共查询到20条相似文献,搜索用时 31 毫秒
1.
H. Gerhauser G. Mank R. Zagórski T. Loarer J. Gunn C. Boucher 《Czechoslovak Journal of Physics》2001,51(10):1033-1046
The 2D multifluid code TECXY has been used to model the experimental biasing of the toroidal belt limiter ALT-II on the tokamak TEXTOR-94 with respect to the first wall. It is well known that the edge flow pattern can be influenced by the poloidal electric drifts from imposing radial electric fields. The modelling with TECXY introduces imprinted bias currents in the scrape-off layer for the case of negative (limiter) biasing, and imprinted bias potentials for the case of positive biasing. This allows to simulate sufficiently well the experimental current-voltage characteristics for either biasing and also reproduces the essential features and trends of the observed plasma profiles in the SOL. A moderate negative biasing is found to be optimal for the exhaust efficiency of the pump limiter. 相似文献
2.
Measurements of the radial electric field profile in magnetically confined plasmas have yielded important new insights in
the physics of L-H transitions, edge biasing and/or the active control of Internal and Edge Transport Barriers. The radial
electric field is not an easy plasma parameter to diagnose. Techniques to measure the radial electric field in the plasma
core are the Heavy Ion Beam Probe and the Motional Stark Effect. An indirect method that is quite often applied is to derive
the electric field from measurements of the poloidal and toroidal rotation velocities via the radial ion force balance. This
paper will first briefly explain the need for detailed measurements of the radial electric field profile. Subsequently, the
various diagnostics to measure this parameter will be reviewed. The emphasis will be especially put on recent trends, rather
than on an exhaustive overview.
Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24,
2002.
Partner in the Trilateral Euregio Cluster 相似文献
3.
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. 相似文献
4.
T. Loarer J. Gunn J. L. Lachambre E. Gravier C. Boucher K. H. Finken M. Lehnen G. Mank S. Jachmich H. Van Goubergen G. Van Oost 《Czechoslovak Journal of Physics》2001,51(10):1021-1031
Particle collection by the ALT-II belt limiter in the TEXTOR-94 tokamak is exclusively limited to the parallel outflux because the scoop walls that are oriented parallel to the field lines obstruct the poloidal E×B mass flow. With normal B
tor direction (E×B towards the scoops), a threefold decrease of plenum pressure is measured during negative biasing, while with reversed B
tor (E×B away from the scoops), a 60% pressure increase is observed. This behaviour is exactly opposite to that observed in X-point divertors. A simple fluid model explains this apparent contradiction, and gives good quantitative agreement with measurements of the parallel Mach number in the SOL. The essential physics is governed by the Bohm-Chodura criterion. 相似文献
5.
在托卡马克KT-5C上,我们首次采用可灵活组合的多块限制器进行了施加偏压以控制等离子体边缘电场的实验,结果表明,在本装置上限制器加正偏压优于加负偏压,正偏压改变等离子体边缘电场效果更明显。偏压限制器收集面积、纵场和偏置电压的大小对偏压效果的影响都是敏感的。改变限制器收集面积和偏压导致的边缘电场的变化最终将趋于饱和,另外发现,偏压限制器与等离子体柱的相对位置对等离子体边缘电场的影响也是重要的。 相似文献
6.
Guido Van Oost James P. Gunn Alexander Melnikov Jan Stöckel Michael Tendler 《Czechoslovak Journal of Physics》2001,51(10):957-975
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. 相似文献
7.
An experiment to investigate the source of plasma equilibrium of the residual plasma at zero cross over of plasma current is presented. The role of limiter in providing this equilibrium by short circuiting the electric field developed due to the toroidal drifts is examined by measuring the current flowing through the limiter. The role of a fast poloidal rotation observed by a set of Mach probes, during zero cross over is also examined in providing the equilibrium. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
P. Helander S. J. Fielding R. H. Cohen D. D. Ryutov 《Czechoslovak Journal of Physics》2000,50(12):1421-1430
It has been suggested that by electrically biasing the divertor tiles in a tokamak, one could create a toroidally-asymmetric
potential structure in the scrape-off layer (SOL) plasma. The resultingE×B convective motion should increase the plasma transport in the SOL and thereby reduce the heat load on the divertor plates.
This paper describes plans for such experiments on COMPASS-D and preliminary theoretical modelling. The COMPASS-D divertor
target consists of 24 graphite tiled toroidal segments. The inner and outer strike point tiles on all these segments will
be insulated from each other, and cabling will be installed to allow for biasing of individual tiles in any combination. Theoretical
analysis suggests that the electrostatic potential perturbations caused by the biasing will be confined to the divertor region
below the X-point, and that substantial SOL broadening can be achieved by applying modest voltages. Aside from active control
of SOL transport, it is hoped that the biasing will be useful to probe other divertor and SOL physics issues.
Presented at the Workshop on the Role of Electric Fields in Plasma Confinement and Exhaust, Budapest, 18–19 June, 2000.
This work was jointly funded by the UK Department of Trade and Industry and Euratom, and was supported by US DoE under contract
W-7405-ENG-48 at LLNL. 相似文献
9.
P. Devynck J. Stöckel J. Adámek I. Ďuran M. Hron G. Van Oost 《Czechoslovak Journal of Physics》2003,53(10):853-862
The poloidal structure of the turbulence and the turbulent particle flux in the scrape-off layer (SOL) of the CASTOR tokamak are analysed by means of a poloidal ring of 124 probes distributed uniformly along the whole poloidal circumference. Fluctuation measurements are performed in standard ohmic regime as well as in discharges when a biased electrode is inserted either into the SOL or deeper into the confinement region. It is found that in both cases a strongly sheared radial electric field is created in the SOL, which de-correlates the density and radial velocity fluctuations and reduces their levels. Consequently, the turbulent flux is reduced. However, no phase shift is observed between density and radial velocity fluctuations. When the electrode is localized in the confinement region, all the above effects are less pronounced because of a smaller shear. In addition, the increase of the E × B velocity at biasing leads in both cases to the formation of oscillations in the temporal correlation function. These oscillations are specifically associated to the poloidal mode (m = q), which is created for a limited time and rotates poloidally. This mode does not modify the phase between density and radial velocity fluctuations and has no further effect on the turbulent flux. 相似文献
10.
HL—1装置等离子体粒子平衡的光谱研究 总被引:1,自引:1,他引:0
本文描述HL-1装置器壁碳化,观察了碳化前后氢的约束时间和再循环现象,同时还观察了加抽气孔栏条件下粒子约束时间和再循环的变化。实验表明,碳化后氢的再循环增大,使用抽气孔栏可以控制壁附近边缘等离子体的粒子密度,粒子约束时间比不用抽气孔栏增大17.7%,再循环系数减小13.2%。 相似文献
11.
J. P. Gunn 《Czechoslovak Journal of Physics》2004,54(3):C135
A simple fluid model is used to interpret two edge flow phenomena that are observed in the scrape-off layer of the Tore Supra tokamak. (1) The Mach number of the parallel flow midway between the two sides of the toroidal limiter is always a significant fraction of the ion sound speed, typicallyM ?=?0.3÷?0.6. directed towards the high field side. In Tore Supra theE×B drift is relatively unimportant, so the esixtence of alarge parallel flow implies a significant poloidal aysmmetry of the SOL source. (2) Massive injection of neutral gas leads to a recycling source that is poloidally localized near the nozzle. The parallel Mach number changes during injection. The sign of the change is positive for injection on the high field side, and negative for injection on the low field side. The ionization source that is needed to produce the change is about 5÷10% of the total amount of injected gas, consistent with atomic physics calculations. 相似文献
12.
Blob control by creating convective cells using biased electrodes is demonstrated in simple magnetized toroidal plasmas. A two-dimensional array of electrodes is installed on a metal limiter to obtain different biasing schemes. Detailed two-dimensional measurements across the magnetic field reveal the formation of a convective cell, which shows a high degree of uniformity along the magnetic field. Depending on the biasing scheme, radial and vertical blob velocities can be varied significantly. A high level of cross-field currents limits the achievable potential variations to values well below the applied bias voltage. Furthermore, the strongest potential variations are not induced along the biased flux tube, but at a position shifted in the direction of plasma flows. 相似文献
13.
HL-2Aƫ����λ�εı�Ե������������ 总被引:1,自引:1,他引:0
通过中平面活动10探针组、往复快速扫描4探针和低杂波天线口的固定4探针测量了主等离子体边缘的温度、密度、悬浮电位、径向和极向电场、雷诺协强、径向和极向等离子体流速及其径向分布。用偏滤器靶板上的14组嵌入式静电3探针阵列测量了同一环向截面的内外中性化板上的电子温度、密度、悬浮电位及其分布。比较了在孔栏位形和偏滤器位形下边缘等离子体特性的差异,特别是两种位形下边缘温度和密度衰减长度的变化。分析了在多脉冲超声分子束加料和低杂波注入条件下的边界等离子体特性,以及雷诺协强的径向梯度与极向流和径向电场梯度与湍流损失的相互关系。 相似文献
14.
采用立体探针与二次离子质谱计(SIMS)分析相结合,对HL-1装置刮削层空间的杂质沉积特性和分布规律进行了实验研究。测量了在石墨活动孔栏条件下,立体针表面杂质沉积特性和分布规律进行了实验研究。测量了在石墨活动孔栏条件下,立体探针表面杂质沉积的径向分布,纵向分布,极向分布和H^+剖面分布。并讨论了实验结果。 相似文献
15.
利用径向可移动朗缪尔三探针和马赫探针对HT-7超导托卡马克边界等离子体参量及其涨落进行了空时空分辨测量.给出了欧姆放电及其与低杂波电流驱动共同作用下边界等离子体电位φp、电子温度Te和电子密度ne及其涨落的径向分布.实验表明,在限制器附近,存在一由Er×B确定的极向旋转速度剪切层.在剪切层内,Te和ne分布较陡,且φp,Te和ne的相对涨落水平下降明显.这说明剪切层对边界区的等离子体涨落具有抑制作用.低杂波驱动使径向电场梯度变陡,从而使剪切程度加深但对剪切层宽度无影响.此外,测量表明等离子体环向速度马赫数Mφ存在径向梯度.环向流的这种径向梯度可能是形成径向电场所需的平均极向流的一种重要驱动源
关键词:
托卡马克
边界涨落
低杂波驱动 相似文献
16.
17.
To model particle and heat-loss terms at the edge of a tokamak with a divertor or pumped limiter, a simple two-chamber formuluation of the scrapeoff has been constructed by integrating the fluid equations, including sources, along open field lines. The model is then solved for a wide range of density and temperature conditions in the scrapeoff, using geometrical parameters typical of the poloidal divertor in the poloidal divertor experiment (PDX). The solutions characterize four divertor operating conditions for beam-heated plasmas: plugged, unplugged, blowthrough, and blowback. 相似文献
18.
The high-energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactors and reduce their life time. Therefore, finding a method to minimize runaway electron generation during a major disruption is much needed. Tokamak limiter biasing is one of the methods that can be used for controlling the radial electric field and can induce a transition to an improved confinement state. This paper attempts to examine the effect of limiter biasing on the generation of runaway electrons during a major disruption. To do so, a horizontal biased limiter placed on the tokamak was used. Main parameters such as plasma current, loop voltage, emitted hard X-ray intensity, magnetohydrodynamic (MHD) oscillation and Hα radiation and spectrum of hard X-rays, in the presence and absence of negative and positive limiter biasing, were measured. The results show that the application of limiter biasing during a major disruption can reduce runaway electron generation. 相似文献
19.
The coupling of lower hybrid wave to the plasma is a
crucial issue for efficient current drive in tokamaks. This paper
establishes a new coupling model which assumes the antenna to be a
curved face and the plasma to be a cylinder. Power spectrum considering
the coupling between wave-guides in both poloidal and toroidal
direction is simply estimated and discussed. The effect of the poloidal wave
vector on wave propagation, power deposition and driven current is
also investigated with the help of lower hybrid current drive code.
Results show that the poloidal wave vector affects the ray tracing,
and also has effect on power deposition and driven current. The
effect of the poloidal wave vector on power deposition and driven
current profile depends on plasma parameters. Preliminary studies
suggest that it seems possible to control the current profile by
adjusting the poloidal phase difference between the waveguide in
poloidal direction. 相似文献
20.
G.S. Kirnev S.A. Grashin L.N. Khimchenko N.N. Timchenko G. Van Oost 《Czechoslovak Journal of Physics》2001,51(10):1011-1019
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. 相似文献