Carlos Hernandez-Garcia Don Bullard February 2, 2017 CIS R&D Retreat Carlos Hernandez-Garcia Don Bullard February 2, 2017

Tasks LDRD Magnetized Beam Project UITF Gun high voltage conditioning Fay’s metallic cathode Hydrogen cleaning / QE measurement test stand CEBAF 200kV upgrade gun Summer student from Mexico Help Mamun write the cooled CsK2Sb paper

LDRD Magnetized Beam Conditioned gun to 365kV w/Kr, and to 340kV in vacuum. Still some field emission remains. While at 340kV with magnet at 200A, developed more field emission. Decided to operate gun at 300kV to support the program. Next is to re-condition the gun up to 340kV with the following magnet settings: 100, 200, 300, 400 and A. Gun ion pump current reposnded to magnet coil field. Bubba added mu-metal shielding around the ion pump and effect was reduced from 01.nA max change to 0.05 nA max change with the magnet set to 400 A. The plan is to hand over the GTS to Fay, Riad, Yan and Mamun. But first, the beam line has to be S&A, put under vacuum, bake, add steering coils, and complete diagnostic crosses I&C, and install beam viewer limited mode (SCAM). Jim Coleman, Omar and Pam are aware of this work.

UITF Gun voltage conditioning The gun must operate at 200kV without field emission. Kr processing is not encouraged for risk of deteriorating gun vacuum conditions. We will have to rely on higher voltage under vacuum conditions if needed. To monitor field emission, we can momentarily take the GTS 8RadMon system, any news on DecaRad system?

Fay’s metallic cathode Hydrogen cleaning / QE measurement test stand Study QE of metallic photocathodes (Nb, Ta, Pb, etc) in a dedicated chamber for just het cleaned, and for subsequent hydrogen cleaned samples. We took the hydrogen cleaning chamber in EEL 117 to Lab3A @ LERF where it is being re-assembled with a new cross that has mini-CF UV viewports. Need to find: Manual 4-1/2” gate valve, MKS (or similar) vacuum gauge, RGA. We will take the turbo form one of the HV stands in EEL 117 One of the reasons to have the chamber in LERF is because Shukui has a UV laser in the lab next door!

CEBAF 200kV upgrade gun Marcy suggested to have a complete spare gun in case anything goes wrong with high current higher (>130kV) voltage beam studies proposed by Joe and Riad. I suggest we have T-shape electrodes barrel polished, and if possible, weld one of the black R28 insulators to a flange. Then build the spare using these components. As for the 200kV upgrade, build a new gun using existing vacuum chamber (there is one, right?), with a black R28 insulator, and spherical barrel polished electrode. That configuration is being modeled in POISSON by Gabriel. The model will tell us if the 6” dia. Ball electrode can be used (ie. if the gradient is <10 MV/m @ 200kV), otherwise ball diameter optimization will follow. It is likely that a ‘shed’ needs to be designed for this configuration. Joe / Riad need to tell us what gradient they want on the surface of the photocathode for 200kV operation, this will define anode-cathode gap, etc.

Summer student from Mexico Anahi has been selected for this summer. She wants to become Mexico’s leading expert in vacuum for accelerators. Has taken Mexican Particle Accelerator School, and USPAS courses. I talked to Marcy about mentoring Anahi on the cryo-pump project. I would like to serve as mentor too and liaison between Anahi and Education Department (REU/SULI student group). Anahi is all set, working now on the J1 visa paperwork with Sue Ewing. I’d like Anahi to learn also about the vacuum techniques over in SRF, and of course learn from Marcy and Phil and Bubba all about vacuum practices.

What I want (kind of need) to do: Write a paper about the barrel polished electrodes and compare field emission performance with FEL gun and with previous GTS gun, both had diamond paste polished electrodes. Write a paper about gun performance/conditioning with magnet coil ON, perhaps this does not warrant a paper, maybe combine with barrel polished electrode paper?

What we really really want to do: If the time comes, continue GTS gun high voltage conditioning, perhaps it needs 375kV, perhaps even higher. Find out how high in voltage can this configuration go. It will be costly, must likely we will arc a cable... Explore various electrode/chamber configurations with inverted insulators to be able to condition to 400kV for robust, no field emission operations at 350kV.