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

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

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

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

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

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

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

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). http://dx.doi.org/10.1109/TNS.2013.2291114 2. An observation of the spin dependence of synchrotron radiation intensity. S. A. Belomesthnykh et al., Nucl. Instrum. Methods, 227, 173 (1984). http://dx.doi.org/10.1016/0168-9002(84)90119-0 3. https://wiki.jlab.org/ciswiki/index.php/PQB_Meeting_April_30,_2015 Both cancel with helicity reversal APS Meeting, Salt Lake City, Utah April 16 – 19, 2016

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Conclusions Laser System Still operating with 3-lasers, soon there will be 4 Each now has capability for 249.5 or 499 MHz High-Polarization Photocathode Retired 5247-1 work horse of 6 GeV era 2009-2012 Installed 5756-4 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

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

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