Polarized Electrons for Parity Violation Experiments at Jefferson

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 Ge. V CEBAF Schedule Injector Upgrade • Features that should help: improved ¼ cryomodule, 200 k. V Gun, 200 k. V 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 2

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

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

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

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

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

Issues? Any polarization dependencies? • Both cancel with helicity reversal APS Meeting, Salt Lake City, Utah April 16 – 19, 2016 8

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

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

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 11

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

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

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

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

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

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

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

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

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

Effective Sherman Function (Seff) CEBAF 5 Me. V Mott Polarimeter Sherman function (theory) Target thickness extrapolation (simulation & analysis) Measured asymmetry (statistical + instrumental) Expected Range of Uncertainty Target Thickness Source 2014 Expectation Theory 0. 5 – 1. 0% Extrapolation 0. 2 – 0. 5% Instrumental 0. 2 – 0. 4% BUDGET APS Meeting, Salt Lake City, Utah April 16 – 19, 2016 0. 6 – 1. 2% 21

CEBAF 5 Me. V Mott Polarimeter Run I – January 2015 o Instrument systematics o Extrapolation I (SLSP-5247) Run II – October 2015 o Beam systematics o 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% 0. 2 – 0. 3% BUDGET 0. 6 – 1. 2% 0. 6 – 0. 7% APS Meeting, Salt Lake City, Utah April 16 – 19, 2016 o We are planning publication this Spring, but Users benefit immediately from this work o Future Run 3 may test largest systematic (theory) with low-Z target 22

Issues from QWeak 1. 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? 2. 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 Ø Try new digital receivers Ø Improve phase/amplitude noise of local oscillator APS Meeting, Salt Lake City, Utah April 16 – 19, 2016 23

Laser Table Tasks Task Sub Tasks 2 k. Hz Helicity Reversal Pockels Cell Stewart Platform Date MOLLER Description 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-tolaser-beam-diameter aspect ratio 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 24

Injector Tasks Task Sub Tasks Date Description Improve 2 -Wien Flip Optics PREx-II Injector Matching PREx-II Maximize damping Helicity-correlated Beam Size Monitor PREx-II Looking for ideas! Upgrade Helicity Magnet controls PREx-II 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 PREx-II Share Injector apertures' current read-back with parity DAQ PREx-II MOLLER Feedback on Wien filter to minimize transverse polarization APS Meeting, Salt Lake City, Utah April 16 – 19, 2016 Once a shift, adjust Wien angle 25

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

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 27

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 Ge. V era 2009 -2012 - Installed 5756 -4 for 12 Ge. V (QE > 1%, P ~87%) Gun - Still operating at -130 k. V - Baked gun/activated NEG’s => Charge lifetime >150 C Parity Controls - Intact from 6 Ge. V 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 28

Conclusions cont. Brock Cavity – non-invasive charge asymmetry monitor - Installed after A 1 for bunch length profile measurement - Brock & BCM 0 L 02 span (A 2+Chopper+A 3+A 4) 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 3 D printing of components - Summer intern for calibration and testing When to install the 200 k. V gun and new ¼ cryomodule? - 2018 Shutdown (? ) - 200 k. V Wien filters - Prebuncher will be downstream of 2 -Wien spin flipper APS Meeting, Salt Lake City, Utah April 16 – 19, 2016 29

Conclusions cont. Four Hall Operation - Could be a serious challenge: can we deliver 2 beams through one chopper slit? Hall D beam at 200 n. A through the PV-hall slit Time to begin PV-related beam studies in earnest - How much noise does SR add to beam at 11 Ge. V? Can PV experiments live with wider asymmetry distributions? - Quantify adiabatic damping at 11 Ge. V – 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 30