Low Level RF Research Articles

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.

First annular-ring coupled structure cavity for the Japan Proton Accelerator Research Complex linac

The first annular-ring coupled structure (ACS) cavity for the Japan Proton Accelerator Research Complex (J-PARC) linac has been developed in order to confirm and establish its fabrication processes. This cavity includes 34 accelerating cells, which is 3.4 times as many as the prototype cavity (buncher) of the J-PARC ACS. The cell frequencies before brazing were tuned within the required accuracies. After brazing, the accelerating- and coupling-mode frequencies were 972.19 and 972.63 MHz on average, respectively, which were higher than the operating frequency of 972 MHz. Although the accelerating-mode frequency can be corrected to 972 MHz using adjustable plungers, these frequency errors adversely affected the on-axis electric field. This cavity was successfully conditioned up to 1.6 MW. This power corresponds to an accelerating field of $4.7\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, which is 10% higher than the design value of $4.2\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. In order to find the issue caused by the excited coupling cells, this cavity was also conditioned at the higher and lower frequencies that were detuned from the operating frequency of 972 MHz. Here we present the frequency tuning processes, the low-level rf measurements, and the high-power test results. We also discuss the most reasonable scenario for frequency tuning in future work.

High-Accuracy Amplitude and Phase Measurements for Low-Level RF Systems

This paper presents a detection system for high-accuracy amplitude and phase measurements on RF signals. It is typically used to set up the low-level RF system for particle accelerators. The proposed detector employs the principle of a heterodyne receiver and uses the digital IF architecture with a high oversampling rate to increase the SNR. A discrete Fourier transform-based quadrature demodulator is used to suppress the analog-to-digital converter (ADC) quantization noise and IF harmonics. The system has been evaluated at an IF of 1 MHz and in an RF range of 500-3000 MHz. A graphical user interface is developed to display and record the measured values. The detection accuracy achieved on 500-MHz signals in a 250-kHz bandwidth is better than ±0.0051% for the amplitude and better than ±0.0032 ° for the phase. Experimental results at different frequencies prove that the detection system can meet the demands of state-of-the-art RF control systems for modern particle accelerators.

A digital low-level radio-frequency system R&D for a 1.3 GHz nine-cell cavity

To test and verify the performance of the digital low-level radio-frequency (LLRF) and tuner system designed by the IHEP RF group, an experimental platform with a retired KEK 1.3 GHz nine-cell cavity is set up. A radio-frequency (RF) field is established successfully in the cavity and the frequency of the cavity is locked by the tuner in ±0.5° (about ±1.2 kHz) at room temperature. The digital LLRF system performs well in a five-hour experiment, and the results show that the system achieves field stability at amplitude <0.1% (peak to peak) and phase <0.1° (peak to peak). This index satisfies the requirements of the International Linear Collider (ILC), and this paper describes this closed-loop experiment of the LLRF system.

Non invasive radiofrequency diagnostics of cancer. The Bioscanner — Trimprob technology and clinical applications

A new paper by Pokorny, Vedruccio, Cifra, Kucera, titled Cancer physics: Diagnostics based on damped cellular elasto-electrical vibrations in microtubules, recently available on Eur. Biophys. J., discloses the mechanism of active grown cancer tissues interaction with a Non- Linear Resonance Interaction (NLRI) Bioscanner Trimprob diagnostic device that is certified and ready to be used to investigate suspected cases of disease and cancer. This technology spreads early capabilities of cancer detection by means of low level radiofrequency oscillations in UHF band. The system is based on an unique and extremely innovative non- linear radiofrequency oscillator working on 462-465 MHz plus the harmonics. The diseased tissues suspected of cancer, are irradiated by means of a handy probe near field emission, while a spectrum analyzer placed in the far field detects by means of a small antenna, the oscillator interaction within the tissues. The Bioscanner is characterized by a high dynamic range, in the order of 30 or more decibel, and is useful for detection of small cancer agglomerates, if used by a well trained operator. At the resonance, the free running oscillator locks-in on the specific interaction frequency, in a sharp frequency window centered on 462 MHz; the resulting effect is evidenced by a deep decrease of the 462 MHz spectral line propagation in the far field around the oscillator probe. The NLRI provides a selective characterization, like a sort of a electronic biopsy response of biologic tissues in support of modern imaging diagnostics. Further to existing literature describing methods for cancer detections by means of electromagnetic fields this paper shows this innovative in vivo medical diagnostic equipment and some clinical applications.

Status of the IHEP 1.3 GHz superconducting RF program

The 1.3 GHz superconducting radio-frequency (SRF) technology is one of the key technologies for the ILC and future XFEL and ERL projects in China. With the aim to develop 1.3 GHz SRF technology, IHEP has started a program to build an SRF Accelerating Unit. This unit contains a 9-cell 1.3 GHz superconducting cavity, a short cryomodule, a high power input coupler, a tuner and a low level RF system. This program also includes the SRF laboratory upgrade, which will permit the unit to be built and tested at IHEP. The unit will be used for the 1.3 GHz SRF system integration study, high power horizontal test and possible beam test in the future. In this paper, we report the recent R&D status of this program. The first large grain low-loss shape 9-cell superconducting RF cavity made by IHEP reached 20 MV/m in the first vertical test in July, 2010. The prototype tuner and low level RF (LLRF) system are under test. The high power input coupler and cryomodule are under fabrication. Several key SRF facilities for 9-cell cavity surface treatment and pre-tuning were successfully commissioned and are in operation.

New digital low-level rf system for heavy-ion synchrotrons

In the scope of the Facility for Antiproton and Ion Research (FAIR) project, several new synchrotrons and storage rings will be built. The existing heavy-ion synchrotron SIS18 has to be upgraded to serve as an injector for the FAIR accelerators. All this imposes new requirements on the low-level rf (LLRF) systems. These requirements include fast ramping modes, arbitrary ion species, and complex beam manipulations such as dual-harmonic operation, bunch merging/splitting, barrier bucket operation, or bunch compression. In order to fulfill these tasks, a completely new and unique system architecture has been developed since 2002, and the system is now used in SIS18 operation. The presentation of this novel system architecture is the purpose of this paper. We first describe the requirements and the design of the LLRF system. Afterwards, some key components and key interfaces of the system are summarized followed by a discussion of technological aspects. Finally, we present some beam experiment results that were obtained using the new LLRF system.

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.

Radio frequency noise effects on the CERN Large Hadron Collider beam diffusion

Radio frequency (rf) accelerating system noise can have a detrimental impact on the Large Hadron Collider (LHC) performance through longitudinal motion and longitudinal emittance growth. A theoretical formalism has been developed to relate the beam and rf station dynamics with the bunch length growth [T. Mastorides et al., Phys. Rev. ST Accel. Beams 13, 102801 (2010)]. Measurements were conducted at LHC to determine the performance limiting rf components and validate the formalism through studies of the beam diffusion dependence on rf noise. As a result, a noise threshold was established for acceptable performance which provides the foundation for beam diffusion estimates for higher energies and intensities. Measurements were also conducted to determine the low level rf noise spectrum and its major contributions, as well as to validate models and simulations of this system.

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.

Prostiva RF Therapy (Transurethral Needle Ablation): Evaluation of Results from 127 Patients

Following the latest guidelines, management of LUTS/BPH includes not only conventional prostatic surgery, but also the minimally invasive treatment (MIT) of symptoms, with great attention given to improvement in the quality of life. One such MIT for BPH is the Prostiva RF Therapy (Transurethral Needle Ablation). The aim of the study was to evaluate the results obtained from 127 patients (pts) treated with Prostiva. The Prostiva RF Therapy is a MIT indicated in the treatment of BPH<50 gr with no median lobe and with PSA inside normal limits. This procedure employs low-level radio frequency energy delivered from a generator. From October 2004 to January 2009 120 pts (mean age: 64 years) were treated with Prostiva RF Therapy at two Italian centers. International Prostate Symptom Score (I-PSS), Quality of life (QoL) and Index of Erectile Dysfunction (IIEF5) were compared between baseline and last follow-up. Mean FU was 27 months ± 24. At baseline, the mean prostate size was 36.62±16 gr. At enrollment, 70 of 120 pts (58%) were under pharmacological treatment for BPH. 102 pts were treated under spinal anesthesia and 18 under local anesthesia. The total average time of the procedure was 28'. The average number of ablations was 5. Uroflowmetry showed a significant improvement in 67% of pts. 63% reported overall satisfaction with I-PSS and QoL improvement. 25% pts needed further therapies (15% pharmacological, 10% TURP). There were no serious complications, 12% needed prolonged catheterization (max 7 days), 6% experienced transient irritation (max 2 weeks), 5 pts experienced transitory ejaculation disorders, and 1 pt anejaculation. There were no significant differences in IIEF -5 either before or after the procedure. In our experience the PT was effective in 66% of treated patients. The procedure was easy, safe and feasible to be carried out under local anesthesia.

Low level rf system for the European Spallation Source’s Bilbao linac

Design and some performance results of the pulsed digital low level radio frequency (LLRF) for the radio frequency quadrupole (RFQ) systems of Rutherford Appleton Laboratory--front end test stand and the future European Spallation Source Bilbao linac are presented. For rf field regulation, the design is based on direct rf-to-baseband conversion using an analog in-phase quadrature (IQ) demodulator, high-speed sampling of the I/Q components, baseband signal processing in a field-programmable gate array (FPGA), conversion to analog, and IQ modulation. This concept leads to a simple and versatile LLRF system which can be used for a large variety of rf frequencies and virtually any LLRF application including cw, ramping, and pulsed. In order to improve the accuracy of the probe voltage measurement, errors associated with the use of analog IQ demodulators have been identified and corrected by FPGA algorithms and proper setting of the feedback loop parameters. Furthermore, a baseband-equivalent model for the rf plant is developed in MATLAB-Simulink to study the RFQ transient response under beam loading in the presence of phase and delay errors. The effect of the unwanted resonant modes on the feedback loop stability and the LLRF considerations to avoid such instabilities are discussed and compared to some other machines such as the ILC and the European free electron laser . The practical results obtained from tests with a mock-up cavity and an RFQ cold model verify that amplitude and phase stabilities down to a fraction of one percent and one degree and phase margins larger than $\ifmmode\pm\else\textpm\fi{}50\ifmmode^\circ\else\textdegree\fi{}$ can be achieved with this method preserving the linearity and bandwidth of the feedback loops.

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.

Design approaches for the X band LLRF system

Abstract The low-level RF (LLRF) system regulates disturbances over a limited bandwidth in accordance with its capabilities and the RF loop parameters. The disturbances usually originate in the RF system or can be coupled to the RF system from the environment. In this paper a general overview of the possible design approaches for a digital LLRF system operating in X band is presented. Firstly, the possible design approaches of the RF front/back ends are presented and reviewed. We also define the main design parameters for the RF front/back ends. Parameters like isolation between channels, noise, gain, linearity and number of IF stages are put into the perspective of machines using RF components in the X band. An important part of the LLRF system is the local RF timing generation and distribution, which is also treated in the paper. In the second part of the paper the main design approaches in the digital signal processing part of the LLRF system are presented. The emphasis is on the algorithms that are machine specific. Some standard processing algorithms like adaptive feed-forward and arbitrary shaping of feed-forward pulses are presented. Finally, a suggestion for the X band LLRF design is given.

Autoimmune process after long-term low-level exposure to electromagnetic field (experimental results). Part I. Mobile communications and changes in electromagnetic conditions for the population. Need for additional substantiation of existing hygienic standards

Mobile communications provides a new source of electromagnetic exposure for almost the whole population of Russia. For the first time in the history of civilization, the brain of mobile phone users is exposed to localized radiofrequency (RF) electromagnetic fields (EMF). Base stations are a factor in the exposure of the population. Existing standards for limiting exposure do not account for the role of base stations as a source of EMF and cannot guarantee the absence of adverse health effects. It has become necessary to obtain reliable information to expand databases for the development of new standards. As recommended by the World Health Organization, an additional experiment is performed under the supervision of foreign experts, which shows changes in autoimmune status in rats after long-term low-level RF EMF exposure with an incident power of 500 μW/cm2.

Biological effects from exposure to electromagnetic radiation emitted by cell tower base stations and other antenna arrays

The siting of cellular phone base stations and other cellular infrastructure such as roof-mounted antenna arrays, especially in residential neighborhoods, is a contentious subject in land-use regulation. Local resistance from nearby residents and landowners is often based on fears of adverse health effects despite reassurances from telecommunications service providers that international exposure standards will be followed. Both anecdotal reports and some epidemiology studies have found headaches, skin rashes, sleep disturbances, depression, decreased libido, increased rates of suicide, concentration problems, dizziness, memory changes, increased risk of cancer, tremors, and other neurophysiological effects in populations near base stations. The objective of this paper is to review the existing studies of people living or working near cellular infrastructure and other pertinent studies that could apply to long-term, low-level radiofrequency radiation (RFR) exposures. While specific epidemiological research in this area is sparse and contradictory, and such exposures are difficult to quantify given the increasing background levels of RFR from myriad personal consumer products, some research does exist to warrant caution in infrastructure siting. Further epidemiology research that takes total ambient RFR exposures into consideration is warranted. Symptoms reported today may be classic microwave sickness, first described in 1978. Nonionizing electromagnetic fields are among the fastest growing forms of environmental pollution. Some extrapolations can be made from research other than epidemiology regarding biological effects from exposures at levels far below current exposure guidelines.