LLRF Control Research Articles

CSNS-II multi-harmonic LLRF upgrade and commissioning

The second phase of the China Spallation Neutron Source (CSNS-II) will employ a dual-harmonic RF system to mitigate the significant space charge effects associated with 500 kW beam power. To address this, three magnetic alloy loaded cavities, characterized by their wideband and high-gradient properties, will be integrated as multi-harmonic cavities in the upgrade project. Additionally, the current LLRF control system hardware, based on the CPCI platform, is encountering issues related to discontinuation and performance limitations. This paper presents the testing and verification of hardware upgrades and multi-harmonic control system algorithms for the magnetic alloy loaded cavity LLRF control system, ensuring the effective implementation of the multi-harmonic control algorithm within the new hardware framework.

Status and upgrades of radio frequency system at Taiwan Photon Source

In order to meet the upcoming RF power requirements of TPS, a five-year upgrade project to construct a new RF station was completed in early 2022. This new RF station mainly consists of an SRF module, a 300-kW SSPA, an analog LLRF control system, RF transmission components, and accessary cooling systems. Test results of the SRF module and 300-kW SSPA met the expected performances. Also presented are the operation statistics of the two original RF stations and the ongoing upgrades. Meantime between RF failures during TPS user time reached 600 hours in 2022, while the construction and tests on DLLRF control system, power combination of klystron and SSPA, and 2-cell 1.5-GHz SRF module have all progressed well.

Design and performance of the digital LLRF control system for isotope production cyclotron

Design and performance of the digital LLRF control system for isotope production cyclotron

LLRF Control and Synchronization System of the ARES Facility

LLRF Control and Synchronization System of the ARES Facility

Deployment of the Next-Generation LLRF Control System for the J-PARC RCS

Deployment of the Next-Generation LLRF Control System for the J-PARC RCS

Beam gap transient analysis and mitigations in high-current storage rings for an electron-ion collider

The U.S. electron ion collider will utilize high current electron and ion storage rings with many bunches and large rf systems. Because of the dissimilarity of the two rings, the rf transients created by gaps or variations in the current distributions will be very different in the two rings. These transients cause a shift in the synchronous phase of the beams as a function of rf bucket position, can impact the luminosity through shifts in longitudinal position of the IP, will affect the performance of the rf and LLRF control loops, and may require significant rf power overhead to control. A machine design that uses superconducting crab cavities will also have sensitivity to gap transients and synchronous phase variations along the bunch train with variations in crab cavity voltage seen by each bunch, since the high $Q$ of the crab cavities precludes modulating them to compensate for the time of arrival shifts caused by the gap transients in the main rf systems. All these effects make the problem of managing gap transients crucial to the operation of the EIC. This work presents methods to study the dynamics of the rf and LLRF systems for these heavily beam loaded facilities. An illustrative machine design example is presented and used to investigate the expected magnitudes of the rf gap transients, and exploration of various possible remedies to match the gap transients in the two dissimilar EIC rings. In addition to the study of the power required and gap transients, this work also estimates longitudinal coupled-bunch instabilities due to the baseline cavity fundamental impedance. The work is motivated to emphasize the importance of tools and methods to estimate these effects as part of the early design phase of the Electron-Ion Collider or any high current storage ring design.

A digital phase-locked loop based LLRF system

TRIUMF’s ARIEL pre-buncher is powered by a sawtooth waveform which is the combination of 11.79 MHz, 23.57 MHz and 35.36 MHz harmonics. To upgrade the existing analog and digital hybrid LLRF control system, reduce the hardware cost, and achieve more flexible control of the system, an FPGA based digital daughter board is designed. The generation, control, and regulation of these three harmonics are all incorporated digitally inside a single FPGA. To reduce the number of RF interfaces on the motherboard, the new daughter board is designed to control the amplitude and phase of the sawtooth waveform with one channel ADC and DAC. To lock the output phase of the sawtooth waveform to the reference signal, a digital phase-locked loop is designed to lock all three harmonics to the external reference signal. The related work, including the system design of the LLRF control system and the development of the digital phase-locked loop, are presented in this paper.

Simulation of Quench Detection Algorithms for Helmholtz Zentrum Berlin SRF Cavities

The Helmholtz Zentrum Berlin is carrying out two accelerator projects which make use of high gradient Continuous Wave (CW) Superconducting Radiofrequency (SRF) cavities: bERLinPro and BESSY-VSR. In both projects, a prompt detection of a quench is crucial to avoid damages in the cryomodules and cavities themselves. In this paper, the response of real time estimation of the cavity parameters using the transmitted and forward RF signals is simulated, in order to perform the quench detection. The time response of the estimated half bandwidth is compared with the dissipated energy in the cavity walls for the different type of SRF cavities used in both projects, i.e., bERLinPro's photoinjector, booster and linac, and BESSY-VSR 1.5 GHz and 1.75 GHz cavities. As an intermediate step prior to the implementation in an mTCA.4 system together with the LLRF control and test with a real cavity, the algorithm has been implemented using a National Instruments FPGA board to check its proper behavior.

Simulation of quench detection algorithms for Helmholtz Zentrum Berlin SRF cavities

The Helmholtz Zentrum Berlin is carrying out two accelerator projects which make use of high gradient Continuous Wave (CW) Superconducting Radiofrequency (SRF) cavities: bERLinPro and BESSY-VSR. In both projects, a prompt detection of a quench is crucial to avoid damages in the cryomodules and cavities themselves. In this paper, the response of real time estimation of the cavity parameters using the transmitted and forward RF signals is simulated, in order to perform the quench detection. The time response of the estimated half bandwidth is compared with the dissipated energy in the cavity walls for the different type of SRF cavities used in both projects, i.e., bERLinPro’s photoinjector, booster and linac, and BESSY-VSR 1.5 GHz and 1.75 GHz cavities. As an intermediate step prior to the implementation in an mTCA.4 system together with the LLRF control and test with a real cavity, the algorithm has been implemented using a National Instruments FPGA board to check its proper behavior.

LLRF Control System for RF GUN at SXFEL Test Facility

LLRF Control System for RF GUN at SXFEL Test Facility

Progress on the multi bunch FEL performance at FLASH

At the SASE-FEL user facility FLASH, superconducting TESLA-type cavities are used for acceleration. The high achievable duty cycle allows for operating with long bunch-trains, hence considerably increasing the efficiency of the machine. However, RF induced intra-bunch-train trajectory variations were found to be responsible for significant variations of the SASE intensity within one bunch train. This work presents the latest achievements in improving the multi-bunch FEL performance by reducing the intra-bunch-train variation of RF parameters. Particular attention is given to the static and dynamic detuning of the cavities. It will be shown that the current level of LLRF control is suitable to limit the variation of RF parameters considerably.

MTCA.4-based LLRF control system for the C-ADS proton Linac injector I

The Chinese ADS proton Linac injector I composed of an electron cyclotron resonance ion source, a low-energy beam transport line, a radio frequency quadrupole (RFQ) accelerator, a medium-energy beam transport (MEBT) line, a superconducting section and beam dump with design goal to achieve CW proton beam with beam current 10 mA and energy gain around 10 MeV. In order to maintain the stability of the RF system, to compensate for the beam load effect and to provide the GUI required for the operation of the RF power system, we have established a LLRF control system. This LLRF system for ADS proton Linac injector I in IHEP consists of RF reference system and LLRF controllers for one RFQ cavity, two MEBT bunching cavities and 14 superconductive spoke cavities. We have adopted a new development mTCA.4-based hardware platform, and it has some characteristics such as faster bandwidth, standardized design, easy operation and maintenance and good expansibility. The LLRF system has been improved and optimized and has now been put into operation. It takes into account the pulse and CW beam flow mode, feedforward and feedback control functions. With the help of this system, we achieved stable operation with narrow pulses, long pulses, and CW modes under different beam loads. This article describes the implementation of this system and presents some initial the CW beam acceleration results with the help of this system at the end of 2016.

An Updated LLRF Control System for the TLS Linac

An Updated LLRF Control System for the TLS Linac

Polish electronics in high energy physics & aerospace technology

Department of Microelectronics and Computer Science of Lodz University of Technology has high expertise in the field of design of electronic and microelectronic systems for wide range of applications. DMCS design teams participated in large number of national and international scientific research programs, grants and commercial contracts. Many of these works resulted in an introduction of new systems into scientific installations or putting new product into general markets. The paper presents selected works focused on aspects of research on accelerator control systems for high energy physics, nuclear fusion based new energy sources and design of integrated electronics for space applications. Full Text: PDF References http://tesla.desy.de DirectLink D. Makowski, et al., Solid state neutron detector system, Germany, Switzerland, France, European Patent Office, Patent no 05011654.0-1240, EP20050011654. DirectLink W. Giergusiewicz, W. Jalmuzna, K. Pozniak, N. Ignashin, M. Grecki, et al., Low latency control board for LLRF system: SIMCON 3.1, Proc. SPIE 5948, Photonics Applications in Industry and Research (2005). CrossRef D. Makowski, A. Mielczarek, P. Perek, A. Napieralski, L. Butkowski, J. Branlard, M. Fenner, H. Schlarb, and B. Yang, High-Speed Data Processing Module for LLRF, IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 62, NO. 3, JUNE (2015). CrossRef K. Przygoda, T. Poźniak, A. Piotrowski, D. Makowski, G. Jabłoński, A. Napieralski, Prototype Control System for Compensation of Superconducting Cavities Detuning Using Piezoelectric Actuators, IEEE Transactions on Nuclear Science, vol. 56, no. 4, pp.2336–2340, Aug. (2009). CrossRef D. Makowski, et al., Interfaces and Communication Protocols in ATCA-Based LLRF Control Systems, IEEE Transactions on Nuclear Science, vol.56, no.5, pp.2814-2820, Oct. (2009). CrossRef D. Makowski, et al., Prototype Real-Time ATCA-Based LLRF Control System, IEEE Transactions on Nuclear Science, vol. 58, no. 4, pp. 1553–1561, Aug. (2011). CrossRef D. Makowski, et al., High-Performance Image Acquisition and Processing System with MicroTCA.4, IEEE Transactions on Nuclear Science, vol. 62, no. 3, pp. 925–931, June (2015). CrossRef G. Jabłoński, et al., IEEE 1588 Time Synchronization Board in MTCA.4 Form Factor, IEEE Transactions on Nuclear Science, vol. 62, no. 3, pp. 919–924, June (2015). CrossRef S. Simrock, at all, Maturity assessment of ITER diagnostics plant instrumentation and control design, Fusion Engineering and Design, pp. 952-956, (2015). CrossRef K. Skup, P. Orleański, W. Nowosielski, M. Jankowski, G. Jabłoński, Ł. Starzak, M. Szermer Michał, A. Napieralski, R. Darakchiev, M. Mroczkowski, Mixed Signal ASIC Controller for Satellite Medium Power DC/DC Converters, Proc. Conf. "Mixed Design of Integrated Circuits and Systems". Poland, Toruń, pp. 359-363, (2015). CrossRef K. R. Skup, P. Grudziński, P. Orleański, Application of Digital Control Techniques for Satellite Medium Power DC –DC Converters, Int. Journal of Electronics and Telecommunications, pp. 77 83, 2011. CrossRef M. Brown, Power Sources and Supplies: World Class Designs, Newnes, (2007). DirectLink M. Santos, C. Pires, J. Guilherme, N. Horta, Overview of Radiation Effects and Design Constraints off Fully Custom SMPS, IEEE Asia Pacific Conference on Circuits and Systems, APCCAS 2008, pp. 372 375, (2008). CrossRef L. Balogh, A Practical Introduction to Digital Power Supply Control, Power Supply Design Seminar 2004/05, (2005). DirectLink

Digital control in LLRF system for CYCIAE-100 cyclotron

As a driven accelerator, the CYCIAE-100 cyclotron is designed by China Institute of Atomic Energy for the Beijing Radio Ion-beam Facility project. The cyclotron RF system is designed to use two RF power sources of 100kW to drive two half-wavelength cavities respectively. Two Dee accelerating electrodes are kept separately from each other inside the cyclotron, while their accelerating voltages are maintained in phase by the efforts of LLRF control. An analog–digital hybrid LLRF system has been developed to achieve cavity tuning control, dee voltage amplitude and phase stabilization etc. The analog subsystems designs are focused on RF signal up/down conversion, tuning control, and dee voltage regulation. The digital system provides an RF signal source, aligns the cavity phases and maintains a Finite State Machine. The digital parts combine with the analog functions to provide the LLRF control. A brief system hardware introduction will be given in this paper, followed by the review of several major characteristics of the digital control in the 100MeV cyclotron LLRF system. The commissioning is also introduced, and most of the optimization during the process was done by changing the digital parts.

RF control hardware design for CYCIAE-100 cyclotron

The Beijing Radioactive Ion-beam Facility project is being constructed by BRIF division of China Institute of Atomic Energy. In this project, a 100MeV high intensity compact proton cyclotron is built for multiple applications. The first successful beam extraction of CYCIAE-100 cyclotron was done in the middle of 2014. The extracted proton beam energy is 100MeV and the beam current is more than 20μA. The RF system of the CYCIAE-100 cyclotron includes two half-wavelength cavities, two 100kW tetrode amplifiers and power transmission line systems (all above are independent from each other) and two sets of Low Level RF control crates. Each set of LLRF control includes an amplitude control unit, a tuning control unit, a phase control unit, a local Digital Signal Process control unit and an Advanced RISC Machines based EPICS IOC unit. These two identical LLRF control crates share one common reference clock and take advantages of modern digital technologies (e.g. DSP and Direct Digital Synthesizer) to achieve closed loop voltage and phase regulations of the dee-voltage. In the beam commission, the measured dee-voltage stability of RF system is better than 0.1% and phase stability is better than 0.03°. The hardware design of the LLRF system will be reviewed in this paper.

PXIe-Based LLRF Architecture and Versatile Test Bench for Heavy Ion Linear Acceleration

This paper describes the architecture of a digital LLRF system for heavy-ion acceleration developed under the specification of the projected future heavy-ion accelerator facility in Huelva, Spain. A prototype LLRF test bench operating at 80 MHz in CW mode has been designed and built. The core LLRF control has been digitally implemented on a PXIe chassis, including an FPGA for digital signal processing and a real time controller. The test bench is completed with a low phase and amplitude noise signal generator used as master frequency reference, an analog front end for reference modulation and signal conditioning, some RF components completing the circuit, as well as a tunable resonant cavity at 80 MHz, whose RF amplitude, phase and frequency are real-time controlled and monitored. The presented LLRF system is mainly digitally implemented using a PXIe platform provided by National Instruments , and is based on IQ modulation and demodulation. The system can be configured to use both direct sampling and undersampling techniques, resulting thus in a high performance and versatile RF control system without the need of excessive computational resources or very high speed acquisition hardware. All the system is programmed using the LabVIEW environment, which makes the prototyping process and its reconfigurability much easier.

FPGA-based klystron linearization implementations in scope of ILC

We report the development and implementation of four FPGA-based predistortion-type klystron linearization algorithms. Klystron linearization is essential for the realization of ILC, since it is required to operate the klystrons 7% in power below their saturation. The work presented was performed in international collaborations at the Fermi National Accelerator Laboratory (FNAL), USA and the Deutsches Elektronen Synchrotron (DESY), Germany. With the newly developed algorithms, the generation of correction factors on the FPGA was improved compared to past algorithms, avoiding quantization and decreasing memory requirements. At FNAL, three algorithms were tested at the Advanced Superconducting Test Accelerator (ASTA), demonstrating a successful implementation for one algorithm and a proof of principle for two algorithms. The functionality of the algorithm implemented at DESY was demonstrated successfully in a simulation.Besides this, a proof of principle of an FPGA-based klystron and cavity simulator implemented at the High Energy Accelerator Research Organization (KEK), Japan was demonstrated. Its purpose is to allow the development and test of digital LLRF control systems including klystron linearization algorithms when no actual klystron and cavity are available.

FPGA-based klystron linearization implementations in scope of ILC

We report the development and implementation of four FPGA-based predistortion-type klystron linearization algorithms. Klystron linearization is essential for the realization of ILC, since it is required to operate the klystrons 7% in power below their saturation. The work presented was performed in international collaborations at the Fermi National Accelerator Laboratory (FNAL), USA and the Deutsches Elektronen Synchrotron (DESY), Germany. With the newly developed algorithms, the generation of correction factors on the FPGA was improved compared to past algorithms, avoiding quantization and decreasing memory requirements. At FNAL, three algorithms were tested at the Advanced Superconducting Test Accelerator (ASTA), demonstrating a successful implementation for one algorithm and a proof of principle for two algorithms. The functionality of the algorithm implemented at DESY was demonstrated successfully in a simulation.Besides this, a proof of principle of an FPGA-based klystron and cavity simulator implemented at the High Energy Accelerator Research Organization (KEK), Japan, was demonstrated. Its purpose is to allow the development and test of digital LLRF control systems including klystron linearization algorithms when no actual klystron and cavity are available.

R&D of an LLRF control system for a 162.5 MHz radio frequency system

This paper describes a low level radio frequency control system that was developed by the Institute of Modern Physics Chinese Academy of Sciences, and will be used in Injector II of the China-ADS project. The LLRF control system consists of an RF modulated front end, fast analog-to-digital converter (ADC) modules, and a digital signal processing board based on a field programmable gate array. The system has been tested on a room temperature cavity with 12-hr, and the results illustrate that the stability of amplitude and phase achieved ±0.32% and ±0.35 degrees, respectively.