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arXiv 2102.04289physics.plasm-ph
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强磁化等离子体中扩展的时空关联

Extended space and time correlations in strongly magnetized plasmas

Keith R. Vidal, Scott D. Baalrud

摘要:

分子动力学模拟表明,强磁化显着增加与粒子间的关联的空间和时间尺度。其物理机制是沟道效应,即粒子被限制在窄柱体上运动,窄柱体的宽度由回旋半径表征,长度由碰撞平均自由程表征。主要的相互作用是在碰撞柱体两端的$180^\circ$碰撞,导致与磁场平行的长程关联。它的影响表明,通过依赖的速度自相关函数和自扩散系数的域的大小和运行时间在模拟的单组分等离子体。大量的粒子,因此域的大小,必须用来解决长程相关性,这表明在收集的带电粒子的数量必须增加,以构成等离子体。相应地,这种效应显著延迟了达到扩散状态所需的时间,在扩散状态中,颗粒的均方位移随时间线性增加。这一结果提出了挑战,连接测量非中性和超冷中性等离子体实验,以及分子动力学模拟,由于其有限的尺寸与流体传输特性。

英文摘要:

Molecular dynamics simulations are used to show that strong magnetization significantly increases the space and time scales associated with interparticle correlations. The physical mechanism responsible is a channeling effect whereby particles are confined to move along narrow cylinders with a width characterized by the gyroradius and a length characterized by the collision mean free path. The predominant interaction is $180^\circ$ collisions at the ends of the collision cylinders, resulting in a long-range correlation parallel to the magnetic field. Its influence is demonstrated via the dependence of the velocity autocorrelation functions and self-diffusion coefficients on the domain size and run time in simulations of the one-component plasma. A very large number of particles, and therefore domain size, must be used to resolve the long-range correlations, suggesting that the number of charged particles in the collection must increase in order to constitute a plasma. Correspondingly, this effect significantly delays the time it takes to reach a diffusive regime, in which the mean square displacement of particles increases linearly in time. This result presents challenges for connecting measurements in non-neutral and ultracold neutral plasma experiments, as well as molecular dynamics simulations, with fluid transport properties due to their finite size.

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