Effect of parallel currents on drift-interchange turbulence: Comparison of simulation and experiment

Abstract

Two-dimensional (2D) turbulence simulations are reported in which the balancing of the parallel and perpendicular currents is modified by changing the axial boundary condition (BC) to vary the sheath conductivity. The simulations are carried out using the 2D scrape-off-layer turbulence (SOLT) code. The results are compared with recent experiments on the controlled shear de-correlation experiment (CSDX) in which the axial BC was modified by changing the composition of the end plate. Reasonable qualitative agreement is found between the simulations and the experiment. When an insulating axial BC is used, broadband turbulence is obtained and an inverse cascade occurs down to low frequencies and long spatial scales. Robust sheared flows are obtained. By contrast, employing a conducting BC at the plate resulted in coherent (drift wave) modes rather than broadband turbulence, with weaker inverse cascade, and smaller zonal flows. The dependence of the two instability mechanisms (rotationally driven interchange mode and drift waves) on the axial BC is also discussed.

Understanding the impact of insulating and conducting endplate boundary conditions on turbulence in CSDX through nonlocal simulations

“…In general, the endplate change affects the momentum equation, polarization current, vorticity flux, and shear layer generation. These results are qualitatively consistent with the experimental report of Thakur et al 23 and previous 2D slab simulations of D'Ippolito et al 15 In addition, we have shown that in the CSDX insulating case, the electron temperature does not significantly alter the nature of instabilities, while in the CSDX conducting case, the electron temperature can be an …”

“…Unlike D'Ippolito et al 15 simulation which had a dipolar azimuthal velocity with zero net azimuthal momentum, our IBC simulation (Fig. 14(f)) shows non-symmetric lobes …”

“…While that work showed self-regulating drift-wave/zonal flow dynamics similar to experiments, this simulation overestimated turbulence levels by an order of magnitude. D'Ippolito et al 15 simulated an axially averaged domain in slab geometry using the SOLT code, which differentiated insulating and conducting endplates by adding a sheath closure term. In these simulations, the time averaged quantities and frequency domain result of these simulations were in better qualitative agreement with experimental results.…”

Edge turbulence measurement in Heliotron J using a combination of hybrid probe system and fast cameras

“…Blob experiments were also held at the basic plasma experimental devices [23][24][25][26][27]. In the recent review paper [28] the filamentary structure in the edge plasma is well defined and characterized, and the features of blobs such as radial speed, blob size, birth rate and skewed PDF were summarized successfully.…”

Investigating flow patterns and related dynamics in multi-instability turbulent plasmas using a three-point cross-phase time delay estimation velocimetry scheme

“…In previous studies, it was shown that the end boundaries are crucial for the system to be driven into broadband turbulence. 8,36 The azimuthal plasma cross-section is diagnosed by fast imaging. A Phantom V710 high speed camera detects emission from neutral atoms and ions, respectively, with a typical sampling frequency of 210 and 526 Hz.…”