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Spin-Light Polarimeter for the Electron Ion Collider

Spin-Light Polarimeter for the Electron Ion Collider. Prajwal Mohanmurthy , Mississippi State University with Dr. Dipangkar Dutta, Mississippi State University Medium Energy Physics Group. PSTP 2013 Sep 2013 Charlottesville, VA. Outline (CHANGE). Synchrotron Radiation (SR) “Spin-Light”

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Spin-Light Polarimeter for the Electron Ion Collider

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  1. Spin-Light Polarimeter for theElectron Ion Collider Prajwal Mohanmurthy, Mississippi State Universitywith Dr. Dipangkar Dutta, Mississippi State UniversityMedium Energy Physics Group PSTP 2013 Sep 2013Charlottesville, VA

  2. Outline (CHANGE) Synchrotron Radiation (SR) “Spin-Light” Wiggler Magnets Collimators Ionization Chambers Geant4 Simulations Topic by Topic Case Studies (Only a Few Presented) Summary

  3. Comparative Introduction

  4. What is Synchrotron Radiation? First seen in General Electric Lab, 1947 Angular Distribution

  5. So where is spin dependence? With QED Correctionsby A.A.Sokolov and I.M.Ternov (1960s) Spin dependent term Spin flip dependent term Verified at VEPP-4 storage ring in Novosibirsk Belomesthnykh et. al., NIM 227, 173 (1984)

  6. So where is spin dependence? With QED Correctionsby A.A.Sokolov and I.M.Ternov (1960s) Spin dependent term Spin flip dependent term Verified at VEPP-4 storage ring in Novosibirsk Belomesthnykh et. al., NIM 227, 173 (1984)

  7. Longitudinal Spin Light

  8. What are Spin-Light Characteristics? Spin light characteristics A=

  9. Conceptual Design

  10. 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.

  11. 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.

  12. Detecting the Collimated SR A schematic for detection of SR (alternative arrangements are a possible)

  13. What will be the signal?

  14. How does the dipole field look like? Magnet Face BEAM Edge fringe field Conceptual Design Central Uniform field Beam Pipe

  15. How does the dipole field look like? Magnet Face BEAM Central Uniform field Edge fringe field Simulated using LANL Poisson EM Code Beam Pipe

  16. Geant 4 Simulation

  17. Geant 4 Simulation Results Simulation reproduces photon spectrum and asymmetry Only a single DIC is being simulated along with collimators

  18. What about Background Simulations? Background events are mostly Bremsstrahlung events from the collimators

  19. 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.

  20. How does this scale with EBeam and IBeam? Number Spectra

  21. How does this scale with EBeam and IBeam? Power Spectra

  22. How does this scale with Ebeamand Ibeam? Asymmetry

  23. How does this scale with Ebeamand Ibeam? Asymmetry Not too bad

  24. How does this scale with Ebeamand Ibeam? Asymmetry Not too bad That’s good

  25. How does this scale with Ebeamand Ibeam? Asymmetry Not too bad That’s good That’s bad (with HE beams)

  26. How does this scale with Ebeamand Ibeam? Asymmetry Not too bad That’s good Bad too! (with HE beams) That’s bad (with HE beams)

  27. Uncertainities Background and background asymmetry has to be measured with the wiggler on/off Simulation was used to estimate background

  28. It can work! • 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 SUMMARY • Minimal effect due to B field asymmetries & non uniform beam profile Acknowledgements This 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.

  29. Collaboration

  30. Backup

  31. 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)

  32. 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.

  33. Does the Gaussian Beam profile change anything? Beam Pipe Point Beam SR Profile for Point Cross section of Beam The graph shows events as seen at the DIC For a point beam cross section, the SR profile is “box” like. 2inch

  34. Does the Gaussian Beam profile change anything? Finite Beam size Beam Pipe SR Profile for Gaussian Beam Profile The 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. 200μ Note: Has been scaled to make it visible 2inch

  35. Do the B field and dimensions affect? YES! B field was chosen to be 4T And the corresponding pole length of 10cm. This corresponds to a 10mrad angular beam bend.

  36. What are Spin-Light Characteristics? Beam Energy dependence

  37. How does this scale inclusion of Beam Halo? Asymmetry

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