SRF Technology - Ancillaries
LLRF
Paper Title Page
SATU2
LLRF Controls and RF Operation  
 
  • J. Branlard
    DESY, Hamburg, Germany
 
  This tutorial presents the challenges and techniques involved in low level radio frequency (LLRF) controls of superconducting (SRF) cavities. The fundamentals of the electro-mechanical model of SRF cavities are recalled; the principles of frequency and bandwidth tuning and its impact on cavity field regulation are presented as well. The basic elements of standard digital LLRF systems are introduced: feed forward, feedback, up and down conversion, sampling, IQ detection and digital processing. The difference between single cavity regulation and vector sum control, pulsed and continuous wave operation are discussed. When applicable, the introduced concepts will be illustrated with real examples, taken from machine operation.  
slides icon Slides SATU2 [9.177 MB]  
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WETEB4 Virtual SRF Cavity: Testing SRF Cavity Support Systems Without the Hassle of Liquid Helium and Klystrons 770
 
  • P. Echevarria, J. Knobloch, A. Neumann, A. Ushakov
    HZB, Berlin, Germany
  • E. Aldekoa, J. Jugo
    University of the Basque Country, Faculty of Science and Technology, Bilbao, Spain
 
  Setting up and debugging SRF support systems, such as LLRF control, quench detection, microphonics and Lorentz-force detuning control, etc., often requires extensive time spent operating the cavities. This results in time consuming and costly operation. Early into the development stages the actual cavity system may not even be available. It is therefore highly desirable to pre-evaluate these systems under realistic conditions prior to final testing with the SRF cavities. We devised an FPGA-based "virtual cavity" that takes a regular low-level RF input and generates the signals for RF-power reflection, transmission and detuning that mimic the response of a real cavity system. As far as the user is concerned, the response is the same as for a real cavity. This "black-box" model includes mechanical modes, Lorentz force detuning, a field depended quality factor, quenches and variable input coupling and is currently being expanded. We present the model and show some applications for operating the quench detection, LLRF and microphonics control for 1.3 GHz BERLinPro cavities. The same system can be used for other cavity types, including normal conducting cavities.  
slides icon Slides WETEB4 [9.784 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-WETEB4  
About • paper received ※ 23 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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WETEB5
Modular Digital Low Level Radio Frequency Control (LLRF) for CW Operation at ELBE  
 
  • M. Kuntzsch, R. Steinbrück, K. Zenker
    HZDR, Dresden, Germany
  • Ç. Gümüş, M. Hierholzer, S. Pfeiffer, Ch. Schmidt
    DESY, Hamburg, Germany
 
  A digital LLRF control has been implemented at the CW linac ELBE at Helmholtz-Zentrum Dresden-Rossendorf. The system is based on the MicroTCA.4 standard and drives four superconducting TESLA cavities and two normal conducting buncher cavities. The system enables a higher flexibility of the field control, improved diagnostics and field stability compared to the analogue system which was used before. The presentation will give an overview on the design specification, detailed system structure, software architecture and latest performance test results.  
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WETEB6 Active Suppression of Microphonics Detuning in High QL Cavities 776
 
  • N. Banerjee, G.H. Hoffstaetter, M. Liepe, P. Quigley
    Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
 
  Funding: This work was performed through the support of New York State Energy Research and Development Agency (NYSERDA). SRF 2019 provided travel support in the form of a student grant.
Accelerators operating with low beam loading such as Energy Recovery Linacs (ERL) greatly benefit from using SRF cavities operated at high loaded quality factors, since it leads to lower RF power requirements. However, large microphonics detuning several times the operating bandwidth of the cavities severely limit the maximum accelerating fields which can be sustained in a stable manner. In this talk, I will describe an active microphonics control technique based on the narrow band Active noise Control (ANC) algorithm which we have used in CBETA, a multi-turn SRF ERL being commissioned at Cornell University. I will describe its stability and performance during beam operations of CBETA with consistent reduction of peak detuning by almost a factor of 2 on multiple cavities.
 
slides icon Slides WETEB6 [10.296 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-WETEB6  
About • paper received ※ 23 June 2019       paper accepted ※ 29 June 2019       issue date ※ 14 August 2019  
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THP073 Advanced LLRF System Setup Tool for RF Field Regulation of SRF Cavities 1063
 
  • S. Pfeiffer, J. Branlard, M. Hoffmann, Ch. Schmidt
    DESY, Hamburg, Germany
 
  Feedback operation at the European XFEL ensures an amplitude and phase stability of 0.01% and 0.01 deg, respectively. To reach such high RF field stability, model-based approaches for RF field system characterization and RF field controller design are in use. High demand on this system modelling is set especially to the characterization of additional passband modes for small bandwidth SRF cavities operated in pulsed mode and vector-sum regulation. This contribution discusses the developed "Advanced system setup tool" using a graphical user implementation in Matlab® for the RF field system characterization and the multiple-input-multiple-output feedback controller setup. Examples and current limitations will be presented.  
poster icon Poster THP073 [0.873 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP073  
About • paper received ※ 19 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP074 Microphonics Noise Suppression with Observer Based Feedback 1068
SUSP004   use link to see paper's listing under its alternate paper code  
 
  • M. Keikha, K. Fong
    TRIUMF, Vancouver, Canada
  • M. Moallem
    SFU, Surrey, Canada
 
  Funding: TRIUMF
Detuning of superconducting radio frequency (SRF) cavities is mainly caused by the Lorentz force, which is the radiation pressure induced by a high radio frequency (RF) field, and environmental mechanical vibrations that induce undesirable interference signals referred to as microphonics. Both of these influences can be described by a second order differential equation of the mechanical vibration modes of the cavity. In this paper we consider three dominant mechanical modes of the system and develop a control scheme based on input-output linearization. It is shown through simulation studies that the proposed control technique can successfully the suppress microphonic noise due to the SRF cavity’s dynamics.
 
poster icon Poster THP074 [0.610 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP074  
About • paper received ※ 22 June 2019       paper accepted ※ 01 July 2019       issue date ※ 14 August 2019  
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THP075 Development of a 166.6 MHz Digital LLRF System for HEPS-TF Project 1073
 
  • Q.Y. Wang, J.P. Dai, T.M. Huang, D.B. Li, H.Y. Lin, Z.H. Mi, P. Zhang
    IHEP, Beijing, People’s Republic of China
 
  A 166.6 MHz superconducting RF system has been proposed for the High Energy Photon Source (HEPS), a 6 GeV kilometer-scale light source. A 166.6MHz digital low-level RF system for HEPS-TF project has been developed firstly. And the digital low-level RF system has been successfully applied to the horizontal high power test of 166.6MHz superconducting cavity. The cavity field stability has been successfully achieved about ±0.03% (pk-pk) in amplitude and ±0.02 degree (pk-pk) in phase while the cavity field voltage is up to 1.2MV. It can meet the field stability requirements towards ±0.1% in ampli-tude and ±0.1 degree in phase of HEPS project. Further study and optimization of the system is under way.  
poster icon Poster THP075 [1.612 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP075  
About • paper received ※ 29 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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THP076 Simulation Analysis of Lorentz Force Induced Oscillations in RF Cavities in Vector Sum and Cw Operation 1078
 
  • R. Leewe, K. Fong
    TRIUMF, Vancouver, Canada
 
  Within TRIUMFs electron LINAC, two TESLA type cavities are operated with a single klystron in CW mode. Vector sum control is applied for field stabilization and the resonance frequencies are individually tuned with a proportional feedback controller. First operational experiences showed that amplitude oscillations can start in both cavities, while the vector sum is perfectly stable. These instabilities occur at high operating fields and are driven by Lorentz force changes. This paper presents a simulation study of multiple cavities in vector sum operation with respect to Lorentz force oscillations. It will be shown that all cavities in operation have to be damped to guarantee system stability.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP076  
About • paper received ※ 22 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
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THP078 CERN’s SRF Test Stand for Cavity Performance Measurements 1082
 
  • N. Stapley, J. Bastard, M.R. Coly, A.E. Ivanov, A. Macpherson, N.C. Shipman, K. Turaj
    CERN, Geneva, Switzerland
  • I. Ben-Zvi
    BNL, Upton, New York, USA
  • A. Castilla
    Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
  • K. Hernandez-Chahin
    Universidad de Guanajuato, División de Ciencias e Ingenierías, León, Mexico
  • M. Wartak, A. Zwozniak
    IFJ-PAN, Kraków, Poland
 
  Recent deployment of a digital LLRF system within the cavity testing framework of CERN’s vertical test cryostats has permitted a full revamp of cavity performance validation. With both full continuous and pulse mode operation, steady state a transient RF behaviour can be effectively probed. Due to direct and integrated control and monitoring of environmental test conditions, standard and novel RF measurement procedures have been developed and integrated into the testing infrastructure, along with a coherent data flow of high granularity measurement data. We present an overview of this cavity measurement system and address the underlying architectural structure, data handling and integration of user interfaces. In addition we highlight the benefits of variety of RF cavity measurements that can now be accommodated in our large 2 K cryostats.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-THP078  
About • paper received ※ 23 June 2019       paper accepted ※ 30 June 2019       issue date ※ 14 August 2019  
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