Observation of multi-scale turbulence and non-local transport in LHD plasmas

Abstract

We have studied two types of spatio-temporal turbulence dynamics in plasmas in the Large Helical Device, based on turbulence measurements with high spatial and temporal resolution. Applying conditional ensemble-averaging to a plasma with Edge-Localized Modes (ELMs), fast radial inward propagation of a micro-scale turbulence front is observed just after ELM event, and the propagation speed is evaluated as ∼100 m/s. A self-organized radial electric field structure is observed in an electrode biasing experiment, and it is found to realize a multi-valued state. The curvature of the radial electric field is found to play an important role for turbulence reduction.

Boundary condition for toroidal plasma flow imposed at the separatrix in high confinement JT-60U plasmas with edge localized modes and the physics process in pedestal structure formation

“…9(a)-9(c), we have compared these experimental results with a theoretical model. 24,25 Note that we found that the location at which ÀrT i has a local maximum value was seen near the location at which the E r and/or its curvature (E 00 r ) have local peak values rather than that of the E r -shear (E 0 r ). In a previous study, 23 it was shown that the radial electric field jumps to a larger value during an ELM-free H-mode phase, but, simultaneously, the ion temperature gradient changes little.…”

On the Origin of Steep and Localized Radial Electric Field in the Transport Barrier at Plasma Edge

“…When biased electrode is installed on the LHD plasma, the strongly localized radial electric field appears. What is striking is that the double peaks of radial electric field are established [24]. In this case, the region where E † r E r > 0 holds appears.…”

“…Experiments have reported the number of about 10 13 [V 2 /m 4 ] [28,29]. For the case of helical plasmas, this value is suppressed by the factor of S −2 owing to the helical-ripple trapped particles, while the width of the peak is independent of S. Considering the fact that the parameter S is in the range of a few 10 [24], the reduction factor is about ∼ 10 −3 times smaller compared to tokamaks. Experiments have reported the value of ∼ 10 9 [V 2 /m 4 ] [24].…”

“…Sequential repetition of growth and decay of the transport barrier was observed just before the L-H transition (so-called limit-cycle oscillation (LCO) [12][13][14][15][16][17][18][19][20][21]), and has stimulated the study of physics of H-mode (see a review [22] and references therein). Electrode-biasing experiments [23,24] have also contributed to our understanding of H-mode transition.…”

Study of Nonlinear Behavior of Low-Frequency MHD Mode Caused by Transition of Radial Electric Field in LHD

“…In addition, the edge harmonic oscillation (EHO) mode is significantly observed at 4.1 s < t < 5.1 s. It is reported that the EHO mode enhances the plasma transport through the edge without significantly increasing the thermal transport [12]. In order to fully understand the MHD mode driven plasma transport phenomena in the transition of edge E r plasma [13], it is necessary to identify the magnetic fluctuation with f 2 -5 kHz. Fig.…”