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 ? Q degradation due to Magnetic Field ?

Before Cool-Down B After Cool-Down B

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

LCLS GUN + SOLENOID

Gun Working Point

these slices also carry the most pronounced energy spread

Matching Conditions with the Linac

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

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

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

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

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

PARMELA simulations J. B. Rosenzweig

SCRF GUN

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

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

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

Small perturbations around the equilibrium solution Same Plasma Frequencies Different Amplitudes

Envelope oscillations drive Emittance oscillations sr(z) e(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