1. with help from Riad Sulieman, Arne Freyberger, and Joe Grames
Polarized Electrons for Parity Violation Experiments at Jefferson Lab APS Meeting, Salt Lake City, Utah April 16 – 19, 2016
Matt Poelker
with help from Riad Sulieman, Arne Freyberger, and Joe Grames

2. Outline Historical background 12 GeV CEBAF Schedule Injector Upgrade
Features that should help: improved ¼ cryomodule, 200kV Gun, 200 kV spin flipper with prebuncher located downstream, improved Mott polarimeter, etc.,
Upgrade Injector Test Facility
Test bed for developing and commissioning new CEBAF hardware including some components mentioned above
Learning from Qweak
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

3. CEBAF Overview Thanks to Arne Freyberger for slides
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

4. CEBAF Upgrade
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

5. CEBAF 12 GeV Upgrade Schedule
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

6. Some Challenges
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

7. Synchrotron radiation-driven emittance growth as predicted
Performance to date
Synchrotron radiation-driven emittance growth as predicted
Successful Model-Based Optics Matching
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

8. Both cancel with helicity reversal
Issues? Any polarization dependencies?
Yves Roblin has implemented an ELEGANT model to calculate spin precision with synchrotron radiation (SR) included – standard 6 GeV formula will not work
Adiabatic Damping: emittance grows but amplitude of betatron oscillations (e.g., helicity-correlated position and angle differences) should still be damped by square root of ratio of momenta
Beam energy distribution stays symmetric, no energy tails
Polarization Dependencies (?):
Total SR power depends on transverse polarization, 𝑃 𝑝𝑜𝑙 / 𝑃 𝑢𝑛𝑝𝑜𝑙 ~ 10 −4
Spin-flip SR (Sokolov–Ternov self-polarization effect) of about
Total SR power for longitudinal polarized electrons is spin independent but power radiated into space above and below orbital plane is different and thus spin dependent (𝐴~ 10 −5 ) – principle of Spin-Light Polarimeter
Helicity-correlated SR → Helicity-correlated emittance growth
References:
1. A Spin-Light Polarimeter for Multi-GeV Longitudinally Polarized Electron Beams.
P. Mohanmurthy and D. Dutta, IEEE TRANSACTIONS ON NUCLEAR SCIENCE 61, 528 (2014).
2. An observation of the spin dependence of synchrotron radiation intensity.
S. A. Belomesthnykh et al., Nucl. Instrum. Methods, 227, 173 (1984). 3.
Both cancel with helicity reversal
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

9. Nuclear Physics Schedule
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

10. CEBAF Parity Violation Experiments
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

11. CEBAF Polarized Electron Injector
Comprehensive measurement and control of the electron beam during helicity reversal remains the critical strategy
During Summer 2016 the source laser table will be configured with an additional laser, enabling simultaneous 4-Hall capability
Completion of the Injector Upgrade includes a higher voltage gun and improved cryounit to better retain the PQB generated at the source
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

12. Beamline vacuum window
Laser Table Now
3-laser
configuration
Pockels Cell
RWP IA
IHWP
Beamline vacuum window
Tune Mode Generator
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

13. Beamline vacuum window
Laser Table Summer 2016
New 4-laser
configuration IA
Pockels Cell
RWP
IHWP
Tune Mode Generator
Beamline vacuum window
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

14. CEBAF Injector Upgrade
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

15. CEBAF Injector Upgrade Status
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

16. Commissioning the CEBAF Upgrade at UITF
TESTING MORE ROBUST (>300KV) INVERTED GUN
TEST 200KV WIEN FILTER
COMMISSIONING NEW 2/7 CELL CRYOUNIT
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

17. CEBAF – ILC 200 kV Inverted Gun
Developed and ready for installation
Commissioned at Test Cave to 225 kV w/o field emission
Large Grain Niobium electrode
But prefer a bit more voltage headroom….
-200kV
light in
e- out
photocathode
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

18. Testing > 300 kV Inverted Guns at GTS / UITF
11 MV/m
Commissioned to 325 kV
8 MV/m
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

19. Bunchlength + Charge Asymmetry Monitor
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

20. CEBAF 5 MeV Mott Polarimeter
X. Roca-Maza
Mott polarimetry exploits the elastic scattering asymmetry of spin polarized electrons from the nuclear Coulomb field.
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

21. Expected Range of Uncertainty
CEBAF 5 MeV Mott Polarimeter
Target Thickness
Effective Sherman Function (Seff)
Target thickness extrapolation (simulation & analysis)
Sherman function (theory)
Measured asymmetry (statistical + instrumental)
Expected Range of Uncertainty
Source
2014 Expectation
Theory
0.5 – 1.0%
Extrapolation
0.2 – 0.5%
Instrumental
0.2 – 0.4%
BUDGET
0.6 – 1.2%
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

22. Expected Range of Uncertainty
CEBAF 5 MeV Mott Polarimeter
Run I – January 2015
Instrument systematics
Extrapolation I (SLSP-5247)
Run II – October 2015
Beam systematics
Extrapolation II (SLSP-5756)
Expected Range of Uncertainty
Source
2014 Expectation
2016 Preliminary
Theory
0.5 – 1.0%
0.5 – 0.6%
Extrapolation
0.2 – 0.5%
0.2 – 0.3%
Instrumental
0.2 – 0.4%
BUDGET
0.6 – 1.2%
0.6 – 0.7%
We are planning publication this Spring, but Users benefit immediately from this work
Future Run 3 may test largest systematic (theory) with low-Z target
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

23. Issues from QWeak
Beam Halo with a large helicity-correlated charge asymmetry
It varied with:
Beam loss at Injector Apertures
Laser phase (which leads to beam loss on apertures)
Machine tuning (also an aperture/beam loss issue?)
How to fix this?
BCM Resolution not suitable for MOLLER:
QWeak achieved 65 ppm but MOLLER requires 10 ppm
BCM digital receiver bench studies found that local oscillator phase and amplitude noise was likely cause of 65 ppm noise floor
Try new digital receivers
Improve phase/amplitude noise of local oscillator
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

24. Laser Table Tasks Task Sub Tasks Date Description
2 kHz Helicity Reversal
MOLLER
Requires 10 µs settle time – No ringing
(not required for PREX-II, but hoped to test at this time). No Kerr Cell.
RTP Pockels Cell
Very fast transition but not very good circ. polarization. Buy/test crystals to characterize, design RTP quarter-wave system.
KD*P
re-design
Model E-field to maximize Pockels Cell uniformity, buy a properly engineered, one with the correct cell-diameter-to-laser-beam-diameter aspect ratio
Pockels Cell Stewart Platform
2016
For remote optimization using e-beam.
Assemble, build control software, qualify
Parity Quality Beam Focus Group: Riad Suleiman JLab Point of Contact
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

25. Injector Tasks Task Sub Tasks Date Description
Improve 2-Wien Flip Optics
PREx-II
Injector Matching
Maximize damping
Helicity-correlated Beam Size Monitor
Looking for ideas!
Upgrade Helicity Magnet controls
Locate Helicity Magnets to span (x,x') and (y,y') to minimize both position and angle
Fall 2015
Augment helicity steering dipoles with helicity size quads
Share Injector apertures' current read-back with parity DAQ
MOLLER Feedback on Wien filter to minimize transverse polarization
Once a shift, adjust Wien angle
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

26. Accelerator Tasks Task Sub Tasks Date Description
Study Depolarization at Higher Passes
Now
Energy stability and precession to Hall
Synchrotron Radiation
MOLLER
Beam noise, width of asymmetry distribution
Adiabatic damping
Polarization dependence
Helicity-correlated emittance growth
MOLLER (g-2) Spin Flip
Change beam energy by 100 MeV
(few reversals)
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

27. Hall Tasks Task Sub Tasks Date Description Beam Halo
Install QWeak halo monitors in Hall A
Now
BCM Resolution
New cavities and receivers
BCM receiver bench studies and beam studies
Beam Modulation
Beam Polarimetry
Spin Dance
Beam Matching and Optics
Phase Trombone
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

28. Conclusions Laser System
Still operating with 3-lasers, soon there will be 4
Each now has capability for or 499 MHz
High-Polarization Photocathode
Retired work horse of 6 GeV era
Installed for 12 GeV (QE > 1%, P ~87%)
Gun
Still operating at -130 kV
Baked gun/activated NEG’s => Charge lifetime >150C
Parity Controls
Intact from 6 GeV program
Helicity Magnets
Retained if needed for sensitivity or feedback, but…
Requires ioc/hardware upgrade + new locations.
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

29. Conclusions cont. Brock Cavity – non-invasive charge asymmetry monitor
Installed after A1 for bunch length profile measurement
Brock & BCM0L02 span (A2+Chopper+A3+A4)
Mott Polarimeter
3 year upgrade effort wrapping up
Stewart Platform – remote positioning of Pockels cell
Wes Moore wrote EPICS driver for embedded machine linux
John Hansknecht planning for 3D printing of components
Summer intern for calibration and testing
When to install the 200kV gun and new ¼ cryomodule?
2018 Shutdown (?)
200 kV Wien filters
Prebuncher will be downstream of 2-Wien spin flipper
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

30. Conclusions cont. Four Hall Operation
Could be a serious challenge: can we deliver 2 beams through one chopper slit? Hall D beam at 200 nA through the PV-hall slit
Time to begin PV-related beam studies in earnest
How much noise does SR add to beam at 11 GeV? Can PV experiments live with wider asymmetry distributions?
Quantify adiabatic damping at 11 GeV – does SR pose a problem for HC position asymmetry?
Parity Quality Beam focus group: it‘s time to start working through the task list
Source Group and CASA should have more time to work this stuff, how about Physics staff?
APS Meeting, Salt Lake City, Utah April 16 – 19, 2016