Abstract
Operation of superconducting radio frequency (SRF) cavities with high loaded quality factors is becoming increasingly preferred for applications which involve low beam loading including energy recovery linacs (ERL). Vibration induced microphonics detuning poses a major operational bottleneck in these low bandwidth systems, adversely affecting field stability. Besides passive measures of mitigating the vibration sources, modern SRF cavities are also attached to fast tuners incorporating piezoelectric actuators. We demonstrate the narrow band active noise control algorithm for realizing active resonance control and propose a modification based on the least mean square approach to adaptively tune the control parameters and study its stability and performance. We discuss our experience of using passive mitigation techniques while commissioning the main linac cryomodule of the Cornell-BNL ERL test accelerator and report a net reduction in peak detuning by more than a factor of 2 in its unstiffened cavities. Finally, we demonstrate stable performance of our resonance control system with consistent reduction of peak microphonics detuning by almost a factor of 2 on multiple cavities.
Highlights
Modern particle accelerators are reaching the pinnacle of efficiency using superconducting radio frequency (SRF) cavities which are characterized by low loses arising from high intrinsic quality factors (Q0 ≳ 1010) [1]
We develop a least mean square (LMS) control system based on narrow band active noise control to command the piezoelectric actuators and analyze its performance and stability
The operation of SRF cavities with high QL using solid state amplifiers of limited power present a significant constraint on the peak microphonics detuning which we can tolerate in order to maintain a stable field
Summary
Modern particle accelerators are reaching the pinnacle of efficiency using superconducting radio frequency (SRF) cavities which are characterized by low loses arising from high intrinsic quality factors (Q0 ≳ 1010) [1]. The microwave power requirements of such SRF cavities depend on the effective beam loading and the loaded quality factor QL used in operation. The interaction of the field with the wall currents is one mechanism leading to mechanical deformation and is known as Lorentz force detuning (LFD) This leads to transient detuning as a function of the field inside the cavity and is important for pulsed rf systems. Vibrations inside cryomodules couple into the cavity walls causing transient deformations in its shape resulting in microphonics detuning. Suppression of peak detuning is important in machines operating with high QL especially in multiturn ERLs such as CBETA, where there are tight tolerances on field stability (rms amplitude stability of 1 × 10−4 and phase stability of 0.1°) to preserve the intrinsic energy spread of the beam. We present a summary of our work and propose some improvements to the resonance control system
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