GTS 350kV Inverted Gun Update June C. Hernandez-Garcia

Update The vacuum chamber is with Ken Worland for tack-welding the rails that hold the NEG sheet + screen. POISSON modeling indicates that 9 cm anode-cathode gap renders 9.75 MV/m max field on 25 deg angle Pierce geometry front-end electrode. Max field can be further decreased by utilizing 15 degree angle Pierce geometry front-end electrode, thanks to larger radius of curvature. D. Machie is working on adjusting the length of the anode spacer to provide 9 cm anode-cathode cap. Shukui is evaluating options for GTS beam line lightbox, based on FEL’s Mamun has demonstrated 9% QE on CsK2Sb photocathode with a very thick Sb layer (after an accidental leak introduced water into the system, replicating D. Dowell’s observations with the BOEING RF injector back in 1991), in contrast with previous observations by Cornell and BNL that claim Sb layer >10 nm renders very low QE. Work in progress!

15 deg 9 MV/m 25 deg 9.75 MV/m POISSON modeling indicates that 9 cm anode-cathode gap renders 9.75 MV/m max field on 25 deg angle Pierce geometry front-end electrode. Field maps for 350kV & 9 cm gap Max field can be further decreased by utilizing 15 degree angle Pierce geometry front-end electrode, thanks to larger radius of curvature.

The field on the cusp of the electrode decreases when the radius of curvature is increased

Mamun achieved 9% QE on a CsK2Sb