prajwal t. mohan murthy laboratory for nuclear science, mit νdm group spin-light polarimeter for...
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Prajwal T. Mohan Murthy Laboratory for Nuclear Science, MIT
νDM Group
Spin-Light Polarimeterfor the
Electron Ion Collider
EIC Users Meeting 2014Jun 2014
Story Brook, NY
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Synchrotron Radiation (SR)“Spin-Light”
Wiggler MagnetsCollimators
Ionization ChambersGeant4 Simulations
Topic by Topic Case Studies (Only a Few Presented)
Summary
Outline (CHANGE)
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Synchrotron Radiation (SR)“Spin-Light”
Wiggler MagnetsCollimators
Ionization ChambersGeant4 Simulations
Topic by Topic Case Studies (Only a Few Presented)
Possible Location at mEICSummary
Outline (CHANGE)
Quick parts, for details, please refer to:
• arXiv:1401.6744• arXiv:1309.6711• arXiv:1309.2988
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Synchrotron Radiation (SR)“Spin-Light”
Wiggler MagnetsCollimators
Ionization ChambersGeant4 Simulations
Topic by Topic Case Studies (Only a Few Presented)
Possible Location at mEICSummary
Outline (CHANGE)
Quick parts, for details, please refer to:
• arXiv:1401.6744• arXiv:1309.6711• arXiv:1309.2988
Latest Updates
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Comparative Introduction
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What is Synchrotron Radiation?First seen in General Electric Lab, 1947
Angular Distribution
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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)
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Longitudinal Spin Light
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What are Spin-Light Characteristics?Spin light characteristics
A=
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Conceptual Design
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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.
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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.
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A schematic for detection of SR (alternative arrangements are a possible)
Detecting the Collimated SR
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What will be the signal?
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Geant 4 Simulation
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Geant 4 Simulation ResultsSimulation reproduces photon spectrum and asymmetry
Only a single DIC is being simulated along with collimators
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What about Background Simulations?
Background events are mostly Bremsstrahlung events from the collimators
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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.
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How does this scale with EBeam and IBeam?Number Spectra
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How does this scale with EBeam and IBeam?Power Spectra
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How does this scale with Ebeam and Ibeam?Asymmetry
Power output remains to be a challenge for high energy EIC
Spin-Light Polarimeter is best suited for:• E(e) = [2,20]GeV• I(e) < 10mA
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Where could this be accommodated in mEIC?
Ample real-estate near the 8 dipoles and the fact that the magnets are of 20mrad bend angle (twice as much as initial proposal design) allows for convenient sized collimators.
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Updated Geant4 ResultsTheory Plots: Updated Spectra and Corresponding Asymmetry
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Updated Characteristic PlotsTheory Plots: Updated Spectra and Corresponding Asymmetry
The spectra now is completely in the hard
X-ray Spectrum
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Updated Geant4 ResultsNumber Spectra for beam energy of 5GeV, magnet
pole strength of 0.22T
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Updated Geant4 ResultsPower Spectra for beam energy of 5GeV, magnet
pole strength of 0.22T
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Updated Geant4 ResultsNumber Spectra for beam energy of 12GeV,
magnet pole strength of 0.5T
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Updated Geant4 ResultsPower Spectra for beam energy of 12GeV, magnet
pole strength of 0.5T
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Updated Geant4 ResultsBut the Geant4 asymmetry for both the energy
configurations (12GeV @ 0.5T and 5GeV @ 0.22T) match within about 5%
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Slit Width EffectsFor 5GeV @ 0.22T
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Slit Width EffectsFor 12GeV @ 0.5T: Completely resolved even if the
e-beam is allowed a 4cm wide passage.
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UncertaintiesBackground and
background asymmetry has to be measured with
the wiggler on/off
Simulation was used to estimate background
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SUMMARY
AcknowledgementsThis work is supported by the U.S. Department of Energy under contract number DE-FG02-07ER41528 ‘10 – ’13 and MIT Frank Fellowship.
• 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
• Possible location at mEIC zeroed on
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Backup
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How does the dipole field look like?
Central Uniform field
BEAM
Magnet Face
Beam Pipe
Edge fringe field
Conceptual Design
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How does the dipole field look like?
Edge fringe field Central Uniform field
BEAM
Magnet Face
Simulated using LANL Poisson EM Code Beam Pipe
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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)
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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.
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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.
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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
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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.
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What are Spin-Light Characteristics?Beam Energy dependence
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How does this scale inclusion of Beam Halo?Asymmetry
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Collaboration