Transcript Lifetime Measurements using the Jefferson Lab (JLAB) Load-Lock Gun J. Grames, P.

Lifetime Measurements using the
Jefferson Lab (JLAB) Load-Lock Gun
J. Grames, P. Adderley, M. Baylac, J. Brittian, D. Charles,
J. Clark, J. Hansknecht, M. Poelker, M. Stutzman, K. Surles-Law
October 7-9, 2004
PESP 2004
Mainz, Germany
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Lifetime Studies
Our job at JLAB is to provide up to 200 mA CW of
polarized electrons (~20 C/day). Future photoinjectors
will require 10’s of milliAmps of polarized electrons.
Photocathode quantum efficiency (QE) degrades with gun
operation, correlated with the charge evolved.
If QE were initially exceptionally high or laser power were
unlimited then degradation of the QE might be tolerable,
but neither are practically so.
Additionally, non-uniform QE across the illuminated surface
may be intolerable for some parity violation experiments.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Presentation Outline
A 100 keV load lock gun and beam line have been
installed for the studies of QE degradation as a
function of gun operation.
Part 1 (Summer-Fall ‘03)
Gun/Beamline Commissioning
QE Degradation Trends
vs. vacuum level
vs. laser spot location
vs. active area
Lifetime Rates
Part 2 (Spring-Summer ’04)
Mask vs. Anodization
Improved vacuum monitoring
Higher current studies
Model construction
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
100 keV Load-Lock Electron Gun
High Voltage
Chamber
Load-Lock
Chamber
Preparation
Chamber
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
100 keV Beam line for Lifetime Studies
Summer-Fall ‘03
780 nm diode, 50 mW, 500 mm
Commissioned to 350 mA
Spring-Summer ‘04
780 nm diode, 50 mW, 500 mm
532 nm Nd:YVO4, 11 W, 1000 mm
Commissioned to 8 mA
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Versus: Vacuum, Anodization, Beam Location
Unanodized (11 mm)
Leak
Fix/Bake
>15.0
4.9
Anodized (5mm)
NEG’s w/ IP
NEG’s w/ Turbo
2.3
1.9
(x10-11 Torr)
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
QE Degradation vs. Gun Pressure (Extractor Gauge)
~2.5E-11 Torr
~5.0E-11 Torr
>15.0E-11 Torr
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
QE Degradation Trend vs. Laser Spot Location
2.4 mm
1.6 mm
0.8 mm
Center
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
QE Degradation Trend vs. Anodization Size
Location #1
5mm (red)
anodized
11 mm (green)
unanodized
Location #2
Location #3
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Lifetime vs. Time (fast & slow process ?)
Data
Lifetime(s) = QE falls by 1/e
Slow Lifetime Fit
Fast Lifetime Fit
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Part 2: Mask Activation & Vacuum Monitoring
A mask to limit activation surface (as
demonstrated at Mainz) was installed to
the prep chamber (5, 7, 9 mm).
Improved UHV on-line vacuum
monitoring using nAmp holding ion
pump power supplies.
Manipulator mis-alignment has resulted in dropped “pucks” and detours…
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Lifetime vs. Time (9 mm mask)
Bin Samples
(~5 min)
Goal: Develop self-consistent
model.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Lifetime vs. Intensity (7 mm & 9 mm mask)
Threshold ?
7 mm
9 mm
Beam
Off
7 mm
9 mm
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Lifetime vs. Laser Spot Location (7 mm & 9 mm mask)
Electrostatic
Center
Mask Radius
Cathode
Radius
7 mm (’04)
9 mm (’04)
7 mm (’03)
Lifetime dependence
on spot location can
be sensitive to optics.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
QE: 300 V vs. 100 kV
QE at 300 V
4.15 mA
QE at 100 kV (2500,3500)
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Transient & Steady State Details
0.1 C
0.01 C
59 C
19 C
4C
8C
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004
Summary
We are using a 100 keV load-lock gun and beamline to study photocathode
lifetime vs. gun operating parameters. Our experimental setup evolves often.
Measurements consistently indicate that improved vacuum and limited active area
enhance photocathode lifetime.
Measurements indicate that photocathode lifetime as a function of laser spot
location may depend upon a greater set of parameters, such as beam line optics
and laser spot size.
In the coming months emphasis will be placed to develop a quantitative lifetime
model to better describe collected data and design future measurements.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
PESP 2004, Mainz, Germany, Oct.7-9, 2004