Transcript JLab Polarized Source Group • We are: Phil Adderley, Maud Baylac, Joshua Brittian, Daniel Charles, Jim Clark, Joe Grames, John Hansknecht, Matt Poelker,

JLab Polarized Source Group
• We are: Phil Adderley, Maud Baylac, Joshua Brittian,
Daniel Charles, Jim Clark, Joe Grames, John
Hansknecht, Matt Poelker, Marcy Stutzman
• 1 student, 4 technical staff, 4 scientists
• Source Group Hall of Famers: Charlie Sinclair,
Bruce Dunham, Scott Price, Peter Hartmann,
Michael Steigerwald, Tony Day, Kim Ryan, Danny
Machie, John Hogan, Bill Schneider, Reza Kazimi,
Paul Rutt, Ganapati Rao Myneni
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
GaAs Photoemission Guns
• An invention nearly 30 years old.
• Spin-dependent electron scattering tells us something
about the structure of the target (e.g., molecule, atom,
proton, neutron).
• Good tool for Condensed Matter and Atomic Physics
research.
• Great tool for High Energy and Nuclear Physics
research.
• Relatively new application; Unpolarized electrons for
Light Sources.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
The First GaAs Photoemission Gun
P=
3-1
= 50%
3+1
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
First High Voltage GaAs Photogun
Electrons into the accelerator Dec., 1977
Collaboration announces parity violation June, 1978
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Gun Issues Today and Tomorrow
• Lifetime at High Current (vacuum issues)
• Adequate photocathode QE and polarization
• Adequate Laser Power with RF pulse structure
• Control of Helicity Correlated Systematics
• Beam handling (space charge induced
emittance growth)
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
A good day when…
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Photocathode Lifetime
Vacuum not perfect. QE degrades via ion backbombardment
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Charge Lifetime at CEBAF
Gun charge lifetime degrading with time.
Limited NEG pump lifetime/capacity?
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Vacuum Considerations
Ultimate Pressure = Outgassing Rate x Surface Area
Pump Speed
We need;
Smaller outgassing rate, Less surface area, More pump speed.
discrepancy
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Lasers at CEBAF
Diode lasers and
SPIRE photocathodes
can’t provide 100 uA
at high polarization.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Lasers at CEBAF
Homemade Ti-Sapphire laser for GEp and GEn
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Lasers at CEBAF
Modelocked TiSapphire lasers from
Time-Bandwidth very
promising. Reliable.
High rep rates available.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Laser Table Configuration Jan., 2004
We rearrange the lasers every ~ three months
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Parity Violation Experiments at CEBAF
Parity violation experiments continue to set the standard for Polarized Source performance.
Experiment
Physics
Asymmetry
Max run-average
helicity correlated
Position Asym.
Max run-average
helicity correlated
Current Asym.
HAPPEX-I
HAPPEX-II
13 ppm
1.3 ppm
10 nm
2 nm
1.0 ppm
0.6 ppm
HAPPEX-He
8 ppm
3 nm
0.6 ppm
G0
Qweak
Lead
2 to 50 ppm
0.3 ppm
20 nm
20 nm
1 nm
1.0 ppm
0.1 ppm
0.1 ppm
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Built at
U of I
Feb. 1995
through
Dec. 1998
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Feb. 1998
through
Spring 1999
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
July 1999 to present
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
JLab’s 100 kV load-locked gun at Test Cave
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Immediate Projects
• Install new superlattice photocathodes; high
polarization (85% vs 75%), high QE (1% vs
0.1%) and small analyzing power (2% vs 10%).
• Ti-Sapphire lasers for Halls A and C
• Install load-locked gun at injector by 2005
• Better management of helicity correlated beam
parameters. Routine delivery of “parity quality”
beam.
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004
Future Projects
• More interaction with FEL gun group
• Play active role in development of high
current 100 mA gun for FEL (unpolarized
beam) and ELIC (polarized beam)
Thomas Jefferson National Accelerator Facility
Operated by the Southeastern Universities Research Association for the U.S. Depart. Of Energy
M. Poelker, Core Manager’s Meeting, 12 Feb., 2004