Design and implementation of quench detection instrumentation for TF magnet system of SST-1

Steady State Superconducting Tokamak-1 (SST-1) at Institute for Plasma Research (IPR), India is now in engineering validation phase. The assembled Toroidal Field (TF) magnet system of SST-1 will be operated at 10 kA of nominal current at helium cooled condition of 4.5 K. A reliable and fail proof quench detection (QD) system is essential for the safety and the investment protection requirements of the magnets. This QD system needs to continuously monitor all the superconducting coils, which include 16 TF magnets, return-loop, bus bars and current leads. In case of any event initiating the normal resistive zone and reaching thermal run-away, the QD system needs to trigger the magnet protection circuits. Precision instrumentation and control system with 204 signal channels had been developed for detection of quench anywhere in the entire TF magnet system. In the present configuration of quench detection scheme, the voltage drop across each double pancake (DP) of each TF coil are compared with its two adjacent DPs for the detection of normal zone and cancelation of inductive couples. Two identical redundant systems with one out of two configurations are successfully commissioned and tested at IPR. This paper describes the design and implementation of the QD system, Installation experience, validation test and initial results from the recent SST-1 magnet system charging.     

1-D thermal-hydraulic analysis of the high temperature superconducting current leads for the ITER magnet system from 5 K to 300 K

The magnet system of ITER includes high temperature superconducting (HTS) current leads with a maximum current of 68 kA for the toroidal field (TF) coils, 55 kA for the poloidal field (PF)/central solenoid (CS) coils and 10 kA for the control coils (CC), respectively. Although different in terms of size and operative conditions, the ITER HTS current leads have been all designed on the basis of an established concept, which was successfully developed for the LHC at CERN and proven by the so-called 70 kA “demonstrator” lead made by KIT and by the ITER pre-prototypes made by ASIPP in China. A broad R&D campaign has been undertaken by ASIPP and CERN in order to find optimized designs for each component of the leads. Nevertheless, a comprehensive picture of the performance of the entire HTS current leads is not yet available. In this paper, a steady state, full length, thermal-hydraulic 1-D modeling is applied to the study of the three types (TF, PF/CS, CC) of ITER HTS current leads. The results of this predictive analysis are then compared with relevant ITER requirements. It was found that the present design of the HTS current leads will fulfill these specifications.     

The design and the manufacturing process of the superconducting toroidal field magnet system for EAST device

The toroidal field (TF) magnet system of EAST (HT-7U), which consists of 16 superconducting coils enclosed in steel cases, has been manufactured to generate the magnetic field of 3.5 T at the plasma center to maintain plasma in a tokamak configuration with a current up to 1 MA. The TF coils have an approximately D-shape geometry of 2.6 m wide and 4.0 m high, and operate at a maximum field of 5.8 T. The conductor used in the TF coil is NbTi/Cu cable-in conduit (CIC) conductor, and its operating current is 14.3 kA.In March 2006, the first cooling down of the EAST device has been carried out successfully. The total of TF magnet system has been cooled down from room temperature to 4.5 K, and the TF system has been energized up to 8.2 kA with 5 A/s ramp rate. In September 2006, full performances of the TF magnet system have been reached, and the device of EAST has delivered its first plasma. In addition, the TF magnet system has been routinely operated with a current maintained constant on a whole day basis, for a preliminary program of more than 500 shots.In this paper, the main parts of the design, developmental tests, and the fabrication and assembly of TF coils are described in detail.     

A first characterization of the quench detection system for ITER

The purpose of this paper is to assess the expected response of conventional and non-conventional quench detection sensors proposed for the ITER coils, and to be tested in the QUELL experiment in SULTAN. The assessment is based on simulation of thermohydraulic transients in the ITER coils for various operating conditions, and a tentative definition of the transfer functions of each sensor concept. It is shown that, for the investigated conditions, the co-wound voltage taps are more accurate than hydraulic systems and conventional voltage balance methods. The additional complication associated with the insertion of taps in the conductor is well offset by the low sensitivity to external disturbances.     

EAST托卡马克新型积分器系统控制器的研制

为了满足EAST托卡马克的实验需求,提升积分器系统的可维护性和可测试性,研制了新型积分器系统控制器。该控制器采用ARM微控制器和轻量级IP协议栈,实现了积分器系统的网络化控制。所提供的参数设置指令可远程设置和读取积分器板卡上放大器的放大倍数,而控制指令则提供了初始化、标准信号积分、脉冲积分、积分保持、标定和探针测试功能。经实验和EAST现场测试,该积分器系统控制器可满足EAST装置的实验要求。     

EAST分布式定时同步系统的实现

分布式定时同步系统在国家大科学工程EAST中有重要作用,它用于同步EAST各子系统精准投入实验的时序。分布式定时同步系统利用PXI工业级设备并结合虚拟仪器技术实现定时同步系统,可提供1 Hz～80 MHz频率的参考时钟信号,产生1 ms～6 872 s延迟触发信号（精度达10 ns）。该系统能采集信号,并能根据检测的信号实时触发相应处理机制。分布式定时同步系统精度高且运行稳定可靠,已成功应用于2010年秋季EAST放电实验。     

Study of electromagnetic noise influence on quench detection system under different discharge conditions for EAST

EAST is the first Tokamak device whose toroidal and poloidal magnet are superconducting. The enormous magnetic field energy stored in the magnet system will transfer into thermal energy and cause the damage of superconducting magnet, if a quench happened. Therefore, reliable quench detection is a key issue for steady-state operation. In addition to electromagnetic noise from poloidal magnet fields and plasma current which will experience fast current ramp rate, radio frequency noise from heating system also have some interference on quench detection system to a certain degree. The most difficult point for quench detection system is required to have more detail evaluation on electromagnetic noise interference.Recently experiments have been carried out successfully in EAST device. The steady-state operation with 1 MA of plasma current and more than 100-s plasma duration has been obtained. In the paper, the electromagnetic noise interference on quench detection system under different discharge conditions are analyzed and relative process methods are also introduced. The technological experience and experimental data are significant for the constructing ITER and similar superconducting device have been mentioned which will supply significant technological experience and experimental data for constructing ITER and similar superconducting device.     

EAST托卡马克绝缘子低温力学性能理论及实验分析

复合材料绝缘子是EAST托卡马克磁体系统的关键部件，担负着整个磁体系统低温冷却回路与高压部件的对地绝缘作用。运行中，绝缘子在低温下要承受较高的内压及电压，保持绝缘子在低温状态下的机械整体性是运行安全的必要保证。从整个装置的使用安全考虑，有必要对绝缘子低温力学性能作全面分析。本工作首先对绝缘子的机械低温力学性能进行理论分析，然后通过设计的低温力学实验验证理论分析结果。以此为基础，对装置中的损坏绝缘子进行分析，确定损坏原因。     

Spontaneous current relaxation in NBI heated plasmas on EAST

We report on current profile evolution in EAST NBI driven plasmas where two neutral beams are injected,one during the current ramp phase and the second during flattop.At the end of the current ramp phase,it is found that a flat q profile with q0?~?1 is achieved with low magnetic shear in the core.It is observed that plasma current and density both relax much faster than resistive time,even in the absence of sawtooth activity when H–L transition occurs.Density fluctuations associated with magnetic perturbations(3/2) as a precursor to the H–L transition are observed.It is likely that these modes play a role in fast current transport.     

Data monitoring system of technical diagnosis system for EAST

<正>Technical diagnosis system(TDS)is an important subsystem to monitor status parameters of EAST (experimental advanced superconducting tokamak).The upgraded TDS data monitoring system is comprised of management floor,monitoring floor and field floor.Security protection,malfunction record and analysis are designed to make the system stable,robust and friendly.During the past EAST campaigns,the data monitoring system has been operated reliably and stably.The signal conditioning system and software architecture are described.     

EAST上快波电流驱动的数值模拟

针对EAST全超导托卡马克的参数,利用射线追踪法在离子回旋共振频段（ICRF）发射机的工作频段内进行快波电流驱动的数值模拟,找到了一组适合于快波电流驱动的参数。模拟结果表明,发射频率只要避开基频吸收和二次谐频吸收,电流驱动的效果就很明显。     

EAST全超导托卡马克上硅漂移探测器软X射线能谱诊断

采用性能优越的15道硅漂移探测器（SDD）阵列,在EAST全超导托卡马克上建立了1套较为完善的软X射线能谱诊断系统,用以测量等离子体在软X射线辐射能段(1～20keV)的能谱。该诊断系统的观测范围基本覆盖了整个等离子体空间,因此,可满足EAST不同放电位形下电子温度测量的要求。利用该诊断系统,可获得时间分辨达50ms、空间分辨约为7cm的电子温度剖面。通过对比发现,由该诊断系统所得到的电子温度与其它电子温度诊断系统所测量的电子温度基本一致。此外,该诊断系统还可监测在软X射线能量范围内出现的一些金属杂质的特征线辐射。     

EAST装置的连续数据采集与服务系统的设计与实现

介绍了应用于EAST超导托卡马克装置的连续数据采集与数据服务系统的设计思路与具体实现过程,该系统能使实验人员了解EAST装置在降温以及实验过程中各系统与重要设备的运行状态,以保证系统的正常运转与安全.该系统经测试与实验表明,整个系统稳定、灵活、有效.     

Lower hybrid heating and current drive system for a tokamak reactor

A lower hybrid heating system has been designed for heating a tokamak reactor to ignition and for sustaining steady-state operation by driving the toroidal plasma current. The power spectrum from an active/passive waveguide grill is computed, and the resulting equilibrium current density profile is computed from a full electromagnetic WKB analysis of wave propagation in a cylinder. The corresponding toroidal current profile is a low-current equilibrium which is stable to various ideal modes at an economically acceptable beta. The electronic circuitry is designed to minimize the electric power required for current drive, and the resulting design appears to provide reliable operation in a reactor environment. The same system can drive current during reactor startup if some of the waveguides are modified slightly. A typical sequence of startup equilibria is calculated.     

Thermo-mechanical analysis of RMP coil system for EAST tokamak

Resonant magnetic perturbation (RMP) has been proved to be an efficient approach on edge localized modes (ELMs) control, resistive wall mode (RWM) control, and error field correction (EFC), RMP coil system under design in EAST tokamak will realize the above-mentioned multi-functions. This paper focuses on the thermo-mechanical analysis of EAST RMP coil system on the basis of sensitivity analysis, both normal and off-normal working conditions are considered. The most characteristic set of coil system is chosen with a complete modelling by means of three-dimensional (3D) finite element method, thermo-hydraulic and thermal-structural performances are investigated adequately, both locally and globally. The compromise is made between thermal performance and structural design requirements, and the results indicate that the optimized design is feasible and reasonable.     

Numerical Study of Tokamak Equilibrium with Toroidal Flow on EAST

The effect of the toroidal flow on the equilibrium of tokamak plasmas is a sensitive point for high performance plasma and its precise control. In this paper the effect is studied numerically using the EFIT （Equilibrium Fitting） code on EAST （Experimental Advanced Superconducting Tokamak）. Firstly, the numerical calculation exhibits a clear outward shift of pressure contour from the magnetic surfaces in the plasma core and the shift grows with the increase of the toroidal velocity. The peak shift of 8% is observed when the ratio between the plasma velocity and the Alfvdn speed equals to 0.15. Secondly, it is shown that the magnetic surfaces shift outwards from those without flow. With a certain plasma current the safety factor on the magnetic axis decreases as the plasma flow velocity increases. The magnetic shear increases about 10% on the plasma boundary compared with the case without flow.     

Design and test of voltage and current probes for EAST ICRF antenna impedance measurement

On the experimental advanced superconducting tokamak(EAST), a pair of voltage and current probes(V/I probes) is installed on the ion cyclotron radio frequency transmission lines to measure the antenna input impedance, and supplement the conventional measurement technique based on voltage probe arrays. The coupling coefficients of V/I probes are sensitive to their sizes and installing locations, thus they should be determined properly to match the measurement range of data acquisition card. The V/I probes are tested in a testing platform at low power with various artificial loads. The testing results show that the deviation of coupling resistance is small for loads RL??2.5 Ω, while the resistance deviations appear large for loads RL??1.5 Ω, which implies that the power loss cannot be neglected at high VSWR. As the factors that give rise to the deviation of coupling resistance calculation, the phase measurement error is the more significant factor leads to deleterious results rather than the amplitude measurement error. To exclude the possible ingredients that may lead to phase measurement error, the phase detector can be calibrated in steady L-mode scenario and then use the calibrated data for calculation under H-mode cases in EAST experiments.     

CT-6B托卡马克的交流运行实验研究

在CT—6B托卡马克上首次实现了多周期交流运行，对多个周期中等离子体进行比较发现，尽管在每个周期的两个半周中等离子体与壁的相互作用有所不同，但等离子体中的杂质积累并未受到严重影响。通过内磁探针测量了等离子体电流密度的分布，发现等离子体电流首先从弱场区开始反相，电流反相过零时同时存在正负局部等离子体电流，此时的磁面结构有效地约束了粒子。     

EAST托卡马克中央定时系统的实现

中央定时系统是EAST托卡马克装置总控系统的重要组成部分,是总控系统对各子系统进行时序和触发控制的基础.本工作建立的EAST中央定时系统采用分布式的系统结构,可对32 MHz的系统时钟信号进行0-65535的任意整数分频;能对系统触发进行延迟输出,最大的延迟时间为4294s、延迟的分辨率为1 μs.该系统性能稳定,并已成功地投入到2006年9月EAST托卡马克装置的首轮正式物理放电实验中.     

Study of load balancing technology for EAST data management

With the continuous renewal and increasing number of diagnostics, the EAST tokamak routinely generates ∼3 GB of raw data per pulse of the experiment, which is transferred to a centralized data management system. In order to strengthen international cooperation, all the acquired data has been converted and stored in the MDSplus servers. During the data system operation, there are some problems when a lot of client machines connect to a single MDSplus data server. Because the server process keeps the connection until the client closes its connection, a lot of server processes use a lot of network ports and consume a large amount of memory, so that the speed of access to data is very slow, but the CPU resource is not fully utilized. To improve data management system performance, many MDSplus servers will be installed on the blade server and form a server cluster to realize load balancing and high availability by using LVS and heartbeat technology. This paper will describe the details of the design and the test results.