gaas photocathode performance - ucla

Operated by the Southeastern Universities Research Association for the U.S. Dept. of Energy

Thomas Jefferson National Accelerator FacilityFEL

40 cm Photocathode

Ball cathode

Drive Laser

GaAs Photocathode Performance

•Photocathode QE~6% after initial activation

•Photocathode delivers ~200 C between re-cesiations

•Typical day of operations draws ~35 Coulombs

•About 96% of previous QE is recovered with each re-cesiation

•12 activated cathodes and close to 40 re-cesiations performed on a singleGaAs wafer in one year

Operated by the Southeastern Universities Research Association for the U.S. Dept. of Energy

Thomas Jefferson National Accelerator FacilityFEL

Demonstrated DC Photocathode Gunperformance

•Pulsed operation at 8 mA/pulse (110 pC/bunch) in 16 ms-longpulses at 2 Hz repetition rate

•CW operation at 9.1 mA (75 MHz) with 122 pC/bunch

•Routinely delivers 5 mA CW and pulse current at 135 pC/bunchfor FEL operations

•400 A peak current at wiggler

•Vacuum environment: 4.0E-11 Torr, 99.9% H2

Operated by the Southeastern Universities Research Association for the U.S. Dept. of Energy

Thomas Jefferson National Accelerator FacilityFEL

7% QE 2% QE

Operated by the Southeastern Universities Research Association for the U.S. Dept. of Energy

Thomas Jefferson National Accelerator FacilityFEL

Cathode camera image taken while running 7 mA CW

Operated by the Southeastern Universities Research Association for the U.S. Dept. of Energy

Thomas Jefferson National Accelerator FacilityFEL

Transverse halo contributes to energy spread

Operated by the Southeastern Universities Research Association for the U.S. Dept. of Energy

Thomas Jefferson National Accelerator FacilityFEL

10 kW Upgrade FEL photocathode performanceafter vacuum improvements

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Operated by the Southeastern Universities Research Association for the U.S. Dept. of Energy

Thomas Jefferson National Accelerator FacilityFEL

RGA