Drift-wave-like density fluctuations in the Advanced Toroidal Facility (ATF) torsatron

Abstract

Density fluctuations in low-collisionality, low-beta (p-O.1 %), currentless plasmas produced with electron cyclotron heating (ECH) in the Advanced Toroidal Facility (ATF) torsatron [Fusion Technol. 10, 179 (1986)] have been studied using a 2 mm microwave scattering diagnostic. Pulsed gas puffing is used to produce transient steepening of the density profile from its typically flat shape; this leads to growth in the density fluctuations when the temperature and density gradients both point in the same direction in the confinement region. The wave number spectra of the fluctuations that appear during this perturbation have a maximum at higher k,p, (-1) than is typically seen in tokamaks. The in-out asymmetry of the fluctuations along the major radius correlates with the distribution of confined trapped particles expected for the ATF magnetic field geometry. During the perturbation, the relative level of the density fluctuations in the confinement region (integrated over normalized minor radii p from 0.5 to 0.85) increases from Z/n-1% when the density profile is flat to i/n-3% when the density profile is steepened. These observations are in qualitative agreement with theoretical expectations for helical dissipative trapped-electron modes (DTEMs), which are drift-wave instabilities associated with particle trapping in the helical stellarator field; they suggest that trapped-electron instabilities may play a role in constraining the shape of the density profile in ATF, but have little effect on global energy confinement. 0 199.5 American Itwtitute of Physics.

Collisionality dependence and ion species effects on heat transport in He and H plasma, and the role of ion scale turbulence in LHD

“…This is consistent with the result of linear calculation of core turbulence, which shows that the most dominant instability is ITG. This is in clear contrast to the turbulence characteristics of ECRH plasma of ATF [51,52] and ECRH + NBI plasma of Heliotron-E [53]. The core fluctuation in both devices increases with increase of electron density gradient.…”

Isotope effects on energy, particle transport and turbulence in electron cyclotron resonant heating plasma of the Large Helical Device

“…In ATF, of which magnetic configuration is similar to LHD, it was reported that measured core turbulence was dissipative trapped electron mode (DTEM) [29]. The linear growth rate of DTEM increase with increase of collisionality.…”

Core density turbulence in the HSX Stellarator

“…Linear 3D gyrokinetic calculations [7,8] have predicted that the anomalous electron thermal transport in the HSX stellarator may be caused by trapped-electron mode drift wave turbulence. While significant effort has been made to study the ion temperature-gradientdriven (ITG) [9], and trapped electron modes (TEM) [10] in conventional stellarator/heliotron configurations, theoretical and experimental studies on turbulence-induced transport for stellarators with quasi-symmetry will provide important new contributions to the goal of future fusion reactor development.…”