Process Modeling and Dynamic Simulation for EAST Helium Refrigerator

In this paper,the process modeling and dynamic simulation for the EAST helium refrigerator has been completed.The cryogenic process model is described and the main components are customized in detail.The process model is controlled by the PLC simulator,and the realtime communication between the process model and the controllers is achieved by a customized interface.Validation of the process model has been confirmed based on EAST experimental data during the cool down process of 300-80 K.Simulation results indicate that this process simulator is able to reproduce dynamic behaviors of the EAST helium refrigerator very well for the operation of long pulsed plasma discharge.The cryogenic process simulator based on control architecture is available for operation optimization and control design of EAST cryogenic systems to cope with the long pulsed heat loads in the future.     

EAST Cryogenic Supervisory and Control System Based on Delta-V DCS

The control system for the Experimental Advanced Superconductive Tokamak （EAST） cryogenic system is designed and constructed based on Delta-V DCS （Distribution Control System）, which consists of engineering workstations, operator workstations, application workstations, redundant controller units, input/output （I/O） cards and a redundant control network. Our task is to design a supervisory and control system to provide the operator interface for control and monitoring, sending alarms, archiving of selected signals, and other routines to analyze realtime and historic data. The hardware configuration, software structure and control algorithms are illustrated in detail in this paper. Hvpothetic oroblems and further research are also mentioned.     

Present status and one upgrading method with a cold compressor of the EAST sub-cooling helium cryogenic system

Since 2006,the superconducting toroidal field (TF) coils of the Experimental Advanced Superconducting Tokomak (EAST) have been successfully cooled by supercritical helium at a temperature of 4.5 K and a pressure of 4 bara in eleven experiments.To obtain higher operating currents and magnetic fields it is necessary to lower the operating temperature of the TF coils.The EAST sub-cooling helium cryogenic system,with a warm oil ring pump (ORP),was tested twice in cool-down experiments,which made the TF coils operate at 3.8 K.However,the long term operational stability of the sub-cooling system cannot be guaranteed because of the ORP's poor mechanical and control performance.In this paper,the present status of the EAST subcooling helium cryogenic system is described,and then several cooling methods below 4.2 K and their merits are presented and analyzed.Finally,an upgrading method with a cold compressor for an EAST sub-cooling helium cryogenic system is proposed.The new process flow and thermodynamic calculation of the sub-cooling helium system,and the main parameters of the cold compressor,are also presented in detail.This work will provide a reference for the future upgrading of the sub-cooling helium system for higher operation parameters of the EAST device.     

Study on the Dynamic Performance of the Helium Turboexpander for EAST Subsystems

An increase of the cooling capacities in the liquid helium temperature area is required by Experimental Advanced Superconducting Tokamak(EAST) due to the extension of its subsystems in the near future.Limited by the heat exchangers,cryogenic pipes,and cryogenic valves,it is difficult to enlarge the present EAST helium system.10~2 W@4.5 K level helium cryogenic systems are needed in view of feasibility and economy.A turboexpander is the key component of a helium cryogenic system.In this article,a hydrostatic gas lubricated cryogenic helium turboexpander for a 900 W@4.5 K cryogenic helium system was developed for the EAST updated subsystem by the Institute of Plasma Physics,Chinese Academy of Sciences and the Institute of Cryogenic and Refrigeration of Xi'an Jiaotong University.The main components,such as gas bearings,expansion wheel,shaft,and brake wheel,were briefly presented.The dynamic performance of the journal and thrust gas bearings was investigated numerically.The rotordynamic performance of the developed turboexpander was studied experimentally.The results show that the axial and radial load capacities supplied by the journal gas bearing and thrust gas bearing are enough to balance the axial force and radial force of the rotor.A 43%overspeed operation was achieved,which validated the reasonable design of the turboexpander.     

Application of MDSplus on EAST Tokamak

EAST is a fully superconducting Tokamak in China used for controlled fusion research. MDSplus, a special software package for fusion research, has been used successfully as a central repository for analysed data and PCS （Plasma Control System） data since the debugging experiment in the spring of 2006 [1]. In this paper, the reasons for choosing MDSplus as the analysis database and the way to use it are presented in detail, along with the solution to the problem that part of the MDSplus library does not work in the multithread mode. The experiment showed that the data system based on MDSplus operated stably and it could provide a better performance especially for remote users.     

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。     

The Procedure for Assembling the EAST Tokamak

Due to the complicated constitution and high precision requirements of the EAST superconducting tokamak, a meticulous assembling procedure and measurement scheme must be established. The big size and mass of the EAST machine＇s components and complicated configuration with tight installation tolerances call for a highly careful assembling procedure. The assembling procedure consists of three main sub-procedures for the assembling of the base, of the tori of the VV, the vacuum vessel TS and the TF, and of the peripheral parts respectively. Before the assembly, a reference framework has been set up by means of an industrial measurement system with reference fiducial targets fixed on the wall of the test hall. In this paper, the assembling procedure is described in detail, the survey control system of the assembly is discussed, and progress in the assembly work is also reported.     

Numerical analysis of the static performance of an annular aerostatic gas thrust bearing applied in the cryogenic turbo-expander of the EAST subsystem

The EAST superconducting tokamak,an advanced steady-state plasma physics experimental device,has been built at the Institute of Plasma Physics,Chinese Academy of Sciences.All the toroidal field magnets and poloidal field magnets,made of NbTi/Cu cable-in-conduit conductor,are cooled with forced flow supercritical helium at 3.8 K.The cryogenic system of EAST consists of a 2 kW/4 K helium refrigerator and a helium distribution system for the cooling of coils,structures,thermal shields,bus-lines,etc.The high-speed turbo-expander is an important refrigerating component of the EAST cryogenic system.In the turbo-expander,the axial supporting technology is critical for the smooth operation of the rotor bearing system.In this paper,hydrostatic thrust bearings are designed based on the axial load of the turbo-expander.Thereafter,a computational fluid dynamics-based numerical model of the aerostatic thrust bearing is set up to evaluate the bearing performance.Tilting effect on the pressure distribution and bearing load is analyzed for the thrust bearing.Bearing load and stiffness are compared with different static supply pressures.The net force from the thrust bearings can be calculated for different combinations of bearing clearance and supply pressure.     

超流氦低温恒温器冷质量准直调节及低温变形分析

为满足超导射频腔及超导磁体低温下的加速器准直精度要求,对超流氦低温恒温器冷质量的准直调节方案进行分析。通过对冷质量的低温位移进行有限元模拟计算,获得其在2 K超流氦温区的位移变形量,利用拉伸丝型位移监测仪（WPM）在线测量数据来验证模拟分析方法。结果表明,模拟值与测量值具有较好的一致性,为底部支撑型式低温恒温器的准直调节方案设计提供了重要的数据基础。     

The Alignment and Assembly for EAST Tokamak Device

EAST （HT-7U） is a large fusion experimental device. It is a full superconducting tokamak with 1 MA of plasma current, 1000 s of plasma duration, high elongation and triangularity. It mainly consists of superconducting magnets of poloidal and toroidal field （PF ＆ TF）, vacuum vessel （VV）, thermal radiation shield （TRS） and cryostat vessel （CV）. The significant difficulty for assembly of EAST is tight installation tolerances, which are in the order of several tenth of a millimeter. In particular, the alignment of plasma facing components to the magnetic axis of the device is less than ±0.5 mm. At present, a reasonable assembly process of EAST has been defined, and based on it, the alignment method for EAST, including the survey control network, the location of the main components in different directions, the magnetic axis determination and the accurate positioning of the plasma facing components inside of the vacuum vessel and so on, has been defined by using the sophisticated optical metrology system （SOMS）. This paper describes the assembly procedure of EAST and the installation tolerances associated with the main components. Meanwhile, how to establish the assembly survey control network, magnetic axis determination methods, are introduced in detail.     

Alignment and Cryogenic Deformation Analysis of Cold Mass-in Superfluid Helium Cryomodule

To meet the alignment requirement of superconducting radio frequency (SRF) cavity and superconducting magnet at cryogenic temperature in the accelerator system, the design of adjustment and alignment of the cold mass in superfluid helium cryomodule should be analyzed. The cryogenic deformation of the cold mass at the 2 K superfluid helium temperature level was simulated and obtained by the finite element method, meanwhile the simulation analysis method was checked by the cryogenic deformation data of the cold mass online measured by the wire of position monitor (WPM). The results show that the simulation result and measurement result have a good consistency, and it provides an important data foundation for the alignment design in the type of bottom supported cryomodule.     

Measurement of Neutron Flux at the Initial Phase of Discharge in EAST

Neutron emission in EAST was investigated by a time-resolved monitor systems which consist of four 3He proportion counters and a 235U fission chamber. The D-D neutron flux increased approximately an order of magnitude during the 27 MHz Ion-cyclotron resonance frequency (ICRF) heating, demonstrating that the ICRF wave heated the plasma effectively. In addition in LHW experiment with higher plasma parameters D-D neutrons were also detected. However, a mass of photoneutrons were generated in ohmic discharges with low plasma density. Effect of plasma density on the production of photoneutrons was studied, and it is found that LHW can suppress the runaway electrons and reduce the photoneutrons effectively.     

Dependence of the internal inductance on the radial distance between the primary and secondary X-point surfaces in the EAST tokamak

In view of their advantage in long-pulse high-performance operations, low internal inductance scenarios are being developed and tested for the EAST and other tokamaks. Dependence of the internal inductance on several main plasma configuration parameters are statistically analyzed. It is found that the internal inductance of the plasma is closely related to the radial distance dR_sep between the primary and secondary X-point surfaces on the outer mid-plane as well as the poloidal field of the last closed flux surface. Moreover,dR_sep is also related to the distribution of the fast electrons driven by the injected lower-hybrid waves, which is partially responsible for the observed relation betweendR_sep and the internal inductance. The results here should therefore be helpful as a guide for future experiments on internal inductance control and long-pulse operations of the EAST and other tokamaks, as well as for detailed theoretical study of the underlying physics.     

Simulation Analysis of Divertor Performance in EAST

A detailed study of the divertor performance in the EAST has been conducted for both its double null and single null configurations. The results of the application of the SOLPS （B2/Eirene） code package to the analysis of the EAST divertor are summarized. Here we concentrate on the effects of the increased geometrical closure and variation in the magnetic topology on the behavior of divertor plasmas. The results of numerical predictions for the EAST divertor＇s operational window are also described in this paper.     

Combined Langmuir-magnetic probe measurements of type-I ELMy filaments in the EAST tokamak

Detailed investigations on the filamentary structures associated with the type-I edge-localized modes (ELMs) should be helpful for protecting the materials of a plasma-facing wall on a future large device. Related experiments have been carefully conducted in the Experimental Advanced Superconducting Tokamak (EAST) using combined Langmuir-magnetic probes. The experimental results indicate that the radially outward velocity of type-I ELMy filaments can be up to 1.7 km s^-1 in the far scrape-off layer (SOL) region. It is remarkable that the electron temperature of these filaments is detected to be ～50 eV, corresponding to a fraction of 1/6 to the temperature near the pedestal top, while the density (~3×10 ¹⁹ m ^-3) of these filaments could be approximate to the line-averaged density. In addition, associated magnetic fluctuations have been clearly observed at the same time, which show good agreement with the density perturbations. A localized current on the order of ～100 kA could be estimated within the filaments.     

EAST4.6GHz/4MW低杂波电流驱动系统隔直器优化设计

为了研究全超导托卡马克稳态高参数等离子体性能,2008年在EAST托卡马克装置上研制并成功建成了一套能最大传输2兆瓦,工作频率是2450MHz的低混杂波电流驱动系统,要实现低杂波长时间地维持等离子体电流,还需要对低杂波系统的输出功率大小及运行时间长度提出更高要求,拟研制一套波源输出功率4 MW,中心频率4.6GHz,波谱范围为1.7< N_(//)< 2.5,运行脉冲宽度0～1000秒低杂波电流驱动系统.在EAST4.6GHz/4MW低杂波电流驱动系统中,因为速调管放大器和低杂波天线有共同的接地点,速调管放大器电源为负高压,有接地点,低杂波天线有接地点,并且和EAST托卡马克相连,在系统中要求不能有两个接地点,所以要通过隔直器来隔断托卡马克和速调管之间的的直流通路.论文详细介绍了隔直器的原理和设计过程,在以4.6GHz为中心频率,150MHz的频带范围内,隔直器各个端口微波性能良好.     

Assessment of Radiation Damage to the Structural Material of EAST Tokamak

Radiation damage to structural material of fusion facilities is of high concern for safety. The superconducting tokamak EAST will conduct D-D plasma experiments with the neutron production of 1015 neutrons per second. To evaluate the material radiation damage a programme system has been devised with the Monte Carlo transport code MCNP-4C, the inventory code FISPACT99, a specific interface, and the fusion evaluated nuclear data library FENDL-2. The key nuclear responses, i.e. fast neutron flux, displacement per atom, and the helium and hydrogen production, are calculated for the structural material SS-316L of the first wall, and the vacuum vessel, using this programme. The results demonstrate that the radiation damage to the structural material is so little that it will not lead to any significant change of material properties according to the reference design. This indicates that there is a large potential space for EAST to test advanced operation regime from the viewpoint of structural material safety.     

Calorimetric power measurements in the EAST ECRH system

In this paper,the measurement method of calorimetric power for an electron cyclotron resonance heating (ECRH) system for EAST is presented.This method requires measurements of the water flow through the cooling circuits and the input and output water temperatures in each cooling circuit.Usually,the inlet water temperature stability is controlled to obtain more accurate results.The influence of the inlet water temperature change on the measurement results is analyzed for the first time in this paper.Also,a novel temperature calibration method is proposed.This kind of calibration method is accurate and effective,and can be easily implemented.     

EAST低温系统主运行模式的控制流程设计与分析

EAST托卡马克核聚变实验装置是世界上从事核聚变研究的先进科学设备。EAST低温系统是该装置的主要子系统之一,其相应DCS控制系统具有很高的稳定性和可扩展性,各部分的控制相互独立、并行执行。本文详细介绍和分析了EAST低温控制系统及在正常降温、稳态和失超模式下的控制流程设计。     

Study of Scrape-Off-Layer Width in Ohmic and Lower Hybrid Wave Heated Double-Null Divertor Plasma in EAST

Edge profiles in Ohmic and lower hybrid （LH） wave heated discharges in EAST are presented. A comparison of the measured profiles is made with those from the the...