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Coulomb collisions in strongly anisotropic plasmas II. Cyclotron cooling in laboratory pair plasmas
Journal of Plasma Physics ( IF 2.1 ) Pub Date : 2021-02-03 , DOI: 10.1017/s0022377820001233
D. Kennedy , P. Helander

The behaviour of a strongly magnetised collisional electron–positron plasma that is optically thin to cyclotron radiation is considered, and the distribution functions accessible to it on the various timescales in the system are calculated. Particular attention is paid to the limit in which the collision time exceeds the radiation emission time, making the electron distribution function strongly anisotropic. Indeed, these are the exact conditions likely to be attained in the first laboratory electron–positron plasma experiments currently being developed, which will typically have very low densities and be confined in very strong magnetic fields. The constraint of strong magnetisation adds an additional complication in that long-range Coulomb collisions, which are usually negligible, must now be considered. A rigorous collision operator for these long-range collisions has never been written down. Nevertheless, we show that the collisional scattering can be accounted for without knowing the explicit form of this collision operator. The rate of radiation emission is calculated and it is found that the loss of energy from the plasma is proportional to the parallel collision frequency multiplied by a factor that only depends logarithmically on plasma parameters. That is, this is a self-accelerating process, meaning that the bulk of the energy will be lost in a few collision times. We show that in a simple case, that of straight field-line geometry, there are no unstable drift waves in such plasmas, despite being far from Maxwellian.

中文翻译:

强各向异性等离子体中的库仑碰撞 II。实验室对等离子体中的回旋加速器冷却

考虑了对回旋辐射光学薄的强磁化碰撞电子-正电子等离子体的行为,并计算了系统中不同时间尺度上它可访问的分布函数。特别注意碰撞时间超过辐射发射时间的限制,使电子分布函数具有很强的各向异性。事实上,这些正是目前正在开发的第一个实验室电子-正电子等离子体实验中可能达到的确切条件,这些实验通常具有非常低的密度并被限制在非常强的磁场中。强磁化的约束增加了一个额外的复杂性,即现在必须考虑通常可以忽略不计的远程库仑碰撞。这些远程碰撞的严格碰撞算子从未被记录下来。然而,我们表明,在不知道这种碰撞算子的显式形式的情况下,可以解释碰撞散射。计算辐射发射率,发现等离子体的能量损失与平行碰撞频率乘以仅与等离子体参数成对数关系的因子成正比。也就是说,这是一个自加速过程,这意味着大部分能量将在几次碰撞中损失掉。我们表明,在一个简单的情况下,即直线场线几何,尽管远离麦克斯韦,但在这种等离子体中没有不稳定的漂移波。我们表明,在不知道这种碰撞算子的显式形式的情况下,可以解释碰撞散射。计算辐射发射率,发现等离子体的能量损失与平行碰撞频率乘以仅与等离子体参数成对数关系的因子成正比。也就是说,这是一个自加速过程,这意味着大部分能量将在几次碰撞中损失掉。我们表明,在一个简单的情况下,即直线场线几何,尽管远离麦克斯韦,但在这种等离子体中没有不稳定的漂移波。我们表明,在不知道这种碰撞算子的显式形式的情况下,可以解释碰撞散射。计算辐射发射率,发现等离子体的能量损失与平行碰撞频率乘以仅与等离子体参数成对数关系的因子成正比。也就是说,这是一个自加速过程,这意味着大部分能量将在几次碰撞中损失掉。我们表明,在一个简单的情况下,即直线场线几何,尽管远离麦克斯韦,但在这种等离子体中没有不稳定的漂移波。计算辐射发射率,发现等离子体的能量损失与平行碰撞频率乘以仅与等离子体参数成对数关系的因子成正比。也就是说,这是一个自加速过程,这意味着大部分能量将在几次碰撞中损失掉。我们表明,在一个简单的情况下,即直线场线几何,尽管远离麦克斯韦,但在这种等离子体中没有不稳定的漂移波。计算辐射发射率,发现等离子体的能量损失与平行碰撞频率乘以仅与等离子体参数成对数关系的因子成正比。也就是说,这是一个自加速过程,这意味着大部分能量将在几次碰撞中损失掉。我们表明,在一个简单的情况下,即直线场线几何,尽管远离麦克斯韦,但在这种等离子体中没有不稳定的漂移波。
更新日期:2021-02-03
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