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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. 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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  1. Electron Spin Precession at CEBAF Douglas W. Higinbotham Jefferson Lab and Marie-Isabelle Holdrinet Université Blaise Pascal

  2. 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)

  3. Continuous Electron Beam Accelerator Presently a 6 GeV machine, scheduled to be upgraded to a 12 GeV accelerator.

  4. Spin Precession In Storage Ring Beautiful demonstration of the electron’s anomalous magnetic moment and QED.

  5. Spin Precession At CEBAF

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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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