spin-light polarimeter for the electron ion collider

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