Invalidity of Local Thermodynamic Equilibrium for Electrons in the Solar Transition Region. I. Fokker-Planck Results,
Abstract
An effective numerical method for solving boundary value problems for the Landau Fokker-Planck equation is developed and applied to calculating the electron velocity distribution function in model solar transition regions. Numerical results illustrating the speed, pitch angle and spatial dependence of the distribution function are presented. From these it is concluded that the widely-invoked assumption that in weakly inhomogeneous collisional plasma the angle-averaged distribution function remains close to local-Maxwellian distribution is incorrect. Instead, the distribution function forms an anisotropic, high velocity tail in the lower temperature regions due to the diffusion of fast electrons anti-parallel to the temperature gradient. It is shown that as a result of there being an excess of fast electrons in the low transition region (T < or about 3 x 10 to the 5th power K, say), inelastic electron-ion collision rates are significantly enhanced over the Maxwellian values. Attendant effects on the ionization balance of a typical metal (magnesium) are shown to be significant. Implications of the breakdown of the loca-Maxwellian approximation for several outstanding questions related to the solar transition region are discussed, including: energy balance in low transition region and upper chromosphere, the helium resonance line spectrum, the Schmahl-Orrall observation of continuum absorption by neutral hydrogen, and the origin of the 20,000 K temperature plateau.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1982
- Accession Number
- ADA120515
Entities
People
- Edward C. Shoub
Organizations
- Stanford University