Negative edge plasma currents in the SINP tokamak

A tokamak plasma discharge having an increase in duration accompanied with enhanced runaway electron flux has been experimentally studied in this paper. The discharges have been obtained by controlling the applied vertical magnetic field (B_v^applB_{\rm{v}}^{\rm{appl}}) to below a critical value. Such discharges have been observed to have ‘negative edge plasma currents’, detected using an internal Rogowskii coil (IRC). We have tried to correlate the runaway behaviour with the negative edge plasma currents and have explained that these observations are a result of beam plasma instabilities.     

Effect of resonant magnetic perturbations on edge plasma parameters in the STOR-M tokamak

Edge plasma properties have been modified in the Saskatchewan Torus-Modified tokamak by means of resonant magnetic perturbations (RMP). It has been found that the radial profiles of ion saturation current and floating potential in the edge region can be modified by an externally applied static (m?=?2, n?=?1) RMP field. An increase in the pedestal plasma density (n) and more negative electric field (E_r) have been observed in the plasma edge region. It is believed that the RMP field altered the plasma transport in the edge and scrape-off layer regions, leading to a higher density pedestal and a potential drop in some cases. During the enhanced confinement phase, it is possible to identify a region where intermittent transport events, the so-called blobs, are created and the holes of lower density left behind.     

Novel high-voltage power device based on self-adaptive interface charge

This paper presents a novel high-voltage lateral double diffused metal--oxide semiconductor (LDMOS) with self-adaptive interface charge (SAC) layer and its physical model of the vertical interface electric field. The SAC can be self-adaptive to collect high concentration dynamic inversion holes, which effectively enhance the electric field of dielectric buried layer (E_I) and increase breakdown voltage (BV). The BV and E_I of SAC LDMOS increase to 612 V and 600 V/μm from 204 V and 90.7 V/μm of the conventional silicon-on-insulator, respectively. Moreover, enhancement factors of η which present the enhanced ability of interface charge on E_I are defined and analysed.     

Ehrenfest’s Paradox and Radial Electric Field in Quasi-Neutral Tokamak Plasma

A relation between physical consequences of the so-called Ehrenfest’s Paradox and the radial electric field E _r (r) in the classical quasi-neutral tokamak plasma is shown. Basic author’s approach to the relativistic nature of the tokamak E _r (r) has been described in Romannikov (J. Exp. Theor. Phys. 108:340–348, 2009). The experiment which can resolve the Ehrenfest’s Paradox is presented.     

HL-1M装置边缘参数测量

在HL－1M装置上利用马赫／郎缪尔探针分别在欧姆放电,低杂波注入,中性束注入,离子回旋加热和电子回旋加热等情况下测量下刮离层和等离子体边缘的极向流速度和电场,得到了它们的径向分布,研究了LHW,NBI,ICRH和ECRH对改善等离子体约束性能,边缘粒子的径向传输的影响。     

A novel partial silicon on insulator high voltage LDMOS with low-k dielectric buried layer

A novel partial silicon-on-insulator (PSOI) high voltage device with a low-k (relative permittivity) dielectric buried layer (LK PSOI) and its breakdown mechanism are presented and investigated by MEDICI.At a low k value the electric field strength in the dielectric buried layer (E I) is enhanced and a Si window makes the substrate share the vertical drop,resulting in a high vertical breakdown voltage;in the lateral direction,a high electric field peak is introduced at the Si window,which modulates the electric field distribution in the SOI layer;consequently,a high breakdown voltage (BV) is obtained.The values of EI and BV of LK PSOI with kI=2 on a 2 μm thick SOI layer over 1 μm thick buried layer are enhanced by 74% and 19%,respectively,compared with those of the conventional PSOI.Furthermore,the Si window also alleviates the self-heating effect.     

A method to separate conservative and magnetically-induced electric fields in calculations for MRI and MRS in electrically-small samples

This work presents a method to separately analyze the conservative electric fields (E_c, primarily originating with the scalar electric potential in the coil winding), and the magnetically-induced electric fields (E_i, caused by the time-varying magnetic field B1) within samples that are much smaller than one wavelength at the frequency of interest. The method consists of first using a numerical simulation method to calculate the total electric field (E_t) and conduction currents (J), then calculating E_i based on J, and finally calculating E_c by subtracting E_i from E_t. The method was applied to calculate electric fields for a small cylindrical sample in a solenoid at 600 MHz. When a non-conductive sample was modeled, calculated values of E_i and E_c were at least in rough agreement with very simple analytical approximations. When the sample was given dielectric and/or conductive properties, E_c was seen to decrease, but still remained much larger than E_i. When a recently-published approach to reduce heating by placing a passive conductor in the shape of a slotted cylinder between the coil and sample was modeled, reduced E_c and improved B1 homogeneity within the sample resulted, in agreement with the published results.     

HT-7超导托卡马克边缘涨落谱特征及湍流输运研究

用郎缪尔三探针对HT-7超导托卡马克边缘等离子体涨落进行了高时空分辩测量.给出了欧姆放电下涨落幅度的径向分布、谱特征及传播特性.实验观察表明,在由E_r×B确定的极向旋转速度剪切层附近,等离子体电位、电子温度和电子密度的相对涨落水平和两两间的相干系数均有明显下降,其极向互相关函数亦减小,这说明剪切层对涨落具有去相关作用.由涨落驱动的径向局域粒子输运通量Γ_tur测量显示出湍动输运具有时间上的阵发特性。将悬浮电位涨落φ_f2的自动率谱P_{( 关键词： 托卡马克 边界涨落 湍流输运}     

Numerical investigation of the theta pinch in intrinsic indiumantimonide

The electron-hole plasma in intrinsic InSb at 300 K can be compressed by electric and magnetic fields. In the theta-pinch configuration one applies, by a capacitor discharge over a one-winding coil around the sample, a magnetic field (0, 0,B _z), which induces an electric field (0,E _φ, 0); both fields cause the ambipolar motion (v _r, 0, 0) of the plasma. We describe the electron-hole plasma by means of a magnetohydrodynamical two-fluid model. The resulting system of differential equations is solved numerically under the assumptions of scalar hydrodynamic pressure and field-independent mobilities. The influence of the plasma properties on the theta pinch is studied as well as the dependence on the experimental conditions like radius of the sample, maximum value and risetime of the magnetic field.     

Volume charge density and radial electric field <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">r</Emphasis></Subscript>(<Emphasis Type="Italic">r</Emphasis>) in a moving tokamak plasma

Electric field E _r transverse to the current in a moving quasi-neutral plasma can (and should) be considered using Poisson equations and densities of volume charges emerging in the plasma. In the general case, E _r becomes nonlocal; i.e., remote volume charge densities are not screened but affect the formation of E _r at the points under investigation. This approach is used for describing a phenomenological theory of radial electric field E _r (r) and velocity of toroidal rotation of the plasma in the tokamak. Examples of application of this theory to actual experiments are considered.     

预试环垂直杂散场

通过氢气击穿实验从数量级上推算了预试环(一个无铜壳的小托卡马克装置)的垂直杂散场。结果符合于按环向场绕组的过渡线和补偿回线的汁算值以及用磁探针对加热场杂散场的测量值。     

Antenna coupling study for ICWC plasma characterization in TEXTOR

Ion cyclotron wall conditioning (ICWC) discharges, in pulsed-mode operation, were carried out in the limiter tokamak TEXTOR to explore safe operational regimes for the experimental parameters for possible ICWC-discharge cleaning in International Thermonuclear Experimental Reactor (ITER) at half field. Antenna coupling properties obtained during the ion cyclotron range of frequencies (ICRF) wall conditioning experiments performed in helium–hydrogen mixture in TEXTOR were analysed in relation to the obtained ICWC-plasma characterization results. Satisfactory antenna coupling in the mode conversion scenario along with reproducible generation of ICRF plasmas for wall conditioning, were achieved by coupling radio frequency (RF) power from one or two ICRF antennas. The plasma breakdown results obtained in the TEXTOR tokamak have been compared with the predictions of a zero-dimensional RF plasma production model. The present study of ICWC emphasizes the beneficial effect of application of an additional (along with toroidal magnetic field) stationary vertical (B _V???B _T) or oscillating poloidal magnetic field (B _P???B _T) on antenna coupling and relevant plasma parameters.     

场效应管并联作为托卡马克垂直场反馈系统调节器的研究

一、引 言 利用垂直场反馈控制等离子体位移是所有托卡马克装置运行的重要组成部分。对于中小型的托卡马克装置,人们曾倾向于用大功率晶闸管作反馈系统的调节器。它所遇到的主要困难有:第一需要有一个较大功率的中频电源。无论是中频发电机或者是逆变器都需要有较大的投资。另一方面受到中频电源的频率及晶闸管的关断时间的限制使反馈系统的时间响     

SnSe分子外场下的基态性质和激发态性质

对Sn原子使用SDB-cc-pVTZ基组, Se原子采用6-311++G^**基组, 利用密度泛函中的B3LYP方法研究了电场强度为-0.04–0.04 a.u.的外电场对SnSe基态分子的几何结构、 电荷布居分布、 HOMO能级、 LUMO能级、 能隙、 费米能级、 谐振频率和红外光谱强度的影响. 继而使用含时密度泛函(TD-B3LYP) 方法研究了SnSe分子在外场下的激发特性. 结果表明, 外电场的大小和方向对SnSe分子基态的这些性质有明显影响. 在所加的电场范围内(-0.04 a.u.–0.04 a.u.), 随着正向电场的增大, 核间距先减小后增大, 在F=0.03 a .u.时取得最小值0.2317 nm; 分子电偶极矩μ近似线性地增大; E_L, E_H、 费米能级E_F和能隙E_g均减小. 随着正向电场逐渐增大, 分子总能量和谐振频率均先增大后减小; 红外谱强度则先减小后增大, 在F=0.03 a.u.时, 取得最小值 0.1138 km·mol^-1. 由基态到第1–10个单重激发态的波长均随着正向电场的增大而增大. 激发能均随着正向电场的增大而减小. 电场的引入可改变SnSe分子激发态出现的顺序并使得一些禁止的跃迁变得可能. 关键词： SnSe 外电场 能隙 激发特性     

The stability margin on EAST tokamak

The experimental advanced superconducting tokamak (EAST) is the first full superconducting tokamak with a D-shaped cross-sectional plasma presently in operation. Its poloidal coils are relatively far from the plasma due to the necessary thermal isolation from the superconducting magnets, which leads to relatively weaker coupling between plasma and poloidal field. This may cause more di?culties in controlling the vertical instability by using the poloidal coils. The measured growth rates of vertical stability are compared with theoretical calculations, based on a rigid plasma model. Poloidal beta and internal inductance are varied to investigate their effects on the stability margin by changing the values of parameters αn and γn(Howl et al 1992 Phys. Fluids B 4 1724), with plasma shape fixed to be a configuration with k = 1.9 and δ = 0.5. A number of ways of studying the stability margin are investigated. Among them, changing the values of parameters κ and li is shown to be the most effective way to increase the stability margin. Finally, a guideline of stability margin Ms(κ,li,A) to a new discharge scenario showing whether plasmas can be stabilized is also presented in this paper.     

Improvement on the breakdown voltage for silicon-on-insulator devices based on epitaxy-separation by implantation oxygen by a partial buried n+-layer

A novel silicon-on-insulator (SOI) high-voltage device based on epitaxy-separation by implantation oxygen (SIMOX) with a partial buried n⁺-layer silicon-on-insulator (PBN SOI) is proposed in this paper. Based on the proposed expressions of the vertical interface electric field, the high concentration interface charges which are accumulated on the interface between top silicon layer and buried oxide layer (BOX) effectively enhance the electric field of the BOX (E_I), resulting in a high breakdown voltage (BV) for the device. For the same thicknesses of top silicon layer (10 μm) and BOX (0.375 upmum), the E_I and BV of PBN SOI are improved by 186.5% and 45.4% in comparison with those of the conventional SOI, respectively.     

The Role of Radial Electric Fields in the Tokamaks TEXTOR-94, CASTOR, and T-10

Radial electric fields (E _r) and their role in the establishment of edge transport barriers and improved confinement have been studied in the tokamaks TEXTOR-94 and CASTOR, where E _r is externally applied to the plasma in a controlled way using a biased electrode, as well as in the tokamak T-10 where an edge transport barrier (H-mode) is obtained during electron-cyclotron resonance heating (ECRH) of the plasma.The physics of radial currents was studied and the radial conductivity in the edge of TEXTOR-94 (R = 1.75 m, a = 0.46 m) was found to be dominated by recycling (ion-neutral collisions) at the last closed flux surface (LCFS) and by parallel viscosity inside the LCFS. From a performance point of view (edge engineering), such electrode biasing was shown to induce a particle transport barrier, a reduction of particle transport, and a concomitant increase in energy confinement. An H-mode-like behaviour can be induced both with positive and negative electric fields. Positive as well as negative electric fields were shown to strongly affect the exhaust of hydrogen, helium, and impurities, not only in the H-mode-like regime.The impact of sheared radial electric fields on turbulent structures and flows at the plasma edge is investigated on the CASTOR tokamak (R = 0.4 m, a = 0.085 m). A non-intrusive biasing scheme that we call "separatrix biasing" is applied whereby the electrode is located in the scrape-off layer (SOL) with its tip just touching the LCFS. There is evidence of strongly sheared radial electric field and E×B flow, resulting in the formation of a transport barrier at the separatrix. Advanced probe diagnosis of the edge region has shown that the E×B shear rate that arises during separatrix biasing is larger than for standard edge plasma biasing. The plasma flows, especially the poloidal E×B drift velocity, are strongly modified in the sheared region, reaching Mach numbers as high as half the sound speed. The corresponding shear rates ( 5×10⁶ s^-1) derived from both the flow and electric field profiles are in excellent agreement and are at least an order of magnitude higher than the growth rate of unstable turbulent modes as estimated from fluctuation measurements.During ECRH in the tokamak T-10 (R = 1.5 m, a = 0.3 m), a regime of improved confinement is obtained with features resembling those in the H-mode in other tokamaks. Using a heavy ion beam probe, a narrow potential well is observed near the limiter together with the typical features of the L-H transition. The time evolution of the plasma profiles during L-H and H-L transitions is clearly correlated with that of the density profile and the formation of a transport barrier near the limiter. The edge electric field is initially positive after the onset of ECRH. It changes its sign during the L-H transition and grows till a steady condition is reached. Similar to the biasing experiments in TEXTOR-94 and CASTOR, the experimentally observed transport barrier is a barrier for particles.     

铁磁/反铁磁双层膜中冷却场对交换偏置场的影响

用铁磁畴壁模型研究了非补偿界面铁磁/反铁磁双层膜中冷却场（包括大小及其方向）对交换偏置场h_E的影响.结果表明：当冷却场的方向与反铁磁层磁易轴一致时,h_E大小与冷却场大小无关.当冷却场的方向偏离磁易轴时,h_E的大小随偏离角度的增大有缓慢的改变,但当冷却场的方向偏离到临界角度γ_c处,h_E的大小发生突变,其γ_c的大小随冷却场的增大而增大.特别是当冷却场的偏离角度大于γ_c后,h_E出现由负转正的现象,其转变点还与冷却场的大小有关.另外,h_E与铁磁层原子层数N_F的关系会发生由h_E∝N^-1_F向h_E∝N^-λ_F的转变,其中λ>1.其发生转变的条件与N_F、冷却场大小和方向密切相关. 关键词： 铁磁/反铁磁双层膜 交换偏置 冷却场     

Influence of peripheral radial electric field on L-H transition in T-10 tokamak

In this paper the peripheral plasma behaviour during and after L-H transition on the tokamak T-10 is considered. Abrupt changes of Scrape-Off Layer (SOL) plasma parameters (ion saturation current, floating potential, electron temperature) are observed in regimes with transition to the improved plasma confinement. Such changes begin (5–150) ms prior to the L-H transition. The time delay of a transition depends on auxiliary plasma heating powerP _aux and plasma currentI _p (at constant toroidal magnetic field inductionB _t). Presented at the Workshop on the Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June, 2000. This work is supported by Ministry of Atomic Energy of Russia (contract 69F) and by Ministry of Science and Technology of Russia (Federal Program “Controlled Thermonuclear Fusion and Plasma Processes”).     

Decay of enhanced density and damping of plasma flows after the electrode biasing termination on the CASTOR tokamak

Electrode biasing is a standard tool for modification of both edge and global plasma parameters on the CASTOR tokamak (R=0.4 m,a=85 mm,B _T=1.3 T,I _p1≈9 kA,q _a≈10). During a steady state phase of a discharge, a polarization voltage is applied on an electrode immersed into the edge plasma. This voltage causes radial currents that create radial electric field and, due to theE×B drift, they cause an enhanced rotation. Then, as a consequence, the interaction with walls decreases and particle confinement and density increase. Recently, the decay of plasma density and plasma flows after the termination of the biasing period was investigated on the CASTOR tokamak. These observations are linked to processes and mechanisms that control generation of radial electric fields in plasmas and damping ofE×B sheared flows and that therefore represent a key issue for understanding the transition to improved confinements modes. In the contribution, measured time scales of the transition to the ohmic regime after the biasing termination will be shown. Further, possible consequences of these measured scales for the valuation and explanation of important processes in the plasma will be discussed.