Transcript JLab Polarized Source Happex Collaboration Meeting May 18, 2007 P. Adderley, J. Brittian, J.

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
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 …
G0 Experience: Laser-Table Setup
and Halls Crosstalk
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).
On the Laser Table
IN / PITA=0
Choose: x=0, y=90 mils
On the Laser Table
OUT / PITA=0
Choose: x=70, y=90 mils
With the electron beam
OUT / PITA=0
Choose: x=67, y=91 mils
Laser Table Setup and Pockels Cell Alignment (G0 Experience):
•
Laser Table:
1.
2.
•
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:
1.
2.
3.
4.
5.
6.
Establish electron beam in the injector. Find the BPMs pedestals by doing a current scan
with the iocse’s 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 it’s 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 PITA=0 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.
361 MeV, 35 uA January LD2
Halls A & C Cross-talk
1. 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)
2. Hall C Charge Asymmetry Width:
Hall C @ 20 uA
Hall A @ 90 uA
Hall C @ 20 uA
Hall A OFF
Helicity Magnets Commissioning
Injector Helicity Magnet
Installation (0L01-0L03)
January 5-6, 2004
MHE0L03V,
MHE0L03H
MHE0L02H
MHE0L01V
Tube protecting
Litz magnet wire
Grounded cage containing
electrically isolated helicity
magnet controls (VME)
110 VAC
Isolation
Transformer
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
Position Feedback Test I
• Introduce large position differences:
Magnet 1 at even DAC = 500
• Turn ON position feedback:
Zero position differences at 0L05 and 0L06
Position Feedback Test II
• Introduce large position differences:
Move the Pockels Cell from its optimal position on the laser table
• Turn ON position feedback:
Zero position differences at 0L05 and 0L06
Position Feedback Test III:
• 1-day G0 Production:
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.
• Turn ON magnet 1:
Power it to 1000 times its operational value. Look for
position differences upstream the magnet
Summary:
Helicity Magnets can be used to do
position feedback
Some improvements are still needed
1.
2.
Increase the DAC resolution by at least a factor of 10.
Better selection of BPMs to do feedback on.
…
Commissioning of the 250 Hz Helicity
Flip and the New HV Switch
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
Issue I: New Switch Electrical Pickup
30 Hz Flip
PC OFF, new Switch
30 Hz Flip
PC OFF, old Switch
Issue II: 60 Hz Position Noise
Can 60 Hz
noise be
used to
study the
beam
envelope?
More 60 Hz
noise
search to
be
continued
…
After moving an ion-pump
power supply away
from the beam-line
FBB Diagnostic and Measuring
Parity-Quality of Beam
Richard Dickson
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.
Measuring Position Differences
Helicity Magnet 1 ON
+/- 150 DACs
Results
• Charge asymmetry and position differences agree to better
than 10%.
FFB Diagnostic
Hall A
Dx_1C08 (um) -8
+7
Dy_1C08 (um) -19
+18
Dx_1C12 (um) 18
-14
Dy_1C12 (um) -43
+40
• 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
Paper: “Conducting Parity Violation
Experiments at CEBAF”
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 ☺)
Pockels cell properties
Pockels cell alignment techniques (Happex method)
Laser table components: IA, pzt, insertable halfwave plate, Rotatable HWP
Pockels cell HV switch (Hansknecht ☺)
Comparison of commercial PCs (Cleveland, lasermetrics, 10mm, 20mm, RTP)
PZT mirror position feedback (Pitt ☺)
Flipping schemes (pairs, quartets), delayed reporting (Pitt ☺)
Ground loop management (Hansknecht ☺)
Photo-cathodes: types, Residual LP, Analyzing power, QE gradients…
Accelerator:
Beam position monitors (Dickson☺)
Beam charge monitors
Using the bpm system to measure asymmetries (Dickson☺)
Beam envelop management at injector (beam through holes) (Kazimi ☺)
Beam envelop matching throughout machine, adiabatic damping (Chao☺):
Characterization and control of global transport optics
Correction of XY coupling and transport singularity from 100 keV to 60 MeV
Tools and methods for minimizing transport irregularities
Phase Trombone to minimize position differences at target (Bogacz ☺)
Halls Crosstalk and beam loading
Feedback
Coil Modulation, Dithering vs. Regression
Position feedback using helicity magnets (Grames, Suleiman ☺)
Summary: (Armstrong ☺)
What has been achieved so far in terms of position differences and charge asymmetries?
Future experiments (Qweak and Lead neutron radius) and their requirements, trends and need for continued R&D.
Mott Polarimetry, Load-Lock Gun,
and more …
• 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/pockels.htm
G0 Cavities