柱面内爆磁通量压缩实验中的磁扩散过程

利用一维磁流体力学程序MC11D，对套筒材料为不锈钢的柱面内爆磁通量压缩实验进行了数值模拟，研究了其中的磁扩散过程。计算结果表明:当套筒空腔中的磁场被压缩到350 T左右时，峭面磁扩散波开始形成，磁扩散波的波前从套筒内壁开始以0.75 km/s的平均速度向外快速推进，给磁场的压缩带来了不利影响；随着套筒内壁温度迅速升高，内壁附近会形成一个电阻率仅有0.3 mcm左右的等离子体保护层，又极大地减缓了空腔磁场向套筒中扩散的速度。在磁压缩过程中，峭面磁扩散波和等离子体层对于空腔磁场的扩散起着相反的作用，两者在发展的过程中相互竞争，在不同的阶段分别起着主导作用。

Magnetic diffusion process in cylindrical implosion magnetic flux compression experiment

When a strong magnetic field (above megagauss) diffuses into a solid metal, the magnetic field will diffuse into the metal in the form of a sharp-front wave. The phenomenon of sharp-front magnetic diffusion wave is studied using 1D MHD simulation for cylindrical implosion magnetic flux compression experiment, in which the liner is stainless steel304. Results indicate that sharp-front magnetic diffusion wave will happen when the magnetic field in cavity is compressed above 350 T. The magnetic diffusion wavefront advances rapidly from the inner of the liner to the outer, causing partial leakage of the magnetic field. It is adverse to the magnetic flux compression process. At the same time, as the inner of the liner is rapidly heated to the ionization temperature, a plasma layer will be formed near the inner, which greatly slows down the velocity of the magnetic field diffusing from the cavity to the liner. In the process of magnetic flux compression, sharp-front magnetic diffusion wave and the plasma layer have opposite effects to magnetic diffusion. They compete with each other in the development, and play the dominant role in different stage respectively.