MHD MODELING OF DENSITY LIMIT DISRUPTIONS IN TOKAMAKS
MHD MODELING OF DENSITY LIMIT DISRUPTIONS IN TOKAMAKS
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DOI：
10.1088/0029-5515/31/9/008
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发表时间：
1991-09-01
期刊：
影响因子：
3.3
通讯作者：
SMEULDERS, P
中科院分区：
文献类型：
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作者：
BONDESON, A;PARKER, RD;SMEULDERS, P
托卡马克密度极限破裂过程中的磁流体力学(MHD)活动是用一个包含辐射损失的简单输运模型的三维减阻MHD模拟来数值模拟的。模拟再现了实验观察到的现象，如在轮廓收缩早期阶段等离子体边缘附近的MHD模失稳，随后m=2/n=1模增长到大幅度，一系列小破裂和大破裂。给出了一个新的理论模型，它分两个阶段发生：(1)内部弛豫使放电中心部分的温度变平；(2)电流分布变宽。第一相的内部不稳定性主要是m=1/n=1对流型，但由于与大的m=2/n=1模的非线性耦合，磁扰动具有很强的m=3/n=2分量。在内弛豫过程中，大幅度的2/1、1/1和3/2微扰分裂了磁面，使Q几乎等于1的区域与Q=2附近的随机区域隔离，整个Q小于或等于2的区域的磁场变为随机的。在大扰动的第二阶段，MHD湍流首先在随机场上发展，导致电流丝状化，最初在中心区域Q小于或等于2。这导致中心电流轮廓加宽和2/1模的强烈不稳定性。这种颠覆以m>；2/n=1模式的快速增长而结束。其结果是整个等离子体上的随机磁场和电流分布的大规模加宽。
The magnetohydrodynamic (MHD) activity during density limit disruptions in tokamaks is modelled numerically by three-dimensional resistive reduced MHD simulations with a simple transport model including radiation losses. The simulations reproduce experimentally observed phenomena such as the destabilization of MHD modes near the plasma edge during the early profile contraction phase, followed by growth of the m = 2/n = 1 mode to large amplitude, a sequence of minor disruptions and the major disruption. A new theoretical model is given for the major disruption, which takes place in two phases: (1) an internal relaxation flattens the temperature in the central part of the discharge and (2) the current profile broadens. The internal instability of the first phase has a mainly m = 1/n = 1 convection pattern, but, because of non-linear coupling to the large m = 2/n = 1 mode, the magnetic perturbation has a strong m = 3/n = 2 component. During the internal relaxation, the large amplitude 2/1, 1/1 and 3/2 perturbations break up the magnetic surfaces isolating the q almost-equal-to 1 region from the stochastic region around q = 2, and the magnetic field becomes stochastic in the entire q less-than-or-equal-to 2 region. In the second phase of the major disruption, MHD turbulence first develops on the stochasticized fields, resulting in current filamentation, initially in the central region where q less-than-or-equal-to 2. This leads to a broadening of the central current profile and a strong instability of the 2/1 mode. The disruption ends with rapid growth of the m > 2/n = 1 modes. The result is stochastic magnetic fields across the entire plasma and a large scale broadening of the current profile.