Prajwal Mohanmurthy, Mississippi State Universitywith Dr. Dipangkar Dutta, Mississippi State University
Medium Energy Physics Group
Spin-Light Polarimeterfor the
Electron Ion Collider
PSTP 2013Sep 2013
Charlottesville, VA
Synchrotron Radiation (SR)“Spin-Light”
Wiggler MagnetsCollimators
Ionization ChambersGeant4 Simulations
Topic by Topic Case Studies (Only a Few Presented)
Summary
Outline (CHANGE)
Comparative Introduction
What is Synchrotron Radiation?First seen in General Electric Lab, 1947
Angular Distribution
So where is spin dependence?With QED Corrections by A.A.Sokolov and I.M.Ternov (1960s)
Spin dependent term Spin flip dependent term
Verified at VEPP-4 storage ring in NovosibirskBelomesthnykh et. al., NIM 227, 173 (1984)
So where is spin dependence?With QED Corrections by A.A.Sokolov and I.M.Ternov (1960s)
Spin dependent term Spin flip dependent term
Verified at VEPP-4 storage ring in NovosibirskBelomesthnykh et. al., NIM 227, 173 (1984)
Longitudinal Spin Light
What are Spin-Light Characteristics?Spin light characteristics
A=
Conceptual Design
Won’t all the fans of SR merge?The SR fans may be selected out after each dipole and collimated before being fed into the DIC.
Notice only 2 fans are required for polarimetry, 4 fans are for statistics.
What are Spin-Light Characteristics?A differential ionization chamber can be used to measure the asymmetry.
SR (+ SpinLight)
• The ionization chamber can use Xenon• A split plane IC can pick out small up-
down asymmetries in SR - influx.• At the IC, the collimated SR beam spots
shall be about 1cm.• Notice: Figure on left is only one half of
the actual IC. The middle plate is held at an intermediate potential.
A schematic for detection of SR (alternative arrangements are a possible)
Detecting the Collimated SR
What will be the signal?
How does the dipole field look like?
Central Uniform field
BEAM
Magnet Face
Beam Pipe
Edge fringe field
Conceptual Design
How does the dipole field look like?
Edge fringe field Central Uniform field
BEAM
Magnet Face
Simulated using LANL Poisson EM Code Beam Pipe
Geant 4 Simulation
Geant 4 Simulation ResultsSimulation reproduces photon spectrum and asymmetry
Only a single DIC is being simulated along with collimators
What about Background Simulations?
Background events are mostly Bremsstrahlung events from the collimators
SR Spots from GEANT4?
Notice only 2 fans are required for polarimetry, 4 fans are for statistics.
Note: The Geant4 simulation plots are all for just one split plane IC, on one side of beamline.
How does this scale with EBeam and IBeam?Number Spectra
How does this scale with EBeam and IBeam?Power Spectra
How does this scale with Ebeam and Ibeam?Asymmetry
How does this scale with Ebeam and Ibeam?Asymmetry
Not too bad
How does this scale with Ebeam and Ibeam?Asymmetry
Not too bad That’s good
How does this scale with Ebeam and Ibeam?Asymmetry
Not too bad
That’s bad (with HE beams)
That’s good
How does this scale with Ebeam and Ibeam?Asymmetry
Not too bad
That’s bad (with HE beams)
That’s good
Bad too!(with HE beams)
UncertainitiesBackground and
background asymmetry has to be measured with
the wiggler on/off
Simulation was used to estimate background
SUMMARY
AcknowledgementsThis work is supported by the U.S. Department of Energy under contract number DE-FG02-07ER41528 ‘10 – ’13 and DOE-JSA-JLAB Fellowship Grant ‘12 – ‘13.
• 3 dipole magnet: .1m dipoles separated by 1m. DIC 10m away
• Asymmetry in SR gives spin light component -> Polarization
• A non invasive and continuous method• Minimal effect due to B field asymmetries & non uniform beam profile
It can work!
Collaboration
Backup
Does the asymmetry in B field change anything?
For each dipole Magnet:There is a reduction in
both the total events and spin-light events (Plot:
Events vs. E(MeV) of the light emitted)
Does the asymmetry in B field change anything?
For each dipole Magnet:Even though there was a
decrease in SR and SpinLight events, the asymmetry
remains the same.
Does the Gaussian Beam profile change anything?
Point Beam Beam Pipe
2inch
SR Profile for Point Cross section of BeamThe graph shows events as seen at the
DICFor a point beam cross section, the SR
profile is “box” like.
Does the Gaussian Beam profile change anything?Finite Beam size
Beam Pipe
2inch
SR Profile for Gaussian Beam ProfileThe graph shows events as seen at the DIC
For a Gaussian beam profile, the SR profile is “box” with smooth edges. Notice the
asymmetry has not changed. 200μNote: Has
been scaled to make it
visible
Do the B field and dimensions affect?
B field was chosen to
be 4T
YES!
And the corresponding pole length of 10cm. This corresponds to a 10mrad angular beam
bend.
What are Spin-Light Characteristics?Beam Energy dependence
How does this scale inclusion of Beam Halo?Asymmetry
