Experimental observation of drift wave turbulence in an inhomogeneous six-pole cusp magnetic field of MPD

TL;DR

This study experimentally observes drift wave turbulence in an inhomogeneous six-pole cusp magnetic field, analyzing how plasma density gradients influence instability frequency and drift velocities, providing insights into plasma behavior in cusp magnetic configurations.

Contribution

It is the first detailed experimental investigation of drift wave instabilities in a six-pole cusp magnetic field with controlled density gradients, linking observed frequencies and drift velocities to theoretical models.

Findings

Instability frequency varies with plasma density gradient.

Measured drift velocities match theoretical predictions.

Drift velocity sign alternates in non-cusp regions.

Abstract

This paper presents a detailed study on the controlled experimental observation of drift wave instabilities in an inhomogeneous Six pole cusp magnetic field generated by an in-house developed Multi-pole line cusp magnetic field device (MPD) [Patel et al. Rev. Sci. Instrum., 44, 726 (2018)]. The device is composed of six axially symmetric cusps and non-cusp (in between two consecutive magnets) regions. The observed instability has been investigated in one of these non-cusp regions by controlling the radial plasma density gradient with changing pole magnetic field which is a unique feature of this device. It has been observed that the frequency of the instability changes explicitly with the density gradient. Moreover the scale length of plasma parameters, frequency spectrum, cross-correlation function, and fluctuation level of plasma densities has been measured in order to identify the instability. The cross field drift velocity due to fluctuation in plasma parameters have been measured from the wave number- frequency S (kz, {\omega}) spectrum and verified with the theoretical values obtained from density scale length formula. Further from the S (kz, {\omega}) spectrum it has been found that the drift velocity alternates the sign in the consecutive non-cusp regions.