High Power RF System Research Articles

Energy Saving Measures in the High-Power RF System of the European XFEL

The high-voltage modulators of the 26 klystrons in the XFEL represent the largest power consumer of the accelerator facility. The beam energy is usually 14 GeV, but a few weeks a year, lower and higher beam energies are also produced. For example, 11.5 and 16.3 GeV. Until mid-2022, the modulator voltages were set so that enough RF power for 16.3 GeV beam energy could be provided at all times. In order to save energy, the modulator voltages will now be lowered to a sufficient level for beam energies of ≤ 14 GeV. In this way, the previous power consumption of the modulators of 5 MW can be reduced up to 1 MW depending on the operation mode. Over the course of a year, this will save several GWh of energy. In the following, the relationship between the output voltage and the power consumption of the modulators is described. Afterwards, it is reported how the power consumption was reduced in various operating conditions in 2022.

Nb$_{3}$Sn SRF Photogun High Power Test at Cryogenic Temperatures

Superconducting RF (SRF) photoguns are emerging as promising candidates to produce highly stable electrons for Ultra fast Electron Diffraction/Microscopy (EUD/UEM) applications due to the ultrahigh shot-to-shot stability compared to room temperature RF photoguns. SRF technology was prohibitively expensive for industrial use until two recent advancements: Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn [1] and conduction cooling [2], [3]. SRF gun can provide a CW operation capability while consuming only several Watts of RF power which eliminates the need of an expensive high power RF system and saves a facility footprint. Euclid is developing a continuous wave (CW), 1.5-cell, MeV-scale SRF conduction cooled photogun operating at 1.3 GHz. In this paper, we present first high power results of the gun covered with Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn.

Active control of amplitude and phase of high-power RF systems in EAST ICRF heating experiments

The EAST ICRF system operating space has been extended in power and phase control with a low-level RF system for the new double-strap antenna. Then the multi-step power and periodic phase scanning experiment were conducted in L-mode plasma, respectively. In the power scanning experiment, the stored energy, radiation power, plasma impedance and the antenna's temperature all have positive responses during the short ramp-ups of PL,ICRF. The core ion temperature increased from 1 keV to 1.5 keV and the core heating area expanded from |Z|≤5cm to |Z|≤10cm during the injection of ICRF waves. In the phasing scanning experiment, in addition to the same conclusions as the previous relatively phasing scanning experiment, the superposition effect of the fluctuation of stored energy, radiation power and neutron yield caused by phasing change with dual antenna, resulting in the amplitude and phase shift, was also observed. The active control of RF output facilitates the precise control of plasma profiles and greatly benefits future experimental exploration.

Status and Progress of the High-Power RF System for High Energy Photon Source

Status and Progress of the High-Power RF System for High Energy Photon Source

European XFEL High-Power RF System - the First 4 Years of Operation

European XFEL High-Power RF System - the First 4 Years of Operation

Test and operation of high-power RF system for KSTAR helicon current drive system

The helicon current drive system for the efficient off-axis current drive of KSTAR is currently being upgraded with 476 MHz, 1.2 MW klystrons and a new high-voltage power supply (HVPS). Four klystrons, which were used in PEP-II, were transferred to NFRI from the Stanford Linear Accelerator Center. Each klystron can generate 1.2 MW of CW RF power at 476 MHz with an 84 kV 24 A beam. Two klystrons will be powered in parallel using a single pulse step modulator HVPS with a rating of 92 kV and 64 A. Herein, a detailed description of the klystron test setup and results obtained during its test is presented. A high-power test of the klystrons is performed, wherein an RF power of 620 kW is generated by a 70 kV and 18.8 A beam.

Application of a drift compensation low-level radio frequency system based on time-multiplexing pick-up/reference signals.

The high accuracy, low drift low-level radio frequency (LLRF) system is essential for the long-term stability of the accelerator RF and the acquirement of low emittance, high intensity electron beams. A time-multiplexing pick-up/reference signal based LLRF system is proposed to deal with the component temperature related phase drift and has been deployed and applied at the Xi'an Gamma-ray Light Source (XGLS) injector. The long term dual-receiver out-of-loop stability experiments with a continuous wave laser based phase reference distribution system (PRDS) show that the LLRF system can achieve ∼40 fs Root-Mean-Square (rms) phase accuracy and 51 fs/52 fs peak-peak drift (in 7 days/17 h with the high power RF system, respectively) while the reference phase varies both ∼30 ps. An ∼4 h beam-based experiment has also been conducted to evaluate the overall performance of the whole XGLS timing and synchronization system, which shows that the PRDS, LLRF system, high power RF system, and laser oscillator laser-RF synchronization system can keep long-term phase stability.

Review of the JET ILA scattering-matrix arc detection system

Arc detection is an essential protection system for high power RF systems. It is commonly realised by monitoring the Voltage Standing Wave Ratio (VSWR) in the transmission lines. The JET ILA is a load-tolerant ICRF antenna with a low impedance section, for which the standard VSWR protection is ineffective.The Scattering-Matrix Arc Detection (SMAD) was proposed and implemented on JET to protect the low-impedance section around the T-junction against arcing. It is based on a consistency check of the RF signals around this section using a table of coefficients obtained from RF modelling.The paper reviews the SMAD principle, its commissioning on JET and the latest improvements to the system. It shows an example of operation and the time response of the system is analysed. The latest improvements have increased the robustness and reliability of SMAD, making it a choice of arc detection system for critical sections on existing and future RF systems.

High power RF system for transverse deflecting structure XFEL TDS INJ

The high power RF system (HPRF) is designed for RF feeding of the transverse deflecting structure of the transverse deflecting system XFEL TDS System INJ of the European X-ray Free Electron Laser. The HPRF system includes klystron, waveguide ceramic windows, directional couplers, waveguide vacuum units, spark detector and waveguide line. Operating frequency is 2997.2 MHz. Peak input power is up to 3 MW. The HPRF system has been developed, manufactured and assembled in the XFEL Injector building. The total length of the waveguide line is 55 m from the klystron at the -5 floor to the transverse deflecting structure at the -7 floor. All designed RF parameters have been obtained experimentally at low RF power level.

A new slip stacking RF system for a twofold power upgrade of Fermilab׳s Accelerator Complex

Fermilab׳s Accelerator Complex has been recently upgraded, in order to increase the 120GeV proton beam power on target from about 400kW to over 700kW for NOνA and other future intensity frontier experiments. One of the key ingredients of the upgrade is the offloading of some Main Injector synchrotron operations – beam injection and RF manipulation called “slip stacking” – to the 8GeV Recycler Ring, which had until recently been used only for low-intensity antiproton storage and cooling. This required construction of two new 53MHz RF systems for the slip-stacking manipulations. The cavities operate simultaneously at Vpeak≲150kV, but at slightly different frequencies (Δf=1260Hz). Their installation was completed in September 2013. This paper describes the novel solutions used in the design of the new cavities, their tuning system, and the associated high power RF system. First results showing effective operation of the RF system, beam capture and successful slip-stacking in the Recycler Ring are presented.

Normal conducting linac designs for low beam loading

To drive future X-ray FELs, normal-conducting linacs with a wide range of rf are being considered. In this paper, we present accelerator structure and high power rf system designs at three rf (2.856GHz, 5.712GHz and 11.424GHz) that are optimized for single bunch and multi-bunch linac operation with very low beam loading. General scaling laws for the main linac parameters are derived to serve as guidelines to optimize such linacs at other frequencies. The linac costs at the three rf are also discussed. High rf linacs are shown to provide compact, low cost and reasonably efficient drivers for X-ray FELs.

Performance and Operation Results of the RF Systems for the KEK B-Factory

KEK B-Factory (KEKB) was terminated in 2010 after achieving the world record luminosity of 2.11 × 1034 cm−2s−1. This paper describes the design features, performance, and operation results of the KEKB RF systems, which include a lot of original RF technologies and methods to store an electron/positron beam over 1 A stably. To cope with beam instabilities caused by large beam currents, two new types of normal and superconducting (SC) cavities with large stored energy were developed and successfully operated. For a new beam colliding scheme called crab crossing, two SC crab cavities were introduced and boosted the peak luminosity. Performance of these cavities is reported, along with the lowlevel and high-power RF systems, and the cryogenic system for the SC cavities. The status of the RF system upgrade towards SuperKEKB, which aims at a luminosity of 8.0 × 1035 cm−2s−1, is briefly described. © The Author(s) 2013. Published by Oxford University Press on behalf of the Physical Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Disclaimer: Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department. Copyright © 2013 The Physical Society of Japan Other Oxford University Press sites: Oxford University Press

A design study on high power RF system for the TARLA facility of TAC

The Turkish Accelerator and Radiation Laboratory in Ankara (TARLA) is a superconducting electron linac based IR FEL and Bremsstrahlung facility and it is under construction in Ankara as the first facility of the Turkish Accelerator Center (TAC) Project. TARLA will compose of two optical cavity systems to produce oscillator FEL in infrared region (2–250μm) and also Bremsstrahlung radiation to be used in basic and applied sciences.In this study, main parameters of TARLA's high power RF and power transmission line systems are defined and a 20kW RF solid state power amplifier is optimized.

Phase space analysis of multipactor saturation in rectangular waveguide

In certain high power RF systems multipactor cannot be avoided for all operating points, but its existence places limits on performance, efficiency, lifetime, and reliability. As an example multipactor in the input couplers of superconducting RF cavities can be a major limitation to the maximum RF power. Several studies have concentrated on rectangular waveguide input couplers which are used in many light sources. Most of these studies neglect space charge assuming that the effect of space charge is simply to defocus the electron bunches. Modelling multipactor to saturation is of interest in determining the performance of waveguide under a range of conditions. Particle-in-cell modelling including space charge has been performed for 500 MHz half-height rectangular waveguide. Phase plots of electron trajectories can aid understanding the processes taking place in the multipactor. Results strongly suggest that the multipacting trajectories are strongly perturbed by space charge causing the electrons to transition from two-surface to single-surface trajectories as the multipactor approaches saturation.

Design optimization of a C-band traveling-wave accelerating structure for a compact X-ray Free Electron Laser facility

The research and development of a C-band (5712 MHz) high gradient traveling-wave accelerating structure has been in progress for some years at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. Conceptual design of the accelerating structure has been accomplished, and verified by cold testing an experimental model. The first prototype structure is now ready for high RF power tests. To develop a robust high gradient C-band accelerating structure, an optimized constant gradient structure with a 4π/5 operating mode for future X-ray Free Electron Laser facilities is proposed in this paper. This scheme can improve the breakdown stability and beam quality. The high power RF system, four operating modes and disk iris shape are analyzed and optimized.

60kV, 10Amp DC power supply multiple input control and monitoring provision for the operation of various high power RF generation systems

A 60 kV, 10 A DC power supply is used for testing of high power RF and microwave tubes e.g. Klystron, Gyrotron. Two 500 kW, 3.7 GHz klystrons, and one 82.6 GHz Gyrotron are located in SST1 Hall where as 200 kW; 28 GHz Gyrotron is located in Aditya Hall. The same power supply is required to operate, control and monitor various systems at different locations with easy change over from one system to other as per experimental requirements.An off line, control change over system, is designed to accomplish the above requirements, with control panels installed at desired different locations. The input (0 to 11 kV) A.C. voltage to power supply is given from a motorized voltage variation system (VVS). The control panels provide indication of A.C. input voltage to power supply from 11 kV potential transformers of VVS. In addition, the control panel is provided with 11 kV circuit breaker status indication and control i.e. Emergency OFF switch. The control panels are designed and developed indigenously which are successfully installed and are in continuous use for the safe and easy operation of different high power rf systems from the same DC power supply.The paper presents the design of the controls, monitoring and indications. Safety aspects of the system are also highlighted.

Steady state operation and control experiments on Tore Supra

The main programme of the Tore Supra tokamak is to investigate the route towards long pulse plasma discharges. Tore Supra is thus equipped with a superconducting toroidal magnet, a full set of actively cooled plasma facing components, and a heating and current drive capability based on high power RF systems connected to actively cooled antennas. After pioneering investigations using the LHCD system alone (2 min and zero loop voltage discharges), recent efforts have concentrated on finding scenarios to couple the two RF heating systems in order to perform high power, long duration discharges. To this aim, 6.5 MW, 25 s as well as 4 MW, 60 s discharges have been successfully achieved. At these high power levels, the plasma-wall interaction becomes a critical issue, and recycling fluxes must be controlled to maintain density and to avoid plasma contamination. All these results contributed to the validation of the upgrade of the Tore Supra first wall components (CIEL project) scheduled for 2000.

Measuring the DTV signal

Since the adoption of the FCC mask for out-of-band emissions in its Sixth Recon Order, broadcasters and equipment manufacturers alike have been struggling to understand the implications not only from a performance standpoint, but also from a compliance measurement standpoint. The quality of the in-band signal is insured by measurements that bear little resemblance to what is presently done for analog television. The physical limitations of standard test equipment and the inaccuracies of broadband samples from high power RF systems make demonstrating out of band compliance very difficult. This paper explains methods of measurement used by Thomcast Communications to verify compliance of a transmission system from "DC to light." The paper gives an explanation of the technical limitations of existing equipment and methods used by broadcasters in NTSC transmission. It also offers real solutions to the measurement difficulties.

Rise time analysis of pulsed klystron-modulator for efficiency improvement of linear colliders

In linear accelerators, the periods during the rise and fall of a klystron-modulator pulse cannot be used to generate RF power. Thus, these periods need to be minimized to get high efficiency, especially in large-scale machines. In this paper, we present a simplified and generalized voltage rise time function of a pulsed modulator with a high-power klystron load using the equivalent circuit analysis method. The optimum pulse waveform is generated when this pulsed power system is tuned with a damping factor of ∼0.85. The normalized rise time chart presented in this paper allows one to predict the rise time and pulse shape of the pulsed power system in general. The results can be summarized as follows: The large distributed capacitance in the pulse tank and operating parameters, V s× T p , where V s is load voltage and T p is the pulse width, are the main factors determining the pulse rise time in the high-power RF system. With an RF pulse compression scheme, up to ±3% ripple of the modulator voltage is allowed without serious loss of compressor efficiency, which allows the modulator efficiency to be improved as well. The wiring inductance should be minimized to get the fastest rise time.

High performance FEL for the proposed PEARL research platform

A consortium of Pacific Rim institutions is proposing to construct a sea-going facility based on a free electron laser lidar. Called PEARL, for Pan-Oceanic Environmental and Atmospheric Research Laboratory, the platform will be a powerful tool for atmospheric and marine research on topics involving the global environment and US and international security matters. Numerous security issues, and understanding the impact of human activities on the environment, require observing wide varieties of chemical compounds in situ and often at considerable range from the observer. Optical remote sensing, with instruments such as light detection and ranging (lidar) systems, have the potential for the necessary studies, but their performance has heretofore been restricted by low power and limited wavelength tunability. In contrast, the FEL for the PEARL platform will have continuous wavelength tunability from 250 nm to 20 μm and the power to project beams over large ocean expanses or basin-sized land regions. This paper summarizes the principal features of the PEARL FEL, in the context of PEARL's missions. Directly descended from the MkIII, the PEARL FEL will incorporate highly-traceable developments including a photoinjector, high current linac, high power RF system, and several features to increase efficiency. The challenges of giving the mobility needed for environmental and defense remote sensing applications to an instrument as large and heavy as a FEL will be met by mounting the laser in a large ship. Using a former US Naval vessel and existing FEL and optical apparatus result in an estimated cost less than one-fourth that of all-new construction.