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.     

Mitigation of radio frequency sheaths through magnetic field-aligned ICRF antenna design

One of the primary challenges of auxiliary heating of tokamaks in the ion cyclotron range of frequencies (ICRF) is the reduction of impurities associated with ICRF operation. On Alcator C-Mod, a new magnetic field-aligned antenna was optimized for magnetic flux coupling, power handling, and minimized integrated parallel electric field (E_∥). Initial simulations performed using both slab and cylindrical geometry suggested nearly complete cancellation of E_∥ in front of the antenna structure for certain toroidal phasings. Using toroidal models, the cancellation of E_∥ is more modest, suggesting 3-D geometrical effects are important. Using finite element method simulations with a 3-D toroidal cold plasma model, multiple antenna phases were analyzed: [0, π, 0, π], [0, 0, π, π], [0, π, π, 0], [0, 0, 0, 0], [0, π/6, 0, π/6], and [0, π/2, π, 3π/2]. In each case, the field-aligned antenna had reduced integrated E_∥ relative to the existing non-aligned antenna geometry, with the greatest reduction for monopole [0, 0, 0, 0] phasing.     

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.     

High Power RF Transmitters for ICRF Applications on EAST

An Ion Cyclotron Range of Frequency (ICRF) system with a radio frequency (RF) power of 4×1.5 MW was developed for the Experimental Advanced Superconducting Tokamak (EAST).High RF power transmitters were designed as a part of the research and development (R&D) for an ICRF system with long pulse operation at megawatt levels in a frequency range of 25 MHz to 70 MHz.Studies presented in this paper cover the following parts of the high power transmitter:the three staged high power amplifier,which is composed of a 5kW wideband solid state amplifier,a 100kW tetrode drive stage amplifier and a 1.5MW tetrode final stage amplifier,and the DC high voltage power supply (HVPS).Based on engineering design and static examinations,the RF transmitters were tested using a matched dummy load where an RF output power of 1.5MW was achieved.The transmitters provide 6MW RF power in primary phase and will reach a level up to 12MW after a later upgrade.The transmitters performed successfully in stable operations in EAST and HT-7 devices.Up to 1.8MW of RF power was injected into plasmas in EAST ICRF heating experiments during the 2010 autumn campaign and plasma performance was greatly improved.     

Mechanical design features and challenges for the ITER ICRH antenna

The ITER Ion Cyclotron Resonant Heating (ICRH) antenna provides plasma heating at a power of 20 MW. Operation in the ITER environment imposes significant thermal power handling capability, structural integrity, shielding and operations requirements. The design will require a step change over any predecessor in terms of power, scale and complexity. This paper reports the main mechanical design features that address the challenges and often conflicting requirements during the conceptual design phase.     

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.     

Results of ICRF Heating Experiments from the EAST 2010 Campaign

Radio frequency(RF) plasma heating in ion cyclotron range of frequencies(ICRF)was successfully performed on the Experimental Advanced Superconducting Tokamak(EAST).This is mainly because lithium wall conditioning was routinely used to reduce both impurity and hydrogen(H) recycling and to improve the ICRF power absorption.Mainly ICRF heating of the H minority regime at 27 MHz has been applied in deuterium plasmas.The ion cyclotron resonance heating(ICRH) is found to depend strongly on plasma preheating.The ICRH efficiency can be much improved in conjunction with the lower hybrid wave(LHW).Effective ion and electron heating was observed with the H minority heating mode.The increase of the stored energy reached30 kJ in L-mode plasma by using the ICRF power of 1.0 MW alone when the H cyclotron resonance layer was at plasma center.     

The Upgrade of Fast Ferrite Tuning Matching System for ICRF in EAST

The fast ferrite tuning (FFT) real-time matching system has been designed and tested for the ion cyclotron range of frequency (ICRF) in EAST tokamak, which is necessary to transfer ICRF power to the plasma against variations in the antenna impedance. Through the test results, we proved this FFT system is feasible in EAST. Therefore this system have been upgraded recently to achieve real-time matching by the upgrading of the coil power supply and optimizing of the tuning structure. Finally the new FFT system achieved a response time of 10 ms and operated with a peak power of 1.5 MW, which satisfied the requirements of matching system in EAST.     

Electromagnetic Analysis of the EAST 4-Strap ICRF Antenna with HFSS Code

A new ICRF antenna has been designed in EAST,whose aims are to reduce the parallel RF electric fields E_‖ and to investigate the current drive using the fast magnetosonic wave.This antenna consists of four toroidally spaced radiating straps.The electrical characteristics of the new antenna are estimated by using a three-dimensional electromagnetic commercial code.The S-parameters,RF current distribution and electromagnetic field distribution on and near the 4-strap antenna are analyzed,and the RF potentials influenced by antenna phasing and radial position are investigated.     

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.     

Performance of the Scattering Matrix Arc Detection System on the JET ITER-like ICRF antenna

Ion Cyclotron Radio Frequency (ICRF) antennas operating under high voltage to couple high power to fusion plasmas are at risk of electrical arcing. The standard Voltage Standing Wave Ratio (VSWR) system does not protect low impedance areas, which are used in antennas to achieve load tolerance to variations in plasma loading during Edge Localised Modes (ELMs). The Scattering Matrix Arc Detection System (SMAD) was designed to create additional protection for these areas, and 4 complete systems were implemented and tested on the ITER-like antenna (ILA) on JET. This paper describes the performance under relevant experimental conditions of load tolerance and/or high voltage and electrical arcing causing generator trip events.     

Neutron Yields Based on Transport Calculation in EAST ICRF Minority Heating Plasmas

Neutron diagnostics, including flux and energy spectrum measurements, have been applied on the experimental advanced superconducting tokamak (EAST). The absolute calibration of neutron yields has been achieved by a calculation method using the Monte Carlo automatic modeling (MCAM) system and the Monte Carlo N-Particles (MCNP) code. Since the neutron yield is closely related with the ion density and temperature, it is a good measure of plasma performance, especially the wave heating effect. In ion cyclotron range of frequencies (ICRF) experiments, the increase in the ion temperature derived by the neutron yield indicates an effective plasma heating. Minority protons damp a large fraction of the total wave power, and then transfer part of the energy to deuterium by collisions. Neutron spectrum measurements also indicate that no tail is created by high energy deuterons during ICRF heating. However, the ion temperature derived by the neutron yield is consistent with the result by using a poloidal X-ray imaging crystal spectrometer (PXCS), showing a reliable transport calculation.     

基于嵌入式系统的离子回旋数据采集交换系统的开发和实现

为提高现有EAST离子回旋共振加热监测系统的性能,为EAST物理实验提供稳定可靠的加热手段,针对目前监控系统的多卡数据采集和交换过程中出现的实时问题及多卡采集出现的问题,文章提出了在EAST装置高功率离子回旋共振加热监控系统的设计的总体基本解决方案和实现过程,设计了双操作系统下多卡数据采集交换可行的实现模型,使用Visual C＋＋及Tornado for Windows开发相应的驱动及应用程序,对在嵌入式系统VxWorks和Windows操作系统下的通讯方式及系统性能进行了重点分析和讨论,使用嵌入式系统的软件逻辑分析仪对嵌入式系统的任务调度、信号量使用、内存使用情况、系统空闲时间等作了分析,为多操作系统多卡采集交互式系统提供了参考,测试结果表明该系统基本满足要求。     

Influence of the plasma profile and the antenna geometry on the matching and current distribution control of the ITER ICRF antenna array. Optimization of the decoupling-matching system

The eight triplets of straps of the ITER ICRF antenna array are fed through 8 matching circuits and 4 hybrids to ensure load resilience. Decouplers are used to mitigate the effects of triplet mutual coupling. They also control the array phasing. The electrical constraints on the decouplers for different layouts with heating (H) or current drive (CD) phasing are compared starting from the TOPICA matrix computed for the last antenna plug design and the reference (most pessimistic) plasma profile “2010low” provided by IO. It is shown that this last profile provides a significant decrease of plasma coupling and increase of mutual coupling with respect to the previous reference profile “Sc2short17”. This results in a larger range of decoupler reactance X_dec and voltage V_Xdec needed. This range can be reduced when using 10 decouplers instead of the 7 needed for the same forward power P_Gk+ of the 4 power sources. For H phasing only 4 decouplers could be used but with different P_Gk+ (P_Gk+ ratio up to 1.5–2.5). For CD phasing and same plasma profile the power capability P_tot is increased by 25% with a decoupler layout allowing much smaller poloidal phasing than the 90° provided by the hybrids. A decrease of the distance antenna-plasma profile reduces the normalized decoupler voltage V_Xdec/√P_tot with no significant change of the X_dec range. The recess of the vertical septa between the strap boxes increases the plasma coupling but has the drawback of also increasing the mutual coupling between triplets: the needed range of X_dec and of V_Xdec/√P_tot is increased in proportion.     

Conceptual design of Remote Control System for EAST tokamak

The international collaboration becomes popular in tokamak research like in many other fields of science, because the experiment facilities become larger and more expensive. The traditional On-site collaboration Model that has to spend much money and time on international travel is not fit for the more frequent international collaboration. The Remote Control System (RCS), as an extension of the Central Control System for the EAST tokamak, is designed to provide an efficient and economical way to international collaboration. As a remote user interface, the RCS must integrate with the Central Control System for EAST tokamak to perform discharge control function. This paper presents a design concept delineating a few key technical issues and addressing all significant details in the system architecture design. With the aim of satisfying system requirements, the RCS will select rich Internet application (RIA) as a user interface, Java as a back-end service and Secure Socket Layer Virtual Private Network (SSL VPN) for securable Internet communication.     

Commissioning the ICRF system and an ICRF assisted discharge cleaning at the KSTAR

Korean superconducting tokamak advanced research (KSTAR) is a national superconducting tokamak with the aim of a high beta operation based on advanced tokamak (AT) scenarios, and an ion cyclotron ranges of frequency (ICRF) heating is one of the essential tools to achieve this goal. The fabrication and high voltage (HV) test of the antenna and the matching system were finished in 2006 and the installation of the antenna, matching system and the transmitter at the KSTAR site was completed in 2007. Antenna conditioning was carried out to improve the HV holding condition of the antenna installed on the KSTAR and to check on the electro-magnetic (EM) interference with other equipments such as the superconducting magnet monitoring system and other machine and/or plasma diagnostic systems. The first KSTAR tokamak experimental campaign started by a vacuum pumping, a cryostat cooling and an ICRF system contributed to the successful tokamak shots through an ICRF assisted discharge cleaning of the vacuum vessel. In this paper, the installation processes of the ICRF system (with an emphasis on the quality assurance procedures of KSTAR), as well as the results from the first RF discharge experiment for the discharge cleaning and FWEH (fast wave electron heating) experiment for the KSTAR 1st experimental campaign are outlined.     

Static and Dynamic Mechanical Analyses for the Vacuum Vessel of EAST Superconducting Tokamak Device

EAST （experimental advanced superconducting tokamak） is an advanced steadystate plasma physics experimental device, which is being constructed as the Chinese National Nuclear Fusion Research Project. During the plasma operation the vacuum vessel as one of the key component will withstand the electromagnetic force due to the plasma disruption, the Halo current and the toroidal field coil quench, the pressure of boride water and the thermal load due to 250℃ baking by pressurized nitrogen gas. In this paper a report of the static and dynamic mechanical analyses of the vacuum vessel is made. Firstly the applied loads on the vacuum vessel were given and the static stress distribution under the gravitational loads, the pressure loads, the electromagnetic loads and thermal loads were investigated. Then a series of primary dynamic, buckling and fatigue life analyses were performed to predict the structure＇s dynamic behavior. A seismic analysis was also conducted.