Self—Organized Criticality Processes in HL—1M Tokamak Plasma

We study the dynamics of laminar time between successive bursts in anomalous particle flux measured at the HL-1M tokamak plasma edge.The results reveal that the flux fluctuations are self-similar in a narrow range of time scales and that their probability distribution function is not Gaussian.These properties are not consistent with those predicted by self-organized criticality(SOC)models as well as the running sand-pile SOC model developed by Hwa and Kardar.     

Bootstrap Current Increment After Siliconization on the HT—7 Tokamak

We present some results for the estimation of the bootstrap current after sillconization on the HT-7 tokamak.After siliconization,the plasma pressure gradient and the electron temperature near the boundary are larger than before siliconization.These factors influence the ratio of the bootstrap current to the total plasma current which increases from several per cent to above 10%.The results are expected to explain the previous experimental phenomena that,after siliconization,the plasma current profile is broadened and the higher current can be obtained easily on the HT-7 tokamak experiment.     

Statistical Characterization of Boundary Fluctuations in the HT—7 Tokamak

The statistical properties of plasma fluctuations are characterized in the boundary region of HT-7 tokamak. A non-Gaussian feature is observed in fluctuations of ion saturation current and floating potential in most of the scrape-off layer regions. The statistical properties of fluctuations have a clear radial dependence, showing a near-Gaussian character in the proximity of the velocity shear layer location and another region where the poloidal velocity has a trend to zero. Fluctuations show a bursty character with pulses asymmetric in time and the time asymmetry reaches the minimum around the shear layer. From the results, we can see an obvious coupling of the pulses and the poloidal flow.     

Modification of Boundary Fluctuations by LHCD in the HT—7 Tokamak

Measurements of boundary fluctuations and fluctuation driven electron fluxes have been performed in ohmic and lower hybrid current drive enhanced confinement plasma using a graphite Langmuir probe array on HT-7 tokamak. The fluctuations are significantly suppressed and the turbulent fluxes are remarkably depressed in the enhanced plasma. We characterized the statistical properties of fluctuations and the particle flux and found a non-Gaussian character in the whole scrape-off layer with minimum deviations from Gaussian in the proximity of the velocity shear layer in ohmic plasma. In the enhanced plasma the deviations in the boundary region are all reduces obviously. The fluctuations and induced electron fluxes show sporadic bursts asymmetric in time and the asymmetry is remarkably weakened in the lower hybrid current driving (LHCD) phase. The results suggest a coupling between the statistical behaviour of fluctuations and the turbulent flow.     

An Analytical APproach to the Turbulence—Relaxed State in Tokamak Plasmas

Starting from the continuity, temperature, and motion equations of the trapped electron fluid in general tokamak magnetic field with positive or reversed shear and the definition of Lagrangian invariant, dL/dt≡(\partial_t+ u•▽)L=0, where u is convective velocity, the trapped electron dynamics is considered in the following two assumptions: (i) the turbulence is low frequency electrostatic, and (ii) L is a functional only of the density n, temperature T, and magnetic field B, and the effect of perturbation potential φ is included in the convective velocity u, i.e., u is a functional of n, T, B, and φ. The Lagrangian invariant hidden in the trapped electron dynamics is strictly found: L=ln[(n/B)^c₁(T/B^2/3)^c₂], where c₁ and c₂ are dimensionless changeable parameters and c₁∝c₂. From this Lagrangian invariant the turbulent particle and electron thermal transport scaling laws are derived: 〈n>_ψq(ψ)=const. and 〈T^3/2>_ψq(ψ)=const., which, in the limit of large aspect ratio, reduce to n(r)q(r)=const. and T^3/2(r)q(r)=const., respectively. The latter two scaling laws are compared with existent experimental results, being in good agreement.     

Dynamic Stabilization by Modulated Toroidal Current on the HT—7 Superconducting Tokamak

The technique of toroidal current modulation has been successfully used in suppressing magnetohydrodynamic (MHD) perturbations effectively on the HT-7 superconducting tokamak.When the ratio of amplitude of plasma modulated current ΔIp versus the equilibrium plasma current Ipo is about 12-30%,the resonance surface is moved outside the island width,and the suppression of MHD perturbations is observed.The disruption induced by tearing mode intability is delayed or avoided.Different formats of frequency modulated are compared.     

Tokamak中磁力线的随机特性

在直柱近似下，运用哈密顿非线性振荡系统理论研究了平衡态磁场在磁扰动下进入随机状态的过程．结果表明：一阶扰动哈密顿量仅与径向扰动磁场有关；在单模扰动下，磁力线呈规则磁岛结构；在双模扰动下，给出了磁力线进入随机态的重叠判据；在特定多模优动下，将Ｐｏｉｎｃａｒé截面上点演化关系化为一类标准映象。 关键词：     

相对论性电子束的类Tokamak平衡

本文对具有双δ函数速度分布的相对论性电子束,考察了其环形平衡性质。通过对反环径比展开,得到了关于磁通函数及电势的一级近似解析解。还讨论了电子漂移轨道的近似描述。 关键词：     

Investigation of the First Mirror on Tokamak

The study progress of NNSF in 2006 has been presented in this paper. The aim and plan of this item have been described briefly. Three test mirror exposure experiments have been done in this year. The main components of the deposited materials on the first mirror are carbon and iron analyzed by AES. The first mirror is polluted easier during glow discharge and wall processing than omhic discharge.     

Density Modulation Experiments on HT-7 Tokamak

Density modulation experiments are successfully conducted on HT-7 ohmic discharge to investigate particle transport coefficients: diffusion coefficients D and convection velocity V. The particle transport is studied at low (1.5×10¹⁹m^-3) and high (3×10¹⁹ m^-3) density regimes. The clear differences are observed that D is 0.42m²/s and 0.17m²/s, V is 4.7m/s (outward) and 1.6 m/s (inward) for low and high density plasmas respectively, where spatially constant D and V(r) = (r/a)V₀ were assumed for the analysis.     

Microwave Reflectometry on HL-2A Tokamak

One of the most important electron density diagnostics, microwave reflectometry, has been developed on many large and medium nuclear fusion devices in recent years . Not only the electron density profiles with high temporal and spatial resolutions, but also the profiles of plasma rotation and turbulence can be obtained with this diagnostic system.     

HL-2A Tokamak Experiment Data System

HL-2A tokamak experiment data system （ HL-2A EDS ） consists of an experiment network, various of dada acquiring sub-systems, a great deal of realtime data processing applications, a display system, a lot of interacting data analyzing workstations, a data storage system, a management platform, and a high performance computer. The system was built start in 2002, and has been modified greatly since then.     

Characteristic of Disruption on HL-2A Tokamak

The tokamak disruption is a dramatic event in which the plasma confinement is suddenly destroyed. Detailed experimental studies of disruptions have been made in many machines. During disruption, the plasma current and plasma thermal energy content collapse in an uncontrollable way, thereby applying mechanical forces and heat loads onto the vacuum vessel components. For that reason, the disruptions in a tokamak must be investigated and the physical processes leading to and occurring at the disruption need to be understood.     

Vacuum System for HL-2A Tokamak

The vacuum system of today＇s tokamak devices is designed to meet the operational requirements of the experiments. The operation can be divided into five modes, （1） pumping down and leak detecting of the vacuum vessel, （2） baking, （3） plasma-facing component （PFC） conditioning, （4）evacuating and controlling of the particles at plasma edge, （5） plasma discharge experiments.     

Construction of the HL-2A Tokamak

HL-2A is the first tokamak with divertor in China. The objectives of HL-2A are to produce more adaptable divertor configurations to study energy exhaust and impurity control, and to study enhanced core plasma confinement by profile control and moderate plasma shaping. HL-2A has well optimized operational flexibility and excellent accessi-bility for the diagnostic systems to facilitate various plasma experiments.     

HL-2A Tokamak Gas Puff Imaging

Gas puff imaging （GPI） is one of the important diagnostics for the （ITPAC international tokamak physics activity ） and entering the ITPA IDD （ international diagnostics database ） . GPI is related to many investigations, for example, edge radiations, etc.     

Conditional Analysis and Biorthogonal Decomposition of Plasma Turbulence in the CT—6B Tokamak

Coherent structures in the CT-6B tokamak plasma turbulence are detected by using conditional averaging.The results show that the coherent structures are short-lived and do not propagate in the radial direction.The biorthogonal decomposition technique is adopted to analyse further the coherent structure in the turbulence,The time evolution and spatial distribution of the coherent structures are obtained.     

Hybrid Method for Tokamak MHD Equilibrium Configuration Reconstruction

A hybrid method for tokamak MHD equilibrium configuration reconstruction is proposed and employed in the modified EFIT code. This method uses the free boundary tokamak equilibrium configuration reconstruction algorithm with one boundary point fixed. The results show that the position of the fixed point has explicit effects on the reconstructed divertor configurations. In particular, the separatrix of the reconstructed divertor configuration precisely passes the required position when the hybrid method is used in the reconstruction. The profiles of plasma parameters such as pressure and safety factor for reconstructed HL-2A tokamak configurations with the hybrid and the free boundary methods are compared. The possibility for applications of the method to swing the separatrix strike point on the divertor target plate is discussed.