Wall stabilization of high-beta anisotropic plasmas in an axisymmetric mirror trap

Abstract

The stabilization of the ``rigid'' flute and ballooning modes both with and without the effect of additional MHD anchors in an axisymmetric mirror trap with the help of a perfectly conducting lateral wall is studied using a model pressure distribution of a plasma with a steep-angle neutral beam injection at the magnetic field minimum. The calculations were performed for an anisotropic plasma in a model that simulates the pressure distribution during the injection of beams of fast neutral atoms into the magnetic field minimum. It is assumed that the lateral wall is an axisymmetric shell surrounding the plasma that follows the shape of the magnetic field line and is placed at a certain distance to the plasma border.

 It has been found that for the effective stabilization of the modes by the lateral wall only, the parameter beta ($\beta$, ratio of plasma pressure to the magnetic field pressure) must exceed some critical value $\beta_{\text{crit}}$. When combined with the conducting end plates imitating the MHD end stabilizers, there are two critical beta values and two stability zones $0<\beta<\beta_{\text{ crit}1}$ and $\beta_{\text {crit}2}<\beta<1$ that can merge, making the entire range of allowable beta values $0<\beta<1$ stable.

 The dependence of the critical betas on the degree of plasma anisotropy, the mirror ratio, and the width of the vacuum gap between the plasma and the lateral wall is studied. In contrast to the previous studies focusing on a plasma model with a sharp boundary, we calculated the stability zones for a number of diffuse radial pressure profiles and several axial magnetic field profiles.

Progress of open systems at Budker Institute of Nuclear Physics

“…The results of a recent analysis by Kotelnikov, Prikhodko & Yakovlev (2023) predict the effectiveness of this method of MHD stabilisation, starting from the values achievable using vortex confinement.…”

“…Further steps in this direction are planned in the near future: Operation time of neutral beam injection (NBI) will be increased from 5 to 10 ms in order to further increase the plasma diamagnetism. A recently upgraded microwave heating system will be used to increase , the plasma diamagnetism and . In modes with the maximum achieved value of diamagnetism, measurements will be made of the radial profiles of the magnetic field inside the plasma and the distribution of the magnetic field associated with diamagnetic currents near the plasma boundary. Using the results of Kotelnikov et al. (2023) and the results of measurements, conductive structures surrounding the plasma with an optimal shape for MHD stabilisation will be designed. Conductive structures will be fabricated and assembled at the GDT facility. The efficiency of this method of MHD stabilisation will be studied in a real experiment.…”

“…Using the results of Kotelnikov et al. (2023) and the results of measurements, conductive structures surrounding the plasma with an optimal shape for MHD stabilisation will be designed.…”

“…• In modes with the maximum achieved value of diamagnetism, measurements will be made of the radial profiles of the magnetic field inside the plasma and the distribution of the magnetic field associated with diamagnetic currents near the plasma boundary. • Using the results of Kotelnikov et al (2023) and the results of measurements, conductive structures surrounding the plasma with an optimal shape for MHD stabilisation will be designed. • Conductive structures will be fabricated and assembled at the GDT facility.…”

Influence of the shape of a conducting chamber on the stability of rigid ballooning modes in a mirror trap

“…Continuing the study of large-scale magnetohydrodynamic (MHD) instabilities, begun in our papers [1,2], below we present new results of studying the so-called wall stabilization of rigid flute and ballooning perturbations with azimuthal number m = 1 in an axially-symmetric mirror trap (also called linear or open trap) with anisotropic plasma. According to the physics of the case, wall stabilization of a plasma with a sufficiently high pressure is achieved by inducing image (Foucault's) currents in the conducting walls of the vacuum Proportional wall shape vs. straightened wall shape.…”