• S.A. Belomestnykh, R.P.K. Kaplan, H. Padamsee, P. Quigley, J.J.R. Reilly, J. Sears, V. Veshcherevich
  Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
• S. Bauer, M. Pekeler, H. Vogel
  ACCEL, Bergisch Gladbach
• L.-H. Chang, C.-T. Chen, F.-Z. Hsiao, M.-C. Lin, G.-H. Luo, C. Wang, T.-T. Yang, M.-S. Yeh
  NSRRC, Hsinchu
• E. Matias, J. Stampe, M.S. de Jong
  CLS, Saskatoon, Saskatchewan

Upon signing a technology transfer agreement with Cornell University, ACCEL began producing turn-key 500 MHz superconducting cavity systems. Four such cryomodules have been delivered, commissioned and installed in accelerators for operation to date. Two more cryomodules are scheduled for testing in early 2005. One of them will be put in operation at Canadian Light Source (CLS); the other will serve as a spare at Taiwan Light Source (TLS). The commissioning results and operational experience with the cryomodules in CESR, CLS and TLS are presented.

• S.A. Belomestnykh, R.P.K. Kaplan, J.J.R. Reilly, V. Veshcherevich
  Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York

An instability of the active RF cavity field control loop was observed during experiments with beam-driven (passive) superconducting cavities in CESR when the cavity external Q factor was raised to a value above 1x10⁷. A computer model was developed and further experiments have been performed to study this instability and find a way to cure it. The results of simulations are presented alongside the experimental results.

• M. Liepe, S.A. Belomestnykh, J. Dobbins, R.P.K. Kaplan, C.R. Strohman, B.K. Stuhl
  Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York

A new digital control system has been developed, providing great flexibility, high computational power and low latency for a wide range of control and data acquisition applications. This system is now installed in the CESR storage ring and stabilizes the vector sum field of two of the superconducting CESR 500 MHz cavities and the output power from the driving klystron. The installed control system includes in-house developed digital and RF hardware, very fast feedback and feedforward control, a state machine for automatic start-up and trip recovery, cw and pulsed mode operation, fast quench detection, and cavity frequency control. Several months of continuous operation have proven high reliability of the system. The achieved field stability surpasses requirements.

• M. Liepe, S.A. Belomestnykh, J. Dobbins, R.P.K. Kaplan, C.R. Strohman, B.K. Stuhl
  Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
• C. Hovater, T. Plawski
  Jefferson Lab, Newport News, Virginia

The superconducting cavities in an Energy-Recovery-Linac will be operated with a high loaded Q of several 1E7, possible up to 1E8. Not only has no prior control system ever stabilized the RF field in a linac cavity with such high loaded Q, but also highest field stability in amplitude and phase is required at this high loaded Q. Because of a resulting bandwidth of the cavity of only a few Hz, this presents a significant challenge: the field in the cavity extremely sensitive to any perturbation of the cavity resonance frequency due to microphonics and Lorentz force detuning. To prove that the RF field in a high loaded Q cavity can be stabilized, and that Cornell's newly developed digital control system is able to achieve this, the system was connected to a high loaded Q cavity at the JLab IR-FEL. Excellent cw field stability – about 2·10^-4 rms in relative amplitude and 0.03 deg rms in phase - was achieved at a loaded Q of 2.1·10⁷ and 1.4E8, setting a new record in high loaded Q operation of a linac cavity. Piezo tuner based cavity frequency control proved to be very effective in keeping the cavity on resonance and allowed reliable to ramp up to high gradients in less than 1 second.