基于等离子体粒子模拟的喷气Z箍缩过程物理研究

给出了喷气Z箍缩动力学过程在二维柱坐标系下的等离子体粒子模拟物理模型,编写了相应的程序.对低电流驱动下的稀薄喷气Z箍缩动力学过程进行了验证性的等离子体粒子模拟,得到了许多微观的Z箍缩物理信息,如负载中的电流(密度)、电磁场、粒子位置和密度的时空演化,以及总的z箍缩拖尾质量和拖尾电流等信息.发现在Z箍缩过程中,模拟得到的等离子体电流随时间的变化反映出了等离子体箍缩到心和反弹的过程特征,磁场随径向的变化与长直导线电流给出的磁场很接近;电子所受到的电场力和磁场力(洛伦兹力)是相当的,而离子所受到的力主要是电场力;电子首先在z方向加速,然后在自身运动产生电流的磁场的作用下向轴心箍缩,而离子是在电子和离子电荷分离所产生的电场力的作用下向轴心运动;在压缩到轴心附近时,电子首先因静电排斥而飞散,而离子则在惯性的作用下继续向轴心箍缩,而后滞止飞散.Z箍缩等离子体的拖尾质量在20%左右,拖尾电流最大时在7%左右.

Physical investigation of dynamic process of the gas-puff Z-pinch through particle-in-cell simulation

In this paper the physical model and numerical algorithm of particle-in-cell (PIC) simulation for gas-puff Z-pinch in two-dimensional cylindrical coordinates are briefly introduced. The code is also developed according to the model and algorithm. The rarefied gas-puff Z-pinch driven by a low current is simulated through the code, and some reasonable results are obtained. The results include the spatiotemporal distributions of current, electromagnetic field, particle positions and density, as well as the trailing mass and current. It is found that the simulated current reflects the plasma Z-pinch characteristics, i.e., the plasma current arrives at a minimum when the plasma enters into stagnation, and it begins to increase after the plasma has moved outwards. The simulated magnetic field agrees well with the theoretic value. The electric field force and magnetic field force experienced by electron are almost the same in magnitude, while the force acting on ion is mainly the electric field force. Firstly the electron is accelerated in the z direction and reaches a velocity, then it moves inward the axis in the same time by the Lorentz force. That causes the separation between electron and ion, and a strong electric field is produced. The produced electric field attracts the ion inward the electron. When the electrons arrive at the axis, they move inversely due to the static repellency among them, while the ions continue to move initially inwards, and later enter into stagnation, and finally collapse. The trailing mass is about 20% of the total Z-pinch plasma, and the maximum trailing current is about 7% of the driven current. In the future the code needs to develop further and realize parallel computation in order to simulate the practical Z-pinch processes by PIC simulation.
Keywords：gas-puff Z-pinch2D electromagnetic PIC simulationforces of particletrailing plasma