­line to block the dark cur­rent, being con­cerned that the dark cur­rent sit­u­a­tion might worsen with time. Since no spare lon­gi­tu­di­nal space is avail­able, the new de­vice takes place of the ex­ist­ing YAG screen. The new de­vice is made of a 15 mm thick cop­per plate, with four round aper­tures of 6, 8, 10, and 12 mm ra­dius re­spec­tively. At the end of the col­li­ma­tor plate, fea­tures are made for clamp­ing two YAG screens and mount­ing their cor­re­spond­ing mir­rors for beam/halo pro­file imag­ing. The col­li­ma­tor plate is elec­tri­cally in­su­lated from the cham­ber so that it can also be used for mea­sur­ing the dark cur­rent. A mo­tor-dri­ven UHV com­pat­i­ble lin­ear trans­la­tor shifts the de­vice be­tween po­si­tions. Be­sides de­sign de­tails, re­lated ther­mal, beam dy­nam­ics, and ra­di­a­tion analy­ses as well as op­er­a­tion ex­pe­ri­ence will be pre­sented.

* Work supported by US DOE under contract AC02-76SF00515. 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA08  
About • Received ※ 02 August 2022 — Revised ※ 09 August 2022 — Accepted ※ 12 August 2022 — Issue date ※ 13 September 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA09 A Parallel Automatic Simulation Tool for Cavity Shape Optimization 634
 
  • L. Ge, Z. Li, C.-K. Ng, L. Xiao
    SLAC, Menlo Park, California, USA
  • M. Beall, B.R. Downie, O. Klaas
    Simmetrix Inc., Clifton Park, USA
  
  Funding: U.S. Department of Energy under contract No. DE-SC0018715.
We pre­sent a par­al­lel au­to­matic shape op­ti­miza­tion work­flow for de­sign­ing ac­cel­er­a­tor cav­i­ties. The newly de­vel­oped 3D par­al­lel op­ti­miza­tion tool Opt3P based on dis­crete ad­joint meth­ods is used to de­ter­mine the op­ti­mal ac­cel­er­a­tor cav­ity shape with the de­sired spec­tral re­sponse. Ini­tial and up­dated mod­els, meshes, and de­sign ve­loc­i­ties of de­sign pa­ra­me­ters for defin­ing the cav­ity shape are gen­er­ated with Sim­metrix tools for mesh gen­er­a­tion (Mesh­Sim), geom­e­try mod­i­fi­ca­tion and query (Ge­om­Sim), and user in­ter­face tools (Sim­Mod­eler). Two shape op­ti­miza­tion ex­am­ples using this au­to­matic sim­u­la­tion work­flow will be pre­sented here. One is the TESLA cav­ity with higher-or­der-mode (HOM) cou­plers and the other is a su­per­con­duct­ing rf (SRF) gun. The ob­jec­tive for the TESLA cav­ity is to min­i­mize HOM damp­ing fac­tors and for the SRF gun to min­i­mize the sur­face elec­tric and mag­netic fields while main­tain­ing its op­er­at­ing mode fre­quency at a pre­scribed value. The re­sults demon­strate that the au­to­matic sim­u­la­tion tool al­lows an ef­fi­cient shape op­ti­miza­tion pro­ce­dure with min­i­mal man­ual op­er­a­tions. All sim­u­la­tions were per­formed on the NERSC su­per­com­puter Cori sys­tem for so­lu­tion speedup. 		 
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA09  
About • Received ※ 03 August 2022 — Revised ※ 05 August 2022 — Accepted ※ 09 August 2022 — Issue date ※ 08 October 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
WEPA10 Determination of LCLS-II Gun-2 Prototype Dimensions 637
 
  • L. Xiao, C. Adolphsen, E.N. Jongewaard, X. Liu, F. Zhou
    SLAC, Menlo Park, California, USA
  
  The LCLS-II spare gun (Gun-2) de­sign is largely based on the ex­ist­ing LCLS-II gun (Gun-1), in which there is sig­nif­i­cant cap­tured dark cur­rent (DC) that orig­i­nates on the high field cop­per sur­face near the cath­ode plug gap open­ing. To help sup­press DC, the Gun-2 cath­ode and anode noses and the cath­ode plug open­ing are el­lip­ti­cally shaped to min­i­mize the peak sur­face field for a given cath­ode gra­di­ent. Stain­less steel (SS) cath­ode and anode in­serts are used in Gun-2 to fur­ther re­duce dark cur­rent. The RF sim­u­la­tions were per­formed using a model that in­cludes all the 3D fea­tures. The ther­mal and struc­tural analy­ses were done to in­ves­ti­gate the ef­fects of the air pres­sure and RF heat­ing. The multi-physics sim­u­la­tion re­sults pro­vided the in­for­ma­tion needed to com­pute the over­all fre­quency change from the basic 2D model to the nom­i­nal fre­quency dur­ing op­er­a­tion. The Gun-2 cath­ode-to-an­ode gap dis­tance will be made 1 mm longer than the nom­i­nal gap with the ex­pec­ta­tion that less than 1 mm will be ma­chined off to meet the tar­get fre­quency. In this paper, the Gun-2 fre­quency cor­rec­tion cal­cu­la­tions are pre­sented, and the cath­ode-to-an­ode gap de­ter­mi­na­tion is dis­cussed.  
DOI • reference for this paper ※ doi:10.18429/JACoW-NAPAC2022-WEPA10  
About • Received ※ 30 July 2022 — Revised ※ 03 August 2022 — Accepted ※ 08 August 2022 — Issue date ※ 10 August 2022
Cite • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)