Pressure-driven relaxation instability in a current-free high-shear helical system
Pressure-driven relaxation instability in a current-free high-shear helical system
复制标题
无电流高剪切螺旋系统中压力驱动的松弛不稳定性
DOI：
10.1088/0029-5515/24/11/003
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发表时间：
1984
期刊：
影响因子：
3.3
通讯作者：
M. Yamagiwa
中科院分区：
文献类型：
--
作者：
M. Wakatani;H. Shirai;M. Yamagiwa
研究了极向模数m=1，环向模数n=1的直螺旋系统中ιh=1面的交换不稳定性的非线性演化，其中ιh表示转动变换.在利用星子展开导出的非线性简化MHD方程中，加入了热扩散项和外部加热项，以考虑不稳定性非线性演化过程中的快速能量损失和持续加热。为了解释在高β无电流氦加速器E实验中观察到的电子温度和密度的锯齿状振荡，我们将它们作为阻性圆柱等离子体的初边值问题来求解。-在没有加热项的情况下，m=1压力驱动模变得不稳定，并显著改变了中心β，β(0)≳2%的压力分布，初始分布为p(R)∝(1−(r/a)2)2。当ιh，=1共振面周围的面状电流增加时，由于变形的压力分布的抗磁效应，发生了磁力线的重新连接，所得到的磁通表面呈现m=2模结构。在热扩散和外部加热的情况下，压力行为在对m=1压力驱动模式不稳定的峰值轮廓和对m=1压力驱动模式稳定的宽轮廓之间振荡。-这些结果与实验数据是一致的。
The non-linear evolution of the interchange instability with a poloidal mode number m = 1 and a toroidal mode number n = 1 is investigated in a straight helical system with the ιh= 1 surface in a vacuum magnetic configuration like that of Heliotron E, where ιh, denotes the rotational transform. In the non-linear reduced MHD equations derived by using the stellarator expansion, a thermal-diffusion term and an external-heating term are added to include rapid energy loss and continued heating during the non-linear evolution of the instability. They are solved as an initial and boundary value problem for resistive cylindrical plasmas, in order to explain the sawtooth-like oscillation of electron temperature and density observed in the high-beta current-free Heliotron E experiment. – Without the heating term, the m = 1 pressure-driven mode becomes unstable and changes the pressure profile significantly for central beta, β(0) ≳ 2%, with an initial profile of p(r) ∝ (1 −(r/a)2)2. When a surface-like current increases around the ιh, = 1 resonant surface, because of the diamagnetic effect of the deformed pressure profile, reconnections of the magnetic field lines occur, and the resulting flux surfaces show an m = 2 mode structure. In the case of both thermal diffusion and external heating, the pressure behaviour oscillates between peaked profiles unstable against the m = 1 pressure-driven mode and broad profiles that are stable against it. – These results are consistent with the experimental data.