Coexistence of Collisional Drift and Flute Wave Instabilities in Bounded Linear ECR Plasma

Abstract

This paper reports the experimental and theoretical investigation on the coexistence of the collisional drift and flute wave instabilities in the bounded linear electron cyclotron resonance (ECR) plasma. The drift wave instability is excited by the steep density gradient and imposed axial boundary conditions in the device. The flute instability is excited by the bad curvature of the magnetic field. Emphasis is made on the effect of the ion-neutral (i-n) particle collisions. It is observed that the drift wave instability is excited when the in particle collision frequency in is low, but it is stabilized when in is high. Furthermore, the drift and flute modes are coexistent for the intermediate values of in. The Hasegawa-Wakatani model which describes the dispersion relation of the collisional drift-interchange mode is used for understanding the experimental observations. It is found that the experimentally observed drift frequency is consistent with the numerical calculation. The present result has shown that the in particle collisions play an important role in the stabilization of the collisional drift wave instability in the ECR plasma.

Fluctuations in electron cyclotron resonance plasma in a divergent magnetic field

“…4. 9 Instead, upon further investigation as will be shown later, we find that this pressure region (p Շ 1.5 mTorr) is dominated by drift waves.…”

“…The coexistence between the drift and flute wave instabilities in a linear ECR plasma has been studied with an axially imposed boundary. 9 Shoyama et al 10 found intense coherent fluctuations in the ion saturation current when a negative bias was applied to a hollow cathode target in an ECR plasma. Later, lowfrequency fluctuations in an ECR plasma source have been investigated with respect to stabilization by localized, radial electric fields by means of a biased, segmented end plate.…”

Observation of Zonal Flow Type Oscillation in Linear Cylindrical ECR Plasmas

“…Here, z is measured from the coaxial waveguide converter. The θ coordinate is defined such that the vertical (downward) direction from the center of the device has a θ of 270 degrees [13]. The cross phases in both azimuthal and axial directions are regarded as near zero within the present error bars, and show the azimuthal and axial symmetric structures of (m, n) = (0, 0), similar to a zonal flow structure.…”

“…However, the interaction of externally induced time varying E × B shear flow with the drift mode has not been reported. In this letter, we present experimental observations of the impact of an oscillation driven by a small modulation of ECR power, which has the zonal flow structure (called a zonal flow type author's e-mail: kamataki@riam.kyushu-u.ac.jp oscillation in this letter), on the drift wave.Experiments are performed in the region of lower ionneutral collision frequency ν in /Ω i ∼ 0.4 (filling gas pressure p (Ar) = 0.6 ×10 −3 Torr), where the drift mode is strongly excited in a linear cylindrical electron cyclotron resonance (ECR) plasma [13]. Here, ν in and Ω i indicate the ion-neutral collision frequency and the ion cyclotron frequency, respectively.…”

“…Experiments are performed in the region of lower ionneutral collision frequency ν in /Ω i ∼ 0.4 (filling gas pressure p (Ar) = 0.6 ×10 −3 Torr), where the drift mode is strongly excited in a linear cylindrical electron cyclotron resonance (ECR) plasma [13]. Here, ν in and Ω i indicate the ion-neutral collision frequency and the ion cyclotron frequency, respectively.…”