JLab Polarized Source

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JLab Polarized Source

• Happex Collaboration Meeting
• May 18, 2007
• P. Adderley, J. Brittian, J. Clark, J. Grames, J.
  Hansknecht, M. Poelker,
• M. Stutzman, R. Suleiman, K. Surles-Law

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Outline

• G0 Experience Laser-Table Setup, Halls
  Cross-talk,
• Helicity Magnets Commissioning
• Q-weak 250 Hz Helicity Flip Test and the New HV
  Switch
• FFB Diagnostic and Measuring Parity-Quality of
  Beam
• Paper Conducting Parity Violation Experiments
  at CEBAF
• Mott Polarimetry, Load-Lock Gun, and more

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G0 Experience Laser-Table Setup and Halls
Crosstalk
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Summary of G0 Experience

• Pockels Cell (PC) HVs, roll, pitch, and yaw
  should be optimized using the spinning HWP and a
  scope.
• No need to do laser work with the QPD in the
  tunnel.
• PC x y should be optimized to minimize the
  steering with the electron beam since Jan 07,
  automated PC X Y stages were installed.
• Use PITA and RHWP to zero the charge asymmetry
  and position differences (with the electron beam).

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IN / PITA0
On the Laser Table
Choose x0, y90 mils
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OUT / PITA0
On the Laser Table
Choose x70, y90 mils
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OUT / PITA0
With the electron beam
Choose x67, y91 mils
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• Laser Table Setup and Pockels Cell Alignment (G0
  Experience)
• Laser Table
• Check laser spot is round (1mm diameter) and has
  no tails or satellites and centered on the
  Pockels Cell.
• With the spinning HWP in front of LP, minimize
  the residual linear polarization. Find the
  optimal HV, -HV, roll, pitch, and yaw of the PC.
  Check for both IHWP IN OUT.
• Electron Beam
• Establish electron beam in the injector. Find the
  BPMs pedestals by doing a current scan with the
  iocses set in Gains off mode.
• Turn OFF the PC and take a long run to check for
  electronic noise. Turn it back ON.
• You will use IPM1I02 to finish the setup but its
  good to check IPM1I04 and IPM1I06.
• Do an x y translational scans for both IN and
  OUT. Find PC x y that minimize the PC steering.
• For IN, do a RHWP at PITA0 and another one at
  PITA-180 V. Find the RHWP angle that further
  minimizes the position differences and charge
  asymmetry, you will have to change the PC high
  voltage to new values. Repeat this for OUT.
• Now for both IN and OUT you have determined PC
  x, PC y, HV, -HV, RHWP angle. The IA voltage
  should be 5 V for both IN and OUT. Over time, IN
  and OUT will drift to their own IA values.

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361 MeV, 35 uA January LD2
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Halls A C Cross-talk

• Hall A IA Scan

• Hall A IA Scan (80 uA)
• Hall C Charge asymmetry and position differences
  during the Hall A IA Scan (20 uA)

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• Hall C Charge Asymmetry Width

Hall C _at_ 20 uA Hall A _at_ 90 uA
Hall C _at_ 20 uA Hall A OFF
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Helicity Magnets Commissioning
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Calibration

• Each magnet can kick both helicity states
• Very small coupling to charge asymmetry (100
  times smaller than PZT)
• The position feedback is not coupled to the
  charge feedback
• Can do position feedback on both position and
  angle in x y

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Position Feedback Test I

• Introduce large position differences Magnet 1
  at even DAC 500

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• Turn ON position feedback
• Zero position differences at 0L05 and 0L06

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Position Feedback Test II

• Introduce large position differences
• Move the Pockels Cell from its optimal
  position on the laser table

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• Turn ON position feedback
• Zero position differences at 0L05 and 0L06

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Position Feedback Test III

• 1-day G0 Production

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Electrical Pick-up

• One big concern Will other elements on the
  beam-line see the helicity signal?
• Check this with Pockels Cell OFF and Helicity
  Magnets OFF.

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• Turn ON magnet 1
• Power it to 1000 times its operational value.
  Look for position differences upstream the magnet

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• Summary
• Helicity Magnets can be used to do
• position feedback
• Some improvements are still needed
• Increase the DAC resolution by at least a factor
  of 10.
• Better selection of BPMs to do feedback on.

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Commissioning of the 250 Hz Helicity Flip and the
New HV Switch
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Changes needed to run at 250 Hz

• New Pockels Cell HV Switch to replace the old
  switch
• The Helicity Board is programmed for either 30 Hz
  or 250 Hz with Time-Settle of 60 us, 100 us, 200
  us, or 500 us
• Check that tools we need still can work at 250 Hz
  and 60 us T-Settle
• Parity DAQs
• Mott and Moller Polarimeters
• Helicity Magnets

Worked Fine
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Issue I New Switch Electrical Pickup
30 Hz Flip PC OFF, new Switch
30 Hz Flip PC OFF, old Switch
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Issue II 60 Hz Position Noise
Can 60 Hz noise be used to study the beam
envelope?
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More 60 Hz noise search to be continued
After moving an ion-pump power supply away from
the beam-line
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FBB Diagnostic and Measuring Parity-Quality of
Beam

• Richard Dickson

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The Accelerator BPM Measurement

• Developed by Richard Dickson.
• It uses the FFB diagnostic system to read the
  BPMs wires. Currently running on iocse9 in Hall A
  and iocse14 in Hall C. These two IOCs receive
  only the delayed helicity signal.
• Each wire is sampled at 1800 Hz for Hall A
  (Linac style SEE BPM) each sample is 64 us long
  and consists of 8 sub-samples each 8 us. For
  Hall C (Transport style BPM) a single sample is
  taken at the 1800 Hz rate. Two seconds of data
  are acquired for each helicity state (3600
  samples). For each five second readout, one
  second is reserved for computation and output by
  EPICS.
• For each sample
• The 4-wires (pedestal subtracted) are added for
  all the BPMs in each feedback system (eight), and
  x y positions are calculated individually for
  each BPM
• Data Processing
• Data is summed for any given helicity window and
  the sum stored for later correlation with the
  delayed helicity signal. There is a dead time at
  both beginning and end of the helicity window.
  Beam trips are filtered away.
• This results in roughly 60 samples being summed
  together in any helicity window.
• The helicity correlated sum for a window are then
  further summed into a running total for that
  state until approx two seconds of data are
  acquired per state.
• After completion of data acquisition, asymmetries
  and differences are computed. These are then
  available via EPICS as well as values that are
  further digitally filtered.

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Measuring Position Differences
Helicity Magnet 1 ON /- 150 DACs
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Results

• Charge asymmetry and position differences agree
  to better than 10.
• Modify the BPM software to calculate also error
  bars or RMSs.
• Hardware and software changes to the Injector
  IOCs to be able to measure helicity correlated
  properties in the Injector (iocse11, iocse12,
  iocse19 23 BPMs) July Sept. 07

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Paper Conducting Parity Violation Experiments
at CEBAF
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• Paper Idea Conducting Parity Violation
  Experiments at CEBAF.
• Target Journal Phys Rev A or Nuclear Instr and
  Methods A or Rev of Scientific Instr.
• First draft due by July 1st, 2007.
• Format plain text or doc or latex I will put
  things together in Latex.
• Figures eps format.
• Collaboration (in no particular order, who did I
  forget?)
• JLab Suleiman (POC), Hansknecht, Poelker,
  Grames, Chao, Kazimi, Bogacz, Dickson
• HAPPEx Paschke (POC), Cates, Kumar, Souder,
  Michaels, Kaufman, Snyder
• G0 Pitt (POC), Armstrong, Nakahara, Bailey
• Topics (in no particular order, what did I
  forget?)
• Introduction (Armstrong?)
• Recall first parity violation experiments at
  accelerators
• Discuss the family of recent parity violation
  experiments, what makes them different, what
  makes them possible?
• How do we do a parity violation experiment?
• Laser table
• Lasers (diodes, ti-sap, fiber) (Poelker ?)

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Mott Polarimetry, Load-Lock Gun, and more
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• Upgrade the 5 MeV Mott DAQ Reduce background and
  improve the statistical error bar
• Install new 100 keV / 500 keV Mott in Injector in
  August 07
• Load-Lock Gun will be installed in July 07 (4
  photo-cathodes)
• Now running using fiber-lasers
• PC HV Switches and Ground Loop Elimination
  (Hansknecht)
• Switch Designs
• Eliminating Ringing in Pockels Cells used in
  Parity experiments
• Ground loop elimination for Parity experiments
• http//www.jlab.org/accel/inj_group/laser2001/pock
  els.htm

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G0 Cavities
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