Investigation of the effect of electron cyclotron heating on runaway generation in the KSTAR tokamak

Wave enhanced runaway generation is expected to play an important role in the conversion of plasma current into runaway current during major disruptions. The fast electrons created by electron cyclotron heating (ECH) were used to study this issue in KSTAR. It is found that the fast electrons driven by ECH can enhance runaway production in the flat top phase with high loop voltage. The runaway current in disruptions was not enhanced by the ECH produced fast electron population due to the strong magnetic fluctuations which inhibited the generation of runaway electrons. It is found that a complete loss of existing REs during thermal quench has occurred in KSTAR limiter configuration discharges.     

Experimental characterization of the electron heat transport in low-density ASDEX upgrade plasmas.

The electron heat transport is investigated in ASDEX Upgrade conventional L-mode plasmas with pure electron heating provided by electron-cyclotron heating (ECH) at low density. Under these conditions, steady-state and ECH modulation experiments indicate without ambiguity that electron heat transport exhibits a clear threshold in inverted Delta T(e)/T(e) and also suggest that it has a gyro-Bohm character.     

Inductive current density perturbations to probe electron internal transport barriers in tokamaks

Improved electron energy confinement in tokamak plasmas, related to internal transport barriers, has been linked to nonmonotonic current density profiles. This is difficult to prove experimentally since usually the current profiles evolve continuously and current injection generally requires significant input power. New experiments are presented, in which the inductive current is used to generate positive and negative current density perturbations in the plasma center, with negligible input power. These results demonstrate unambiguously for the first time that the electron confinement can be modified significantly solely by perturbing the current density profile.     

HT-7超导托卡马克调制电流改善等离子体约束

 在HT-7超导托卡马克上进行了电流调制改善等离子体约束物理实验，获得了初步的实验结果。对电流调制时的径向电场进行了数值计算和讨论。当等离子体环向电流以适当的频率和幅值周期性调制时，低模数的磁流体不稳定性得到明显的抑制，等离子体中心电子温度增加了33%，等离子体电子密度分布明显陡化，能量约束时间增加了27%~45%。杂质辐射周期性减少,粒子约束时间增加了2倍。在等离子体边界产生更强的径向负电场。     

HL-1装置脉冲送气的数值研究

本文采用一维等离子体输运模型,研究了脉冲送气对HL-1装置等离子体的影响。脉冲送气使等离子体密度提高1—2倍,能量约束时间增长50％,离子温度也有所提高;脉冲送气过程中,等离子体边缘迅速冷却,电流通道收缩,中心区域电子温度平直化。     

Particle confinement and density profile behaviour on HL-1M

In this paper the density profile behaviour and the particle confinement operation regime on HL-1M have been studied under the pellet injection (PI), supersonic molecular beam injection (SMBI), gas puffing (GP) and lower hybrid current drive experimental situations. The relationships between density profile, particle confinement time and edge safe factor have been explored. The density profile, which is measured by six-channel far-infrared ray laser interferometer has been analysed by using the peaking coefficient calculation code. Changes of the outward and inward diffusion velocities before and after the peaking of the central density profile have been calculated using the global particle balance equations. The particle confinement operation regimes have been discussed. The peaking density profile can be easily obtained under the condition of efficient fuelling. In ohmic discharges, confinement time increases as the peaking density profile factor rises, and is saturated at a critical value related to the fuelling efficiency. The particle confinement time of SMBI lies between the values of GP and PI, and its value is about 3-5 times of the energy confinement time.     

Direct determination of the electron energy confinement time of a tokamak plasma

A method of determining the electron energy confinement time τ_E is presented which does not require the absolute electron temperatures and densities, or their spatial profiles. A short heating pulse is applied to the plasma; the subsequent decay of electron temperature yields τ_E.     

EAST 电子回旋共振加热效果的数值模拟和分析

为了给EAST 电子回旋共振加热物理实验提供理论依据和模拟预测,从电子热输运方程出发,运用 CRONOS 输运程序对不同等离子体和波参数下,电子回旋加热效果进行了数值模拟计算。给出不同电子回旋波功率、入射角、电子密度和纵场等参数对电子回旋加热效果的影响,预测在不同参数下,电子温度、等离子体总内能和能量约束时间的变化,分析了其原因,并与实验结果进行了初步的比较。     

HT-7托卡马克大功率低混杂波电流驱动的实验研究

在HT-7超导托卡马克成功进行了大功率（P_LHW=100—800 kW,f=2.45 GHz）低混杂波电流驱动实验.研究了不同入射功率和等离子体密度下的低混杂波电流驱动效率.获得了以平均电子密度增加、氘阿尔法（D_α）线辐射减少为特征的粒子约束改善;粒子约束时间τ_p增加了约1.5倍.仔细研究了能量约束时间与等离子体密度和低混杂波功率的关系. 关键词： 托卡马克 低混杂波 约束改善 电流驱动效率     

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在HL-2A装置孔栏位形放电的等离子体实验中,电子回旋辅助加热期间观察到了等离子体约束改善的现象,并对等离子体从低约束模式(L模)向约束改善模式转换时的等离子体线平均电子密度、等离子体储能、分界面内辐射功率、能量约束时间、Hα辐射等进行了研究。同时,分析了电子密度和等离子体辐射功率的空间分布随时间的演化。对改善约束的相关功率(辅助加热、欧姆加热功率和损失功率)进行了分析,并研究了等离子体约束改善转换时的边界净输入功率(阈值)与电子线平均密度和环向磁场的关系。     

HL-2A装置的约束改善和边界净输入功率分析

在HL-2A装置孔栏位形放电的等离子体实验中,电子回旋辅助加热期间观察到了等离子体约束改善的现象,并对等离子体从低约束模式(L模)向约束改善模式转换时的等离子体线平均电子密度、等离子体储能、分界面内辐射功率、能量约束时间、H_α辐射等进行了研究。同时,分析了电子密度和等离子体辐射功率的空间分布随时间的演化。对改善约束的相关功率(辅助加热、欧姆加热功率和损失功率)进行了分析,并研究了等离子体约束改善转换时的边界净输入功率(阈值)与电子线平均密度和环向磁场的关系。     

Experimental studies on E×B drift rotational transform andconfinement in the bumpy torus NBT-1M

Experimental studies on E×B drift rotational transform for toroidal plasma confinement were carried out using a bumpy torus NBT-1M. An inward radial electric field was observed, which induced E×B poloidal precession and formed closed drift surfaces in a conventional ECH configuration. However, the confinement was degraded by the plasma convective loss due to the asymmetric potential profile and core electrostatic fluctuations. By the use of a combination of two frequencies for ECH (18 GHz and 8.5 GHz), we could reduce both the potential asymmetry and the fluctuation. In this operation, the plasma confinement by E×B drift rotational transform was demonstrated more clearly than that in the conventional single frequency operation     

Density Profile and Diffusion Coefficient During IBW Heating in the HT-7 Superconducting Tokamak

The electron density coefficient was studied during IBW heating in the HT-7 tokamak. The frequency of IBW was 30 MHz, and the injected power was 130 kW. An improved confinement mode was induced by IBW heating in the HT-7. The peaked density profile was formed gradually, and the Ha radiation intensity was decreased abruptly. A five-channel far-infared (FIR) hydrogen cyanide (HCN) laser interferometer was used to measure the electron density profile. The evolution of the density profile and the soft X ray intensity profile were studied during the improved confinement phase. The electron density diffusion coefficient was studied carefully for IBW heating discharges. The results were compared with Ohmic heating plasma and with different toroidal field Bt (2.0 T and 1.8 T). For 30MHz frequency of IBW heating, the higher Bt leads the lower electron density diffusion coefficient at the region of r/a > 0.6 in the HT-7.     

利用软X射线锯齿振荡研究托卡马克等离子体的热输运

用Au(Si)面垒探测器阵列测定了CT-6B托卡马克等离子体的软X射线辐射及其涨落。本文给出了内破裂期间等离子体中心区的软X射线锯齿振荡的经验定标律,利用电子温度的锯齿振荡研究了内破裂期间中心区的电子加热率,电子能量平衡,电子能量约束时间,电流密度分布和电子温度等电子热输运结果。 关键词：     

HL-1M托卡马克氦输运和排除

研究了HL－1M托卡马克常规欧姆放电和改善的束状态下的氦输运和排除,并与一维蒙特卡罗中性氦输运程序IDHET的计算结果进行了比较。实验结果表明,真空泵能有效地抽除辉光放电清洗后在剩余气体中的氦,使真空室内的氦趋于一个较低的固有水平。在改善约束实验中,发现氦有积累增加的趋势,氦谱线发射强度径向分布峰向内移,在对总体约束影响很小的情况下,利用低水平的MHD扰动,采取LHCD与ECH辅助加热功率组合等进行了一些选择性排氦实验,并对将来堆条件下或HL－2A装置上利用射频场有质动力改善排氦效率的前景进行了讨论。     

Ion and electron heating characteristics of magnetic reconnection in a two flux loop merging experiment

Characteristics of the high-power reconnection heating were measured for the first time directly by two-dimensional measurements of ion and electron temperatures. While electrons are heated mainly inside the current sheet by the Ohmic heating power, ions are heated mainly by fast shock or viscosity damping of the reconnection outflow in the two downstream areas. The magnetic reconnection converts the energy of reconnecting magnetic field B(p) mostly to the ion thermal energy, indicating that the reconnection heating energy is proportional to B(p)(2).     

Potential Confinement of a High Density Plasma in the GAMMA 10 Tandem Mirror

Potential confinement was demonstrated experimentally under various electron cyclotron resonance heating (ECRH) scenarios. The particle confinement time and the plasma confining potential increased with ECRH power. The plug potential formation by means of only _ce ECRH was studied by Monte-Carlo simulation. Potential confinement experiments have advanced in higher density region up to 4×10¹² cm^-3. The higher density plasma was obtained by high frequency ICRF heating and recently installed neutral beam injector in the central cell. Studies of scaling relation of the potential confinement with respect to the plasma density have started with the high density plasma.     

HL-2M装置中心螺线管线圈电源变流器过流保护的仿真研究

利用MATLAB仿真工具,搭建HL-2M中心螺线管(CS)电源系统模型,研究了CS电源变流器过流保护策略。通过仿真研究,为HL-2M CS电源系统中变流器制定了最优的过流保护策略,这为电源安全可靠的运行提供了理论依据。     

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.     

低杂波控制电流分布与改善约束研究

在HT-7超导托卡马克装置上利用低杂波电流驱动有效地控制了等离子体电流分布,并使等离子体约束性能改善。数值模拟与硬X射线测量结果均表明,低杂波的发射功率谱、纵场和等离子体密度对改变等离子体电流分布有明显的影响。在优化低杂波电流驱动实验参数的条件下,等离子体密度、温度分布发生了理想的变化。在电子和离子温度分布上出现了内部输运垒,同时等离子体的能量约束时间和粒子约束时间均有提高。