1. CsI Photocathode Production and Testing
Bob Azmoun
Brookhaven National Lab
12/8/04
12/8/04
B. Azmoun

2. CsI Deposition @ Stony Brook
Objective: To develop and test the technique of CsI evaporation at Stony Brook for production of CsI coated GEM foils for HBD prototypes and possibly even the final detector.
Method
Use high purity CsI (Scintillator grade)
High Vacuum (1E-7 Torr) [diffusion pump w/ N2 trap]
Thoroughly clean vessel and all components
Bake the CsI
Mask substrates
Evaporate very small amount of CsI
This vaporizes any contaminants on molybdenum
boat and/or outer surface of CsI crystals
Vessel walls coated with CsI will also act as a “getter”
Warm up substrates before, during and after evaporation
Withholds water and contaminants from condensing onto
the substrates before deposition, and onto the CsI after
deposition
Thickness monitor
Quartz crystal oscillator, Al foil control substrate
Transportation/ Storage of Photocathodes (vacuum, gas flow)
12/8/04
B. Azmoun

3. Dimensions of Evaporator Vessel
Max. Height
~80cm
Scaffolding: Photocathode
substrate/Thickness monitors
Bell Jar
Diameter ~ 43cm
mask
Electrodes/CsI crystal/
Molybdenum Boat
12/8/04
B. Azmoun

4. Thickness Uniformity r Underside of Scaffolding
CsI Thickness Target: 2000 Angstroms
Al Foil Control Substrates
for measuring CsI thickness r
Quartz Crystal Thickness Monitor
Quartz crystal
thickness monitor
Au-Ni-Cu clad
G-10 Photocathode
Substrates
12/8/04
B. Azmoun

5. Testing Apparatus @ BNL
Absolute QE of produced Photocathodes Vs Wavelength
Photoelectron signal in CF4 (CF4 transmittance)
GEM systematics (gain, stability, etc.)
Systematic Measurements of CsI Coated Triple GEM
(pe collection efficiency Vs ED, etc)
Beam splitter/Collimator
MgF2
Windows
VUV beam
Photocathode or
Triple GEM
Absorption Length
~ 30cm
Independent Lamp Monitor
Photocathode Test
Vacuum Vessel (“cross”)
12/8/04
B. Azmoun

6. Preliminary Measurements
12/8/04
B. Azmoun

7. Initial Use for CsI Photocathodes
Preliminary Tests in Idealistic Stainless steal vessel (Cross)
GEM + CsI + CF4 + single pad + gas tight vessel (minimal out-gassing, high purity gas)
Systematic measurements of CsI coated triple GEM detector (Gain, stability, QE measurement, transmittance, pe collection efficiency Vs ED, etc)
Install (10x10cm) CsI coated GEM into “simple” HBD prototype with “realistic vessel” (made of G-10)
GEM + CsI + CF pads (~1x1”) + ~50cm radiator
In Lab tests: gas quality (H2O/O2 ppm’s, transmittance), performance of GEMs/CsI in more realistic conditions (gain, stability, aging studies of CsI QE in gas, etc)
Test at Light Source: N0 measurement
Test inside PHENIX IR: Stability of GEMs, background, etc. ???
12/8/04
B. Azmoun