Electron spin precession at cebaf
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Electron Spin Precession at CEBAF. Douglas W. Higinbotham Jefferson Lab and Marie-Isabelle Holdrinet Université Blaise Pascal. Polarized Source. C. Hernandez-Garcia, P. G. O'Shea and M . L. Stutzman , Physics Today 61N2 (2008) 44. Strained GaAs Photocathode

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Electron Spin Precession at CEBAF

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Electron spin precession at cebaf

Electron Spin Precession at CEBAF

Douglas W. Higinbotham

Jefferson Lab

and

Marie-Isabelle Holdrinet

Université Blaise Pascal


Polarized source

Polarized Source

C. Hernandez-Garcia, P. G. O'Shea and M. L. Stutzman, Physics Today 61N2 (2008) 44.

  • Strained GaAs Photocathode

  • Ultra-High Vacuum (Ions Destroy Cathodes)


Continuous electron beam accelerator

Continuous Electron Beam Accelerator

Presently a 6 GeV machine, scheduled to be upgraded to a 12 GeV accelerator.


Spin precession in storage ring

Spin Precession In Storage Ring

Beautiful demonstration of the electron’s anomalous magnetic moment and QED.


Spin precession at cebaf

Spin Precession At CEBAF


Example cebaf setup

Example CEBAF Setup

Select a beam energy and Wien angle based on physics requirements of the Halls

(63.5 MeV Injector Energy and 565 MeV Per Linac Per Pass)

  • Machine setup with balanced or energy match linacs.

  • Hall C required polarization (GEP-III) and Hall’s A & B requested polarization.


Imbalanced linacs

Imbalanced Linacs

Needed to give Hall A & C high polarization without changing the beam energy for Hall B.

(63.5 MeV Injector Energy and 555 MeV & 575 MeV Per Linacs)

  • With imbalanced the linacs, we were able to boost the polarization.

  • 10 MeV was removed from the North linac and 10 MeV was added to the South linac.


Future conditions 2010 2012

Future Conditions (2010 – 2012)

A two year long parity experiment requires first pass and no transverse polarization.

  • The machine needs to be setup to give all Halls high polarization.

  • Either with energy (as shown above) or deliberately running off crest.


Magic cebaf energy 2 12 gev pass

Magic CEBAF Energy (2.12 GeV/pass)

37,5°

A

B

South Linac

C

-37,5168°

With the 12 GeV upgrade, these energies become available.


Summary

Summary

  • Many Jefferson Lab experiments require polarized electrons.

  • The source can produce 200uA of 85% polarized beam.

  • Historically to maximize the long. polarization, the energy and Wien were fixed.

  • Demonstrated a third parameter of imbalanced linacs.

  • A future parameter could be deliberately running a pass off crest.

  • As the figure of merit goes as P2, even small improvements can have a real impact.


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