Preliminary result of an advanced tangential X-ray pinhole camera system with a duplex MWPC on KSTAR plasma

An advanced tangential X-ray pinhole camera (TXPC) has been developed for KSTAR by utilizing a 2-D duplex multi-wire proportional counter (MWPC) detector. The KSTAR MWPC employs a 2-D parallel type readout system for high temporal resolution and adopts a duplex type for the capability of electron temperature measurement via the multi-color method. This paper presents the performance test result of the developed MWPC system utilizing a Fe-55 X-ray source. As a preliminary experimental result from the 2012 KSTAR campaign, the clear presentation of sawtooth activities and its frequency change, and 2-D plasma images during the vertical disruption event are given.     

Prism tuner for single frequency operation of CW dye laser

A cw dye laser capable of single longitudinal mode operation and linear reproducible wavelenght tuning over a relatively wide spectral range is described. By employing a novel scheme of four intracavity highly dispersive Abbe prisms output powers of 5 mW with a linewidth less than 30 MHz for an input power of 700 mW have been obtained.     

Coupling Analysis for the ICRF Resonant Cavity Launcher on DIII-D

The coupling properties of the ion-cyclotron range of frequencies (ICRF) resonant cavity launcher for DIII-D were investigated with a two-dimensional (2-D) model. In the context of the magnetostatic approximation, Poisson's equation was solved for the vector potential with a self-consistent antenna current distribution. The tool of analysis is a fast 2-D Poisson solver which takes into account the plasma medium and the shape of the cavity wall and antenna cross section. This permits the design of the optimum configuration for such a launcher to be used on the DIII-D tokamak. Extensive parametric studies of the launcher loading impedance were carried out. It was found that the antenna-plasma distance and the edge density gradient are the two most critical parameters determining the coupling. Criteria were also established to optimize the power-handling properties of the cavity coupler.     

一种大口径无液氦低温超导磁体系统的研制

将铜和不锈钢材料制作成Φ646mm×1175mm大口径低温超导磁体复合骨架,骨架两端设计有传热热桥。选用1.5W@4.2K的G-M制冷机作为冷源,采用高导热的无氧铜编织带作为制冷机二级冷头和传热热桥之间的柔性连接件,来实现柔性传热。经过124h后,实现了低温超导磁体系统的冷却。超导磁体闭环运行后,磁场强度达到设计值,均匀区内不均匀度优于指标要求。     

An analysis of the folded waveguide: a compact waveguide launcherfor ICRF heating

Theoretical and experimental investigations of the folded waveguide launcher as proposed for use in the ion-cyclotron range of frequencies (ICRF) heating of tokamak plasmas are presented. Theoretical results include an analysis of the folded waveguide using Ritz's method to obtain various field quantities. The cutoff wavenumbers from this analysis are within 10% of those calculated using an unfolded equivalent rectangular waveguide model. Measurements of cavity resonances for a scale-model ICRF-folded waveguide with a cutoff frequency of 2.4 GHz also agree closely with those calculated using an unfolded equivalent model. An unfolded equivalent waveguide model is used to evaluate the properties of an inductive strip placed in the folded waveguide. Applying variational analyses provides upper and lower bounds to the reflection magnitude |S₁₁| that are in good agreement with measured values. Polarizing plates (which have been proposed to increase the on-axis directivity of the radiated power) are modeled using an unfolded equivalent waveguide. A variational analysis is used to determine an upper-bound value of |S₁₁| in air due to a polarizing plate inside a matched folded waveguide. Measured values are found to be within 3% of the calculated values, with |S₁₁|>0.95 for frequencies between 2.5 and 4.5 GHz     

Development of discharge in a system of electrodes situated on interface of liquid and solid dielectrics

The development of a discharge in the case where the electrodes are situated at the interface of solid and liquid dielectrics was investigated with the aid of an apparatus based on two photomultipliers and an electrolytic tank. In these conditions the discharge develops along a single pathway, which runs along the interface for part of its length and then passes into the solid dielectric. Possible factors that predetermine the pathway of the spark channel in the considered system of electrodes and dielectrics are examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 61–66, September, 1978.     

Model of pressure variation in a vacuum system for volatile liquid evacuation

The behavior of the total and partial pressure in a vacuum system is studied for the case of volatile liquid evacuation. A mathematical model of the process is developed that is based on the joint solution of the balance equations for gas and vapor flows. The influence of the vacuum system parameters and liquid properties on the pressure variation is found. The equilibrium pressure and evacuation time are numerically calculated for different system’s parameters.     

Analysis of Dielectrc-Filled Waveguide Coupling to Plasmas in the ICRF

Dielectric-filled waveguides may be advantageous for heating reactor-grade tokamak plasmas, due to their compactness and power-handling capability. We present a theoretical analysis of coax excitation and plasma impedance for a dielectric-filled rectangular waveguide. The plasma reflection coefficient is obtained by matching plasma and waveguide fields at the interface. The numerical results show that the reflection coefficients can be made small by careful tailoring of the waveguide dimensions to the density profile for heating at the second or third harmonic of deuterium. We present a scattering matrix approach for the design of a coaxial feed to match the waveguide in the presence of a wide range of plasma loading. For a waveguide filled with a high permittivity dielectric, a shorted probe gives better coupling than an open-ended probe.     

Study of Power Coupling through an Electrostatic Shield on a Loop Antenna for ICRF Heating of EBT-S

The effects of electrostatic shields around the antenna used for ICRF heating in the EBT-S fusion experiment on the efficiency of power transfer from the antenna to the plasma were studied in bench tests using resonant coupling loops placed near the antenna to simulate plasma behavior. For the frequency range of interest in these experiments, the length of the antenna was much shorter than the free-space wavelength. Coupling efficiencies in excess of 90 percent were obtained under best conditions. There was a reduction in coupling efficiency due to the presence of the shield, which was found to be dependent on the proximity of the loop to the antenna and on the Q of the loop. The change in coupling efficiency of the antenna with the shield compared to the antenna without a shield was greater the farther the loop was removed from the antenna and the lower the Q of the loop. In general, the reduction in coupling efficiency due to the shield is probably tolerable, with the advantages of having an electrostatic shield outweighing the disadvantage of a lower power coupling efficiency.     

Chaotic dynamics in the electroconvection system of a nematic liquid crystal

The transition from a steady domain structure to turbulence in the electroconvection system of a nematic under the action of a constant electric field is studied using the methods of optical and acoustic responses. The chaotic dynamics is investigated both by conventional methods (Fourier signal spectrum) and by methods of nonlinear dynamics. From the quantitative estimates of basic characteristics of the chaotic behavior (namely, the correlation dimension, leading Lyapunov exponent, K-entropy, and embedding dimension), one can conclude that temporal chaos arises in the system, giving rise to a strange attractor, as the control parameter increases at ɛ ≥ ɛ _c ≈ 0.5. The fact that the distribution of laminar domains in the liquid-crystal layer depends on their length under the conditions of developed turbulence indicates that the dynamics of the nematic demonstrates the intermittent behavior.     

Development of a stereo-TV system for recording and measurement

The development and use of a stereo-TV system to observe, record and measure spatial coordinates is described.     

Experimental Investigation of the Shielding of the Heating Field by the Electrostatic Shield of a Stripline ICRF Antenna

Measurements of the partial shielding of the current-generated heating field of an electrostatically shielded stripline antenna have been performed. An understanding of this adverse shielding is relevant to optimizing the heating of tokamaks in the ion cyclotron range of frequencies. These measurements verify the predictions of an earlier theoretical study.     

On confinement characteristics of the newly developed sawtooth-free plasmas in KSTAR tokamak

Development of advanced scenarios, an important experimental goal of the Korea superconducting tokamak advanced research (KSTAR) project, has just begun. The safety factor (q) profile is a key to achieve these advanced scenarios. Particularly the hybrid scenario, one of the advanced scenarios, can be established generally with low magnetic shear (s) at the center with central q-value above unity so to avoid sawtooth instability. This q-profile was successfully produced using early divertor formation during a plasma current ramp-up phase in KSTAR. Auxiliary heating was also employed during the current ramp-up phase to delay the inductive current diffusion to the center of the plasma. In addition to the early divertor formation method, the target q-profile was attempted to be achieved by modifying the plasma current waveform using the so-called, ‘current-overshoot’ method and the timing of L-mode to H-mode transition. In this work, the confinement characteristics of these sawtooth-free regimes are investigated. The global energy confinement time is calculated and compared with that of conventional H-modes in KSTAR. The confinement enhancement factor reveals that the newly developed discharges are not improved over H-modes contrary to results of other tokamaks. To investigate the reason, transport modeling is performed self-consistently with an integrated simulation package incorporating plasma equilibrium, transport, and heating and current drive. The current ramp-up phase is simulated and impact of early divertor formation, current-overshoot, and early L–H transition on the target q-profile and s/q profile is addressed. The s/q profile is found to be not improved in these discharges compared with hybrid scenarios reported in other tokamaks. Based on these results, future experimental directions are addressed to access the hybrid regimes in KSTAR.     

A shock-excitation study of the performance of stub slow-wave systems

Shock excitation (as used with high-Q cavities) is employed to test slow-wave systems, including ones of low Q. Results are given for stub systems tested in this way.     

Development of a terminal voltage stabilization system for the FOTIA at BARC

A terminal voltage stabilization system for the folded tandem ion accelerator (FOTIA) was developed and is in continuous use. The system achieves good voltage stabilization, eliminates ground loops and noise interference. It incorporates a correcting circuit for compensating the mains frequency variations in the GVM amplifier circuit. The present system has two modes of operation namely GVM control mode and slit control mode. A voltage stability of about ± 2 kV has been achieved. In this paper, some of the salient features of the voltage stabilization system are discussed.     

超导重力仪用液氦恒温器研制

介绍了一套超导重力仪用液氦恒温器,包括技术指标要求、总体结构、关键技术、试验步骤及结果.恒温器液氦消耗量为0.8L/h,真空腔体内部温度稳定度为±5mK,低温下真空腔体真空度优于5×10-4pa,各参数均优于技术指标要求,完全满足超导重力仪工作环境要求.表明该设计方案是合理的,试验流程是正确的.     

似生物膜系统之六角液相

首度在二维溶致型层状液晶系统中，发现了液相与固相之间存在一“六角方向性”的新状态．这个状态显示了的六角长程有序与似液相的位置相关连特性之特征，而与熟知的二维融化理论所预期的现象有显著的差异．     

Development of electrochemical oxygen meter for liquid sodium

The development of an electrochemical oxygen meter for liquid sodium is briefly accounted. The current design, based on a solid electrolyte crucible machined out of a sintered pellet is described along with some technological details. Present experience with testing in sodium loops and post-exposure analysis has shown that the chosen assembly is capable of achieving approximately the Nernst voltage. The service period was limited mainly by corrosion and by some incompatibilities in reference electrode compartment materials.     

Development of the liquid level meters for the PandaX dark matter detector

The two-phase xenon detector is at the frontier of dark matter direct search. This kind of detector uses liquid xenon as the sensitive target and is operated in two-phase （liquid/gas） mode, where the liquid level needs to be monitored and controlled in sub-millimeter precision. In this paper, we present a detailed design and study of two kinds of level meters for the PandaX dark matter detector. The long level meter is used to monitor the overall liquid level while short level meters are used to monitor the inclination of the detector. These level meters are cylindrical capacitors that are custom-made from two concentric metal tubes. Their capacitance values are read out by a universal transducer interface chip and are recorded by the PandaX slow control system. We present the developments that lead to level meters with long-term stability and sub-millimeter precision. Fluctuations （standard deviations） of less than 0.02 mm for the short level meters and less than 0.2 mm for the long level meter were achieved during a few days of test operation.     

Development of a laser-based measurement system for evaluation of the scraping workpiece quality

A laser-based measurement system for evaluation of the scraping workpiece quality that can eliminate contact-induced measurement errors and increase measurement accuracy is proposed. The laser-based measurement system comprises a light-scattering-type triangulation laser, a computer numerical control (CNC) machine tool, and an analog-to-digital (A/D) card. The triangulation laser measures the depth of the scraping spots and the CNC machine tool locates their position. The 3D data of the scraping workpiece is then drawn using the least squares method. Cast iron and Turcite workpieces can be measured. Five parameters of the scraping workpiece, namely peak points per square inch, percentage of points, distribution of heights of points or depth of surroundings, edge shape of the grooves, and flatness, can be evaluated. The scanning rate and sampling rate of the laser-based measurement system are 100 mm/s and 10 KHz, respectively. In the future, an appliance machine based on the proposed system will be designed for the on-line detection of scraping workpieces.