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

Main Questions/Concerns 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 ?

Before Cool-Down B After Cool-Down B

Schematic View of the Envelope Equations HOMDYN

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

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

Gun Working Point

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

Homdyn movie

Head and tail slices carry the most pronounced energy spread

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

Small perturbations around the equilibrium solution Same Plasma Frequencies Different Amplitudes

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

Bunch with a Linear Energy Spread Correlation

A Spread in Plasma Frequencies drives a Beating in Emittance Oscillations

On a longer time scale

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

Movable Emittance-Meter envelope Movable Emittance-Meter

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

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

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

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

HOMDYN Simulation n [mm-mrad] 3.3 m Z [m] 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] Z [m] HOMDYN Simulation 6 MeV 3.3 m

PARMELA simulations

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

L-band SC gun design with coaxial coupler

SCRF GUN

Scaling with 

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

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

Is Nb the best superconductor for the photoemission ? Cs (WF=2 .1 eV) Pb (WF= 4.2 eV) Nb (WF= 4.9 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

Very preliminary results measured @ BNL Quantum Efficiency of Pb 248 nm 213 nm 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

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 lithography x7 and x8 of 1.5 µm Picture stolen from Nikon

HOMDYN Simulation n [mm-mrad] x [mm] 3.2 m Z [m] 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]

Velocity bunching option

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

Physics and Applications of High Brightness Electron Beams 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).