lifetime studies
DESCRIPTION
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. Lifetime Studies. - PowerPoint PPT PresentationTRANSCRIPT
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Lifetime Measurements using theJefferson 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 2004Mainz, Germany
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Lifetime Studies
Our job at JLAB is to provide up to 200 A 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.
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Presentation Outline
Gun/Beamline CommissioningQE Degradation Trends
vs. vacuum levelvs. laser spot locationvs. active area
Lifetime Rates
Mask vs. AnodizationImproved vacuum monitoringHigher current studiesModel construction
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)
Part 2 (Spring-Summer ’04)
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
100 keV Load-Lock Electron Gun
Load-LockChamber
High VoltageChamber
PreparationChamber
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
100 keV Beam line for Lifetime Studies
Summer-Fall ‘03
Spring-Summer ‘04
780 nm diode, 50 mW, 500 mCommissioned to 350 A
780 nm diode, 50 mW, 500 m532 nm Nd:YVO4, 11 W, 1000 m
Commissioned to 8 mA
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Versus: Vacuum, Anodization, Beam Location
Leak Fix/Bake
4.9
NEG’s w/ TurboNEG’s w/ IP
(x10-11 Torr)
2.3 1.9>15.0
Unanodized (11 mm) Anodized (5mm)
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
QE Degradation vs. Gun Pressure (Extractor Gauge)
>15.0E-11 Torr
~5.0E-11 Torr
~2.5E-11 Torr
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
QE Degradation Trend vs. Laser Spot Location
Center
0.8 mm
1.6 mm
2.4 mm
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
QE Degradation Trend vs. Anodization Size
Location #1
Location #2
Location #3
5mm (red)anodized
11 mm (green)unanodized
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Lifetime vs. Time (fast & slow process ?)
Fast Lifetime Fit
Slow Lifetime Fit
DataLifetime(s) = QE falls by 1/e
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Part 2: Mask Activation & Vacuum Monitoring
Improved UHV on-line vacuum monitoring using nAmp holding ion pump power supplies.
Manipulator mis-alignment has resulted in dropped “pucks” and detours…
A mask to limit activation surface (as demonstrated at Mainz) was installed to the prep chamber (5, 7, 9 mm).
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Lifetime vs. Time (9 mm mask)
Goal: Develop self-consistent model.
Bin Samples(~5 min)
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Lifetime vs. Intensity (7 mm & 9 mm mask)
BeamOff
Threshold ?7 mm9 mm
7 mm9 mm
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
Lifetime vs. Laser Spot Location (7 mm & 9 mm mask)
7 mm (’04)9 mm (’04)7 mm (’03)
Mask Radius CathodeRadius
Electrostatic Center
Lifetime dependence on spot location can be sensitive to optics.
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
QE: 300 V vs. 100 kV
QE at 300 V
QE at 100 kV (2500,3500)
4.15 mA
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility PESP 2004, Mainz, Germany, Oct.7-9,
2004
4 C
59 C
8 C19 C
0.1 C
0.01 C
Transient & Steady State Details
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
Thomas Jefferson National Accelerator Facility 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.