Ion-acoustic Waves Excitation by a standing Alfvén wave
Abstract
The results of hybrid simulation of standing Alfvén wave in low beta plasma are presented. Plasma is accelerated from the anti-nodes toward the nodes of the standing waves with finite amplitude under the action of the magnetic field pressure. As a result, a sharp maximum of the number density (and electron pressure) arises near the nodes. The plasma flow is modulated by the doubled frequency of the driving Alfvén wave thus giving rise to ion-acoustic waves. The effective parallel electric field appears due to both electron pressure gradient near the nodes and electron pressure variations in the acoustic waves. Landau damping limits the amplitude of the exited ion-acoustic waves. In the 1D case, Landau damping can be avoided only if Te is much larger than Ti, since the electric current is perpendicular to the background magnetic field. However, if ion-acoustic waves are excited by alternating field-aligned current (i.e. by oblique Alfvén wave), the ion-acoustic instability occurs for strong currents with carriers velocity larger than cs, and the excitation becomes more effective. This process may account for the observations of parallel electric field in the auroral ionosphere.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38.2039I