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Title: A new microphonics measurement method for superconducting RF cavities

Abstract

Mechanical vibrations of the superconducting cavity, also known as microphonics, cause shifts in the resonant frequency of the cavity. In addition to requiring additional RF power, these frequency shifts can contribute to errors in the closed loop phase and amplitude regulation. In order to better understand these effects, a new microphonics measurement method was developed, and the method was successfully used to measure microphonics on the half-wave superconducting cavity when it was operated in a production style cryostat. The test cryostat held a single β=0.1 half-wave cavity which was operated at 162.5 MHz [1] and [2]. It's the first time that the National Instruments PXIe-5641R intermediate frequency transceiver has been used for microphonics measurements in superconducting cavities. The new microphonics measurement method and results will be shown and analyzed in this paper.

Authors:
; ; ;  [1]; ; ;
  1. JLAB
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1151795
Report Number(s):
JLAB-ACC-14-1910; DOE/OR/23177-3169
Journal ID: ISSN 0168-9002; National Nature Science Foundation of China (91026001)
DOE Contract Number:
AC05-06OR23177
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment; Journal Volume: 767
Country of Publication:
China
Language:
English

Citation Formats

Gao, Zheng, He, Yuan, Chang, Wei, Powers, Tom, Yue, Wei-ming, Zhu, Zheng-long, and Chen, Qi. A new microphonics measurement method for superconducting RF cavities. China: N. p., 2014. Web. doi:10.1016/j.nima.2014.08.030.
Gao, Zheng, He, Yuan, Chang, Wei, Powers, Tom, Yue, Wei-ming, Zhu, Zheng-long, & Chen, Qi. A new microphonics measurement method for superconducting RF cavities. China. doi:10.1016/j.nima.2014.08.030.
Gao, Zheng, He, Yuan, Chang, Wei, Powers, Tom, Yue, Wei-ming, Zhu, Zheng-long, and Chen, Qi. Mon . "A new microphonics measurement method for superconducting RF cavities". China. doi:10.1016/j.nima.2014.08.030.
@article{osti_1151795,
title = {A new microphonics measurement method for superconducting RF cavities},
author = {Gao, Zheng and He, Yuan and Chang, Wei and Powers, Tom and Yue, Wei-ming and Zhu, Zheng-long and Chen, Qi},
abstractNote = {Mechanical vibrations of the superconducting cavity, also known as microphonics, cause shifts in the resonant frequency of the cavity. In addition to requiring additional RF power, these frequency shifts can contribute to errors in the closed loop phase and amplitude regulation. In order to better understand these effects, a new microphonics measurement method was developed, and the method was successfully used to measure microphonics on the half-wave superconducting cavity when it was operated in a production style cryostat. The test cryostat held a single β=0.1 half-wave cavity which was operated at 162.5 MHz [1] and [2]. It's the first time that the National Instruments PXIe-5641R intermediate frequency transceiver has been used for microphonics measurements in superconducting cavities. The new microphonics measurement method and results will be shown and analyzed in this paper.},
doi = {10.1016/j.nima.2014.08.030},
journal = {Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment},
number = ,
volume = 767,
place = {China},
year = {Mon Sep 01 00:00:00 EDT 2014},
month = {Mon Sep 01 00:00:00 EDT 2014}
}
  • In lightly beam loaded superconducting accelerators the rf power requirements are dictated by the maximum amount of microphonics that the system must be able to control and by the energy content of the cavity. In previous machines, such as heavy-ion boosters, the energy content of the cavities was relatively small and one could afford to specify a large control window and still use low power ({approx}100 W) rf sources. In newer accelerators that are being contemplated--such as the CEBAF 12 GeV upgrade or RIA--the energy content of the cavity is quite large requiring rf sources in excess of 10 kW.more » Conservatism in the control window specification would be quite costly; on the other hand loss of lock could have adverse effect on machine availability or beam property or even, in some cases, result in activation. We present a model to estimate the requirements to be placed on the rf control system based on the properties of the cavities, the frequency tuning system, and the characteristics of the accelerator.« less
  • Mechanical vibrations can detune superconducting radio frequency (SCRF) cavities unless a tuning mechanism counteracting the vibrations is present. Due to their narrow operating bandwidth and demanding mechanical structure, the 13-cell 3.9GHz SCRF cavities for the Charged Kaons at Main Injector (CKM) experiment at Fermilab are especially susceptible to this microphonic phenomena. We present early results correlating RF frequency detuning with cavity vibration measurements for CKM cavities; initial detuning compensation results with piezoelectric actuators are also presented.
  • 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, Ë = 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 Ë = 0.5 triple-spoke-loaded cavity RF field amplitude and phase errors were controlled to ±0.5% and ±30 respectively.
  • 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.