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Beam Dynamics in a Spilt SRF-Gun

Beam Dynamics in a Spilt SRF-Gun M. Ferrario, W. D. Moeller, J. B. Rosenzweig, J. Sekutowicz, G.Travish INFN, UCLA, DESY. Meeting on “ Superconducting RF Gun Simulations“ EUROFEL Work Package 5 2.-3. June 2005 at BESSY. SUPERCONDUCTING RF PHOTO-INJECTORS. Main Advantage:.

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Beam Dynamics in a Spilt SRF-Gun

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  1. Beam Dynamics in a Spilt SRF-Gun M. Ferrario, W. D. Moeller, J. B. Rosenzweig, J. Sekutowicz, G.Travish INFN, UCLA, DESY Meeting on “ Superconducting RF Gun Simulations“ EUROFEL Work Package 5 2.-3. June 2005 at BESSY

  2. 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 ?

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

  4. Schematic View of the Envelope Equations HOMDYN

  5. px x SlicePhase Spaces Projected Phase Space Emittance Oscillations and Growth are driven by space charge differential defocusing in core and tails of the beam

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

  7. Gun Working Point

  8. 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

  9. Homdyn movie

  10. Head and tail slices carry the most pronounced energy spread

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

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

  13. r(z) (z) Envelope oscillations drive Emittance oscillations

  14. Bunch with a Linear Energy Spread Correlation

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

  16. On a longer time scale

  17. 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

  18. emittance envelope Movable Emittance-Meter

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

  20. Main Solenoid Bucking Solenoid 1.3 GHz, 1.5 cell RF Gun TTF VUV-FEL Photoinjector

  21. Y. Kim RPPT008 Emittance Damping in TTF2 Booster Linac with Gaussian Longitudinal Laser Beam Profile

  22. 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

  23. 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]

  24. PARMELA simulations

  25. 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

  26. L-band SC gun design with coaxial coupler

  27. SCRF GUN

  28. Scaling with 

  29. 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

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

  31. Is Nb the best superconductor for the photoemission ? Cs (WF=2 .1 eV) Nb (WF= 4.9 eV) Pb (WF= 4.2 eV) a /pm b /pm c /pm 614 614 614 α / ° β / ° γ / °   90 90 90 a /pm b /pm c /pm 495 495 495 α / ° β / ° γ / °   90 90 90 a /pm b /pm c /pm 330 330 330 α / ° β / ° γ / °   90 90 90

  32. 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

  33. 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

  34. HOMDYN Simulation Q =0.35 nC R =1. mm L =19.8 ps th = 0.7 mm-mrad Epeak = 60 MV/m (Gun) Eacc = 11 MV/m (Cryo1) B = 2.9 kG (Solenoid) I = 18 A E = 100 MeV n = 0.76 mm-mrad n [mm-mrad] x [mm] 3.2 m Z [m]

  35. Velocity bunching option

  36. 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

  37. The following workshop was approved by ICFA at its meeting Feb 10-11, 2005 in Vancouver: Physics and Applications of High Brightness Electron Beams Erice, Sicily, Italy, October 9-14, 2005 Organizers: L. Palumbo (Univ. Roma), J. Rosenzweig (UCLA), L. Serafini (INFN-Milano).

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