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Superconducting High Brightness RF Photoinjector Design

Superconducting High Brightness RF Photoinjector Design M. Ferrario, J. B. Rosenzweig, J. Sekutowicz, G.Travish, W. D. Moeller INFN, UCLA, DESY. Main Questions/Concerns. Emittance Compensation ? High Peak Field on Cathode ? Cathode Materials and QE ?

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Superconducting High Brightness RF Photoinjector Design

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  1. Superconducting High Brightness RF Photoinjector Design M. Ferrario, J. B. Rosenzweig, J. Sekutowicz, G.Travish, W. D. Moeller INFN, UCLA, DESY

  2. Main Questions/Concerns • Emittance Compensation ? • High Peak Field on Cathode ? • Cathode Materials and QE ? • Q degradation due to Magnetic Field ?

  3. B Before Cool-Down B After Cool-Down

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

  5. LCLS GUN + SOLENOID

  6. Gun Working Point

  7. these slices also carry the most pronounced energy spread

  8. Matching Conditions with the Linac

  9. Linac Working Point The emittance compensation occuring in the booster when the invariant envelope matching conditions are satisfied is actually limited by the head and tail slice behavior

  10. 50 cm 25 cm 10 cm Splitting Acceleration and Focusing • The Solenoid can be placed downstream the cavity • Switching on the solenoid when the cavity is cold prevent any trapped magnetic field

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

  12. L-band SC gun design with coaxial coupler J. Sekutowicz

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

  14. PARMELA simulations J. B. Rosenzweig

  15. SCRF GUN

  16. 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

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

  18. CONCLUSIONS • RF focusing is not necessary • 60 MV/m peak field in SC cavity have been already demonstrated • Work in progress @ BNL to demonstrate Nb QE ~10-4 @ 60 MV/m plus new ideas • Multibunch effects • The new working point for a Split Photoinjector can be easily adopted by a SCRF gun

  19. g(x) Simple Case: Transport in a Long Solenoid ==> Equilibrium solution ? ==>

  20. Small perturbations around the equilibrium solution Same Plasma Frequencies Different Amplitudes

  21. sr(z) e(z) Envelope oscillations drive Emittance oscillations

  22. Bunch with a Linear Energy Spread Correlation

  23. A Spread in Plasma Frequencies drives a Beating in Emittance Oscillations

  24. On a longer time scale

  25. increasing the initial envelope offset the emittance evolution is dominated by the beating term and the original minimum is recovered only after a longer period

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