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Optimization and Beam Dynamics in an SRF Gun

This paper explores the optimization of superconducting radio frequency (SRF) guns to enhance beam dynamics for achieving high average current electron beams. Key aspects include energy recovery, emittance compensation, and the impact of various cathode materials. The paper reviews advancements in fourth-generation light sources and examines projects such as 4GLS and LEP. It also addresses operational challenges and potential solutions regarding RF power losses, magnetic field effects, and laser systems. The findings contribute to improving the performance of electron injectors in advanced light sources.

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Optimization and Beam Dynamics in an SRF Gun

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  1. Optimization and Beam Dynamics in an SRF Gun M. Ferrario, W. D. Moeller, J. B. Rosenzweig, J. Sekutowicz, G.Travish INFN, UCLA, DESY

  2. Energy recovery superconducting LINACs can provide a high quality e-beams with high average current • high photon brightness • short pulses • high coherence High Average Current Injector Beam Dump FEL Undulator Radiation Motivation:4TH GENERATION LIGHT SOURCES LINAC SOME PROJECTS: 4GLS, Daresbury, ERLSYN, Erlangen, MARS, Novosibirsk, PERL, BNL

  3. 1650 m ~ 700 m 100 m Optical devices Dump (~1 MW) ~400 m R~200 m RF-Gun BC II: 0.50 GeV En up to 25 GeV BC I :0.12 GeV BC III: 2.00 GeV Ist part IInd part ER Continuous wave energy recovery operation of an XFEL 1 nC 1 MHz 1 mA

  4. Cryoplant capacity 5 kW

  5. SUPERCONDUCTING RF PHOTO-INJECTORS Main Advantage: Low RF Power Losses & CW Operation Main Questions/Concerns • Emittance Compensation ? • Q degradation due to Magnetic Field ? • High Peak Field on Cathode ? • Cathode Materials and QE ? • Laser System ?

  6. B Before Cool-Down B After Cool-Down

  7. Peking Univ. DC-SC Photo-Injector 1.5 cell, 1.3 GHz Field: 15 MV/m ( 5 kW) DC voltage: 70 kV DC gap: 15 mm Charge: 60 pC Simulation: Energy: 2.6 MeV Trans. emittance: 12.5 mm mrad B.C. Zhang et al., SRF Workshop 2001

  8. Rossendorf SC normal-conducting cathode inside SC cavity Cavity: Niobium ½ cell, TESLA Geometry 1.3 GHz Cathode: Cs2Te (262 nm, 1 W laser) thermally insulated, LN2 cooled D. Janssen et al., NIM-A, Vol. 507(2003)314

  9. No independent tuning of accelerating field and RF focusing effects Transverse non linearities

  10. LCLS GUN + SOLENOID

  11. Scaling the LCLS design from S-band to L-band 120-140 MV/m==> 52-60 MV/m 1 nC ==> 2.33 nC

  12. SCRF GUN

  13. Emittance Compensation: Controlled Damping of Plasma Oscillation (LS-JBR)

  14. Homdyn movie

  15. Splitting Acceleration and Focusing 36 cm • The Solenoid can be placed downstream the cavity • Switching on the solenoid when the cavity is cold prevent any trapped magnetic field

  16. L-band SC gun design with coaxial coupler

  17. HOMDYN Simulation Q =1 nC R =1.69 mm L =19.8 ps th = 0.45 mm-mrad Epeak = 60 MV/m (Gun) Eacc = 13 MV/m (Cryo1) B = 3 kG (Solenoid) I = 50 A E = 120 MeV n = 0.6 mm-mrad n [mm-mrad] 6 MeV 3.3 m Z [m]

  18. PARMELA simulations

  19. Coupler port Connection to tuner µ-metal shield solenoid 2K RT ≤4K 130 mm R=125 mm 320 mG 166 mG stainless steel He tank 20 mGauss (2G wo ) niobium 500 mm

  20. BNL All-Niobium SC Gun No contamination from cathode particles 1/2 cell, 1.3 GHz Maximum Field: 45 MV/m Q.E. of Niobium @ 248 nm with laser cleaning before: 2 x 10-7 after: 5 x 10-5 T. Srinivasan-Rao et al., PAC 2003 I. Ben-Zvi, Proc. Int. Workshop, Erlangen, 2002

  21. Measurements at room T on a dedicated DC system Extrapolation to Higher Field SCRF GUN Measured Limited by the available voltage

  22. Very preliminary results measured @ BNL 1•10-4 1.5•10-3 Puv= ƒ * (Q/ )*(h)= 4 W 4 W laser @ 213 nm (V harmonic of 1064 nm laser) can generate 1nC @ 1MHz nominal beam

  23. Conceptual All Fiber System Lots of development in Erbium and Ytterbium doped fiber systems Commercially available 20W, 2MHz systems Progress should be very rapid over next 1-2 years Example: for UV lithographyx7 and x8 of 1.5 µmPicture stolen from Nikon

  24. CONCLUSIONS • Emittance compensation by external solenoid is possible • 60 MV/m peak field in SC cavity have been already demonstrated • Work in progress @ BNL to demonstrate • Pb QE ~10-3 @ 200 nm • Laser System: progress should be very rapid over next 1-2 years

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