Real Time Equilibrium Reconstruction Algorithm in EAST Tokamak

The EAST (HT-7U) superconducting tokamak is a national project of China on fusion research, with a capability of long-pulse (∽1000 s) operation. In order to realize a longduration steady-state operation of EAST,some significant capability of real-time control is required. It would be very crucial to obtain the current profile parameters and the plasma shapes in real time by a flexible control system. As those discharge parameters cannot be directly measured,so a current profile consistent with the magnetohydrodynamic equilibrium should be evaluatedfrom external magnetic measurements, based on a linearized iterative least square method, which can meet the requirements of the measurements. The arithmetic that the EFIT (equilibrium fitting code) is used for reference will be given in this paper and the computational efforts are reduced by parametrizing the current profile linearly in terms of a number of physical parameters.In order to introduce this reconstruction algorithm clearly,the main hardware design will be listed also.     

The Effect of Equilibrium Current Profiles on MHD Instabilities in Tokamaks

A cylindrical model of linear MHD instabilities in tokamaks is presented. In the model, the cylindrical plasma is surrounded by a vacuum which is divided into inner and outer vacuum areas by a conducting wall. Linearized resistivity MHD equations with plasma viscosity are adopted to describe our model, and the equations are solved numerically as an initial value problem. Some of the results are used as benchmark tests for the code, and then a series of equilibrium current profiles are used to simulate the bootstrap current profiles in actual experiments with a bump on tail. Thus the effects of these kinds of profiles on MHD instabilities in tokamaks are revealed. From the analysis of the numerical results, it is found that more plasma can be confined when the center of the current bump is closer to the plasma surface, and a higher and narrower current bump has a better stabilizing effect on the MHD instabilities.     

Microwave Reflectometry for Plasma Density Profile Measurements on HL-2A Tokamak

A modulated microwave reflectometry has been successfully developed on HL-2A, which can be used to measure the plasma density profile with time-delay method. This microwave reflectometry has two frequency ranges （26.5 to 40 GHz and 40 to 60 GHz） and it is suitable for measuring the plasma density ranging from 0.8×10^13 cm^-3 to 4.5×10^13 cm^-3. The temporal resolution is i ms and the spatial resolution is about 1 cm. This paper will present the basic principle of the microwave reflectometry, parameters calibration of the equipment and the experimental results on HL-2A tokamak.     

Edge density profile variation during a magnetic axis shift in the CHS heliotron/torsatron

Edge density profiles were measured during natural and forced magnetic axis shifts in the lowaspect-ratio heliotron/torsatron CHS, using an 8 keV fast neutral lithium beam probe. The Shafranov shift of the magnetic axis (and hence the dislocation of the LCFS) that was negligible for a low density ECH discharge became substantial (4.5 cm) for a high density NBI discharge (n _e2.5× 10¹³cm^–3) and the corresponding radius of the LCFS increased about 1.2 cm in major radius compared to the vacuum case. For NBI discharges with different settings of the vacuum magnetic axisR _ax (fixed during the discharge), the measured edge density profiles indicated reasonable agreement between the theoretically and experimentally obtained LCFS radii for 90 cm <R _ax<101.6cm, while forR _ax<90 cm the measured radius was 10% larger than expected. When a change ofR _ax from 94.7 cm to 89.9 cm during a discharge was imposed externally, a well behaved plasma boundary moved inward smoothly by about 7.5 cm, while the steepness of the edge density profile changed for different values ofR _ax. The steepest profile was attained forR _ax=92.1 cm when the highest energy content and average density were achieved.     

A Possible New Data Archive Format for EAST

A new possible data archive format for storing huge amounts of data for EAST control anddata acquisition system is presented. This new general-purpose data archive format is network-transparent, i.e, machine-independent and has been implemented in terms of XDR （eXternal Data Representation）. We test this format by using EFIT （Equilibrium Fitting） code on different operation systems, namely Linux and Windows, different processors, namely Sun and Pc, and different programs, namely in Fortran and C language. It can be easily used by different computers and different programming languages.     

321型束流剖面监测仪在离子束技术中的应用

束流剖面监测仪是监测带电粒子束在传输过程中状态变化的一种装置。该装置的叶片式探针（以下简称探针）安装在粒子加速器、同位素分离器和离子注入机等监测位置上并由它把截获的信号显示在示波器屏上便可观察到沿束横截面束流密度分布曲线（以下简称束形）。通过束形变化我们可定性地判断束流强度、束流品质和它在束管道中的相对位置等。因此,它在国外各种类型的粒子加速器上广为使用。     

动态膜电解制备四价铀中电流效率的讨论

进行了不同电流密度（40～160 mA/cm²）下电解制备四价铀的研究。研究结果表明,采用动态膜电解制备四价铀,能在保证六价铀转化率的前提下维持较高的电流效率,最终保证了四价铀制备过程的高效率。但在电解过程后期（大部分六价铀已转化为四价铀）,若采用高电流密度,电流效率迅速下降,而采用低电流密度时仍能维持较高的电流效率。为进一步提高四价铀制备过程的电流效率,研究了程序控制电流密度阶梯减小的电解方式对电解过程后期的电流效率的影响。研究结果表明,与恒定电流密度电解方式相比,采用阶梯形减小电流密度的电解方式,可有效地提高电解过程的电流效率,有助于减少副反应的发生。     

Measurement of Density Profile with Step—Swept Microwave Reflectometry

A one-channel microwave reflectometer is used to measure the electron density profile in a low-density plasma experiment (ne < 0.27 × 10~19 m-3) sustained by 2.45 GHz lower hybrid current drive (LHCD) on TRIAM-IM. In order to remove the effect of phase runaway phenomena, a step-like frequency-sweeping way is used and a special phase analysis technique is introduced. The density profile is reconstructed in TRIAM-IM with the swept frequency ranged from 6 GHz to 15 GHz. The corresponding cutoff density is from (0.045 ~ 0.28) × 10~19 m-3 in the ordinary polarization mode. The results are in good agreement with the measurements from a multi-channel 2 mm-wavelength interferometer.     

Development of atomic beam probe for tokamaks

The concept and development of a new detection method for light alkali ions stemming from diagnostic beams installed on medium size tokamak is described. The method allows us the simultaneous measurement of plasma density fluctuations and fast variations in poloidal magnetic field, therefore one can infer the fast changes in edge plasma current. The concept has been worked out and the whole design process has been done at Wigner RCP. The test detector with appropriate mechanics and electronics is already installed on COMPASS tokamak. General ion trajectory calculation code (ABPIons) has also been developed. Detailed calculations show the possibility of reconstruction of edge plasma current density profile changes with high temporal resolution, and the possibility of density profile reconstruction with better spatial resolution compared to standard Li-BES measurement, this is important for pedestal studies.