Current Limitation in Solar Flares

It is shown that the ion-sound current instability will be the relevant mechanism of current dissipation in most instances in the fully ionized part of the solar atmosphere (upper chromosphere and corona). Since this instability has the same initial threshold as the Alfven-Cariqvist instability, but a considerably lower threshold once the instability has started toward saturation, the Affven-Carlqvist instability will not occur. The linear and nonlinear stages of the ion-sound current instability are examined and a turbulent resistivity is given for the saturated state which is in agreement with laboratory experiments. This turbulent resistivity is applied to the Alfven-Carlqvist model of a cylindrical current filament, and it is shown that enough energy could not be dissipated sufficiently fast for a solar flare. This turbulent resistivity is also applied to the "hard" phase of Syrovatsky's dynamic dissipation model, and it is shown that Syrovatsky's electromagnetic instability for instantaneous current-sheet interruption cannot occur. The possibility that the ion-sound can systematically accelerate a select group of particles is investigated. It is concluded that heating rather than acceleration will result. It is suggested that a small electric field acting over large distances is a potentially much more efficient accelerating mechanism.