Instabilities in the solar wind

Recent progress is reviewed in the possible role of microturbulence in the solar wind. The solar wind is expected to excite plasma microinstabilities owing to its transition from a collision-dominated to a collisionless plasma, with potentially drastic consequences for thermal transport and other physical processes. Both the extensive linear theory of this subject and also our present understanding of nonlinear plasma turbulence is discussed. The solar wind is an excellent laboratory for studying many aspects of solar and plasma physics, and may soon provide some answers to several fundamental questions. (author)