• T. Zwart, dc. Cheever, N.T. Cliffer, M. Farkhondeh, W. Graves, W. North, C. Tschalaer, D. Wang, D. Wang, F. Wang, A. Zolfaghari, J. van der Laan
  MIT, Middleton, Massachusetts
• H.-D. Gräf
  TU Darmstadt, Darmstadt

A fast ferrite inductive tuner assembly has been constructed for use at the 3 GHz superconducting S-Dalinac accelerator. This device was installed and tested at the S-Dalinac in April 2005. At a fixed accelerating field of 1.4 MV/m using a simple analog control loop the amplitude of the cavity peak-to-peak phase fluctuations with respect to the phase of the incident RF was reduced from 80 degrees to 10 degrees. The 50 Hz noise which dominated the open loop microphonics was reduced by more than 30 dB. The open loop response of the reactive tuner has also been characterized, yielding a tuning range of ?f greater than 300 Hz at a Qext of 1.5e7. The ferrite tuner was then relocated on the waveguide to a distance of (n+1/4)? from the input coupler. This allowed fast control of the coupling with range of Qext from 1.5 - 8e7.

• M. Farkhondeh, dc. Cheever, W.A. Franklin, E. Ihloff, B. McAllister, R. Milner, W. North, C. Tschalaer, E. Tsentalovich, D. Wang, D. Wang, F. Wang, A. Zolfaghari, T. Zwart, J. van der Laan
  MIT, Middleton, Massachusetts

The MIT Bates Accelerator Center is delivering highly polarized electron beams to its South Hall Ring for use in Nuclear Physics Experiments. Circulating electron currents in excess of 200 mA with polarization of 70% are scattered from a highly polarized, but very thin atomic beam source deuterium target. At the electron source a compact diode laser creates photoemission of quasi-CW mA pulses of polarized electrons at low duty factors from a strained GaAs photocathode. Refurbished RF transmitters provide power to the 2856 MHz linac, accelerating the beam to 850 MeV in two passes before injection into the South Hall Ring. In the ring a Siberian snake serves to maintain a high degree of longitudinal polarization at the BLAST scattering target. A Compton laser back-scattering polarimeter measures the electron beam polarization with a statistical acuracy of 6% every 15 minutes.