Investigation of the perpendicular dynamics of drift-wave turbulence in a toroidal plasma with multi-probe arrays

Abstract

The microscopic structure of drift-wave turbulence perpendicular to the magnetic field is investigated in a toroidal plasma by means of multi-probe arrays. The dependence of structure sizes on the drift-scale ρ s is studied with the objective of classifying the range of perpendicular wavenumbers k ⊥ ρ s with respect to the analytical linear drift-wave dispersion relation. Wavenumbers in the range 0.2-1.5 are found according to a scaling aroundValues k ⊥ ρ s < 0.3, for which a dispersion-free dynamics is expected, are found in H and D. Biasing experiments on discharges in this range show that very strong E × B flow shear changes the characteristic mode structure in favour of coherent large-scale structures, which can be related to local turbulent inward transport as a result of modifications in the phase relation between density and potential fluctuations.

Observation of exponential spectra and Lorentzian pulses in the TJ-K stellarator

“…But the density in the homogeneous SOL, i.e., the region r À r sep > 0, is not altered by the larger field value. The increase in density of the core plasma is attributed to a reduction in the turbulent transport associated with a reduced size of the turbulent eddies, which was shown in a previous study 26,27 to scale inversely with the magnetic field strength, i.e., as $ 1=B. Fig.…”

Poloidal mode structure of long-distance correlation of fluctuations under strong E×B shear in the torsatron TJ-K

“…[13][14][15][16][17] The toroidally confined low-temperature plasma in TJ-K is dimensionally similar to the edge of fusion plasmas. 13 The working gas is helium at a neutral gas pressure of p = 7 mPa.…”

Direct extraction of coherent mode properties from imaging measurements in a linear plasma column

“…29 This procedure is robust for sufficient record length and stationarity, but a single pair of probes can provide only limited information without strong symmetry assumptions. Global measurements using many probes are possible, [30][31][32] but limited port space and probe-induced perturbations 26 are severe obstacles to making measurements of this kind. Visible-light imaging, on the other hand, is non-perturbative, can have broad spatial coverage, and can be robust to asymmetries when the full cross-section of the plasma is imaged (as in this study).…”