Modifications of the Surface of a Stainless Steel Limiter During Operation in the T-10 Tokamak

Parts of a stainless steel limiter used in the T-10 tokamak for about 1000 discharges have been analyzed by several standard analysis techniques as SEM, EDS, SAM, AES, RBS and SIMS with respect to modifications of surface structure and chemical composition. Erosion phenomena due to melting and evaporation, arcing, and sputtering could be observed on limiter parts exposed to the plasma flux. In these regions the chemical composition was changed only slightly, whereas in regions shielded by other internal structures of T-10 impurity layers with a thickness up to about 3000 Å were deposited. Additionally on the limiter surface there has been found a considerable number of microscopic particles. They seem to originate from different internal components of T-10, as the fixed W/Mo-limiter, a Ti-anode, and Inconel made parts of the vessel.     

Analyses of edge plasma characteristics in HL-2A

The edge plasma characteristics are studied by both a movable array of Mach/Reynolds stress/Langmuir 10-probes in the boundary region and the fixed flush probe arrays on the 4 divertor neutralization plates at the same toroidal cross-section in the HL-2A tokamak. The dependence of the Reynolds stress on poloidal flow in the edge plasma is analysed. The result indicates that the sheared poloidal flow in tokamak plasma can be induced by the radial gradient of Reynolds stress. In the divertor experiments of HL-2A, the profiles of the electron temperature, density and floating potential on divertor plates are measured by the flush probe arrays. The edge electron temperature in divertor configuration is higher than that in limiter configuration. The temperature asymmetry between outer and inner target plates is observed. The result of magnetic surface reconstructed from 18 Mirnov coils signals is presented. Both the particle recycling and the impurity flux in the bulk plasma during divertor discharges are discussed. Neutral gas pressure in divertor chamber, measured by fast ionization gauge during divertor discharge, is given.     

氮ECR微波等离子体的电子能量分布研究

为了对ＧａＮ薄膜低温生长提供更多的活性氮，在一个腔耦合电子回旋共振（ＥＣＲ）半导体加工装置上，用朗谬探针和二次微分理论，研究了氮ＥＣＲ等离子体的实际电子能量分布。发现它们都是非麦克斯韦分布，含有高能电子，而且随着放电气压的下降和微波功率的增加，高能电子成分增加。     

Deuterium and Impurity Flux Measurements in the Boundary Plasma of T-10

Time resolved measurements of deuterium and impurity fluxes in the boundary layer of T-10 tokamak were carried out using carbon strips as deposition probes. Analysing these probes by RBS and ERD deuterium impact energies of 25–40 eV could be estimated from the saturation behaviour of deuterium in carbon. The high impurity concentration level and it's time behaviour give indications for local impurity producing sources playing an important role for the impurity transport in the near wall plasma.     

HL-1装置石墨孔栏杂质收集探针的俄歇电子能谱及孔栏表面分析

在HL-1装置的输样机构上安放了硅收集探针。经过55次高功率托卡马克放电辐照后,对于因石墨孔栏被腐蚀而溅射蒸发,并沉积在硅收集探针上的杂质涂层进行了俄歇电子能谱(AES)分析,获得无主动冷却石墨孔栏被腐蚀而溅射蒸发出来的碳杂质流通量约为8×10~(13)cm~(-2)·S~(-1),金属重杂质镍和铬较GH39高镍钢孔栏时降低44％左右。     

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}     

The impact Of impurity ion in deuterium-tritium fuel on the energy deposition pattern Of The Proton Ignitor Beam

The ignition stage of deuterium-tritium fuel in inertial confinement fusion is a challenging task affected by many undesirable processes especially material mixing processes in the hot-spot region. In this research, an alternative proposal of the enhanced energy deposition in the proton fast ignition has been suggested. It consists of two primary assumptions of the beam-plasma system. In the first place, we have adopted the proton beam generated by TNSA or RPA mechanisms, each described by a Maxwellian or Gaussian energy distributions. Next, a realistic, non-uniform fuel plasma was adopted. Then, the cumulative stopping power of a proton beam of 10 kJ energy, penetrating the low content metal-contaminated deuterium-tritium fuel has been examined. It has been shown that in the case of the very low impurity fractions, irregular spatial fluctuations in the cumulative stopping power relative to pure fuel plasma emerges. However, at the higher concentrations, a systematic pattern becomes visible such that the contribution of the deep layers in the stopping power reduces. We observe the enhanced energy deposition close to the corona/dense core interface. It has been shown that the corona/dense core energy deposition ratio differs by up to 2.5% between pure and contaminated DT plasma. In the contaminated fuel plasma, energy deposition in the TNSA regime will effectively heat the plasma corona. While in the RPA counterpart, at a similar level of contamination, most of the incident beam energy remains inside the core fuel region.     

Analysis of the Limiter Material Erosion in T-3M Tokamak

The limiter material erosion dynamics under disruption instability in T-3M tokamak was studied. Erosion mechanisms of graphite (uglesitall) and boron nitride were examined. It was shown that the erosion of the limiter arises not only at the moment of disruption, but also before it, when the MHD perturbations of plasma column emerge. We had evidence of the superthermal electrons playing a significant role in the limiter erosion. The erosion decreases with the plasma density rising above the threshold value.     

Comment on determination of electron temperature from Langmuir probe data in tokamak edge plasma

Langmuir probe measurements of electron temperature in a plasma in the limiter shadow of a tokamak are presented together with a method of probe data analysis which takes into account the influence of the ion current vs voltage dependence in the determination of electron temperature, The method is based on the transformation of a single into a double probe characteristic. Values of the electron temperature calculated using this method are compared with the values estimated from single probe characteristic data.     

长脉冲等离子体放电下HT-7装置限制器温度变化及能流分析

 在HT-7托卡马克等离子体长脉冲放电过程中，作为直接面对等离子体的第一壁限制器表面的温度变化及其承受的能流密度的计算，对于判断限制器的作用和对等离子体的影响都有非常重要的意义。主要从测量到的距离限制器表面3mm处温度变化曲线,采用无限大平面模型计算限制器模头表面能量沉积的能流密度,并讨论了不同等离子体放电下局部点能流密度的差别。多数长脉冲放电下，少数局部点的温升超过1 000℃，最大能流密度超过10MW/m ²；但通过对等离子体位移的控制，局部点温升被抑制，高密度能流持续时间短，有利于长脉冲放电。同时对限制器结构和材料对模头温度的影响也做了比较详细的分析。     

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.     

The effect of LH wave on the peripheral plasma of TM-1-MH tokamak

The work is devoted to the study of the LH wave effect on the peripheral plasma of the TM-1-MH tokamak. The observed enhancement of the ion saturated current in the limiter shadow is interpreted as heating of the peripheral ions by absorption of decay waves generated in this region due to the nonlinear wave-plasma interaction.     

Influence of burrowing the atoms on the density of the Fe and Co nanoclusters on the Cu(100) surface

The dependence of the density of the Co and Fe clusters on the Cu(100) surface on the substrate temperature and the deposition flux of the atoms has been studied by the molecular dynamics method and the kinetic Monte Carlo method. It has been shown that burrowing the impurity atoms into the first substrate layer can considerably increase the density of nanoclusters. The influence of burrowing the atoms on the size distribution of nanoclusters has been investigated.     

About bursty behaviour, coherent structures, wide scrape-off layer and large parallel flows in the edge of the Tore Supra tokamak

We present the measurements of plasma characteristics in the scrape-off layer (SOL) of the Tore Supra tokamak performed by means of reciprocating Langmuir probe. The probe is inserted into the machine from top. As the radial distance from last closed flux surface (LCFS) increases, ion saturation current exhibits stronger bursty character and its probability density function becomes increasingly skewed towards positive values. At the same time, burst duration and inter-burst time increase dramatically. We explain this phenomenon by radial propagation and dynamics of the ensemble of coherent turbulent structures of different size. The results of two-dimensional fluid modelling based of flux-driven interchange instability mechanism are in excellent agreement with experimental results. We obtained clear experimental evidence that most of the coherent structures are formed in poloidally localized region of the SOL around the outboard midplane. If the probe is magnetically connected to this region, the SOL is very wide and we detect bursty behaviour in the far SOL. On the other hand, if the probe is not magnetically connected to the outboard midplane region (magnetic field lines are intercepted by the outboard limiter), then the SOL is very thin and bursty behaviour is much less prominent. Detection of bursty behaviour in the far SOL is correlated with existence of wide SOL pointing on important role of bursty transport by means of coherent turbulent structures in establishing the width of the SOL in tokamaks. The measurements of parallel flow in the SOL shows that plasma particle radial flux coming from confinement region to the SOL is mostly poloidally localized around the outboard midplane. Our estimations show that more than 80% of plasma particle radial flux is coming from confinement region to the SOL in poloidally localized region — approximately ±15° — around the outboard midplane. Presented at the Workshop “Electric Fields, Structures and Relaxation in Edge Plasmas”, Roma, Italy, June 26–27, 2006.     

Investigation of the ETA-BETA II plasma edge by surface analysis of collector probes

To investigate the ion flux escaping from the plasma and the impurity flux released by the wall, collector probes made of graphite, silicon and titanium have been exposed to the deuterium plasma confined in the toroidal device ETA BETA II. The damages on the collector surfaces have been surveyed by a scanning electron microscopy (SEM) apparatus. The deuterium and impurity retention have been measured by elastic recoil detection (ERD) and Rutherford backscattering spectroscopy (RBS) techniques respectively. The implantation build-up has been investigated as a function of the exposure time. The deuterium dose in graphite saturates after a few discharges, whereas the metal impurities exhibit a linear increase in time. The deuterium flux and its radial dependence, inferred from the implanted concentrations, have been compared with those measured by Langmuir probes. Metal impurities have been identified and their relative abundances have been compared with the material wall composition. The impurity flux is found consistent with the global content in the plasma derived by spectroscopic measurements. The deuterium dose measured in different samples has been related to the backscattering coefficient of the materials. Finally, to investigate the damage on sample probes facing the plasma particle flow, erosion probes made of vitreous graphite with silver implanted at a fixed depth have been exposed to the plasma and the thickness change after exposure recovered.     

First Results of Biasing Experiments on the T-10 Tokamak

The first results of the electrode biasing experiments performed on the T-10 tokamak are presented. Positive voltage applied to an electrode inserted inside the tokamak limiter results in the H-mode transition characterised by a decrease of D emission intensity, a rise of line-average plasma density and an increase in energy lifetime. Growth of core electron and ion temperatures during the electrode biasing implies the formation of the thermal barrier in addition to the particle transport barrier.     

Measurements of Reynolds stress and turbulence in the boundary plasma of the HT-7 tokamak

Measurements of electric field fluctuations, Reynolds stress and poloidal flow have been performed in the boundary region of the HT-7 tokamak using a Langmuir probe array.Sheared radial electric field and poloidal flow have been found in the vicinity of the limiter and the turbulence has been clearly modified in this region. Furthermore,the electrostatic Reynolds stress component shows a radial gradient close to the velocity shear layer location.All results here indicate that the radial gradient of Reynolds stress may play an important role in the driving of poloidal flows in the plasma boundary region.     

Pulsed laser deposition of thin-film coatings using an antidroplet shield

The formation of thin-film coatings of molybdenum diselenide is studied during the deposition of a laser-induced material flux using a shield that is placed on the path of the expansion of this flux in order to trap the droplet fraction. To increase the efficiency of atomic scattering into the shadow zone (behind the shield), deposition is carried out in an inert gas (argon). As the argon pressure increases to 2 Pa, low-density coatings with a developed surface relief form in the shadow zone. When a negative bias voltage is applied to a substrate, the quality of the coating increases substantially. Numerical experiments based on the combination of two computer models that describe physical processes on the atomic level using Monte Carlo methods are performed to reveal the factors that affect the thickness, chemical composition, and structure of the MoSe _x coatings deposited in the shadow zone. The results of calculating the dynamics of the laser-induced atomic flux in a chamber with a shield are used to simulate the coating growth. The deposition of a scattered atomic flux under conditions of surface bombardment by incident particles is shown to substantially increase the coating density and to smooth away the surface relief.     

Design and construction of hot limiter biasing system for the tokamak

A hot limiter biasing system with a simplified fast switch circuit was designed, constructed, and installed on the IR-T1 tokamak, and then the negative voltage applied to a hot limiter inserted inside the tokamak fixed limiter and the plasma current, poloidal, and radial components of the magnetic fields, loop voltage, diamagnetic flux, and the ion saturation currents in the absence and presence of the biased limiter were measured. Results of measurements of biasing effects on the plasma equilibrium behavior and edge plasma rotation are compared and discussed.     

HL-1装置掠入射真空紫外杂质谱线观测

本文叙述用掠入射谱仪在HL-1装置上所做的真空紫外光谱测量。根据杂质谱线的相对强度变化,说明可动石墨孔栏和蒸钛技术对控制等离子体杂质有一定效果。通过分析谱线、软X射线和m=2模式信号扰动之间的关系,指出杂质对等离子体不稳定性的影响。