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Accelerator Seminar


"Digital Self-Excited Loop Implementation and Experience"

Trent Allison,
Engineering Division, Jefferson Lab



A self excited loop (SEL) LLRF control algorithm is desired at Jefferson Lab to facilitate the quick recovery of superconducting accelerating cavities after a fault.  Presently, a generator driven resonator (GDR) algorithm is employed which requires mechanical tuners to compensate for Lorentz force detuning effects as the cavity gradient is slowly increased to the desired level.  The SEL control algorithm is tolerant of cavity mistuning and thus allows for gradient to be restored at approximately the fill rate of the cavity.  This eliminates the need for mechanical tuning during cavity recovery as the cavity will be back to the original tune once the gradient is re-established.  The SEL algorithm is being implemented digitally at Jefferson Lab using Field Programmable Gate Array (FPGA) technology.  Multiple digital algorithms and architectures have been explored.  It was determined that working exclusively in the In-phase and Quadrature (IQ) domain complicated the digital SEL algorithm and that converting to magnitude and phase was more intuitive and efficient.  Many bench and superconducting cavity tests have been preformed with encouraging results. 



Thursday, October 15, 2009

3:30 p.m. - 4:30 p.m.
CEBAF Center, L102/104

Talk Slides: (Slides)

Dr. Alex Bogacz or Anne-Marie Valente.