Observations of an ion-driven instability in non-neutral plasmas confined on magnetic surfaces.
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.
Marksteiner
Q R
QR
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA. qrm1@columbia.edu
Pedersen
T Sunn
TS
Berkery
J W
JW
Hahn
M S
MS
Mendez
J M
JM
Durand de Gevigney
B
B
Himura
H
H