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

Synchrotron Radiation (SR)“Spin-Light”

Wiggler MagnetsCollimators

Ionization ChambersGeant4 Simulations

Topic by Topic Case Studies (Only a Few Presented)

Summary

Outline (CHANGE)

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

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

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)

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?

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

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

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.

Updated Geant4 ResultsTheory Plots: Updated Spectra and Corresponding Asymmetry

Updated Characteristic PlotsTheory Plots: Updated Spectra and Corresponding Asymmetry

The spectra now is completely in the hard

X-ray Spectrum

Updated Geant4 ResultsNumber Spectra for beam energy of 5GeV, magnet

pole strength of 0.22T

Updated Geant4 ResultsPower Spectra for beam energy of 5GeV, magnet

pole strength of 0.22T

Updated Geant4 ResultsNumber Spectra for beam energy of 12GeV,

magnet pole strength of 0.5T

Updated Geant4 ResultsPower Spectra for beam energy of 12GeV, magnet

pole strength of 0.5T

Updated Geant4 ResultsBut the Geant4 asymmetry for both the energy

configurations (12GeV @ 0.5T and 5GeV @ 0.22T) match within about 5%

Slit Width EffectsFor 5GeV @ 0.22T

Slit Width EffectsFor 12GeV @ 0.5T: Completely resolved even if the

e-beam is allowed a 4cm wide passage.

UncertaintiesBackground 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 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

Backup

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

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

Collaboration