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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

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.



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.