Polarized GaAs photo cathode development and the preparation of Gatling Gun cathodes at BNL The Single Cathode Activation Chamber

Outline  Motivation  Single Preparation Tree The Cathode Holder The Service Flange Vacuum Management  Current Status  Summary

Motivation  Gatling Gun is going to use GaAs crystals to produce spin polarized electrons  GaAs crystals need to be “activated” before electron production  Procedure of activating one GaAs crystal at a time is well understood and state of the art  Gatling Gun will use 20 crystals simultaneously  Activating 20 GaAs crystals is challenging

Multiple Cathode Preparation System Tree 1/4 Tree 2/4 Manipulator Train Grand Central To gun chamber

Single Preparation System  Going from 2 beams to 20 beams is easy compared to going from 1 beam to 2  Proof of Principle can and will be done by using 2 cathodes only  Develop a single (manually operated) preparation system to feed the Gatling Gun  Use a transport vessel to transport activated cathodes between Tree and Gun

Single Cathode System

Supporting tripod

Single Cathode System Activation chamber (“Tree”)

Single Cathode System Horizontal manipulator (vacuum suitcase)

Single Cathode System Connector

Single Cathode System Vertical manipulator

Single Cathode System

Single Cathode Preparation Tree

Leak valve for O 2 Cooling water (in) Cooling water (out) Thermo couple Heater (in) Heater (out) Service flange (1 st floor)

Single Cathode Preparation Tree 2 nd floor HABS (eventually) Port for 650 nm / 780 nm laser Anode Viewport Thermo couple Cooling water (in) Cooling water (out) Leak valve for H 2 Power connector HABS

Single Cathode Preparation Tree 3 rd floor NEG pump Pressure gauge Ion pump

Single Cathode Preparation Tree 4 th floor Cs dispenser (in) Cs dispenser (out) Residual gas analyzer

Single Cathode Preparation Tree Inside view Feed through for Cs source (in) Feed through for Cs source (out) Support rods for mask Mask Manipulator to move mask Cs source

The Cathode Holder 10 x 10 mm 2 GaAs crystal Conical shape for self alignment, sealing & enhanced heat transfer Spring for conformance & soft stop Cap with 8mm opening for holding sample in place Thermal Break

The Cathode Holder

The Service Flange Heater feed through Oxygen tube Mask Cathode holder Heater wire Heater wire

The Service Flange Heater (out) Leak valve for O 2 Cooling water (in) Cooling water (out) Thermo couple Heater (in)

The Service Flange Heater (out) Leak valve for O 2 Thermo coupleHeater (in) Heater filament O 2 nozzle Cathode

Pumps and Vacuum  Pumps 15 l/s Ion pump (Gamma Vacuum) 80 l/s Ion pump (Gamma Vacuum) 2x 400 l/s CapaciTorr NEG pumps (SAES Getters)  Gauges RGA (Stanford Research Systems) Extremely High Vacuum Gauge AxTRAN (Ulvac) Hot-Cathode Ionization Gauge 3BG-03 (VacLab Inc) Main chamber

Pumps and Vacuum  Pumps 2 l/s Dry Scroll pump (Agilent/Varian) 50 l/s Turbo pump (Agilent/Varian) 15 l/s Ion pump (Gamma Vacuum)  Gauges Convectron Gauge (Granville-Phillips) Bayard-Alpert ionization gauge (Granville-Phillips) Cross

Pumps and Vacuum  Pumps 15 l/s Ion pump (Gamma Vacuum)  Gauges Convectron Gauge (Granville-Phillips) Bayard-Alpert ionization gauge (Granville-Phillips) Vacuum suitcase

Current Status

Summary  Use single cathode preparation tree (“Tree”) to supply Gatling Gun with two cathodes at a time  In the beginning use unpolarized Bulk-GaAs samples  Tree is already assembled and under vacuum in Building 966  First activation will take place very soon

Acknowledgments  J. Pietz (Transfer Engineering)  J. Walsh, W. Smith (Instrumentation Division)  T. Seda, D. Pate (C-AD)