An in-situ photocathode loading system for the SLC Polarized Electron Gun

Abstract

An ultra-high vacuum loadlock system capable of operating at high voltage has been added to the SLC Polarized Electron Gun. The unit incorporates facilities for heat cleaning, activating and measuring the quantum efficiency of photocathodes. A tray of up to four photocathodes can be exchanged without bringing the activation unit or gun up to atmosphere.Low voltage quantum efficiencies of 20% have been obtained for bulk GaAs at 633 nm and 6% for a 0.3 micron GaAs layer at 755 nm. Results for other cathodes as well as operational characteristics are discussed.

Polarization and charge limit studies of strained GaAs photocathodes

“…[28] This isolation has proven beneficial to the HV operation of the gun by protecting the sensitive HV electrodes from contaminants. The loadlock also serves as the transition point for photocathodes between atmosphere and the UHV.…”

“…3.4. The main benefits of the loadlock can be summarized as follows: [28] isolates the gun UHV from the 'harsh' environment of photocathode activation provides a photocathode activation chamber that is connected directly to the gun stores up to four photocathodes in UHV provides the transition point for photocathodes between atmosphere and the UHV of the accelerator stores the photocathodes during the HV processing of the gun Having the photocathode activations done outside the gun UHV protects the gun electrodes from contaminants and thus improves the overall HV performance. The loadlock activation chamber has the capability to heat treat the photocathode, apply layers of Cs and NF3 to its surface, and monitor its QE.…”

Polarization and Charge Limit Studies of Strained GaAs Photocathodes [Thesis]

“…A loadlock system (similar to those used to manipulate samples between chambers in semiconductor physics) was develop to isolate the gun from the maintenance process of the photocathodes. [28] This isolation has proven beneficial to the HV operation of the gun by protecting the sensitive HV electrodes from contaminants. The loadlock also serves as the transition point for photocathodes between atmosphere and the UHV.…”

The high peak current polarized electron source of the Stanford Linear Collider

“…During operation, the cathode potential is held at -120 kV, which gives a space charge limited current of 8.9 amps, or 1.1~1011 electrons in a 2 ns long bunch. 2 The high voltage end of the gun is connected to a load lock system for easy cathode change [4]. The load lock is a vacuum system with a number of manipulators which allows a new photocathode to be installed into the gun without affecting the gun's ultra-high vacuum.…”