1. Prajwal Mohanmurthy, Mississippi State University with Dr. Dipangkar Dutta, Mississippi State University Medium Energy Physics Group Spin-Light Polarimeter for the Electron Ion Collider PSTP 2013 Sep 2013 Charlottesville, VA

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

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 Corrections by 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 Corrections by 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

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

13. What will be the signal?

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

15. How does the dipole field look like? Edge fringe field Central Uniform field BEAM Magnet Face 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 E Beam and I Beam ? Number Spectra

21. How does this scale with E Beam and I Beam ? Power Spectra

22. How does this scale with E beam and I beam ? Asymmetry

23. How does this scale with E beam and I beam ? Asymmetry Not too bad

24. How does this scale with E beam and I beam ? Asymmetry Not too bad That’s good

25. How does this scale with E beam and I beam ? Asymmetry Not too bad That’s bad (with HE beams) That’s good

26. How does this scale with E beam and I beam ? Asymmetry Not too bad That’s bad (with HE beams) That’s good Bad too! (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. SUMMARY 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. 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!

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? Point BeamBeam Pipe 2inch 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.

34. Does the Gaussian Beam profile change anything? Finite Beam size Beam Pipe 2inch 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

35. 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.

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

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