中国环流器2号A托卡马克弹丸注入放电中空电流与反磁剪切位形

具备弱剪切或负磁剪切和内部输运势垒的托卡马克运行方式被认为是提高聚变性能的最有前途的方法.中空电流密度剖面与反磁剪切位形是改进堆芯约束和形成内部输运垒的关键条件之一.在中国环流器2号A(HL-2A)弹丸注入实验中,成功地实现了维持时间约为100 ms的中空电流放电.伴随着中空电流剖面的形成,同时形成了反磁剪切位形.由于欧姆加热功率不太高,且没有外部辅助加热,只能在稳定的中空电流放电阶段看到内部输运垒形成的趋势.在弹丸注入后,电子热扩散系数显著降低,说明弹丸深度注入改善了能量约束.等离子体性能的增强:一方面是由于弹丸注入造成中心高度峰化的电子密度剖面;另一方面是由于等离子体中心存在负磁剪切.同时,中空电流位形有利于改善高密度等离子体的稳定性.结果还表明,在中空电流放电中,等离子体比压值是低的.为了提高βN极限,可在等离子体边界附近放置导电壁.HL-2A弹丸注入实验的结果,为在限制器托卡马克上获得高参数放电提供了一种可能.     

等离子体理论——具有内部输运垒的托卡马克平衡位形关于高n理想磁流体气球模的稳定性

内部输运垒是一种与托卡马克等离子体的改善约束态相联系的现象。在内部输运垒所在区域，等离子体的压强梯度非常大而磁剪切极小，因此，接近内部输运垒的区域，剪切的绝对值很小。与这一现象相关的物理内容非常丰富，如磁流体稳定性问题，以及微观不稳定性（人们认为它们是产生反常输运的原因）的抑制问题等。关于小剪切条件下稳定性的处理方法本身也是一个难题.最近，Connor和Hastie（下面简称CH模型）重新研究了具有内部输运垒的等离子体的高n（环向模数）理想磁流体气球模的稳定性，     

HL-1M装置中电子回旋加热等离子体的热输运研究

研究反常输运一直是托卡马克的重要任务之一，实验已经证明了这些反常输运主要是由等离子体温度和密度梯度驱动的湍流引起的。以前的实验结果表明在具有内部输运垒的高参数等离子体中，离子的热扩散可以减小到新经典水平。这种输运的减小被认为是剪切流对离子温度梯度模的抑制作用。而电子的热输运目前是一个研究的热点。     

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：     

托卡马克等离子体内部输运垒触发机制的数值模拟和并行效率

对托卡马克等离子体内部输运垒触发机制的动力学特征进行了数值模拟,通过区域分解法实现了数值模拟程序并行化,并行效率随计算机规模的增加而提高,结果与理论分析相吻合.并行模拟程序也适合MHD非线性撕裂模的数值求解.     

CT-6B托卡马克装置中软X射线辐射及扰动

软X射线诊断是研究托卡马克等离子体不稳定性的重要手段。本文给出用Au(Si)面垒探测器阵列测量CT-6B托卡马克等离子体软X射线的结果,以及各种等离子体不稳定性时的软X射线辐射空间分布特性。 关键词：     

HL-2A装置高βN双输运垒实验的集成分析

HL-2A托卡马克装置在中性束加热条件下获得了稳定的归一化环向比压(β_N)大于2.5的等离子体,并且实现了瞬态β_N=3.05、归一化密度(n_e,1/n_e,G)～0.6、储能(W_E)～46 kJ和高约束因子(H₉₈)～1.65的高约束性能.本文使用集成模拟平台OMFIT对βN=2.83和βN=3.05时刻的等离子体进行了集成模拟,计算得到的W_E,n_e,1/n_e,G,H₉₈和β_N等与实验参数基本一致,并通过计算发现两种情况下自举电流份额(f_BS)分别约达到45%和46%.此外,还进一步分析了HL-2A装置形成离子温度内部输运垒(ITB)的原因:快离子和E×B剪切流使得芯部湍流输运被抑制,改善了约束,从而形成了离子温度ITB.离子温度的ITB与H模边缘输运垒相互协同形成了高β_N的等离子体.     

托卡马克边界等离子体数值模拟

本文用数值模拟法，通过数值求解二维多流体等离子体输运方程。来模拟托卡马克边界等离子体输运过程和输运特性。模拟计算的结果，对托卡马克偏滤器和第一壁的设计有重要意义。     

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。     

HL—1装置电流上升段辐射与杂质特性

托卡马克等离子体中的杂质会影响托卡马克的放电品质及等离子体特性。许多理论和实验对杂质的产生和输运做了深入详细的研究。等离子体电流起始阶段,由于约束性能不好,会引起大量的杂质产生,辐射损失增大是杂质增加引起的直接后果。杂质辐射是等离子体辐射的主要组成部分之一,等离子体线辐射功率～Z_(eff)~6,复合辐射功率～Z_(eff)~4,轫致辐     

Development and Validation of a Spectrofluorimetric Method for the Determination of Erlotinib in Spiked Human Plasma

A rapid and sensitive spectrofluorimetric method was developed and validated for the determination of erlotinib (ETB), a potent anticancer drug, in spiked human plasma without any derivatization. The described method was validated and the analytical parameters of linearity, accuracy, precision (intra- and inter-day), limit of detection (LOD), and limit of quantification (LOQ) were evaluated. The relation between the fluorescence intensity and concentration was found to be linear (r² 0.9998) over the range 125 to 1000?ng/mL with the detection limit of 15?ng/mL. A simple liquid-liquid extraction method was followed in order to extract the drug from spiked plasma. The mean absolute recoveries of ETB were 85.59?% (±0.57), 86.91?% (±1.77) and 89.31?% (±3.01) at spiked plasma ETB concentration of 5000, 3750 and 2500?ng/mL, respectively. The spectrofluorimetric method presented here is a rapid, simple, specific, and reproducible method and can be used to characterize the plasma pharmacokinetics of ETB.     

Observation of toroidal flow antiparallel to the <E(r) x B(straight theta)> drift direction in the hot electron mode plasmas in the compact helical system

A toroidal flow antiparallel to the drift direction is observed in the hot electron mode plasmas when a large positive electric field and a sharp electron temperature gradient are sustained inside the internal transport barrier in the Compact Helical System. This toroidal flow reaches up to 5x10(4) m/s at the plasma center, and it is large enough to reverse the toroidal flow driven by a tangentially injected neutral beam. These observations clearly show the plasma favors flow in the minimum nablaB direction at the transport barrier.     

Jets in tokamaks: A theoretical study

A new class of bifurcation of the momentum balance equations for a tokamak plasma is presented. The solution exhibits a monopolar localized jet of ExB flow. The jet is generated by the reduction of turbulent viscosity due to ExB velocity shear. Strong jets of localized plasma flow have been observed in tokamaks as a precursor to the development of a transport barrier region with reduced turbulent transport. The jet solution is shown to fit well with the experimental observations.     

Dynamics of the transport barrier formation on the FT-2 tokamak caused by lower hybrid heating

Experiments at the FT-2 tokamak had demonstrated effective plasma LH heating, which was accounted for by both direct absorption of RF power and plasma transport suppression. The improved core confinement accompanied by Internal Transport Barrier (ITB) formation was observed. The RF pulse switch off is followed by triggering of LH transition and the External Transport Barrier (ETB) formation near the last closed flux surface. The present paper is devoted to a much more detailed study of the radial electric fieldE _r behaviour in the region of ITB and ETB and its influence on the tokamak microturbulence in these regions. The new experimental data were obtained by spatial spectroscopic technique using additional pulse helium puffing in hydrogen plasma. Simultaneously microscale plasma oscillations in the frequency band (0.01–2) MHz are observed with local enhanced microwave scattering diagnostics and by x-mode fluctuation reflectometry. Experiments demonstrate that the improved confinement is associated with the modification of microturbulence by the shear of theE×B poloidal velocity. This conclusion is also confirmed by the data obtained by Langmuir probes in the edge plasma. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24, 2002”. The study was performed with the support of the Ministry of General and Professional Education of RF (TOO-7.4-2797), INTAS-01-2056 and the RFBR Grants 00-02-16927, 01-02-17926 and 02-02-17684.     

Self-Similarity of Edge Plasma Fluctuations in TEXTOR

In TEXTOR the long-range time dependence of edge plasma fluctuations has been investigated. The results indicate that the tail of the autocorrelation function decays as a power law for time lags longer than the local decorrelation time. The frequency spectra of the fluctuations show similar features to those obtained in "sandpile" models. Using rescaled range (R/S) analysis techniques the self-similarity parameters have been estimated for the potential fluctuation data detected by Langmuir probes. The results show that the Hurst exponents are well above 0.5 over the self-similarity range at all the measured radial locations. All these facts reveal the self-similar character of the electrostatic fluctuations at the plasma edge of TEXTOR, consistent with plasma transport as characterized by self-organized criticality (SOC). Furthermore, we have analyzed in this respect discharges in which an edge transport barrier was created by means of edge biasing, hitherto limited to floating potential measurements in the scrape off layer outside the barrier region. The results show a decrease of fluctuating amplitudes, a reduction of decorrelation time of local turbulence and, surprisingly, a concomitant increase of the Hurst exponent. This result implies that the mechanisms governing the decorrelation of local turbulence may differ from those governing the decorrelation of SOC transport events.     

Suppression of plasma turbulence during optimized shear configurations in JET

Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB.     

Quasisteady high-confinement reversed shear plasma with large bootstrap current fraction under full noninductive current drive condition in JT-60U

A quasisteady reversed shear plasma with a large bootstrap current fraction ( approximately 80%) has been obtained for the first time in the JT-60U tokamak. The shrinkage of reversed shear region was suppressed by the bootstrap current peaked at the internal transport barrier (ITB) layer and the ITBs at a large radius were sustained, which, by combination with an H-mode edge pedestal, resulted in a high confinement or 2.2 times the H-mode scaling for 6 times energy confinement time or 2.7 s. Furthermore, a full noninductive current drive was obtained by the bootstrap current and the beam driven current.     

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.     

Reaching high poloidal beta at Greenwald density with internal transport barrier close to full noninductive current drive

In the ASDEX Upgrade tokamak, high poloidal beta up to beta(pol) = 3 at the Greenwald density with H-mode confinement has been reached. Because of the high beta, the plasma current is driven almost fully noninductively, consisting of 51% bootstrap and 43% neutral beam driven current. To reach these conditions the discharge is operated at low plasma current ( I(P) = 400 kA) and high neutral beam heating power ( P(NBI) = 10 MW). The discharge combines an edge (H mode) and internal transport barrier at high densities without confinement-limiting MHD activities. The extrapolation to higher plasma currents may offer a promising way for an advanced scenario based fusion reactor.     

Characteristics of electron heat transport of plasma with an electron internal-transport barrier in the large helical device

Associated with the transition from ion root to electron root, an electron internal transport barrier (ITB) appears in the large helical device, when the heating power of electron cyclotron resonance heating exceeds the threshold power. The incremental thermal diffusivity of electron heat transport chi(inc)(e) in the ITB plasma is much lower than that in the plasma with the heating power below the threshold, and the thermal diffusivity chi(e) decreases with increasing of heating power [dchi(e)/d(P/n(e))<0] in helical ITB plasmas.