Neutralization and stabilization of particle streams in the corona and type III radio bursts

Abstract

The processes by which streams of charged particles become charge and current neutralized in the corona are investigated. It is shown that a large amplitude plasma wave, which is related to precursor phenomenon in type III bursts and possibly plasma radiation from type IV bursts, will be excited at the head of the stream. The energy extracted from the stream to produce this plasma wave is computed and used to set conservative upper limits on the densities of possible excitors for type III bursts. For electron streams the density n _s < 10⁻⁵ n _e, where n _e is the density of the background plasma. For proton streams n _s < 1.8 × 10⁻² n _e. The energy extracted from the stream is also used to set upper limits on the lifetimes of relativistic electrons ‘stored’ in the corona and it is concluded that for n _e > 10² cm⁻³ this loss must be taken into account. Since electron streams cannot produce their own stabilizing ionacoustic waves because they would violate the condition n _s < 10⁻⁵ n _e, other mechanisms for producing ion-acoustic waves in the corona are examined. Another stabilization mechanism due to velocity inhomogeneity is investigated.