科研之友
微信
新浪微博
Facebook
分享链接
摘要
This paper outlines the rather narrow conditions on a radiatively decoupled plasma where a Maxwell-Boltzmann (MB) distribution can be assumed with confidence. The complementary non-thermal distribution with non-perturbative kurtosis is argued to have a much broader purview than has previously been accepted. These conditions are expressed in terms of the electron Knudsen number, K-e, the ratio of the electron mean free path to the scale length of electron pressure. Rather generally, f (v %26lt; v(2)(K-e)) will be Gaussian, so that MB atomic or wave particle effects controlled by speeds v %26lt; v(2) = w(15/8K(e))(1/4) will remain defensible, where w is the most probable speed. The sufficient condition for Spitzer-Braginskii plasma fluid closure at the energy equation requires globally K-e(s) %26lt;= 0.01; this global condition pertains to the maximum value of K-e along the arc length s of the magnetic field (to its extremities) provided that contiguous plasma remains uncoupled from the radiation field. The non-thermal regime K-e %26gt; 0.01 is common in all main-sequence stellar atmospheres above approximately 0.05 stellar radii from the surface. The entire solar corona and wind are included in this regime where non-thermal distributions with kurtosis are shown to be ubiquitous, heat flux is not well modeled by Spitzer-Braginskii closure, and fluid modeling is qualitative at best.
- 出版日期2013-6-10
