Author: Powers, T.
Paper Title Page
THTU3
 Practical Aspects of SRF Cavity Testing and Operations  
 
  • T. Powers
    JLab, Newport News, Virginia, USA
  
  Over the past 30 years we have done about 6500 cold cavity tests on more than 800 different cavities at Jefferson Lab. Most of these tests were done with voltage controlled oscillator based phase locked loop systems. More recently we converted most of our systems to digital low level RF based systems. In addition to doing many of these test myself, I have been involved with the development, construction and commissioning of several cavity test systems and the software used to control them. My hope today is to provide you with a basic understanding of the RF systems necessary to perform these tests. I hope you leave here with an understanding of the importance of calibration processes and the control and understanding of potential error sources. I will also provide some information relating to the practical aspects of operating SRF cavities in real machines. Hopefully, A complete set of equations necessary for calculating the cavity parameters and can be found on the website for this conference as an addendum to this talk.  
slides icon Slides THTU3 [9.873 MB]  
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TUP034 Microphonics Testing of LCLS II Cryomodules at Jefferson Lab 493
 
  • T. Powers, N.C. Brock, G.K. Davis
    JLab, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
Jefferson Lab is partnering with Fermilab to build the 36 cryomodules for the LCLS II accelerator that will be installed at SLAC. The cavities have design loaded-Q of 4×107, which means that it has a control bandwidth of 16 Hz. The JLab prototype cryomodule was instrumented with a series of seven accelerometers, and impulse hammer response measurements were made while the cryomodule was being built and after it was installed in the JLab cryomodule test facility. This was done so that we could understand the shapes of the modes of the structure. These results were compared to impulse hammer testing from the outside of the cryomodule and to individual cavity frequency shifts when the cryomodule was cold. The prototype cryomodule had excessive microphonics of 150 Hz peak due to a thermos-acoustic oscillation. Design modifications were implemented and subsequently the cryomodules had microphonics on the order of 10 to 20 Hz. Results of the modal analysis as well as the background microphonics observed when operated under various cryogenic conditions and with different modifications will be presented. 		 
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP034  
About • paper received ※ 21 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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WETEB3 CEBAF C100 Fault Classification based on Time Domain RF Signals 763
 
  • T. Powers, A.D. Solopova
    JLab, Newport News, Virginia, USA
  
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177
The CEBAF 12 GeV upgrade project, which was completed and commissioned in 2014, included the construction and installation of 80 new 7-cell superconducting cavities that were configured in 10 cryomodules. In 2018, the software and hardware in the digital low level RF systems were configured such that a fault would trigger an acquisition process which records waveform records of 17 of the RF signals for each of the 8 cavities within the cryomodule for subsequent analysis. These waveforms are especially useful in C100 cryomodules as there is a 10% mechanical coupling between adjacent cavities. When one cavity has a fault and the gradient is reduced quickly, it will mechanically deform due relaxation of the Lorentz force effects. This deformation change causes perturbations in the adjacent cavities which, in turn, causes a cascade of cavity faults that are difficult to understand without the time domain data. This contribution will describe the types of faults encountered during operation and their signatures in the time domain data, as well as how is being used to modify the setup of the machine and implement improvements to the cryomodules. 		 
slides icon Slides WETEB3 [3.169 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-WETEB3  
About • paper received ※ 21 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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