Abstract
The first detailed experimental study of an instability driven by the presence of a finite ion fraction in an electron-rich non-neutral plasma confined on magnetic surfaces is presented. The instability has a poloidal mode number , implying that the parallel force balance of the electron fluid is broken and that the instability involves rotation of the entire plasma, equivalent to ion-resonant instabilities in Penning traps and toroidal field traps. The mode appears when the ion density exceeds approximately 10% of the electron density. The measured frequency decreases with increasing magnetic field strength, and increases with increasing radial electric field, showing that the instability is linked to the flow of the electron plasma. The frequency does not, however, scale exactly with , and it depends on the ion species that is introduced, implying that the instability consists of interacting perturbations of ions and electrons.
- Received 21 May 2007
DOI:https://doi.org/10.1103/PhysRevLett.100.065002
©2008 American Physical Society