A large-grain-size thick-film polycrystalline diamond detector for x-ray detection

A diamond film with a size of 6 × 6 × 0.5 mm³ is fabricated by electron-assisted chemical vapor deposition. Raman spectrum analysis, x-ray diffraction and scanning electron microscope images confirm the high purity and large grain size, which is larger than 300 μm. Its resistivity is higher than ${10}^{12}\,{\rm{\Omega }}\cdot {\rm{cm}}.$ Interlaced-finger electrodes are imprinted onto the diamond film to develop an x-ray detector. Ohmic contact is confirmed by checking the linearity of its current–voltage curve. The dark current is lower than 0.1 nA under an electric field of 30 kV cm⁻¹. The time response is 220 ps. The sensitivity is about 125 mA W⁻¹ under a biasing voltage of 100 V. A good linear radiation dose rate is also confirmed. This diamond detector is used to measure x-ray on a Z-pinch, which has a double-layer 'nested tungsten wire array'. The pronounced peaks in the measured waveform clearly characterize the x-ray bursts, which proves the performance of this diamond detector.     

A 57-Pin Langmuir Probe Array for Two-Dimensional Diagnosis in the Toroidal KT-5D Steady-State Plasma

In this article, the design idea of a 57-pin Langmuir probe array is presented, together with some experimental results. The manufacture technique of the probe array is discussed. Two-dimensional distributions of the plasma density, the floating potential and their fluctuations in the poloidal cross section are obtained. The blobs, which move radially and poloidally, cause great particle and energy transport. The charge neutralization by the poloidal movement of particles greatly decreases the vertical electric field in the helimak plasma. This leads to a confinement time which is two orders of magnitude larger than the theoretical prediction.     

Impact of resonant magnetic perturbation on blob motion and structure using a gas puff imaging diagnostic on the HL-2A tokamak

The impact of resonant magnetic perturbation(RMP) on blob motion and structure in the SOL of the HL-2A tokamak is studied using a gas puff imaging diagnostic. Ellipse fitting is applied to study the structure and motion of blobs quantitatively. The radial locations, amplitudes and scale sizes of blobs are obtained based on the fitted ellipse. Furthermore, based on the measurement of blob location, the radial and poloidal velocities of blobs are calculated. With the application of RMP, the edge p...     

Steady-State Plasmas in KT5D Magnetized Torus

Steady-state plasma generated by electron cyclotron resonance （ECR） wave in the KT5D magnetized torus was studied using a fast high-resolution camera and Langmuir probes. It was found that both the discharge patterns taken by the camera and the plasma parameters measured by the probes were very sensitive to the working gas pressure and the magnetic configuration of the torus both without and with vertical fields. There existed fast vertical motion of the plasma. Tentative discussion is presented about the observed phenomena such as the bright resonance layer at a high gas pressure and the wave absorption mechanism at a low pressure. Further explanations should be found.     

Upgrading of the Magnetic Confinement Plasma Device KT-5E

In this article we present ideas of providing appropriate poloidal magnetic field for helimaks to help to generate toroidal magnetic plasma torus.Placing a conductive ring in the center of the cross-section to induce a suitable current,we change the helical magnetic field lines in the helimak discharge into magnetic surface.In this kind of discharge,the plasma density is greatly increased,and the corresponding density fluctuation is significantly decreased,showing a better confinement by magnetic shear.It allows more flexible and efficient experimental investigations on the toroidal magnetic confinement plasmas to be carried on in this kind of device.     

Operation Control of a High-resolution Plasma Imaging System in KT5D Torus

1 IntroductionThe light imaging is a very useful tool in monitor-ing plasma discharges with real two dimensional reso-lution, comparing with many commonly used diagnos-tic techniques such as various Langmuir probes, whichmay have good spatial resolution based on point topoint measurements, or chord to chord measurements.TV camera with CCD sensor is one of the imagingtools being used [1~5], however conventional TV cam-eras are usually difficult to program and with ratherlow temporal (typicall…     

Dual-Electrode Biasing Experiments in KT5C Device

Based on the single biasing electrode experiments to optimize the confinement of plasma in the device of KT-5C tokamak, dual-biasing electrodes were inserted into the KT5C plasma for the first time to explore the enhancing effects of biasing and the mechanisms of the biasing. By means of applying different combinations of biasing voltages onto the dual electrodes, the changes of Er, which are the key factor for boosting up the Er × B flow shear, were observed. The time evolution showed that the inner electrode played a major role in dual-biasing, which drew larger current than the outer one. The outer electrode produced little influence. It turned out that the dual-biasing electrodes were as effective as a single one in improving the plasma confinement, for the mechanism of biasing was essentially an edge effect.     

Study of nonlinear mode–mode couplings between Alfvénic modes by the Fourier bicoherence and Lissajous-curve technique in HL-2A

Nonlinear couplings of various Alfvén modes driven by energetic particles in HL-2A are addressed by employing the Fourier bicoherence and Lissajous-curve technique. Long-lived modes and high-frequency coherent modes are presented. Then the squared bicoherence of three waves establishes the existence of three-wave coupling. Lissajous-curves of those waves manifest that their phases are locked, which again confirms that they are nonlinearly coupled to each other. Moreover, coupled modes triggered by supersonic molecular beam injection are investigated. The phase evolution of them is given by the Lissajous-curve. Further details of phase-flip and phase-slip are presented and discussed.     

Preparation of a beam emission spectroscopy diagnostic based on a Lyman-alpha line to diagnose core and edge-plasma density fluctuation on the HL-2A tokamak

In this article, the design of a Lyman-alpha-based beam emission spectroscopy(LAB) diagnostic on the HL-2A tokamak has been proposed for the first time. The purpose of this novel diagnostic is to measure density fluctuations of tokamak plasma. The light-collection system of LAB, which consists of the first mirror and two groups of coaxial double-mirror telescopes, can realize a twosegmented viewing field of ρ = 0–0.2 and ρ = 0.75–1, which is optimized to measure plasma density fluctuation, not o...     

喷嘴角度对水银扩散泵抽气性能影响的DSMC模拟研究

扩散泵由于其大抽速、连续稳态工作的优点,有望应用于未来聚变堆的偏滤器抽气系统中,以降低目前托卡马克装置中广泛采用的捕集式低温泵所带来的高氚存储量问题。由于氚相容性的限制,目前的商业油扩散泵无法直接应用于聚变堆中,水银将是理想的扩散泵工作介质。为了支持未来聚变堆偏滤器抽气系统的水银扩散泵设计,需要针对水银扩散泵开展设计优化研究。本文采用直接模拟蒙特卡洛方法,基于KT-150扩散泵结构,研究了喷嘴角度对水银扩散泵的抽气速度及水银返流率的影响。结果表明喷嘴角度为45°时能够达到最佳的抽气速度1.53m^3/s,同时返流率没有显著提升。