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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 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

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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 Presentation

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Page 1: Lifetime Studies

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

Page 2: Lifetime Studies

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.

Page 3: Lifetime Studies

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)

Page 4: Lifetime Studies

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

Page 5: Lifetime Studies

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

Page 6: Lifetime Studies

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)

Page 7: Lifetime Studies

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

Page 8: Lifetime Studies

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

Page 9: Lifetime Studies

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

Page 10: Lifetime Studies

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

Page 11: Lifetime Studies

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).

Page 12: Lifetime Studies

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)

Page 13: Lifetime Studies

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

Page 14: Lifetime Studies

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.

Page 15: Lifetime Studies

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

Page 16: Lifetime Studies

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

Page 17: Lifetime Studies

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.