RF Power System Research Articles

Highly-Isolated RF Power and Information Receiving System Based on Dual-Band Dual-Circular-Polarized Shared-Aperture Antenna

A highly integrated RF power and information receiving system is proposed in this paper. The system consists of an antenna, a rectifier, and an information receiving module. The information receiving module acts as part of the dc load. To realize high integration, a dual-band, dual-circular-polarized shared- aperture antenna is implemented. The antenna consists of a left-circular-polarized element operating at 2.4-GHz band, and a high-gain, right-circular-polarized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> array operating at 5.8-GHz band. The lower-frequency antenna is for communication, while the higher-frequency one is for power transmission. All the elements share the same aperture, and the radiator of lower- frequency antenna acts as the reflector of higher-frequency elements. Accordingly, a class-F rectifier that matches the higher- frequency array is designed and verified, and a system-level demonstration is implemented. Owing to the high isolation on frequency splitting and polarization diversity, the baseband signal can be successfully demodulated under a 30-dB input-power-level difference at two frequency bands. The base-band information can be displayed by an ink screen. The received RF power can be effectively rectified and power the data-processing modules.

Functional Overview of the RF Power System for the LIPAc RFQ

Design, development, manufacturing, and test activities of the RF power system (RFPS) for Linear IFMIF Prototype Accelerator (LIPAc) were completed in Europe. Installation and commissioning activities were carried out at the International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities (IFMIF/EVEDA) site in Rokkasho, Japan. Challenging IFMIF requirements led to a number of innovations during design and development. Commissioning required a major effort on calibration and fine setting and led to development of new functionalities. The RFPS was validated under full power and 125-mA deuteron beam loading conditions, in the radio frequency quadrupole (RFQ), demonstrating good performance. This article is an overview about how technical challenges impacted the prototype RFPS design and its functional evolution during commissioning, cavity conditioning, and beam operation of the RFQ.

An approach to characterize Lorentz force transfer function for superconducting cavities

Superconducting radio-frequency (SRF) cavities are preferred in many modern accelerator facilities to reduce the operation cost of the RF power systems. SC cavities are usually sensitive to small mechanical perturbations because of their narrow bandwidth. These perturbations such as microphonics and Lorentz force detuning (LFD) can significantly detune the SRF cavity and therefore not only deteriorate the cavity field stabilities but also increase the RF power requirements. Piezo-electric actuators are widely adopted to suppress the cavity detuning caused by LFD and microphonics. Many advanced detuning compensation strategies were proposed to suppress the microphonics and LFD in recent years. The dynamic models of the LFD and piezo actuator are essential in these activities. Generally, the models of LFD can be identified by modulating the cavity field with sinusoidal signals and then measuring the corresponding steady-state amplitude and phase response of the cavity. However, for some SRF cavities, the cavity field may becomes unstable because of the presence of the ponderomotive effects, leading to a unacceptable measurement result. We present a new approach to identify the dominant modes of the LFD model based on a grey-box models estimation method. The validity of the approach was demonstrated by comparing the model output and measurement results on SRF cavities of real accelerator facilities.

Energy recovery operation for continuous-wave X-ray free-electron lasers

A superconducting linear accelerator operating in continuous-wave mode could produce X-ray free electron lasers (XFEL) at megahertz repetition rate, with the capability that delivering wide spectral range coherent radiation to multi end stations. In this paper, the energy recovery Linac (ERL) mode is proposed to flexibly control the electron beam energy for a continuous-wave superconducting Linac. Theoretical investigations and multi-dimensional numerical simulations are applied to the Linac case of Shanghai high-repetition-rate XFEL and extreme light facility. The results show that, with ERL operation in the last 25 cryo-modules, the strict requirements on RF power system could be significantly relaxed. And if one exhaust the RF power, the maximum electron beam energy can be enhanced from 8.74 GeV to 11.41 GeV in ERL mode. The optimization of the ERL operation, the multi-energy electron beam transport and the XFEL performance improvements are presented.

LIPAc RF power system: design and main practical implementation issues

The Linear IFMIF (International Fusion Materials Irradiation Facility) Prototype Accelerator (LIPAc) is a 9 MeV, 125 mA, continuous wave (CW) deuteron accelerator aimed to validate the technology for the IFMIF accelerators. The construction of LIPAc, which is currently the most powerful deuteron accelerator in the world, has been carried out under the Broader Approach (BA) Agreement between EU and Japan, and it is located at Rokkasho (Japan). CIEMAT is one of the five European Institutions that has participated in the design, manufacturing and commissioning/operation of the main accelerator components, among them, the Radio Frequency Power System (RFPS). The RFPS contains all the equipment necessary to generate the required RF power to feed the LIPAc cavities. These cavities demand eighteen RF power chains at 175 MHz being distributed as follows: eight 200 kW tetrode-based chains for the Radiofrequency Quadrupole (RFQ), two 16 kW solid-state chains for the re-buncher cavities, and eight 105 kW tetrode-based chains for the Superconducting RF Linac Half-Wave Resonators. The design of the RFPS main components is presented in this paper, including the tetrode-based chains, the Solid-State Power Amplifier (SSPA) for the re-buncher cavities, the High Voltage Power Supplies (HVPSs) for the final amplifiers anodes and the RF water cooling system. Additionally, the main difficulties encountered during the first months of the RFPS commissioning and operation will be described, together with the applied improvements.

A Compact Impedance Measurement Solution for Systems Operating in Load Varying Scenarios

This paper presents a compact solution for impedance calculation obtained from low phase resolution stationary wave measurements, for RF power systems operating in load varying scenarios. The implemented system is based on a bi-directional coupler and makes use of the stationary wave periodicity, which is synthesized and measured via a digital phase shifter, a power combiner, and an envelope detector, in a specific arrangement. Instead of sampling a transmission line at various spatial points (sampled line architectures), both incident and reflected waves are sampled at one specific position, the stationary wave is obtained by sweeping the incident or reflected waves' phase, mimicking the slotted line principle and, from there, the impedance is obtained using a new signal processing algorithm that is now presented. Taking advantage of the developed technique, this can be done for only three phase shifter states, making the measurement fast and accurate. This compact measurement solution can compute the impedance of both real and complex loads inside a 2.1 voltage standing wave ratio circle with high accuracy (-28.8 dB) at a rate of 1 kHz and is appropriate for high power systems due to its simple architecture and very low total losses (0.075 dB).

Design of 100 MHz RF cavity for the storage ring of the Iranian Light Source Facility (ILSF)

The Iranian Light Source Facility is a fourth-generation low emittance synchrotron light source under development in Iran. The design and in-house fabrication of RF cavities are key elements of this project. The choice of 100 MHz capacity loaded RF cavities offers many advantages compared to other cavity types due to a simpler geometry, ease of fabrication, and lower costs for manufacturing and RF power system development. Here we present comprehensive simulation studies of these accelerating RF cavities. This includes electromagnetic, mechanical, and thermal calculations. In addition, in the electromagnetic design section, discussions of higher-order modes, their impact on beam instabilities during machine operation and beam loading effects are addressed. Finally, thermomechanical simulation results are presented. The fabrication of a 100 MHz capacity-loaded cavity has started based on the design presented in this article.

Validation of the Linear IFMIF Prototype Accelerator (LIPAc) in Rokkasho

For the development of the International Fusion Materials Irradiation Facility (IFMIF) aiming at material tests for fusion power plants, the construction of the Linear IFMIF Prototype Accelerator (LIPAc) has been conducted at Rokkasho, Japan under the Broader Approach Agreement. The commissioning of LIPAc has been progressing significantly. The world most powerful RFQ successfully accelerated proton beam of 58 mA, and an important project milestone of the acceleration of deuteron beam to 5 MeV with the beam current of 125 mA in pulse mode was successfully achieved. The result proves the validity of the present RFQ design. The adjustment and tuning of the RF power system and the injector for enabling an operation at maximum performances played an important role in achieving this result. For the next step, the preparation of the high duty cycle operation of RFQ is underway. The installation of the HEBT (High Energy Beam Transport line) and the beam dump accepting 1 MW, CW beam, has been completed and a new beam transport line is under manufacturing. Also the assembly of the Superconducting RF (SRF) linac to accelerate the beam up to 9 MeV started in a clean room in Rokkasho.

Nano-Power CMOS Voltage Reference for RF-Powered Systems

This brief presents a fully CMOS voltage reference based on a self-biased topology, which provides low current consumption while saving silicon area. Temperature compensation is achieved by means of a subthreshold triode-based Widlar current reference and a proper arrangement of an active load. The proposed voltage reference was fabricated in a standard 0.13- $\mu {\text{m}}$ CMOS technology and occupies a core area as low as 0.003 mm2. The circuit properly operates with a power supply ranging from 2.4 V to 1.1 V while providing a reference voltage of around 800 mV with an average temperature coefficient of 100 ppm/°C and an overall current consumption below 25 nA. This performance makes the proposed voltage reference very suitable for RF-powered applications.

Linear IFMIF Prototype Accelerator (LIPAc): Installation activities for Phase-B beam commissioning in Rokkasho

The construction of the Linear IFMIF Prototype Accelerator (LIPAc) is in progress in order to demonstrate the feasibility of the low energy section of an IFMIF deuteron accelerator up to 9 MeV with a beam current of 125 mA in CW. The next milestone of the project is the so-called Phase-B beam commissioning, and one of the missions is to demonstrate the acceleration of the proton beam up to 2.5 MeV or the deuteron beam up to 5.0 MeV in pulsed mode with a low duty cycle of 0.1% through RFQ. Most of the components and subsystems necessary for Phase-B were delivered by 2016 under the responsibility of Fusion for Energy (F4E) as in-kind contributions of several European institutes, namely CEA (France), CIEMAT (Spain), INFN (Italy), and SCK-CEN (Belgium), and QST is in charge of the installation of the delivered equipment. The installation and check-out of the RFQ subsystem and the RF power system was completed by July 2017, and the RF conditioning of the RFQ cavity started. Also, the installation and the check-out of the important sub-systems for Phase-B, namely MEBT and beam diagnostics, have been completed.

Status of the RFQ linac installation and conditioning of the Linear IFMIF Prototype Accelerator

The Radio Frequency Quadrupole (RFQ) linac and 1.6 MW RF power system of the Linear IFMIF Prototype Accelerator (LIPAc) facility in the International Fusion Energy Research Center (IFERC) in Rokkasho (Japan) has been installed and conditioned. During the assembly and tuning process, the RFQ cavity was protected with a temporary tent from the potential deterioration of performance caused by dust. The vacuum in the cavity was improved through the 100 °C baking process of the cavity. The high power test of the 175 MHz RF systems up to 200 kW in CW for each of the eight RF chains was performed for checking its stable output reproducibility in Japan, before connecting 9–3/16 inch coaxial transmission lines from the RF chains to the RF input couplers of the cavity. It was confirmed that the eight RF chains provided the balanced RF power to the single RFQ cavity in-phase using a feedback loop and a synchronization system. The peak power in the cavity achieved 150 kW in the pulsed mode, which corresponds approximately to the required electric field to accelerate proton beam. Such RF conditioning process is ongoing to achieve 600 kW approximately required for deuteron beam commissioning planned in 2018.

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.

Fundamental cavity impedance and longitudinal coupled-bunch instabilities at the High Luminosity Large Hadron Collider

The interaction between beam dynamics and the radio frequency (rf) station in circular colliders is complex and can lead to longitudinal coupled-bunch instabilities at high beam currents. The excitation of the cavity higher order modes is traditionally damped using passive devices. But the wakefield developed at the cavity fundamental frequency falls in the frequency range of the rf power system and can, in theory, be compensated by modulating the generator drive. Such a regulation is the responsibility of the low-level rf (llrf) system that measures the cavity field (or beam current) and generates the rf power drive. The Large Hadron Collider (LHC) rf was designed for the nominal LHC parameter of 0.55 A DC beam current. At 7 TeV the synchrotron radiation damping time is 13 hours. Damping of the instability growth rates due to the cavity fundamental (400.789 MHz) can only come from the synchrotron tune spread (Landau damping) and will be very small (time constant in the order of 0.1 s). In this work, the ability of the present llrf compensation to prevent coupled-bunch instabilities with the planned high luminosity LHC (HiLumi LHC) doubling of the beam current to 1.1 A DC is investigated. The paper conclusions are based on the measured performances of the present llrf system. Models of the rf and llrf systems were developed at the LHC start-up. Following comparisons with measurements, the system was parametrized using these models. The parametric model then provides a more realistic estimation of the instability growth rates than an ideal model of the rf blocks. With this modeling approach, the key rf settings can be varied around their set value allowing for a sensitivity analysis (growth rate sensitivity to rf and llrf parameters). Finally, preliminary measurements from the LHC at 0.44 A DC are presented to support the conclusions of this work.

Precision vector control of a superconducting RF cavity driven by an injection locked magnetron

The technique presented in this paper enables the regulation of both radio frequency amplitude and phase in narrow band devices such as a Superconducting RF (SRF) cavity driven by constant power output devices i.e. magnetrons [1]. The ability to use low cost high efficiency magnetrons for accelerator RF power systems, with tight vector regulation, presents a substantial cost savings in both construction and operating costs - compared to current RF power system technology. An operating CW system at 2.45 GHz has been experimentally developed. Vector control of an injection locked magnetron has been extensively tested and characterized with a SRF cavity as the load. Amplitude dynamic range of 30 dB, amplitude stability of 0.3% r.m.s, and phase stability of 0.26 degrees r.m.s. has been demonstrated.

The Spallation Neutron Source accelerator system design

The Spallation Neutron Source (SNS) was designed and constructed by a collaboration of six U.S. Department of Energy national laboratories. The SNS accelerator system consists of a 1GeV linear accelerator and an accumulator ring providing 1.4MW of proton beam power in microsecond-long beam pulses to a liquid mercury target for neutron production. The accelerator complex consists of a front-end negative hydrogen-ion injector system, an 87MeV drift tube linear accelerator, a 186MeV side-coupled linear accelerator, a 1GeV superconducting linear accelerator, a 248-m circumference accumulator ring and associated beam transport lines. The accelerator complex is supported by ~100 high-power RF power systems, a 2K cryogenic plant, ~400 DC and pulsed power supply systems, ~400 beam diagnostic devices and a distributed control system handling ~100,000 I/O signals. The beam dynamics design of the SNS accelerator is presented, as is the engineering design of the major accelerator subsystems.

Design of KEK Test Machine for Mo Isotope Separation Based on Ion Cyclotron Resonance Plasma Separation

We discuss the design of a KEK test machine for Mo isotope separation based on the ion cyclotron resonance plasma separation process (KEK-ICR-PSP). The test machine consists of a superconducting magnet of 1.5 T, an Ar sputtering plasma chamber, a helical coil of 30-cm-diameter and 60 cm length, providing an ICR heating field of about 20 V/m, an isotope collector, and RF power systems. The yield and purity of 100Mo and 98Mo are evaluated using a dedicated Monte Carlo simulation program, KEK-ICR-SIM. They are strongly affected by the energy spectra of Mo ions from the sputtering plasma chamber, which can be investigated with the test machine.

Ambient RF Energy Harvesting Sensor Device With Capacitor-Leakage-Aware Duty Cycle Control

In this paper, we present a software control method that maximizes the sensing rate of wireless sensor networks (WSNs) that are solely powered by ambient RF power. Unlike all other energy harvesting WSN systems, RF-powered systems present new challenges for energy management. A WSN node repeatedly charges and discharges at short intervals, depending on the energy intake. Typically in energy harvesting systems, a capacitor is used for energy storage because of its efficient charge and discharge performance and infinite recharge cycles. When the charging time is too short, a node is more likely to experience an energy shortage. On the contrary, if it is too long, more energy is lost because of leakage in the capacitor. In this paper, we introduce an adaptive duty cycle control scheme optimized for RF energy harvesting. This method maximizes the sensing rate by taking into account the leakage problem, a factor that has never been previously studied in this context. Our control scheme improves the efficiency by aggregate evaluation of operation reliability and leakage reduction.

Design of RF Power System for CPHS

Abstract The Compact Pulsed Hadron Source (CPHS) system has been proposed and designed by the Department of Engineering Physics of Tsinghua University in Beijing, China. It consists of an accelerator front-end—a highintensity ion source, a 3 MeV radiofrequency quadrupole linac (RFQ), and a 13 MeV drift-tube linac (DTL), a neutron target station, and some experimental stations. In design of our RF power supply, both RFQ and DTL share a single klystron which is capable of 2.5 MW peak RF power and a 3.33% duty factor. The 325 MHz klystron contains a modulating anode and has a 100 kW average output power. Portions of the RF power system, such as pulsed high voltage power supply, modulator, crowbar protection and RF power transmission are all presented in details in this paper.

Engineering evolution of the FAST machine

FAST (Fusion Advanced Studies Torus) is a proposal for a Satellite Facility which can contribute the rapid exploitation of ITER and prepare ITER and DEMO regimes of operation, as well as exploit innovative plasma facing component systems for DEMO. FAST is a compact (Ro = 1.82 m, a = 0.64 m, triangularity δ = 0.4) and cost effective machine able to investigate, with integration capability, non linear dynamics effects of alpha particle behaviour in burning plasmas. FAST operates in high performance H-mode ( B T up to 8.5 T; I P up to 8 MA), as well as in advanced tokamak mode ( I P = 3 MA), and in full non inductive current mode ( I P = 2 MA). Helium gas at 30 K is used for cooling the resistive copper magnets. This allows for a pulse duration up to 170 s at 3 MA/3.5 T. The vacuum vessel (VV), segmented into 20-degree modules, is capable to accommodate a 40 MW RF power system. The machine has been designed to house a 10 MW Negative Neutral Beam Injection (NNBI) system. Tungsten (W) or liquid lithium (L-Li) have been chosen as the divertor plate materials, and argon or neon as the impurities to be injected for mitigating the thermal loads.

352-MHz Solid State RF System Development at the Advanced Photon Source

An investigation into development of a 200-kW CW solid state rf power system design to replace the existing klystron-based 352-MHz rf systems at the Advanced Photon Source has been started. The baseline 352-MHz solid state system design will consist of multiple 1-kW CW modules combined to produce a total output capability of 200-kW CW, sufficient to drive one single-cell storage ring cavity. A description of the 1-kW CW module building block of the solid state power sistem will be presented, along with results from hardware evaluation tests at the 1-kW CW level.