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Particle simulation of the kinetic Kelvin–Helmholtz instability in a magnetoplasma 磁等离子体中动力学开尔文-亥姆霍兹不稳定性的粒子模拟
Pub Date : 1993-10-01 DOI: 10.1063/1.860826
DongSheng Cai, L. Storey, T. Itoh
The kinetic Kelvin–Helmholtz instability in a collisionless magnetoplasma is simulated numerically in cases where the ion gyroradius is comparable with or larger than the spatial scale of the cross‐field shear. The approach consists of starting the simulation from a state close to equilibrium, then observing the linear growth of instabilities and their ultimate saturation. The initial quasiequilibrium state is set up by a newly developed particle loading method; the instabilities are excited by numerical noise. The simulation is performed in two dimensions, in the plane perpendicular to the magnetic field, using an electrostatic particle code. The results for the kinetic Kelvin–Helmholtz instability are similar to those predicted by a hydromagnetic model, except that they depend slightly on the sign of the shear. Other instabilities are observed also: when the ion gyroradius is small on the scale of the shear, there is an unidentified short‐wavelength instability characterized by k Δx≥1, where k is the wa...
在离子回旋半径等于或大于交叉场剪切的空间尺度的情况下,对无碰撞磁等离子体中的动力学开尔文-亥姆霍兹不稳定性进行了数值模拟。该方法包括从接近平衡的状态开始模拟,然后观察不稳定性的线性增长及其最终饱和。采用新提出的颗粒加载法建立了初始准平衡态;不稳定性是由数值噪声激发的。模拟是在二维,在平面垂直于磁场,使用静电粒子代码。动力学开尔文-亥姆霍兹不稳定性的结果与流体磁模型预测的结果相似,除了它们稍微依赖于剪切的符号。还观察到其他不稳定性:当离子回旋半径在剪切尺度上较小时,存在未知的短波不稳定性,其特征为k Δx≥1,其中k为wa…
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引用次数: 10
Three‐dimensional fluid simulations of the nonlinear drift‐resistive ballooning modes in tokamak edge plasmas 托卡马克边缘等离子体非线性漂阻气胀模式的三维流体模拟
Pub Date : 1993-10-01 DOI: 10.1063/1.860842
P. Guzdar, J. Drake, D. McCarthy, A. Hassam, C. Liu
A three‐dimensional study of the turbulence and sheared flow generated by the drift‐resistive ballooning modes in tokamak edge plasmas has been completed. The fluid simulations show that 10%–15% percent density fluctuations can develop in the nonlinear state when the self‐consistently generated shear flow is suppressed. These modes are also found to give rise to poloidally asymmetric particle transport. Characteristic scale lengths of these fluctuations are isotropic in the plane transverse to B and smaller than the connection length along the field line. Sheared poloidal flow is self‐consistently driven by both the Reynolds stress and the Stringer mechanisms. In the presence of self‐consistent shear flow, the transverse spectrum is no longer isotropic transverse to B. The vortices become elongated in the poloidal direction. Also, there is a substantial reduction in both the level of fluctuations of the density and potential and the associated particle transport. These features are in qualitative agreemen...
本文完成了托卡马克边缘等离子体中由漂移-阻力气球模式产生的湍流和剪切流的三维研究。流体模拟表明,当自一致产生的剪切流被抑制时,在非线性状态下密度波动可以达到10% ~ 15%。这些模式也被发现会产生极性不对称的粒子输运。这些波动的特征尺度长度在横贯B的平面上是各向同性的,小于沿场线的连接长度。剪切极向流是由雷诺应力和斯特林格机制共同驱动的。在自一致剪切流的存在下,横向谱在b方向上不再各向同性,涡旋在极向方向上被拉长。此外,密度和势的波动水平以及相关的粒子输运都大大降低。这些特征在质量上是一致的。
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引用次数: 224
Relativistic and ponderomotive self‐focusing of a laser beam in a radially inhomogeneous plasma. I. Paraxial approximation 激光束在径向非均匀等离子体中的相对论性和自动机自聚焦。一、近轴近似
Pub Date : 1993-10-01 DOI: 10.1063/1.860828
H. Brandi, C. Manus, G. Mainfray, T. Lehner, G. Bonnaud
The propagation of a high‐irradiance laser beam in a plasma whose optical index depends nonlinearly on the light intensity is investigated through both theoretical and numerical analyses. The nonlinear effects examined herein are the relativistic decrease of the plasma frequency and the ponderomotive expelling of the electrons. This paper is devoted to focusing and defocusing effects of a beam assumed to remain cylindrical and for a plasma supposed homogeneous along the propagation direction but radially inhomogeneous with a parabolic density profile. A two‐parameter perturbation expansion is used; these two parameters, assumed small with respect to unity, are the ratio of the laser wavelength to the radial electric‐field gradient length and the ratio of the plasma frequency to the laser frequency. The laser field is described in the context of a time envelope and spatial paraxial approximations. An analytical expression is provided for the critical beam power beyond which self‐focusing appears; it depend...
本文通过理论和数值分析研究了高辐照度激光束在光学指数与光强非线性相关的等离子体中的传播。本文研究的非线性效应是等离子体频率的相对论性降低和电子的有源性驱逐。本文研究了假设保持圆柱形的光束和假设沿传播方向均匀但密度呈抛物线分布的等离子体的聚焦和散焦效应。采用双参数摄动展开;这两个参数是激光波长与径向电场梯度长度之比和等离子体频率与激光频率之比,假设相对于单位较小。激光场是在时间包络和空间近轴近似的背景下描述的。给出了临界光束功率的解析表达式,超过该功率会出现自聚焦;它取决于…
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引用次数: 250
Neoclassical bootstrap current and transport in optimized stellarator configurations 优化仿星器配置中的新古典自举电流和输运
Pub Date : 1993-10-01 DOI: 10.1063/1.860843
H. Maassberg, W. Lotz, J. Nührenberg
The neoclassical bootstrap current properties of optimized stellarators are analyzed in the relevant mean‐free‐path regimes and compared with the neoclassical transport properties. Two methods—global Monte Carlo simulation [Phys. Fluids 31, 2984 (1988)], and local analysis with the drift kinetic equation solver code [Phys. Fluids B 1, 563 (1989)]—are employed and good agreement is obtained. Full consistency with the elimination of the bootstrap current and favorable neoclassical transport are found.
分析了优化后的仿星器在相关平均自由程下的新经典自举电流特性,并与新经典输运特性进行了比较。两种方法——全局蒙特卡罗模拟[物理学]。流体力学31,2984(1988)],以及用漂移动力学方程求解程序进行局部分析[j]。流体B 1563(1989)],得到了很好的一致性。发现了完全符合自举电流的消除和有利的新古典输运。
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引用次数: 43
Sub-Alfvenic plasma expansion 亚阿尔芬等离子体膨胀
Pub Date : 1993-10-01 DOI: 10.1063/1.860825
B. Ripin, J. Huba, E. Mclean, C. Manka, T. Peyser, H. Burris, J. Grun
A large ion Larmor radius plasma undergoes a particularly robust form of Rayleigh–Taylor instability when sub‐Alfvenically expanding into a magnetic field. Results from an experimental study of this instability are reported and compared with theory, notably a magnetohydrodynamic (MHD) treatment that includes the Hall term, a generalized kinetic lower‐hybrid drift theory, and with computer simulations. Many theoretical predictions are confirmed while several features remain unexplained. New and unusual features appear in the development of this instability. In the linear stage there is an onset criterion insensitive to the magnetic field, initial density clumping (versus interchange), linear growth rate much higher than in the ‘‘classic’’ MHD regime, and dominant instability wavelength of order of the plasma density scale length. In the nonlinear limit free‐streaming flutes, apparent splitting (bifurcation) of flutes, curling of flutes in the electron cyclotron sense, and a highly asymmetric expansion are ...
当亚阿尔菲尼膨胀到磁场中时,大离子拉莫尔半径等离子体经历了一种特别强大的瑞利-泰勒不稳定性。报告了这种不稳定性的实验研究结果,并与理论进行了比较,特别是磁流体动力学(MHD)处理,包括霍尔项,广义动力学低混合漂移理论,以及计算机模拟。许多理论预测得到了证实,但仍有一些特征无法解释。在这种不稳定性的发展过程中出现了新的和不寻常的特征。在线性阶段,存在一个对磁场不敏感的起始判据,初始密度团块(相对于交换),线性增长率远高于“经典”MHD体制,以及与等离子体密度尺度长度数量级的主要不稳定波长。在非线性极限自由流的凹槽中,凹槽的明显分裂(分岔),电子回旋意义上的凹槽卷曲,以及高度不对称的膨胀。
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引用次数: 86
Simulation of collisionless electrostatic velocity‐shear‐driven instabilities 无碰撞静电速度-剪切驱动不稳定性的模拟
Pub Date : 1993-10-01 DOI: 10.1063/1.860847
P. Pritchett
The properties of electrostatic instabilities in velocity shear layers in collisionless plasmas are investigated by means of two‐dimensional particle simulations for the case where the ion gyroradius is comparable to the scale length of the velocity shear. For modes exactly perpendicular to the magnetic field, the Kelvin–Helmholtz instability dominates the evolution of the system producing eφ/Te≳1; the observed growth rates show no reduction compared to the hydromagnetic limit. To obtain this result for the case of negative shear (v0y’/Ωi<0), it is necessary to include the kinetic modifications to the structure of the shear layer equilibrium. For finite k∥ in the range 0
采用二维粒子模拟的方法研究了无碰撞等离子体中速度剪切层中静电不稳定性的性质,在这种情况下,离子的回旋半径与速度剪切的尺度长度相当。对于完全垂直于磁场的模式,开尔文-亥姆霍兹不稳定性主导了产生eφ/Te约1的系统的演化;观察到的生长率与水磁极限相比没有减少。为了得到负剪切(v0y ' /Ωi<0)情况下的这一结果,有必要将剪切层平衡结构的动力学修饰包括在内。对于k∥在0 2×10−3。
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引用次数: 19
Experimental investigation of three-dimensional magnetic reconnection by use of two colliding spheromaks 利用两个碰撞球点进行三维磁重联的实验研究
Pub Date : 1993-10-01 DOI: 10.1063/1.860840
Y. Ono, A. Morita, M. Katsurai, M. Yamada
Experimental investigation of three‐dimensional (3‐D) effects of magnetic reconnection dynamics has been extended by use of axially colliding spheromaks [M. Yamada et al., Phys. Fluids B 3, 2379 (1991)]. The two toroidal shape spheromak plasmas with major radii of 15–20 cm and with parallel toroidal currents of up to 30 kA collide to merge in an external equilibrium field. It is important to note that the present experimental setup allows one to investigate magnetic reconnection comprehensively from both local and global points of view. Reconnection angle θ between the merging field lines is varied by changing the polarity of the internal toroidal field and the magnitude of an external toroidal field. It is observed that the speed of counterhelicity merging with θ∼180° is about three times faster than that of cohelicity merging with θ∼90°. This suggests the significance of a 3‐D effect on the reconnection process. This difference is attributed to the property of the neutral current sheets with and without the magnetic field component parallel to the reconnection (X) line. In the counterhelicity merging, the neutral current sheet is compressed in much shorter time than in the cohelicity merging, resulting in much higher current density and subsequent faster decay of the current sheet. This induces a faster magnetic reconnection. The reconnection speed increases proportionally with the initial approaching speed of the spheromaks, suggesting that a compressible driven reconnection model is consistent with the present reconnection experimental results.
利用轴向碰撞球标记扩展了磁重联动力学三维效应的实验研究[M]。Yamada et al.,物理学。[j].生物工程学报,1998,27(5):559 - 567。两个主要半径为15 ~ 20 cm、平行环面电流高达30 kA的环形球体等离子体在一个外部平衡场中碰撞合并。值得注意的是,目前的实验设置允许人们从局部和全局的角度全面地研究磁重联。通过改变内部环面磁场的极性和外部环面磁场的大小,可以改变合并磁场线之间的重联角θ。观察到反螺旋合并θ ~ 180°的速度比共螺旋合并θ ~ 90°的速度快3倍。这表明三维效应对重连过程的重要性。这种差异归因于有和没有平行于重连接(X)线的磁场分量的中性电流片的特性。在反螺旋合并中,中性电流片被压缩的时间比在共螺旋合并中短得多,从而导致更高的电流密度和随后更快的电流片衰减。这会导致更快的磁重联。重联速度随球点初始接近速度成比例增加,表明可压缩驱动重联模型与目前的重联实验结果一致。
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引用次数: 116
Fluid analysis of the collisionless magnetohydrodynamic ballooning mode branch in tokamaks 托卡马克无碰撞磁流体动力气胀模式分支的流体分析
Pub Date : 1993-10-01 DOI: 10.1063/1.860874
H. Nordman, B. Jhowry, J. Weiland
The stability of electromagnetic ballooning modes is investigated using a toroidal two‐fluid model allowing for arbitrary Ln/LB (the characteristic scale lengths of density and magnetic‐field inhomogeneities). The ballooning mode equation is solved numerically and the two‐fluid and magnetohydrodynamic stability properties are discussed and compared. The perpendicular compressibility strongly reduces the growth rate and for Ln/LB∼Ln/LT∼1, the mode is completely stabilized.
利用一个允许任意Ln/LB(密度和磁场不均匀性的特征尺度长度)的环面双流体模型研究了电磁气球模式的稳定性。对气胀模式方程进行了数值求解,讨论并比较了两流体和磁流体的稳定性。垂直可压缩性大大降低了生长速率,对于Ln/LB ~ Ln/LT ~ 1,模态是完全稳定的。
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引用次数: 11
Two‐dimensional studies of stimulated Brillouin scattering, filamentation, and self‐focusing instabilities of laser light in plasmas 激光在等离子体中的受激布里渊散射、成丝和自聚焦不稳定性的二维研究
Pub Date : 1993-10-01 DOI: 10.1063/1.860845
M. Amin, C. Capjack, P. Frycz, W. Rozmus, V. Tikhonchuk
The parametric interaction of an intense laser beam with ion plasma modes in a two‐dimensional Cartesian geometry has been studied for the first time by avoiding the paraxial optics approximation. This model allows investigation of the competition between forward, sideward, and backward stimulated Brillouin scattering (SBS) along with filamentation and self‐focusing instabilities. It is shown that the SBS saturation level, the angular distribution of transmitted and scattered light, and their temporal dependence are governed mainly by two control parameters: the backward SBS gain coefficient G, and the ratio αsf of the incident beam power to its critical value for the onset of self‐focusing. In the case of large values of G≳15, backward SBS dominates and prevents both self‐focusing and forward SBS. For smaller values of G, the interaction exhibits a complex oscillatory behavior, which corresponds to the competition between backward and forward SBS for αsf≲1, and involves also self‐focusing for higher beam...
本文首次研究了二维直角几何中强激光束与离子等离子体模式的参数相互作用,避免了近轴光学近似。该模型允许研究前向、侧向和后向受激布里渊散射(SBS)以及成丝和自聚焦不稳定性之间的竞争。结果表明,SBS饱和水平、透射光和散射光的角度分布及其时间依赖性主要由两个控制参数决定:后向SBS增益系数G和入射光束功率与自聚焦起始临界值之比αsf。当G≤15时,后向SBS占主导地位,阻止了自聚焦和前向SBS。对于较小的G值,相互作用表现出复杂的振荡行为,对应于αsf > 1时后向和前向SBS之间的竞争,并且还涉及到高光束的自聚焦。
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引用次数: 29
Radio‐frequency‐sheath‐driven edge plasma convection and interaction with the H mode 射频鞘层驱动的边缘等离子体对流及其与H模式的相互作用
Pub Date : 1993-10-01 DOI: 10.1063/1.860832
D. D'Ippolito, J. Myra, J. Jacquinot, M. Bureš
It is shown that radio‐frequency (rf) antenna sheaths can bias the edge plasma potential and drive steady‐state convective cells in the scrape‐off layer (SOL). The resulting E×B convective flow opposes the direction of the sheared flow in the SOL induced by the radially decaying Bohm sheath potential. A two‐dimensional fluid simulation shows that the interaction of the opposing poloidal flows produces secondary vortices, which connect the edge of the confined plasma to the antenna limiters, when the antenna–plasma separation is typically of order a few times the local electron skin depth at the antenna. Estimates for typical tokamak edge parameters suggest that the transit time of particles and energy across these vortices is rapid enough to cause the broadening of SOL density and temperature profiles observed during high‐power heating with ion cyclotron range of frequency (ICRF) antennas in monopole phasing. Radio‐frequency‐sheath‐driven convection is also a good candidate to explain the phasing dependen...
研究表明,射频(rf)天线护套可以使边缘等离子体电位偏置,并在刮脱层(SOL)中驱动稳态对流细胞。由此产生的E×B对流流动与径向衰减玻姆鞘势引起的SOL中剪切流动的方向相反。二维流体模拟表明,当天线与等离子体的分离通常是天线处局部电子趋肤深度的几倍时,相反的极向流的相互作用产生了连接受限等离子体边缘和天线限制器的二次涡。对典型托卡马克边缘参数的估计表明,粒子和能量穿过这些漩涡的传递时间足够快,足以导致在单极相移中使用离子回旋加速器频率范围(ICRF)天线进行高功率加热时观察到的SOL密度和温度分布的扩大。射频鞘层驱动的对流也是解释相位依赖的一个很好的候选者。
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引用次数: 66
期刊
Physics of fluids. B, Plasma physics
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