title: Observations of an ion-driven instability in non-neutral plasmas confined on magnetic surfaces.
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 m=1, 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 E x B flow of the electron plasma. The frequency does not, however, scale exactly with E/B, and it depends on the ion species that is introduced, implying that the instability consists of interacting perturbations of ions and electrons.
authors: Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA. qrm1@columbia.edu
authors: Q R
authors: QR
authors: Marksteiner
authors: T Sunn
authors: TS
authors: Pedersen
authors: J W
authors: JW
authors: Berkery
authors: M S
authors: MS
authors: Hahn
authors: J M
authors: JM
authors: Mendez
authors: B
authors: B
authors: Durand de Gevigney
authors: H
authors: H
authors: Himura