Transcript CEBAF Guns July 1999 - Present Present JLab “Vent/Bake” Polarized Electron Gun Cathode Anode (GaAs) 4 days to load, bake, prepare new photocathode Laser eCs NF3 (leaky) (F.E.) -100 kV.

CEBAF Guns July 1999 - Present
Present JLab “Vent/Bake” Polarized Electron Gun
Cathode
Anode (GaAs)
4 days to load,
bake, prepare new
photocathode
Laser
eCs
NF3
(leaky)
(F.E.)
-100 kV
New Load Lock Gun Assembled & Running Spring ‘06
Heat/activation chamber
Goal: 8 hours swap photocathode
Present: ~12 hours
x4
Small bake Load region
Suitcase
NEG-coated HV chamber
Experimental Setup
High Voltage
(-100 kV)
Laser
(1 W @ 532 nm)
& attenuators
Faraday Cup
(450 C bake)
NEG pipe
Activation
(Cs/NF3,
Mask=5 mm)
Solenoid
Centering
Spot Size
Adjustment
Load lock port
(GaAs on puck)
7 Precision
Ion Pump
Supplies
350 mm
1500 mm
Benchmarking the NEW Load Lock Gun (2006-2007)
CEBAF ~2500 C/year
LL Gun ~ 2500 C/week
• No RF structure
• Low-P wavelength
Demonstrated world best
GaAs lifetimes, & up to 10 mA
13 mA!
Future: High Current & High Polarization Programs
Qweak to test standard model >200
mA at 85% polarization
Proposed e-/ion collider facilities
JLab ELIC (>1 mA), BNL eRHIC (>50 mA)
~20 C/day
Circulator <1 C/day
Linac >100 C/day
Now: High Current & High Polarization
Ingredients: Good gun, good photocathode, powerful laser
14 pairs
100 nm
NEW Load Lock Gun
Superlattice GaAs:
Layers of GaAs on
GaAsP
chekc
No strain relaxation
QE ~ 1%
Pol ~ 85%
@ 780 nm
Fiber-based Laser
Friday, Saturday & Sunday
Brief opportunity to use one of the
fiber lasers, before installed into
CEBAF on Monday:
•Superlattice high-P material (85%)
•Very good QE ~1% in New Gun
•First running with 499 MHz RF
Qweak Demonstrated
250 mA (2 days, 70 C)
Lifetime 250-1000 C
(translates > 1 week running/spot)
ELIC Circulator Ring Demonstrated
1 mA (10 hr, 30 C)
Lifetime ~200 C