Low Level RF Control Research Articles

Algorithms for the implementation of a low level RF control system for a klystron amplifier

Klystrons are key components of particle accelerators since they generate the radio-frequency (RF) signals required to produce high energy particle beams. They are amplifiers characterised by nonlinear input/output dynamics and are affected by external disturbances. In order to regulate the output of the klystron to the desired level, a Low Level RF (LLRF) control system is usually employed.This paper proposes three different control methods for the design a LLRF system of a klystron: classical Proportional-Integral control, Iterative Learning Control and Model Predictive Control. Theoretical aspects of the presented control algorithms are reviewed and commented. The resulting LLRF system has been implemented on a FPGA board mounted in a PXIe chassis. Experimental results are shown to compare the algorithms and to provide an evidence of their capability to fulfil the control specifications.

CSNS RCS射频系统双谐波模式低电平控制模拟实验

CSNS RCS射频系统双谐波模式低电平控制模拟实验

EPICS based low-level radio frequency control system in LIPAc

The IFMIF–EVEDA (International Fusion Materials Irradiation Facility – Engineering Validation and Engineering Design Activity) linear accelerator, known as Linear IFMIF Prototype Accelerator (LIPAc), will be a 9MeV, 125mA continuous wave (CW) deuteron accelerator prototype to validate the technical options of the accelerator design for IFMIF. The primary mission of such facility is to test and verify materials performance when subjected to extensive neutron irradiation of the type encountered in a fusion reactor to prepare for the design, construction, licensing and safe operation of a fusion demonstration reactor (DEMO). The radio frequency (RF) power system of IFMIF–EVEDA consists of 18 RF chains working at 175MHz with three amplification stages each. The low-level radio frequency (LLRF) controls the amplitude and phase of the signal to be synchronized with the beam and it also controls the resonance frequency of the cavities. The system is based on a commercial compact peripheral component interconnect (cPCI) field programmable gate array (FPGA) board, provided by Lyrtech and controlled by a Windows host PC. For this purpose, it is mandatory to communicate the cPCI FPGA board from EPICS Channel Access [1]. A software architecture on EPICS framework in order to control and monitor the LLRF system is presented.

Design and development progress of a LLRF control system for a 500 MHz superconducting cavity

The LLRF (low-level radio-frequency) control system which regulates the amplitude and the phase of the accelerating voltage inside a RF cavity is essential to ensure the stable operation of charged particle accelerators. Recent advances in digital signal processors and data acquisition systems have allowed the LLRF control system to be implemented in digitally and have made it possible to meet the higher demands associated with the performance of LLRF control systems, such as stability, accuracy, etc. For this reason, many accelerator laboratories have completed or are completing the developments of digital LLRF control systems. The digital LLRF control system has advantages related with flexibility and fast reconfiguration. This paper describes the design of the FPGA (field programmable gate array) based LLRF control system and the status of development for this system. The proposed LLRF control system includes an analog front-end, a digital board (ADC (analog to digital converter), DAC (digital to analog converter), FPGA, etc.) and a RF & clock generation system. The control algorithms will be implemented by using the VHDL (VHSIC (very high speed integrated circuits) hardware description language), and the EPICS (experiment physics and industrial control system) will be ported to the host computer for the communication. In addition, the purpose of this system is to control a 500 MHz RF cavity, so the system will be applied to the superconducting cavity to be installed in the PLS storage ring, and its performance will be tested.

A low-level rf control system for a quarter-wave resonator

A low-level rf control system was designed and built for an rf deflector, which is a quarter wave resonator, and was designed to deflect a secondary electron beam to measure the bunch length of an ion beam. The deflector has a resonance frequency near 88 MHz, its required phase stability is approximately ±1° and its amplitude stability is less than ±1%. The control system consists of analog input and output components and a digital system based on a field-programmable gate array for signal processing. The system is cost effective, while meeting the stability requirements. Some basic properties of the control system were measured. Then, the capability of the rf control was tested using a mechanical vibrator made of a dielectric rod attached to an audio speaker system, which could induce regulated perturbations in the electric fields of the resonator. The control system was flexible so that its parameters could be easily configured to compensate for the disturbance induced in the resonator.

Design of a low level radio frequency control system for the direct current-superconductive photocathode injector at Peking University

A digital low level radio frequency (LLRF) control system based on a high precision field-programmable gate array (FPGA) is being developed for the stable operation of the upgraded direct current-superconductive (DC-SC) photocathode injector at Peking University The design of this LLRF control system is described, including both the hardware and the internal algorithm. Analysis of disturbances shows that the system can achieve the requirement of ±0.1% for amplitude stability and ±0.1° for phase stability. Through experiments, preliminary results are presented in the paper.

EPICS-Based Software Development of a Low-level RF System for the PEFP 100-MeV Proton Accelerator

Since its launch in 2002, the Proton Engineering Frontier Project (PEFP) has been constructing a 100-MeV proton accelerator. The high-power radio-frequency (RF) signal should be delivered into the radio-frequency quadrupole (RFQ) cavities and drift-tube linac (DTL) tanks for stable and efficient acceleration of a proton beam. The RF amplitude and phase-stability requirements of the accelerating field of a low-level RF (LLRF) system are within ±1% and ±1◦, respectively. In order to achieve a better performance with specially developed software, we developed a remote control system for RF control with experimental physics and industrial control system (EPICS). The LLRF control system was developed with a versa-module eurocard (VME) single board computer (SBC) and a field-programmable gate array (FPGA) peripheral component interconnect (PCI) mezzanine card (PMC) extended board. The EPICS input output controller (IOC) was implemented with an embedded system that could make it easily accessible to operators when using the EPICS standard communication method. The LLRF IOC has been in use at the PEFP 20-MeV proton accelerator for five months. In this paper, the details of the implementation and the configurations will be described.

Improvement of the Low-level RF Control System for the PEFP 100-MeV Proton Accelerator

Improvement of the Low-level RF Control System for the PEFP 100-MeV Proton Accelerator

Prototype Real-Time ATCA-Based LLRF Control System

The linear accelerators employed to drive Free Electron Lasers (FELs), such as the X-ray Free Electron Laser (XFEL) currently being built in Hamburg, require sophisticated control systems. The Low Level Radio Frequency (LLRF) control system should stabilize the phase and amplitude of the electromagnetic field in accelerating modules with tolerances below 0.02 % for amplitude and 0.01 degree for phase to produce ultra-stable electron beam that meets the conditions required for Self-Amplified Spontaneous Emission (SASE). The LLRF control system of 32-cavity accelerating module of the XFEL accelerator requires acquisition of more than 100 analogue signals sampled with frequency around 100 MHz. Data processing in real-time loop should complete within a few hundreds of nanoseconds. Moreover, the LLRF control system should be reliable, upgradable and serviceable. The Advanced Telecommunications Computing Architecture (ATCA) standard, developed for telecommunication applications, can fulfil all of the above mentioned requirements. The paper presents the architecture of a prototype LLRF control system developed for the XFEL accelerator. The control system composed of ATCA carrier boards with Rear Transition Modules (RTM) is able to supervise 32 cavities. The crucial submodules, like DAQ, Vector Modulator or Timing Module, are designed according to AMC specification. The paper discusses results of the LLRF control system tests that were performed at the FLASH accelerator (DESY, Hamburg) during machine studies.

Intelligent Platform-Management Controller for Low-Level RF Control System ATCA Carrier Board

High availability and reliability are among the most desirable features of control systems in modern high-energy physics (HEP) and other big-scale scientific experiments. One of the recent developments that has influenced this field has been the emergence of the Advanced Telecommunications Computing Architecture (ATCA). Designed for the telecommunications industry, it has been successfully applied in other domains, such as accelerator control systems. A good example is the application of ATCA standard for the design of the low-level RF (LLRF) control system for the X-Ray Free Electron Laser (XFEL) being developed in Deutsches Elektronen Synchrotron (DESY). Reliability and availability requirements for such a facility play a crucial role among other parameters. Thus, the ATCA standard, with five-nines availability, is considered to be one of the best candidates for this system. This paper focuses on the central-management unit of every ATCA board, namely, the intelligent platform-management controller (IPMC), developed for the LLRF ATCA carrier board. It is also argued that it is possible to create a fully functional IPMC using base specifications which is only a more economical solution than acquiring such products from ATCA vendors. This work supports the concept of an open-source community solution under the xTCA for physics collaboration dealing with IPMC/MMC development and wishes to contribute to it. The IPMC solution presented here is mainly hardware independent as proper code organization allowed to separate low-level device drivers and high-level application logic dealing with the ATCA standard, which makes it portable for new carrier-board designs. It also follows the latest trends in xTCA development introduced by the xTCA for Physics initiative. A firmware upgrade of programmable devices (field-programmable gate arrays and digital signal processors) has been proposed. Currently, this is not included in the standard. However, this functionality is needed in HEP applications by using xTCA and is useful in these cases.

Achievement of very low jitter extraction of high power proton beams in the J-PARC RCS

The 3 GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) delivers high intensity proton beams to the Materials and Life Science Facility (MLF) and the main ring (MR). The repetition rate of the RCS is 25 Hz. The typical operation period of the J-PARC is 3.2 s, which consists of 80 RCS cycles. Four beam pulses are for the MR and the other pulses are led into the MLF. Since a bucket-to-bucket injection scheme is used for the MR, the beam from the RCS must be injected with a precise phase to the proper rf bucket of the MR. In case of the MLF, the beam has to be synchronized to the Fermi chopper, which has a tolerance of only a few 100 ns. Thus, stable beam timings with a very low jitter are required for both destinations. To realize the stable beam timing, we employ the timing system, which is not synchronized to the AC power line. Also the magnetic-alloy accelerating cavities and the full digital low-level RF control system are the keys for the precise beam phase control. For acceleration of a high power beam, the phase feedback loop, which damps the longitudinal dipole oscillation, is necessary. The phase loop is a cause of the jitter of the beam extraction timing. We apply a gain pattern of the phase loop to avoid the influence on the beam phase at the extraction. We have achieved a very low jitter extraction of a high power beam within 1.7 ns, which corresponds to 1 degree of the rf frequency at the extraction.

3 GHz digital rf control at the superconducting Darmstadt electron linear accelerator: First results from the baseband approach and extensions for other frequencies

The low level rf system for the superconducting Darmstadt electron linear accelerator (S-DALINAC) developed 20 years ago and operating since converts the 3 GHz signals from the cavities down to the baseband and not to an intermediate frequency. While designing the new, digital rf control system this concept was kept: the rf module does the $I/Q$ and amplitude modulation/demodulation while the low frequency board, housing an field programmable gate array analyzes and processes the signals. Recently, the flexibility of this concept was realized: By replacing the modulator/demodulators on the rf module, cavities operating at frequencies other than the one of the S-DALINAC can be controlled with only minor modifications: A 6 GHz version, needed for a harmonic bunching system at the S-DALINAC and a 324 MHz solution to be used on a room temperature cavity at GSI, are currently under design. This paper reviews the concept of the digital low level rf control loops in detail and reports on the results gained during first operation with a superconducting cavity.

Phase Stability in the RF Reference System for the PEFP 100MeV LLRF Control System

The 100-MeV proton linear accelerator of the Proton Engineering Frontier Project (PEFP) has been developed and consists of a 3-MeV radio frequency quadrupole accelerator (RFQ), a 20-MeV drift tube linac (DTL), a medium energy beam transmitter (MEBT), and 100-MeV DTL tanks. The error of the accelerating field in the cavity should be within ±1◦ in phase and ±1% in amplitude, and the phase difference between adjacent cavities should be maintained continuously. To satisfy these requirements, high phase stability is required in the RF reference system for the PEFP lowlevel radio frequency (LLRF) control system. The RF reference system for the PEFP 100-MeV accelerator, which is composed of a local oscillator (LO), a rigid coaxial reference line of about 80-m length, Heliax cables, and LLRF analog components, was designed and its phase stability was evaluated. The reference signal was chosen to be the 300 MHz LO signal for phase stability of the LLRF control system. The phase noise of the local oscillator was measured and calculated as a phase error of 0.058 degrees. In the entire length of the RF reference distribution line, a phase stability of ±0.05 degrees was evaluated for a temperature change of ±0.1 ◦C. The phase stability of the LLRF analog system for up/down-conversion was also measured and depended on the temperature stabilization.

Lessons learned from positron-electron project low level rf and longitudinal feedback

The Positron-Electron Project II (PEP-II) B Factory collider ended the final phase of operation at nearly twice the design current and 4X the design luminosity. In the ultimate operation state, eight 1.2 MW radio-frequency (rf) klystrons and 12 accelerating cavities were added beyond the original implementation, and the two storage rings were operating with longitudinal instability growth rates roughly 5X in excess of the original design estimates. From initial commissioning there has been continual adaptation of the low level rf (LLRF) control strategies, configuration tools, and some new hardware in response to unanticipated technical challenges. This paper offers a perspective on the original LLRF and longitudinal instability control design, and highlights via two examples the system evolution from the original design estimates through to the final machine with $1.2\ifmmode\times\else\texttimes\fi{}{10}^{34}$ luminosity. The impact of unanticipated signals in the coupled-bunch longitudinal feedback and the significance of nonlinear processing elements in the LLRF systems are presented. We present valuable ``lessons learned'' which are of interest to designers of next generation feedback and impedance controlled LLRF systems.

强流质子RFQ加速器高频数字低电平控制系统

强流质子RFQ加速器高频数字低电平控制系统

Interfaces and Communication Protocols in ATCA-Based LLRF Control Systems

Linear accelerators driving Free Electron Lasers (FELs), such as the Free Electron Laser in Hamburg (FLASH) or the X-ray Free Electron Laser (XFEL), require sophisticated Low Level Radio Frequency (LLRF) control systems. The controller of the LLRF system should stabilize the phase and amplitude of the field in accelerating modules below 0.02% of the amplitude and 0.01 degree for phase tolerances to produce an ultra stable electron beam that meets the required conditions for Self-Amplified Spontaneous Emission (SASE). Since the LLRF system for the XFEL must be in operation for the next 20 years, it should be reliable, reproducible and upgradeable. Having in mind all requirements of the LLRF control system, the Advanced Telecommunications Computing Architecture (ATCA) has been chosen to build a prototype of the LLRF system for the FLASH accelerator that is able to supervise 32 cavities of one RF station. The LLRF controller takes advantage of features offered by the ATCA standard. The LLRF system consists of a few ATCA carrier blades, Rear Transition Modules (RTM) and several Advanced Mezzanine Cards (AMCs) that provide all necessary digital and analog hardware components. The distributed hardware of the LLRF system requires a number of communication links that should provide different latencies, bandwidths and protocols. The paper presents the general view of the ATC A-based LLRF system, discusses requirements and proposes an application for various interfaces and protocols in the distributed LLRF control system.

Prototype Control System for Compensation of Superconducting Cavities Detuning Using Piezoelectric Actuators

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Pulsed operation of high gradient superconducting radio frequency (SCRF) cavities results in dynamic Lorentz force detuning (LFD) approaching or exceeding the bandwidth of the cavity of order of a few hundreds of Hz. The resulting modulation of the resonance frequency of the cavity is leading to a perturbation of the amplitude and phase of the accelerating field, which can be controlled only at the expense of RF power. Presently, at various labs, a piezoelectric fast tuner based on an active compensation scheme for the resonance frequency control of the cavity is under study. The tests already performed in the Free Electron Laser in Hamburg (FLASH), proved the possibility of Lorentz force detuning compensation by the means of the piezo element excited with the single period of sine wave prior to the RF pulse. The X-Ray Free Electron Laser (X-FEL) accelerator, which is now under development in Deutsche Elektronen—Synchrotron (DESY), will consists of around 800 cavities with a fast tuner fixture including the actuator/sensor configuration. Therefore, it is necessary to design a distributed control system which would be able to supervise around 25 RF stations, each one comprised of 32 cavities. The Advanced Telecomunications Computing Architecture (ATCA) was chosen to design, develop, and build a Low Level Radio Frequency (LLRF) controller for X-FEL. The prototype control system for Lorentz force detuning compensation was designed and developed. The control applications applied in the system were fitted to the main framework of interfaces and communication protocols proposed for the ATCA-based LLRF control system. The paper presents the general view of a designed control system and shows the first experimental results from the tests carried out in FLASH facility. Moreover, the possibilities for integration of the piezo control system to the ATCA standards are discussed. </para>

FPGA-based amplitude and phase detection in DLLRF

The new generation particle accelerator requires a highly stable radio frequency (RF) system. The stability of the RF system is realized by the Low Level RF (LLRF) subsystem which controls the amplitude and phase of the RF signal. The detection of the RF signal's amplitude and phase is fundamental to LLRF controls. High-speed ADC (Analog to Digital Converter), DAC (Digital to Analog Converter) and FPGA (Field Programmable Gate Array) play very important roles in digital LLRF control systems. This paper describes the implementation of real-time amplitude and phase detection based of the FPGA with an analysis of the main factors that affect the detection accuracy such as jitter, algorithm's defects and non-linearity of devices, which is helpful for future work on high precision detection and control.

Tuning of RF amplitude and phase for the separate-type drift tube linac in J-PARC

It is important to accurately adjust the amplitude and the phase of RF power sources for a high intensity proton linac. J-PARC (Japan proton accelerator research complex) linac is one of those high-intensity linacs. J-PARC linac has 30 SDTL (separate-type drift tube linac) tanks to accelerate the negative hydrogen ions from 50 to 181 MeV. Two neighboring SDTL tanks are driven by one klystron, where the phase and the amplitude of these two tanks are controlled in terms of the vector sum. The target-value of the vector sum control should be determined with a beam-based tuning for each klystron. During the beam commissioning, the RF tuning has been performed with a phase scan method introducing a concept of phase signature matching. In the tuning, the output beam energy from the SDTL module is monitored while scanning the RF phase. Comparing the obtained phase dependence of the output beam energy with those from a numerical model, the target-values for the low-level RF control system has been tuned within the required accuracy of 1° in phase and 1% in amplitude. The same tuning procedure has successfully been applied to the RF tuning of buncher and debuncher cavities.

Design and evaluation of a low-level RF control system analog/digital receiver for the ILC main LINACs

The proposed RF distribution scheme for the two 15 km long ILC LINACs uses one klystron to feed 26 superconducting RF cavities operating at 1.3 GHz. For a precise control of the vector sum of the signals coming from the SC cavities, the control system needs a high-performance, low-cost, reliable and modular multichannel receiver. At Fermilab we developed a 96-channel, 1.3 GHz analog/digital receiver for the ILC LINAC LLRF control system. In this paper we present a balanced design approach to the specifications of each receiver section, the design choices made to fulfill the goals and a description of the prototyped system. The design is tested by measuring standard performance parameters, such as noise figure, linearity and temperature sensitivity. Measurements show that the design meets the specifications and it is comparable to other similar systems developed at other laboratories, in terms of performance.