Polarized GaAs photo cathode development and the

preparation of Gatling Gun cathodes at BNL

TheSingle 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

Single Cathode SystemSupporting tripod

Single Cathode SystemActivation chamber (“Tree”)

Single Cathode SystemHorizontal manipulator (vacuum suitcase)

Single Cathode SystemConnector

Single Cathode SystemVertical manipulator

Single Cathode System

Single Cathode Preparation Tree

Single Cathode Preparation Tree

Leak valve for O2

Cooling water (in)Cooling water (out)Thermo coupleHeater (in)Heater (out)

Service flange (1st floor)

Single Cathode Preparation Tree2nd floor

HABS (eventually)Port for 650 nm / 780 nm laserAnodeViewport

Thermo coupleCooling water (in)Cooling water (out)Leak valve for H2

Power connector

HABS

Single Cathode Preparation Tree3rd floor

NEG pumpPressure gaugeIon pump

Single Cathode Preparation Tree4th floor

Cs dispenser (in)Cs dispenser (out)

Residual gas analyzer

Single Cathode Preparation TreeInside 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 mm2 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

Heaterfeed throughOxygen

tubeMask

Cathode holder

Heater wire

Heaterwire

The Service Flange

Heater (out)

Leak valve for O2

Cooling water (in)

Cooling water (out)Thermo couple

Heater (in)

The Service Flange

Heater (out)

Leak valve for O2

Thermo couple Heater (in)

Heater filamentO2 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)