Design optimization of 3.9 GHz fundamental power coupler for the SHINE project

The third harmonic superconducting cryomodule is being designed for the Shanghai High repetition rate XFEL and Extreme light facility(SHINE)project,which is under construction.In contrast to the European X-ray Free Electron Laser(E-XFEL)project,the 3.9 GHz cryomod-ules in the SHINE project will operate in the continuous wave regime with higher radio frequency average power for both cavities and couplers.We propose a 3.9 GHz fundamental power coupler with an adjustable antenna length,for satisfying the SHINE project requirements.Here,we describe the 3.9 GHz fundamental power cou-pler's design considerations and power requirements for various operating modes of the SHINE Linac.We also present the results of the radio frequency simulation and optimization,including the studies on multipacting and thermal analysis of the proposed 3.9 GHz coupler.     

Room-temperature test system for 162.5 MHz high-power couplers

Fundamental power couplers are crucial components for feeding radio frequency power to accelerating cavities. Couplers must be tested and conditioned on a room-temperature test stand to evaluate and potentially improve their performance before being installed in an accelerating cavity. A new test system has been designed and is under construction at the institute of modern physics.For this test system, multiple conditioning modes, including the pulse mode, CW mode, and amplitude-sweeping mode, have been embedded in the low-level radio frequency system of the test stand. All of these conditioning modes can be run manually or automatically. In addition, a novel test cavity is proposed and has been designed, which facilitates non-contact conditioning and a multi-purpose test stand.     

Design and preliminary test of a 105/140 GHz dual-frequency MW-level gyrotron

A dual-frequency (105/140 GHz) MW-level continuous-wave gyrotron was developed for fusion application at Institute of Applied Electronics, China Academy of Engineering Physics. This gyrotron employs a cylindrical cavity working in the TE18,7 mode at 105 GHz and the TE24,9 mode at 140 GHz. A triode magnetron injection gun and a built-in quasi-optical mode converter were designed to operate at these two frequencies. For the proof-test phase, the gyrotron was equipped with a single-disk boron nitride window to achieve radio frequency output with a power of ∼500 kW for a short-pulse duration. In the preliminary short-pulse proof-test in the first quarter of 2021, the dual-frequency gyrotron achieved output powers of 300 kW at 105 GHz and 540 kW at 140 GHz, respectively, under 5 Hz 1 ms continuous pulse-burst operations. Power upgrade and pulse-width extension were hampered by the limitation of the high-voltage power supply and output window. This gyrotron design was preliminarily validated.     

Investigation on the multi-hole directional coupler for power measurement of the J-TEXT ECRH system

Power measurement is necessary for an electron cyclotron resonance heating (ECRH) system. The directional coupler method has been put forward to monitor high-power microwave from gyrotrons in real time. A multi-hole directional coupler has been designed and manufactured for the 105 GHz/500 kW ECRH system on the J-TEXT tokamak. During the design process, we established the relationships between hole parameters and coupling characteristics based on the multi-hole coupling method and small-hole coupling theory. High-power tests have been carried out. The results indicated the reasonability of the theoretical design and practicality of the fabricated directional coupler. Sources of test errors have been discussed in detail, and the influences of spurious modes on the directional couplers have been emphatically analyzed.     

Experimental study of a single tube high RF power amplifier for ICRF heating system

A concept of a single tube high RF power amplifier was developed for ion cyclotron range of frequency (ICRF) plasma heating system. In the concept, a tetrode was used with a grounded cathode and input power to drive a control grid of the tetrode was provided by a switching circuit. As the new amplifier arrangement can eliminate a low power (10 kW level) and an intermediate power (100 kW level) tetrode amplifiers, their high voltage DC (HVDC) power supplies, and control and monitor system for these amplifiers and HVDC power supplies in a conventional high RF power source of the ICRF heating system, this new high RF power source is more flexible on frequency change and more mechanically reliable than the conventional one. A test amplifier composed of the tetrode and a field effect transistor (FET) switching circuit was constructed. The FET switching circuit was so compact that it could be mounted close to the tetrode socket. The maximum output RF power of 8.5 kW was obtained with a plate efficiency of 82% at 70 MHz. The feasibility of the single tube high RF power amplifier was experimentally proved. The plate efficiency of 82% could not be explained by the standard class-C amplification but by high efficiency amplification under assumptions of a flat-topped plate current pattern and double resonance of an output cavity at the fundamental frequency and the third higher harmonic frequency.     

Power losses caused by longitudinal HOMs in 1.3-GHz cryomodule of SHINE

Shanghai high-repetition-rate XFEL and extreme light facility(SHINE), the first hard XFEL based on a superconducting accelerated structure in China, is now under development at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. In this paper,power losses caused by trapped longitudinal high-order modes(HOM), steady-state loss, and transient loss generated by untrapped HOMs in the 1.3-GHz SHINE cryomodule are investigated and calculated. The heat load generated by resistive wall wakefields is considered as well. Results are presented for power losses of every element in the 1.3-GHz cryomodule, caused by HOM excitation in the acceleration RF system of the continuouswave linac of SHINE.     

中国散裂中子源快周期同步加速器磁铁电源系统的研究

目前正在进行可行性研究的中国散裂中子源的主体结构是1台强流质子同步加速器。该加速器的一期目标为注入能量70MeV、引出能量1.6GeV、束流功率100kW、循环工作频率25Hz。文章阐述系统总体结构的设计原则以及二极磁铁（B）和四极磁铁（Q）磁场的跟踪误差要求。     

SHINE腔式BPM系统射频信号调理前端研制

基于低温超导直线加速器的上海硬X射线自由电子激光装置（SHINE）需1个分辨率可达200 nm的束流位置测量系统,以实现电子束与光子束在波荡器中的紧密相互作用和能量交换。现已研制的束流位置测量系统不能完全满足上述要求,为此,基于对关键技术指标的分配,设计研制了一个由C波段腔式探头、低噪声系数的单路下变频至低中频的射频信号调理前端以及专用数字信号束流位置处理器构成的CBPM系统样机。而作为连接腔式探头和数字信号采集电子学之间的桥梁,射频信号调理前端（radio frequency front end, RF前端）的结构和性能也直接决定了CBPM系统的性能。本文从SHINE对CBPM系统的整体需求为出发点,分析了系统对射频信号调理前端的指标分配,提出了一种放大器开关切换型RF前端的方案设计,并成功搭建了1套可模拟束流条件的离线全锁相采样测试平台。此外,在上海软X射线自由电子激光装置（SXFEL）中搭建了测试平台并完成了射频信号调理前端的带束性能评估,束流实验结果表明,在束团电荷量为100 pC、系统动态范围在±100 μm的条件下,采用腔式探头射频信号一分二的评估方法,位置分辨率可达71 nm,优于设计指标需求。     

DG系列大功率工业辐照电子加速器

中国科学院近代物理研究所成功研制了DG系列中频变压器型工业电子加速器,其中DG-2.5型加速器能量范围1.0-2.5 MeV,最大束流功率90 kw,束流扫描有效宽度1000 mm,适用于各种辐照领域;DG-1.2型能量范围0.8-1.2 MeV,最大功率50 kw;这两种型号加速器均通过了长时间测试,工作稳定、故障率低,采用计算机自动控制,并可与束下传动系统连锁,完全达到了工业应用的标准.     

Experimental Investigation on Electromagnetic Attenuation by Low Pressure Radio-Frequency Plasma for Cavity Structure

This paper reports on an experiment designed to test electromagnetic(EM)attenuation by radio-frequency(RF)plasma for cavity structures.A plasma reactor,in the shape of a hollow cylinder,filled with argon gas at low pressure,driven by a RF power source,was produced by wave-transmitting material.The detailed attenuations of EM waves were investigated under different conditions:the incident frequency is 1-4 GHz,the RF power supply is 13.56 MHz and1.6~(-3) k W,and the argon pressure is 75-200 Pa.The experimental results indicate that 5-15 d B return loss can be obtained.From a first estimation,the electron density in the experiment is approximately(1.5-2.2)×1016m~(-3)and the collision frequency is about 11~(-3)0 GHz.The return loss of EM waves was calculated using a finite-difference time-domain(FDTD)method and it was found that it has a similar development with measurement.It can be confirmed that RF plasma is useful in the stealth of cavity structures such as jet-engine inlet.     

EAST强流离子源电源系统的初步测试运行

测试NBI大功率强流离子源的综合测试台正在建设,已研制了离子源等离子体发生器电源系统、等离子体电极高压电源及梯度极分压器、抑制极负高压电源等电源系统,以及高压传输线及缓冲器,在测试台上开展了对EAST中性束注入器第一台兆瓦级强流离子源样机进行整体电源系统测试和离子源起弧放电的初步测试,完成了离子源电源系统初步性能测试及...     

Varying Electron Cyclotron Resonance Heating on the Levitated Dipole Experiment

Plasmas in the Levitated Dipole Experiment (LDX) are formed and sustained currently via two electron cyclotron resonance heating (ECRH) sources: 2.5 kW at 2.45 GHz and 2.5 kW at 6.4 GHz. An important topic being investigated is how varying the ECRH affects the confinement and stability of the plasma. We report the results of using different operational combinations of our RF sources, such as varying the power composition, changing the power levels, and sequencing of the onset time.     

Design, fabrication and testing of UHV compatible high power RF devices for lower hybrid current drive system on SST-1 tokamak

Maintaining plasma current under steady state conditions is one of the most important pre-requisites for a tokamak-based reactor. Lower hybrid current drive (LHCD) system aims to drive tokamak plasma current by means of RF power. The LHCD system on SST-1 tokamak is based on two 500 kW, CW klystrons operating at 3.7 GHz. A waveguide transmission line transmits power from source to the antenna. A phased array waveguide antenna is used to couple power to the plasma. The antenna side of the transmission line is placed inside the tokamak vacuum vessel. The design and fabrication of this In-Vessel system has to satisfy the demands of high power RF as well as ultra high vacuum (UHV) compatibility. This paper describes some of the critical UHV compatible In-Vessel RF devices, their design, fabrication, and test results.     

Venturi tube application in high power test of the SRF module

In the superconducting RF module, the dissipation power of the niobium cavity is an important parameter. In the Superconducting radio frequency (SRF) module’s acceptance test at Shanghai Synchrotron Radiation Facility (SSRF), the Venturi tube is used to measure the quality factor of SRF cavity at 4.2 K. During the test, the venturi tube is be calibrated by increasing heat load with internal heater. In this paper, the horizontal test principle and venturi effect are briefly introduced. The authors find out a...     

New thermal optimization scheme of power module in solid-state amplifier

The new 1 kW power module for ADS project needs the optimization of cooling design including water flow and tunnel layout, and the water flow of three tons per hour was chosen to be a goal for a 20 kW power source.According to analysis from the insertion and integrated loss, about 24 modules were integrated into the rated power. Thus, every module has a cooling flow of 2.1 L/min for RF heat load and power supply loss, which is very hard to achieve if no special consideration and techniques. A new thermal simulation method was introduced for thermal analysis of cooling plate through CST multi-physics suite,especially for temperature of power LDMOS transistor.Some specific measures carried out for the higher heat transfer were also presented in this paper.     

Development of a helicon-wave excited plasma facility with high magnetic field for plasma-wall interactions studies

The high magnetic field helicon experiment system is a helicon wave plasma(HWP)source device in a high axial magnetic field(B_0)developed for plasma–wall interactions studies for fusion reactors.This HWP was realized at low pressure(5?×?10~(-3)?-?10 Pa)and a RF(radio frequency,13.56 MHz)power(maximum power of 2 k W)using an internal right helical antenna(5 cm in diameter by 18 cm long)with a maximum B_0of 6300 G.Ar HWP with electron density~10~(18)–10~(20)m~(-3)and electron temperature~4–7 e V was produced at high B_0 of 5100 G,with an RF power of 1500 W.Maximum Ar~+ion flux of 7.8?×?10~(23)m~(-2)s~(-1)with a bright blue core plasma was obtained at a high B_0 of 2700 G and an RF power of 1500 W without bias.Plasma energy and mass spectrometer studies indicate that Ar~+ion-beams of 40.1 eV are formed,which are supersonic(~3.1c_s).The effect of Ar HWP discharge cleaning on the wall conditioning are investigated by using the mass spectrometry.And the consequent plasma parameters will result in favorable wall conditioning with a removal rate of 1.1?×?10~(24)N_2/m~2 h.     

Gyrotrons for ECH applications

Gyrotron oscillators have served as effective sources for electron cyclotron heating (ECH) applications in the area of magnetic confinement fusion. Successful development programs at frequencies at 28 GHz, 60 GHz, and 140 GHZ, have led to the availability of wide-range gyrotron sources with high-average-power capabilities. Since 1975, over 100 pulsed and CW gyrotrons with typical power levels of 200 kW at frequencies ranging from 28–106 GHz have been used by various fusion laboratories. Present development activity is aimed at providing sources that will generate power levels up to 1 MW CW at frequencies in the range 100–140 GHz for the ECH experiments that are currently being planned. Initial experimental efforts in this area have verified many of the concepts to be employed in forthcoming 1-MW CW test vehicles. Source requirements, that are even more formidable, are foreseen for the next generation magnetic fusion facilities. Frequencies ranging from 200–300 GHz with power generation capabilities of 1–2 MW CW per tube are being considered for these future applications. To this end, various gyrotron designs have been conceived that address these demanding specifications.     

Thermal and Structural Analysis and its Effect on Beam-Wave Interaction for 170-GHz, 1-MW Gyrotron Cavity

In this paper thermal and structural analysis for 170 GHz, 1 MW gyrotron interaction cavity and the effect of structural deformation on beam wave interaction is presented. Finite element analysis codes ANSYS has been used for the thermal and structural analysis. Electromagnetic simulator-MAGIC, a Particle-in-Cell (PIC) code, has been used to carry out the effect of the radial expansion of the interaction cavity on beam wave interaction. The change in output power and resonant frequency for operating mode TE_34,10 due to thermal expansion is 10 kW and 0.07 GHz, respectively. These values are under the tolerance limit of power and frequency of the gyrotron. The major variation is found in the power growth stability time.     

Formation of Low Aspect Ratio Torus Equilibria by ECH in the LATE Device

By ECH under a steady By field, a closed field equilibrium of a low aspect ratio as low as R/a = 1.4 is spontaneously formed in the LATE device. After the spontaneous formation, the plasma current has increased further up to Ip = 7.2 kA by 2.45 GHz, 30 kW and Ip = 11 kA by 5 GHz, 120 kW, by increasing the microwave power with a slow ramp of By for the equilibrium of the plasma loop at larger currents. Both amount to 12% of the total toroidai coil current. ECH/ECCD at 2nd harmonic resonance of EBW supports the plasma. An outline of the theoretical considerations for the formation process is presented.