Global sound modes in mirror traps with anisotropic pressure

Abstract

Global oscillations of inhomogeneous plasma with frequencies close to the bounce frequency of ions in mirror traps have been studied. It has been shown that, in some cases, the sound can be reflected from the axial plasma inhomogeneity. The ideal magnetohydrodynamic (MHD) model with ChewGoldberger-Low approximation has been utilized to determine conditions of existence of the standing waves in the mirror-confined plasma. Linearized wave equation for the longitudinal plasma oscillations in thin anisotropic inhomogeneous plasma with finite b has been derived. The wave equation has been treated numerically. The oscillations are studied for the case of the trap with partially filled loss-cone and the trap with sloshing ions. It has been shown that in cells of the multiple-mirror trap standing waves can exist. The frequency of the wave is of the order of the mean bounce-frequency of ions. In the trap with sloshing ions, the mode supported by the pressure of fast ions could exist. The results of oscillations observation in the experiment on the Gas Dynamic Trap have been presented. V C 2013 AIP Publishing LLC. [http://dx.

Effects observed in numerical simulation of high-beta plasma with hot ions in an axisymmetric mirror machine

“…The radial distribution of the azimuthal component of the oscillation electric field has a peak in the region where the density of fast ions reaches a maximum. Such oscillations are similar to the global sound modes which were observed earlier in the GDT device (Skovorodin et al 2013).…”

“…Preliminary numerical simulations of a mirror machine with neutral beam injection show that axisymmetric oscillations with the frequency close to the bounce-frequency of sloshing ions between the magnetic mirrors are excited. These oscillations are similar to the global sound modes observed in a GDT device (Skovorodin, Zaytsev & Beklemishev 2013). To study the spatial structure of these oscillations, a set of simulations of plasma with sloshing ions was performed.…”

Overview of ECR plasma heating experiment in the GDT magnetic mirror

“…Other phenomena specific to this particular experiment are the high-amplitude global acoustic mode oscillations [21] traced in the diamagnetic signal (figure 12, top) and in more detail by magnetic probe diagnostics. The oscillations are represented by machine-scale variations of plasma pressure with a frequency of ∼100 kHz.…”

“…The longitudinal wavelength of the observed acoustic mode is estimated to be equal to the overall mirror-to-mirror distance; the azimuthal spectrum is represented exclusively by the m = 0 mode. Without ECRH these oscillations are saturated at low level and are usually awakened by other instabilities such as the Alfvén ioncyclotron instability and die away after 4-5 periods leaving no trace in the diamagnetic signal [21]. In discharges with ECR heating, however, the amplitude of these oscillations is several times higher inducing unprecedented ∼5% variations in the diamagnetic signal of the fast ions during the whole microwave pulse (figure 12, top).…”

Oscillating mirror instability in plasma with sloshing ions

“…In experiment on the GDT the longitudinal oscillations of plasma were observed [1,2]. It has typically zero angular wave-number, seems to be radially correlated and has the frequency about 100 kHz.…”