06 Beam Instrumentation, Controls, Feedback, and Operational Aspects
T27 Low Level RF
Paper Title Page
WEPAF051 LLRF Operation and Performance at the European XFEL 1934
  • M. Omet, V. Ayvazyan, J. Branlard, Ł. Butkowski, M. Hierholzer, M. Killenberg, D. Kostin, L. Lilje, S. Pfeiffer, H. Schlarb, Ch. Schmidt, V. Vogel, N. Walker
    DESY, Hamburg, Germany
  The European X-ray Free-Electron Laser (XFEL) at Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany is a user facility providing ultrashort hard and soft X-ray flashes with a high brilliance. All LLRF stations of the injector, covering the normal conducting RF gun, A1 (8 1.3 GHz superconducting cavities (SCs)) and AH1 (8 3.9 GHz SCs), were successfully commissioned by the end of 2015. The commissioning of LLRF stations A2 to A23 (32 1.3 GHz SCs each) in the XFEL accelerator tunnel (XTL) was concluded in June 2017. SASE light was produced in SASE undulator section SA1 and delivered to the first users in September 2017, marking the beginning of regular user operation. The current state of the LLRF systems, the experience gained during operation and the performance achieved in terms of stability and energy reach are presented.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF051  
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WEPAF052 High QL and High Gradient CW Operation of Tesla SCRF 9-Cell Cavity 1937
  • K.P. Przygoda, V. Ayvazyan, Ł. Butkowski, M. Hierholzer, R. Rybaniec, H. Schlarb, Ch. Schmidt, J.K. Sekutowicz
    DESY, Hamburg, Germany
  In the paper we would like to present Tesla SCRF 9-Cell cavity operated at CW regime with extremely high QL at gradients above 23 MV/m. The design hardware and firmware components as well as developed high level software procedures allows automatic procedure of cavity trip from low to high gradient operation. The microphonics as well as a pendoromotive effects are sensed, identify and applied for cavity detuning correction. The RF and piezo feedbacks performance are demonstrated and preliminary results are briefly discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF052  
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WEPAF063 RF Manipulations for Special LHC-Type Beams in the CERN PS 1971
  • H. Damerau, S. Hancock, A. Lasheen, D. Perrelet
    CERN, Geneva, Switzerland
  Beams with special longitudinal characteristics for the Large Hadron Collider (LHC) have been produced in the Proton Synchrotron (PS) and CERN. The flexibility of its RF systems consisting of in total 25 RF cavities at frequencies from 400 kHz to 200 MHz allows a variety of longitudinal beam manipulations. In particular the main RF system is split into three independent groups tunable from 2.8 MHz to 10 MHz. It is used to merge, split and change the spacing between bunches by applying different voltage and phase programs to the three groups of cavities at different harmonic numbers simultaneously. The batch compression, merging and splitting (BCMS) process has been operationally used for LHC fillings since 2016. To mitigate issues with long bunch trains in the LHC in 2017, short gaps of four bunch positions have been introduced between mini-batches of eight bunches (8b4e). A higher brightness version resulting in four mini-batches per PS extraction has been delivered for luminosity production in the LHC. This paper summarizes the operational experience and indicates possible future RF manipulation schemes.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAF063  
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WEPAK012 Developing Kalman Filter Based Detuning Control with a Digital SRF CW Cavity Simulator 2114
  • A. Ushakov, P. Echevarria, A. Neumann
    HZB, Berlin, Germany
  Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of the Helmholtz Association
Continuous wave operated superconducting cavities experiencing small net beam loading and thus operate potentially at narrow bandwidth require precise detuning control to reach the high stability requirements for RF fields within facilities as FEL or ERL based photon sources. Especially microphonics compensation down to sub-hertz detuning regime besides improving stability reduces the risk of rise of Lorentz force detuning driven ponderomotive instabilities. Usually the complex and second order nature of the mechanical to RF detuning transfer functions of cavity and cavity-tuner system require for more advanced control schemes. In this paper we will show the application of a Kalman filter based detuning estimator algorithm first introduced during IPAC2017 [1] to the SRF cavity simulator developed at Helmholtz Zentrum Berlin [2]. Results using the algorithm in observer mode to detuning compensation attempts in closed loop mode are presented.
* A. Ushakov, P. Echevarria, A. Neumann, Proc. of IPAC 2017, Copenhagen, Denmark
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAK012  
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WEPAK013 SRF Cavity Simulator for LLRF Algorithms Debugging 2118
  • 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
  Funding: Work supported by German Bundesministerium für Bildung und Forschung, Land Berlin, and grants of Helmholtz Association
The availability of niobium superconducting cavities, ei-ther due to a lack of a real cavity or due to the time needed for the experiment set up (vacuum, cryogenics, cabling, etc.), is limited, and thus it can block or delay the develop-ment of new algorithms such as low level RF control. Hardware-in-the-loop simulations, where an actual cavity is replaced by an electronics system, can help to solve this issue. In this paper we present a Cavity Simulator imple-mented in a National Instruments PXI equipped with an FPGA module. This module operates with one intermedi-ate frequency input which is IQ-demodulated and fed to the electrical cavity's model, where the transmitted and re-flected voltages are calculated and IQ-modulated to gener-ate two intermediate frequency outputs. Some more ad-vanced features such as mechanical vibration modes driven by Lorentz-force detuning or external microphonics have also been implemented. This Cavity Simulator is planned to be connected to an mTCA chassis to close the loop with a LLRF control system.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAK013  
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WEPAK016 RF Monitor System for SuperKEKB Injector Linac 2128
  • H. Katagiri, M. Akemoto, D.A. Arakawa, T. Matsumoto, T. Miura, F. Qiu, Y. Yano
    KEK, Ibaraki, Japan
  A new radio frequency (RF) monitor system for the SuperKEKB project has been developed at the KEK in-jector linac. The RF monitor unit, which consists of an analog I/Q demodulator, ADC/DAC board, and FPGA board achieved 50-Hz data acquisition and beam mode identification. On the RF monitor, the amplitude and phase measurement precision has achieved 0.1% rms and 0.1° rms, respectively. Sixty RF monitor units have been installed in the linac. The present status of the RF monitor system will be re-ported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAK016  
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WEPAK017 Low-level RF System for the SuperKEKB Injector LINAC 2131
  • T. Matsumoto, M. Akemoto, D.A. Arakawa, H. Katagiri, T. Miura, F. Qiu, Y. Yano
    KEK, Ibaraki, Japan
  • M. Akemoto, T. Miura, F. Qiu
    Sokendai, Ibaraki, Japan
  The low-level RF (LLRF) system of the KEK injector linac has been upgraded for the SuperKEKB. As a major change, a low-emittance and high-current RF gun was installed to satisfy 40-times higher luminosity at the SuperKEKB. In order to balance the stable RF gun operation and the electron/positron beam acceleration, the phase shifter is developed and the configuration of main drive system in the LLRF system is modified. The present status and future plan of the LLRF system upgraded for the SuperKEKB will be reported.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAK017  
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WEPAK018 LLRF Control Unit for SuperKEKB Injector Linac 2134
  • T. Miura, M. Akemoto, D.A. Arakawa, H. Katagiri, T. Matsumoto, F. Qiu, Y. Yano
    KEK, Ibaraki, Japan
  • N. Liu
    Sokendai, Ibaraki, Japan
  The low-level RF (LLRF) control unit based on the digital system has been developed for a stable and high precision pulse modulation for the SuperKEKB. The RF pulse is changed at a 50-Hz repetition rate for the top-up injection to four different rings by the event system. The LLRF control unit has not only the pulse modulator, but also other functions: VSWR meter, RF monitor, event receiver (EVR), and pulse-shortening detection.  
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WEPAL001 LLRF Control and Master Oscillator System for Damping Ring at SuperKEKB 2137
  • T. Kobayashi, K. Akai, A. Kabe, K. Nakanishi, M. Nishiwaki, J.-I. Odagiri
    KEK, Ibaraki, Japan
  • H. Deguchi, K. Hayashi, J. Mizuno
    Mitsubishi Electric TOKKI Systems, Amagasaki, Hyogo, Japan
  • K. Hirosawa
    Sokendai, Ibaraki, Japan
  For SuperKEKB, new low level RF (LLRF) control systems has ben developed and they worked successfully in the first beam commissioning (Phase-1) of SuperKEKB, which was accomplished in 2016. Damping ring (DR) was newly constructed for positron beam injection, in order to make significantly emittance smaller for SuperKEKB. The beam commissioning of DR will be conducted in JFY2017 for the Phase-2 commissioning. Phase-2 is scheduled in the last quater of JFY2017. DR has an RF station, and two cavities (or three cavities in future) are driven by a klystron. New LLRF control system for DR (DR-LLRF) was also developed and installed. RF frequency of DR operation is common with the main storage rings (MR) of SuperKEKB. The good performance of DR-LLRF was demonstrated in test operation, and RF conditioning of the pair of two cavities was successfully completed in June 2017. This paper reports the detail of the performance results of DR-LLRF controls, and also the other some relevant issues in LLRF controls for DR, including the master oscillator system (synchronization with the injection linac), are introduced.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL001  
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WEPAL003 Baseband Simulation Model of the Vector RF Voltage Control System for the J-PARC RCS 2144
  • F. Tamura, M. Nomura, T. Shimada, M. Yamamoto
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
  • M. Furusawa, K. Hara, K. Hasegawa, C. Ohmori, Y. Sugiyama, M. Yoshii
    KEK, Tokai, Ibaraki, Japan
  Vector rf voltage feedback control for the wideband magnetic alloy cavity of the J-PARC RCS is considered to be employed to compensate the heavy beam loading caused by high intensity proton beams. A prototype system of multiharmonic rf vector voltage control has been developed and is under testing. To characterize the system performance, full rf simulations could be performed by software like Simulink, while the software is proprietary and expensive. Also, it requires much computing power and time. We performed the simplified baseband simulations of the system in z-domain by using free software, Scilab and Python control library. It seems to be beneficial for searching the parameters that the baseband simulation can be performed quickly. In this presentation, we present the setup and results of the simulations. The simulations well reproduce the open and closed loop responses of the prototype system.  
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WEPAL008 Low-level RF System for The Chinese ADS Front-end Demo Linac 2159
  • J.Y. Ma, Z. Gao, G. Huang, L.P. Sun
    IMP/CAS, Lanzhou, People's Republic of China
  The Chinese ADS Front-end Demo Linac (FDL) is constructed to demonstrate the technology of superconducting linac with high proton beam loading of CW 10mA. The low-level RF (LLRF) control system for the ADS FDL is developed by IMP, and the cooperation with TRIUMF. In the normal conducting (NC) section, the normal RF feedback control loop is used. In order to stable the superconducting (SC) cavity with loaded high RF power, the self excited loop with phase locked mode was used on the SC linac. This paper introduces the LLRF control system for buncher, SC linac, and the structures of hardware and the functions of software of these LLRF systems. The operating status of the LLRF systems is also reported.  
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WEPAL010 Review of the ELI-NP-GBS Low Level RF and Synchronization Systems 2162
  • L. Piersanti, D. Alesini, M. Bellaveglia, F. Cardelli, M. Diomede, A. Gallo, V. Martinelli
    INFN/LNF, Frascati (Roma), Italy
  • B.B. Baricevic, R. Cerne, G. Jug
    I-Tech, Solkan, Slovenia
  • M. Diomede
    Sapienza University of Rome, Rome, Italy
  • P.N. Dominguez
    Menlo Systems GmbH, Martinsried, Germany
  ELI-NP is a linac based gamma-source in construction at Magurele (RO) by the European consortium EuroGammaS led by INFN. Photons with tunable energy and with intensity and brilliance well beyond the state of the art, will be produced by Compton back-scattering between a high quality electron beam (up to 740 MeV) and a 515 nm intense laser pulse. Production of very intense photon flux with narrow bandwidth requires multi-bunch operation at 100 Hz repetition rate. A total of 13 klystrons, 3 S-band (2856 MHz) and 10 C-band (5712 MHz) will power a total of 14 Travelling Wave accelerating sections (2 S-band and 12 C-band) plus 3 S-band Standing Wave cavities (a 1.6 cell RF gun and 2 RF deflectors). Each klystron is individually driven by a temperature stabilized LLRF module for a maximum flexibility in terms of accelerating gradient, arbitrary pulse shaping (e.g. to compensate beam loading effects in multi-bunch regime) and compensation of long-term thermal drifts. In this paper, the whole LLRF system architecture and bench test results, the RF reference generation and distribution together with an overview of the synchronization system will be described.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL010  
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WEPAL017 Adaptive Feedforward Control Design Based on Simulink for the J-PARC LINAC LLRF System 2187
  • S. Li
    J-PARC, KEK & JAEA, Ibaraki-ken, Japan
  • Z. Fang, Y. Fukui, K. Futatsukawa, F. Qiu
    KEK, Ibaraki, Japan
  • S. Mizobata, Y. Sato, S. Shinozaki
    JAEA/J-PARC, Tokai-mura, Japan
  In j-parc linac, for dealing with high beam loading effect, an adaptive feedforward control method which based on iterative learning control was put forward. At the same time, in order to verify its effectiveness before it is officially put into use, an llrf system simulation model was built in simulink, matlab. In this paper, the architecture of llrf system simulation model will be introduced. The result of iterative learning control (ILC) is summarized.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL017  
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WEPAL031 RF Interlock Implementation Using Digital LLRF System for 100 MeV Proton Linac at KOMAC 2233
  • H.S. Jeong, Y.-S. Cho, H.S. Kim, J.H. Kim, S.G. Kim, H.-J. Kwon, Y.G. Song
    Korea Atomic Energy Research Institute (KAERI), Gyeongbuk, Republic of Korea
  Funding: This work has been supported through KOMAC (Korea Multi-purpose Accelerator Complex) operation fund of KAERI by MSIT (Ministry of Science and ICT)
KOMAC (Korea Multi-purpose Accelerator Complex) already has operated 100 MeV proton linear accelerator with high availability since 2013. This accelerator is composed of Ion source, LEBT, RFQ and DTL systems to transport proton particles to the target. Total 9 klystrons with 1.6 MWpeak are used to provide controlled RF power to the accelerator cavities with 350 MHz of operating frequency. These klystrons are driven by LLRF systems that the LLRF systems should control the RF and protect the amplifiers and cavities from the abnormal RF. In this article, the RF interlock using cavity pickup signal introduced. When the cavity pickup amplitude breaks away from the adjustable upper or lower limit window, the digital LLRF system interrupts the LLRF output. These implementations were conducted by upgrading the FPGA (Field Programmable Gate Array) logics of the existing digital LLRF system.
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WEPAL039 LCLS-II Gun/Buncher LLRF System Design 2258
  • G. Huang, K.S. Campbell, L.R. Doolittle, J.A. Jones, Q. Qiang, C. Serrano
    LBNL, Berkeley, California, USA
  • S. Babel, A.L. Benwell, M. Boyes, G.W. Brown, D. Cha, J.H. De Long, J.A. Diaz Cruz, B. Hong, A. McCollough, A. Ratti, C.H. Rivetta, D. Rogind, F. Zhou
    SLAC, Menlo Park, California, USA
  • R. Bachimanchi, C. Hovater, D.J. Seidman
    JLab, Newport News, Virginia, USA
  • B.E. Chase, E. Cullerton, J. Einstein-Curtis, D.W. Klepec
    Fermilab, Batavia, Illinois, USA
  • J.A. Diaz Cruz
    CSU, Fort Collins, Colorado, USA
  Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract n. DE-AC02-05CH11231.
For a free electron laser, the stability of injector is critical to the final electron beam parameters, e.g., beam energy, beam arrival time, and eventually it determines the photon quality. The LCLS-II project's injector contains a VHF copper cavity as the gun and a two-cell L-band copper cavity as its buncher. The cavity designs are inherited from the APEX design, but requires more field stability than demonstrated in APEX operation. The gun LLRF system design uses a connectorized RF front end and low noise digitizer, together with the same general purpose FPGA carrier board used in the LCLS-II SRF LLRF system. The buncher LLRF system directly adopts the SRF LLRF chassis design, but programs the controller to run the normal conducting cavities. In this paper, we describe the gun/buncher LLRF system design, including the hardware design, the firmware design and bench test.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPAL039  
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WEPAL046 A New Digital Feedback and Feedforward Controller for Cavity Field Control of the LANSCE Accelerator 2277
  • S. Kwon, L.J. Castellano, D.J. Knapp, J.T.M. Lyles, M.S. Prokop, A. Scheinker, P.A. Torrez
    LANL, Los Alamos, New Mexico, USA
  Funding: Work Supported by DOE
A new digital low-level RF system was designed and has been deployed on the drift-tube-linac section of the Los Alamos Neutron Science Center(LANSCE) proton accelerator. This new system is part of a modernization of the existing analog cavity-field controls that were originally developed and put into service forty-five years ago. For stabilization of the cavity field amplitude and phase during beam loading, a proportional-integral feedback controller, a static beam feedforward controller, and an iterative learning controller working in parallel have been implemented. In this paper, the controller architecture is described, and the performances of the three controllers when beam is being actively accelerated is presented.
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WEPAL053 Dynamic Signal Analysis Based on FPGA for NSRRC DLLRF 2295
  • F.Y. Chang, L.-H. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.T. Li, M.-C. Lin, Z.K. Liu, C.H. Lo, Ch. Wang, M.-S. Yeh, T.-C. Yu
    NSRRC, Hsinchu, Taiwan
  As DLLRF control system designs for SRF cavities have greatly matured and the FPGA technology has im-proved as well, it is possible now to think about incorporating dynamic signal analysis (DSA). Implementation of a DSA in the FPGA is desired to study the frequency response of the open/closed loop gain in a SRF system. Open loop gain is useful to observe the stability of a SRF system while closed loop gain can be applied to investi-gate the operational bandwidth of the system feedback and also to configure the performance of a PID controller. The DSA function was confirmed by analyzing the frequency response of a digital filter and the results of the analysis will be compared with MATLAB simulations.  
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WEPAL054 Digital Low Level Radio Frequency System for the Booster Ring of the Taiwan Photon Source 2298
  • Z.K. Liu, F.Y. Chang, L.-H. Chang, M.H. Chang, S.W. Chang, L.J. Chen, F.-T. Chung, Y.T. Li, M.-C. Lin, C.H. Lo, Ch. Wang, M.-S. Yeh, T.-C. Yu
    NSRRC, Hsinchu, Taiwan
  The purpose of a Low-Level Radio Frequency (LLRF) system is to control the accelerating cavity field amplitude and phase. For the Taiwan Photon Source (TPS) at NSRRC, the currently operating LLRF systems are based on analog technology. To have better RF field stability, precise con-trol and high noise reduction, a digital LLRF control sys-tems based on Field Programmable Gate Arrays (FPGA) was developed. We replaced the analog LLRF system with the digital version for the TPS booster ring at the beginning of 2018, and we will replace those in the storage rings in the future. Test results and operational performance of the TPS booster DLLRF system are reported here.  
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THYGBE3 RF Controls for High-Q Cavities for the LCLS-II 2929
  • C. Serrano, K.S. Campbell, L.R. Doolittle, G. Huang, A. Ratti
    LBNL, Berkeley, California, USA
  • R. Bachimanchi, C. Hovater
    JLab, Newport News, Virginia, USA
  • A.L. Benwell, M. Boyes, G.W. Brown, D. Cha, G. Dalit, J.A. Diaz Cruz, J. Jones, R.S. Kelly, A. McCollough
    SLAC, Menlo Park, California, USA
  • B.E. Chase, E. Cullerton, J. Einstein-Curtis, J.P. Holzbauer, D.W. Klepec, Y.M. Pischalnikov, W. Schappert
    Fermilab, Batavia, Illinois, USA
  • L.R. Dalesio, M.A. Davidsaver
    Osprey DCS LLC, Ocean City, USA
  Funding: This work was supported by the LCLS-II Project and the U.S. Department of Energy, Contract n. DE-AC02-76SF00515.
The SLAC National Accelerator Laboratory is building LCLS-II, a new 4 GeV CW superconducting (SCRF) Linac as a major upgrade of the existing LCLS. The LCLS-II Low-Level Radio Frequency (LLRF) collaboration is a multi-lab effort within the Department of Energy (DOE) accelerator complex. The necessity of high longitudinal beam stability of LCLS-II imposes tight amplitude and phase stability requirements on the LLRF system (up to 0.01% in amplitude and 0.01° in phase RMS). This is the first time such requirements are expected of superconducting cavities operating in continuous-wave (CW) mode. Initial measurements on the Cryomodule test stands at partner labs have shown that the early production units are able to meet the extrapolated hardware requirements to achieve such levels of performance. A large effort is currently underway for system integration, Experimental Physics and Industrial Control System (EPICS) controls, transfer of knowledge from the partner labs to SLAC and the production and testing of 76 racks of LLRF equipment.
slides icon Slides THYGBE3 [14.383 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THYGBE3  
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THPMK096 Tuners Alignment on Two 9-Cell Cavities with Single Amplifier under Self-Excited Loop 4527
  • K. Fong, Z.T. Ang, M.P. Laverty, Q. Zheng
    TRIUMF, Vancouver, Canada
  The TRIUMF eLinac ACM consists of two 9-cell cavities which are driven by a single klystron. The output power from the klystron are split by a variable power divider and send down 2 independently phase adjustable transmission lines to their respective cryomodules. The vector sum of the fields from both cryomodules is used for phase-locked self-excited loop regulation. A semi-automatic procedure to tune the 2 cyromodules to provide the correct amplitudes and phases for self-excitation as well as beam acceleration is described.  
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THPML073 Measurement of the RF Reference Phase Stability in the SuperKEKB Injector LINAC 4815
SUSPL063   use link to see paper's listing under its alternate paper code  
  • N. Liu
    Sokendai, Ibaraki, Japan
  • D.A. Arakawa, H. Katagiri, T. Matsumoto, S. Michizono, T. Miura, F. Qiu, Y. Yano
    KEK, Ibaraki, Japan
  The SuperKEKB injector is a more than 600 m J-shaped LINAC. The requirement of the RF phase refer-ence stability is 0.1 degree (RMS) at 2856 MHz for SuperKEKB PHASE-2 commissioning. In order to clari-fy and improve the reference line performance, the RF reference phase stability is measured. The phase noise of the RF reference at each sector is shown in this paper. A new phase monitor system is implemented to measure the short-term stability and long-term drift due to the temperature and humidity fluctuations in the klystron gallery.  
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THPML082 Reflected Power Based Extremum Seeking Control Algorithm to Tune the Resonance Frequency of Room Temperature Cavities 4844
  • R. Leewe, K. Fong, Z. Shahriari
    TRIUMF, Vancouver, Canada
  • M. Moallem
    SFU, Surrey, Canada
  A sliding mode extremum seeking algorithm to tune the resonance frequency was implemented in two of TRIUMF's DTL tanks. The tuning algorithm searches for the minimum reflected power point and was developed to eliminate the highly temperature dependent phase measurement, which was previously used to tune the resonance frequency. Short and long term measurement results show that the tuning algorithm compensates for the RF heating effect as well as for diurnal temperature variations. Reflected power measurements of TRIUMF's DTL tank 3 were taken for both cases of operating the phase based tuning system and the reflected power based tuning system, with an outcome of a higher tuning accuracy of the newly developed system. Another advantage is a quick cavity start up time, as the reflected power based system does not rely on a reference set point which has do be adjusted manually. The sliding mode extremum seeking control loop is currently commissioned in further room temperature cavities of the TRIUMF's ISAC I facility.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML082  
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THPML083 Iterative Learning Control to Cancel Beam Loading Effect on Amplitude and Phase of the Accelerating Field 4847
  • Z. Shahriari, K. Fong
    TRIUMF, Vancouver, Canada
  • G. A. Dumont
    UBC, Vancouver, Canada
  Funding: This research is supported by TRIUMF through federal funding via a contribution agreement with the National Research Council of Canada.
Iterative learning control (ILC) is an open loop control strategy that improves the performance of a repetitive system through learning from previous iterations. ILC can be used to compensate for a repetitive disturbance like the beam loading effect in resonators. Assuming that the beam loading disturbance is identical for all iterations, the learning law can be non-causal; it can anticipate the disturbance and preemptively counteract its effect. In this work, we aim to use ILC to cancel beam loading effect on amplitude and phase. Feedback controllers are not fast enough for this purpose. A normal feed forward controller may not be sufficient as well if there is a difference between the feed forward signal and the beam loading current. Therefore, the goal is to use ILC to adaptively cancel the beam loading effect.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML083  
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THPML088 Cavity Impedance Reduction Strategies During Multi Cavity Operation in the SIS100 High Intensity Hadron Synchrotron 4863
  • D. Mihailescu Stoica, D. Domont-Yankulova
    Technische Universität Darmstadt (TU Darmstadt, RMR), Darmstadt, Germany
  • D. Domont-Yankulova, H. Klingbeil
    TEMF, TU Darmstadt, Darmstadt, Germany
  • H. Klingbeil, D.E.M. Lens
    GSI, Darmstadt, Germany
  Funding: Supported by GSI Helmholtzzentrum für Schwerionenforschung GmbH
The planned SIS100 heavy ion synchrotron at the GSI Helmholtzzentrum für Schwerionenforschung will possess twenty ferrite accelerating cavities in its final stage of extension. As at injection and at flat top during slow extraction of the planned acceleration cycles the RF voltage will be relatively low, not all cavities will be active in this part of operation. It is important to analyse the impact of the inactive cavities on the overall RF voltage and subsequently their implication on the longitudinal particle dynamics. Classical approaches for reducing the beam impedance consist of active detuning of the cavities to pre-described parking frequencies. The fact that two out of ten buckets have to stay empty in all SIS100 scenarios is of particular interest as additional frequency components appear in the excitatory beam current, which have to be considered when the cavity is detuned. Therefore multi-cavity particle tracking simulations, consisting of twenty cavities and their attached LLRF control systems, are carried out in order to analyse different possibilities to minimize the impact on the beam dynamics and emittance growth.
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML088  
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THPML100 A High Voltage Feedforward Subsystem of Low Level RF System for the High Power RF System 4898
SUSPL062   use link to see paper's listing under its alternate paper code  
  • Z.Y. Lin, Y. C. Du, H.Q. Feng, W.-H. Huang, CY. Song, C.-X. Tang, Y.L. Xu, J. Yang
    TUB, Beijing, People's Republic of China
  • G. Huang
    LBNL, Berkeley, California, USA
  The Low Level Radio Frequency control (LLRF) system measures the RF signals from the accelerator tube, compares it with the phase reference received from the timing distribution system, and provides the drive signal to the high power RF system to provide synchronized RF voltage to the electron beam. Usually, the LLRF system can achieve a ~50 fs RMS phase jitter which is limited by the microwave devices. The phase noise arise from the high voltage variation of the high power system will significantly increase phase noise from low level RF signal to high power RF. A high voltage feed forward subsystem is proposed to deal with the phase noise caused by the high voltage jitter of the modulator. The demo system is depolyed in Thomson scattering X-ray source (TTX).and the primary experiment result anaylse is discussed.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML100  
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THPML121 Compensation of Transient Beam Loading in Ramping Synchrotrons Using a Fixed Frequency Processing Clock 4957
SUSPL061   use link to see paper's listing under its alternate paper code  
  • F.J. Galindo Guarch, J.M.M.A. Moreno Arostegui
    Universitat Politécnica de Catalunya, Barcelona, Spain
  • P. Baudrenghien, F.J. Galindo Guarch
    CERN, Geneva, Switzerland
  Transient beam loading compensation schemes, such as One-Turn-FeedBack (OTFB), require beam synchronous processing (BSP). Swept clocks derived from the RF, and therefore harmonic to the revolution frequency, are widely used in CERN synchrotrons; this simplifies implementation with energy ramping, where the revolution frequency changes. It is however not optimal for state-of-the-art digital hardware that prefers fixed frequency clocks. An alternative to the swept clocking is the use of a deterministic protocol, for example, White Rabbit (WR): a fixed reference clock can be extracted from its data stream, while enabling digital distribution of the RF frequency among other data. New algorithms must be developed for BSP using this fixed clock and the digital data transmitted on the WR link. This is the strategy adopted for the SPS Low Level RF (LLRF) upgrade. The paper gives an overview of the technical, technological and historical motivations for such a paradigm evolution. It lists the problems of fixed clock BSP, and presents an innovative solution based on a real-time variable ratio re-sampler for implementing an OTFB with the new fixed clock scheme.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML121  
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THPML123 The ESR Barrier-Bucket LLRF System - Design and First Results 4964
  • J. Harzheim, D. Domont-Yankulova, K. Groß, H. Klingbeil
    TEMF, TU Darmstadt, Darmstadt, Germany
  • M. Frey, H. Klingbeil, D.E.M. Lens
    GSI, Darmstadt, Germany
  At GSI, Darmstadt, Germany, a Barrier-Bucket (BB) RF System is currently under development for the Experimental Storage Ring (ESR). The system consists of two broadband RF cavities, each driven by a solid state amplifier, with the purpose to produce two voltage pulses per beam revolution. This will enable highly sophisticated longitudinal beam manipulations like longitudinal capture, compression and decompression or stacking of the beam. For the LLRF System, several requirements have to be fulfilled. Besides high standards concerning the pulsed gap signal quality (e.g. ringing <2.5%), the system has to provide the flexibility for adiabatic voltage ramp-up and adiabatic pulse shifting with high timing accuracy. A connection to the FAIR Central Control System (CCS) is necessary, as amplitude and phase ramp data will be provided by the CCS. In this contribution, the structure of the ESR BB LLRF system is presented together with experimental results from the first version of the system, which will be installed in the ESR in March 2018.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML123  
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