Reference Design of ICRF Antenna for EAST

An antenna array suitable for plasma heating and current drive has been designed for the ion cyclotron resonance frequency range （ICRF） heating on the EAST superconducting tokamak. The ICRF heating is planned to operate in a frequency range of 30 MHz to 80 MHz and hence the antenna geometry is optimized for 55 MHz. The design is based on the conventional strap antenna element. The coupling properties of the antenna are calculated with a slab model of the plasma for the antenna simulation. The coupling code is extended for the analysis of the toroidal antenna array separated by septa.     

EAST ICRF天线驱动结构改进设计

针对ICRF天线原有的驱动结构由于无自锁而导致天线移动过程中无法精确定位的缺点,给出了两种新的驱动结构设计方案,两种方案主要由步进电机和涡轮蜗杆减速器组成,均具有启动速度慢,推、拉力大,能精确定位的特点。在设计过程中,对两种驱动结构的启动转矩、丝杠的强度和稳定性进行了校核,通过理论计算分析,两种驱动结构设计均满足设计要求。整个驱动结构改进设计方案和方法可为其他同类装置提供有益的借鉴。     

EAST离子回旋波加热快速阻抗匹配系统的研究

离子回旋波加热是EAST装置最重要的辅助加热方法,在实验中获得了明显的加热效果。射频功率源与天线负载之间阻抗匹配才能保证最大的加热功率输出。在射频加热实验中,等离子体参数的改变将会引起天线负载阻抗的快速变化,为应对这一情况研制出了快速阻抗匹配系统。本文采用解析法和计算机仿真相结合的分析方式,研制了该阻抗匹配系统的铁氧体匹配支节,并对其性能进行了测试。测试结果表明,快速阻抗匹配系统的时间响应速度明显优于传统匹配方式的,可作为实时匹配的候选者。     

EASTICRF天线真空馈口电特性评估

本文对EASTICRF天线真空馈口进行了相关的电特性分析,获得了真空馈口电场分布、电势分布,以及电压驻波比随加热频率的变化情况,分析结果验证了真空馈口的可行性和合理性,并为真空馈口电特性评估提供理论依据。另外,在相同条件下,运用相同的方法对一种新型结构的真空馈口进行了相同的电特性分析,分析结果验证了新型结构真空馈口的优越性。     

Power Compensation for ICRF Heating in EAST

The source system covering a working frequency range of 24 MHz to 70 MHz with a total maximum output power of 12 MW has already been fabricated for Ion Cyclotron Range of Frequency(ICRF) heating in EAST from 2012. There are two continuous wave(CW) antennas consisting of four launching elements each fed by a separate 1.5 MW transmitter. Due to the strong mutual coupling among the launching elements, the injection power for launching elements should be imbalance to keep the k||(parallel wave number) spectrum of the launcher symmetric for ICRF heating. Cross power induced by the mutual coupling will also induce many significant issues,such as an uncontrollable phase of currents in launching elements, high voltage standing wave ratio(VSWR), and impedance mismatching. It is necessary to develop a power compensation system for antennas to keep the power balance between the feed points. The power balance system consists of two significant parts: a decoupler and phase control. The decoupler helps to achieve ports isolation to make the differential phase controllable and compensate partly cross power. After that, the differential phase of 0 or π will keep the power balance of two feed points completely. The first power compensation system consisting of four decouplers was assembled and tested for the port B antenna at the working frequency of 35 MHz. With the application of the power compensation system, the power balance, phase feedback control, and voltage standing wave ratio(VSWR) had obviously been improved in the 2015 EAST campaign.     

Recent ICRF coupling experiments on EAST

Recent ion cyclotron resonance frequency(ICRF) coupling experiments for optimizing ICRF heating in high power discharge were performed on EAST. The coupling experiments were focus on antenna phasing and gas puffing, which were performed separately on two ports of the ion cyclotron resonance heating(ICRH) system of EAST. The antenna phasing was performed on the I-port antenna, which consists of four toroidally spaced radiating straps operating in multiple phasing cases; the coupling performance was better under low wave number ∣k_‖∣(ranging from 4.5 to 6.5). By fuelling the plasma from gas injectors, placed as uniformly spaced array from top to bottom at each side limiter of the B-port antenna, which works in dipole phasing, the coupling resistance of the B-port antenna increased obviously.Furthermore, the coupling resistance of the I-port antenna was insensitive to a smaller rate of gas puffing but when the gas injection rate was more than a certain value(1021 s~(-1)), a sharp increase in the coupling resistance of the I-port antenna occurred, which was mainly caused by the toroidal asymmetric boundary density arising from gas puffing. A more specific analysis is given in the paper.     

Current Status of ICRF Heating Experiments on EAST

Radio frequency (RF) heating in the ion cyclotron range of frequencies (ICRF) is one of the primary auxiliary heating methods for EAST. The ICRF system provides 6 MW power in primary phase and will be capable of 10 MW later. Three 1.5 MW ICRF systems in a frequency range of 25 to 70 MHz have already been in operation. The ICRF heating launchers are designed to have two current straps with each driven by a RF power source of 1.5 MW. In this paper a brief introduction of the ICRF heating system capability in EAST and the preliminary results in EAST are presented.     

Tunable biasing magnetic field design of ferrite tuner for ICRF heating system in EAST

Ion cyclotron range of frequency(ICRF) heating has been used in tokamaks as one of the most successful auxiliary heating tools and has been adopted in the EAST. However, the antenna load will fluctuate with the change of plasma parameters in the ICRF heating process. To ensure the steady operation of the ICRF heating system in the EAST, fast ferrite tuner(FFT) has been carried out to achieve real-time impedance matching. For the requirements of the FFT impedance matching system, the magnet system of the ferrite tuner(FT) was designed by numerical simulations and experimental analysis, where the biasing magnetic circuit and alternating magnetic circuit were the key researched parts of the ferrite magnet. The integral design goal of the FT magnetic circuit is that DC bias magnetic field is 2000 Gs and alternating magnetic field is±400 Gs. In the FTT, E-type magnetic circuit was adopted. Ferrite material is Nd Fe B with a thickness of 30 mm by setting the working point of Nd Fe B, and the ampere turn of excitation coil is 25 through the theoretical calculation and simulation analysis. The coil inductance to generate alternating magnetic field is about 7 m H. Eddy-current effect has been analyzed, while the magnetic field distribution has been measured by a Hall probe in the medium plane of the biasing magnet. Finally, the test results show the good performance of the biasing magnet satisfying the design and operating requirements of the FFT.     

Design of the Vacuum Feedthrough for the EAST ICRF Antenna

Detailed design of the vacuum feedthrough for the Ion Cyclotron Radio Frequency (ICRF) antenna in EAST, along with an electro-analysis and thermal structural analysis, is presented. The electric field, the voltage stand wave ratio (VSWR) and the stresses in the vacuum feedthrough are studied. A method using the rings of oxygen-free copper as the cushion and macro-beam plasma arc welding is applied in the assembly to protect the ceramic from being damaged during welding. The vacuum leak test on the prototype of vacuum feedthrough is introduced.     

EASTICRF天线电流带电磁分析

为了实现EAST托卡马克1000s以上的稳态先进模式运行的最终物理目标,两电流带双环共振(RDL)离子回旋共振（ICRF）天线被选择用来加热,电流带是ICRF天线关键部件,它通过近场区的耦合把能量传输到等离子体中。本文通过有限元方法对电流带在等离子体破裂和等离子体垂直位移事件两种工况下进行了电磁计算,给出了电流带感应电流密度大小分布情况、磁感应强度大小分布情况以及电流带所受的电磁力。利用电流带所受的电磁力作为载荷对电流带进行了结构分析,分析结果为验证电流带结构的可行性提供理论依据,分析方法对未来更高功率的ICRF天线电流带进行电磁分析具有一定的借鉴价值。     

EASTICRF天线真空馈口热-结构分析

真空馈口是ICRF天线中的一个重要部件,它对ICRF天线起真空密封作用。鉴于真空馈口的重要性和安全性,运用有限元方法对两种形式的真空馈口进行了热和热-结构分析,给出了两种形式的真空馈口上的温度分布和应力分布。结果显示：镀银的真空馈口上的温度变化和应力均小于未镀银的真空馈口上的温度变化和应力,但两种形式的真空馈口上的应力均小于材料的许用应力。分析结果验证了真空馈口结构设计的可行性和安全性。     

Water-cooling effects on the high-voltage and long-pulse capabilities of the KSTAR ICRF antenna

A new ICRF antenna originating from the prototype antenna was constructed for the KSTAR tokamak in 2002. The performance of the antenna was experimentally estimated at the RF test stand without a plasma. Recently three series of RF tests were performed at a frequency of 30 MHz; without any cooling, with a water-cooling for only the antenna, and with a water-cooling of the antenna and the transmission line connected to the antenna. In the tests, a half of the current strap was connected to a RF source via a matching circuit with the other half one connected to an open terminated coaxial line, and the other three straps were shorted at the input ports. During the RF pulse, the temperatures at several positions of the antenna cavity wall were measured by embedded thermocouples and the temperature profile of the front face of the antenna was measured by an IR camera. The line voltage, forward and reflected powers, and the RFTC pressure were also measured. The water-cooled antenna showed several enhanced performances in a comparison with the non-cooled case, and the standoff voltage was significantly increased. By utilizing a water-cooling of the antenna and the transmission line, we achieved a standoff voltage of 41.3 kVp for a pulse length of 300 s, and we could extend the pulse length up to 600 s at a maximum voltage of 35.0 kVp without encountering any problems, which considerably exceeds the design requirements.     

Design of a multi-voltage probe system forICRF antenna coupling resistancemeasurement on EAST

A multi-voltage probe array system is designed to measure the coupling resistance of an ioncyclotron resonance frequency antenna. In the process of the antenna coupling resistance dataextraction, the minimization algorithm, the original Levenberg–Marquardt algorithm, is replacedby the Broyden–Fletcher–Goldfarb–Shanno algorithm to achieve more stable and accurateresults. Moreover, a simple model of the multi-voltage probe array was applied to simulate theperformance of the Kalman filter, and to optimize the distance and position of the probes andprobe number to mitigate the influence of the system noise on the rebuilt results. During theEAST experiment in 2019, a four-voltage probe array was applied to measure the couplingresistance of line 6 during high confined mode discharge. The measurement results by the multi-voltage probe array system and the voltage/current probe pair show a good agreement.     

EASTICRF天线法拉第屏蔽的热-结构分析

在EASTICRF天线中,法拉第屏蔽是ICRF天线中的一个非常重要的部件。实验时,它位于真空室内直接面对等离子体,将承受着很大的热负荷。基于EASTICRF天线法拉第屏蔽结构的安全性,本文利用有限元的方法,首先对热负荷最大的法拉第屏蔽冷却管道在不同水流速下进行热分析,考察在不同水流速工况下法拉第屏蔽冷却管道上的温度分布情况,再通过热 结构耦合方法对法拉第屏蔽冷却管道进行结构分析,了解法拉第屏蔽在不同水流速下的应力大小和分布情况,分析结果为未来EASTICRF天线实验提供理论指导。另外,对法拉第屏蔽冷却管道结构进行了优化改进,并对优化改进后的法拉第屏蔽冷却管道在相同工况下进行了热和热 结构分析,分析结果确定了优化改进后的法拉第屏蔽冷却管道结构的优越性,分析数据为未来法拉第屏蔽冷却管道的优化改进提供理论指导,分析方法为其他同类装置提供有益的参考。     

Design of a New Type of Stub Tuner in ICRF Experiment

In the Ion Cyclotron Range of Frequency(ICRF) heating experiment,impedance matching is of great practical significance,because wide variations in antenna loading are observed within the discharge,in tokamaks operating in H-mode.A sudden decrease in antenna loading accompanying the L-mode to H-mode transition typically occurs on a timescale of a few millisec onds,as does the increase in loading at the H- to L-mode transition.Therefore,it is necessary to match dynamically in the transmission line between the generator output and the antenna input connections[1].A new type of stub tuner being developed utilizes the difference in radio-frequency wavelengths between gas and liquid due to different relative dielectric constants.The impedance matching can be adjusted in realtime in an attempt to track the variations in the antenna loading.Since there are no mechanically moving parts in the short ends of stub,the change can be more convenient and safe,moreover,it can withstand higher voltage without breakdown.this system device will be applied in the HT-7 superconductor Tokamak ICRF experiment.     

Study of Liquid Phase Shifter for ICRF on EAST

A method of current drive with Ion Cyclotron Range of Frequency （ICRF） on Experimental Advanced Superconducting Tokomak （EAST） is described. A variety of liquid silicon oil heights in the phase shifter will bring the phase difference to the current drive. It is found that the current drive can be achieved by using the phase shifter. The liquid phase shifter is one of the impedance matching systems too.     

Design of improved compact decoupler based on adjustable capacitor for EAST-ICRF antenna

The Ion Cyclotron Radio Frequency (ICRF) heating antenna on EAST adopts a decoupling device to constrain power coupling among the radiation straps, which was discovered shortcomings such as long size, poor contact, and etc. In order to improve these weak points, a new type decoupler with terminal-loaded tunable capacitor is designed to replace the previous design. Besides the capability of the tunable admittance parameters of decoupler, the withstand voltage of the capacitor is the most significant consideration for working under high power. Therefore, the theoretical analysis carefully elaborates the capacitor withstand voltage, and the detailed analytical equations and criteria for design are given. After the comparative analysis of theoretical calculation and 3D simulation results, the decoupler design scheme is finalized. The capacitor-loaded decoupler has been successfully adopted for ICRF antenna at port N on EAST, and achieved the optimization of adjacent port isolation from −22 to −58 dB at 37 MHz without plasma to restrict mutual coupling. The new design of the decoupler has greatly improved its compactness and automatic adjustment performance, and could be good solution for the decoupling network of ICRF antennas.     

Thermal analysis and optimization of the EAST ICRH antenna

The ion cyclotron resonance of frequency heating(ICRH) plays an important role in plasma heating.Two ICRH antennas were designed and applied on the EAST tokamak.In order to meet the requirement imposed by high-power and long-pulse operation of EAST in the future,an active cooling system is mandatory to be designed to remove the heat load deposited on the components.Thermal analyses for high heat-load components have been carried out,which presented clear temperature distribution on each component and provided the reference data to do the optimization.Meanwhile,heat pipes were designed to satisfy the high requirement imposed by a Faraday shield and lateral limiter.     

Optimization of the FAST ICRF antenna using TOPICA code

Ion Cyclotron Resonance Heating is one of the most important auxiliary heating systems in most plasma confinement experiments. Because of this, the need for very accurate design of ion cyclotron (IC) launchers has dramatically grown in recent years. Furthermore, a reliable simulation tool is a crucial request in the successful design of these antennas, since full testing is impossible outside experiments. One of the most advanced and validated simulation codes is TOPICA, which offers the possibility to handle the geometrical level of detail of a real antenna in front of an accurately described plasma scenario. Adopting this essential tool made possible to reach a refined design of ion cyclotron radio frequency antenna for the FAST (Fusion Advanced Studies Torus) experiment [1]. Starting from a streamlined antenna model and then following well-defined refinement procedures, an optimized launcher design in terms of power delivered to plasma has been finally achieved. The computer-assisted geometry refinements allowed an increase in the performances of the antenna and notably in power handling: the extent of the gained improvements were not experienced in the past, essentially due to the absence of predictive tools capable of analyzing the detailed effects of antenna geometry in plasma facing conditions. Thus, with the help of TOPICA code, it has been possible to comply with the FAST experiment requirements in terms of vacuum chamber constraints and power delivered to plasma. Once an antenna geometry was optimized with a reference plasma profile, the analysis of the performances of the launcher has been extended with respect to two plasma scenarios. Exploiting all TOPICA features, it has been possible to predict the behavior of the launcher in real operating conditions, for instance varying the position of the separatrix surface. In order to fulfil the analysis of the FAST IC antenna, the study of the RF potentials, which depend on the parallel electric field computation, has been carried out with an exceptional level of detail. Finally, in order to provide a more general overview of the antenna performances, two IC launchers have been simulated to determine their mutual influence, achieving an optimum degree of knowledge about the relevant features of the ion cyclotron heating system inside the FAST tokamak.     

The behavior of HfB2 under neutron irradiation

The experimental advanced superconducting Tokamak has two suits of ion cyclotron radio frequency heating systems, in which the two antennas are of different structures. Their performance is assessed and compared by CST microwave studio. The radiating capacity of antennas and the arcing around them are estimated. The impurity release is analyzed by the radio frequency(RF) potential in the plasma sheath. The simulation results show that the radiating capacity for the folded antenna(I-port) is better than those for the double loops antenna(B-port). However,the folded antenna is worse than the double loops antenna in terms of breakdown. Moreover, the impurity production is relevant to spectrum shaping. The RF potential at(0, π,π, 0) phasing with the peak of spectrum k//= 8.5 m~(-1)is lower than the one with other phases. The impurity is reduced obviously when the folded antenna is powered with(0, π, π, 0) phasing.