Delayen J.

Paper	Title	Page
TUP45	Development of a Digital Self-Excited Loop for Field Control in High-Q Superconducting Cavities	230
	J. Delayen, T. Allison, C. Hovater, J. Musson, T. Plawski Thomas Jefferson National Accelerator Facility
	Several near-term (e.g. JLab 12 GeV project) or longer term (e.g. ERLs) projects will involve operation of a large number of high-Q superconducting cavities where the Lorentz detuning is much larger that the loaded bandwidth. Of particular importance in these machines is the stability with respect to ponderomotive instabilities and rapid turn-on time and recovery from a trip. Control systems based on analog self-excited loops have been successfully used for many decades in small low-velocity ion linacs that were operating in that regime. We have developed and tested a control system based on a digital self-excited loop for the 12 GeV upgrade, which could also be used in other superconducting accelerators projects such as the Facility for Rare Isotope Beams.
WE205	Electro-mechanical properties of spoke-loaded superconducting cavities	404
	Z. A. Conway, J. D. Fuerst, M. P. Kelly, K. W. Shepard ANL G. K. Davis, J. Delayen TJNAF
	This paper presents experimental data characterizing the electro-mechanical properties of superconducting spoke-loaded cavities developed for high-intensity ionlinac applications, such as the cw ANL Advanced Exotic Beams Laboratory (AEBL) driver linac and the pulsed FNAL High Intensity Neutrino Source (HINS, now project X) proton driver linac. High-gradient cw operation at 4.2 K can produce violent boiling in the liquid helium coolant causing microphonic frequency noise. A spoke cavity designed to minimize the effects of helium pressure on RF eigenfrequency, the total microphonic induced RF frequency variations, were found to be on the level of the phase noise in the reference oscillator. To determine the pulsed cavity RF performance, the Lorentz transfer function was measured and used to predict the dynamic detuning in pulsed operation. There is good agreement between the predicted fit and the measured data, demonstrating the utility of the Lorentz transfer function, which can completely characterize the dynamics of the coupling between the mechanical cavity structure and the cavity RF field due to the Lorentz force.
	Slides(PDF)
WEP67	Low-level RF control of microphonics in superconducting spoke-loaded cavities	669
	Z. A. Conway, M. P. Kelly, S. I. Sharamentov, K. W. Shepard ANL G. K. Davis, J. Delayen TJNAF L. R. Doolittle LBNL
	This paper presents the results of cw RF frequency control and RF phase-stabilization experiments performed with a piezoelectric fast tuner mechanically coupled to a superconducting, 345 MHz, beta = 0.5 triple-spoke-loaded cavity operating at 4.2K. The piezoelectric fast tuner damped low-frequency microphonic-noise by an order of magnitude. Two methods of RF phase-stabilization were characterized: overcoupling with negative phase feedback, and also fast mechanical tuner feedback. The beta = 0.5 triple-spoke-loaded cavity RF field amplitude and phase errors were controlled to +(-)0.5% and +(-)30 respectively.