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Title |
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| TUP76 |
Adaptive Feedforward Cancellation of Sinusoidal Disturbances in Superconducting RF Cavities
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447 |
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- T.H. Kandil, T.L. Grimm, W. Hartung, H. Khalil, J. Popielarski, J. Vincent, R.C. York
NSCL, East Lansing, Michigan
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A control method, known as adaptive feedforward cancellation (AFC) is applied to damp sinusoidal disturbances due to microphonics in superconducting RF (SRF) cavities. AFC provides a method for damping internal, and external sinusoidal disturbances with known frequencies. It is preferred over other schemes because it uses rudimentary information about the frequency response at the disturbance frequencies, without the necessity of knowing an analytic model (transfer function) of the system. It estimates the magnitude and phase of the sinusoidal disturbance inputs and generates a control signal to cancel their effect. AFC, along with a frequency estimation process, is shown to be very successful in the cancellation of sinusoidal signals from different sources. The results of this research may significantly reduce the power requirements and increase the stability for lightly loaded continuous-wave SRF systems.
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| THP66 |
Measurement and Control of Microphonics in High Loaded-Q Superconducting RF Cavities
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763 |
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- T.L. Grimm, W. Hartung, T.H. Kandil, H. Khalil, J. Popielarski, J. Vincent, R.C. York
NSCL, East Lansing, Michigan
- C. Radcliffe
MSU, East Lansing, Michigan
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Superconducting radio frequency (SRF) linacs with light beam loading, such as the CEBAF upgrade, RIA and energy recovery linacs, operate more efficiently with loaded-Q values >1·107. The narrow band-width puts stringent limits on acceptable levels of vibration, also called microphonics, that detune the SRF cavities. Typical sources of vibration are rotating machinery, fluid fluctuations and ground motion. A prototype RIA 805 MHz v/c=0.47 cryomodule is presently under test in realistic operating conditions [1]. Real-time frequency detuning measurements were made for modulation rates from DC to 1 kHz. At 2 K the maximum frequency deviation was less than 100 Hz peak-to-peak, and was consistent with high loaded-Q operation. The measured modulation spectrum was primarily made up of discrete Fourier components with modulation frequencies less than 80 Hz. Using an accelerometer and helium pressure transducer, the primary sources of vibration were determined to be the high power cryoplant motors and 2 K helium fluctuations. Adaptive feedforward was used to decrease the magnitude of individual Fourier components by four to ten times [2]. Details of the experimental setup and measurements will be presented.
[1] “Experimental Study of an 805 MHz Cryomodule for the Rare Isotope Accelerator”, T.L. Grimm et al., THP70, these proceedings. [2] “Adaptive Feedforward Cancellation (AFC) of Sinusoidal Disturbances in SRF Cavities”, H. Khalil et al., TUP76, these proceedings.
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Transparencies
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| THP70 |
Experimental Study of an 805 MHz Cryomodule for the Rare Isotope Accelerator
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773 |
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- T.L. Grimm, S. Bricker, C. Compton, W. Hartung, M. Johnson, F. Marti, J. Popielarski, R.C. York
NSCL, East Lansing, Michigan
- G. Ciovati, P. Kneisel
Jefferson Lab, Newport News, Virginia
- L. Turlington
TJNAF, Newport News, Virginia
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The Rare Isotope Accelerator (RIA) driver linac will use superconducting, 805 MHz, 6-cell elliptical cavities with geometric β values of 0.47, 0.61 and 0.81. Each elliptical cavity cryomodule will have four cavities [1]. Room temperature sections between each cryomodule will consist of quadrupole doublets, beam instrumentation, and vacuum systems. Michigan State University (MSU) has designed a compact cryostat that reduces the tunnel cross-section and improves the linac real estate gradient. The cold mass alignment is accomplished with a titanium rail system supported by adjustable nitronic links from the top vacuum plate, and is similar to that used for existing MSU magnet designs. The same concept has also been designed to accommodate the quarter-wave and half-wave resonators with superconducting solenoids used at lower velocity in RIA. Construction of a prototype β=0.47 cryomodule was completed in February 2004 and is presently under test in realistic operating conditions. Experimental results will be presented including: alignment, electromagnetic performance, frequency tuning, cryogenic performance, low-level rf control, and control of microphonics.
[1] “Cryomodule Design for the Rare Isotope Accelerator”, T.L. Grimm, M. Johnson and R.C. York, PAC2003, Portland OR (2003)
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