Processes in SOL plasma at the transition into improved confinement mode in FT-2 tokamak

Abstract

Studies of processes in the scrape-off layer (SOL) of the tokamak show a direct influence of periphery effects on confinement parameters of the plasma core. This paper illustrates experimentally observed transport barrier formation initialized by the low hybrid (LH) heating of the hydrogen plasma. The experimental data near last close flax surface (LCFS) and in SOL were obtained by means of an enhanced movable multielectrode Langmuir probe and spatially resolved spectroscopic technique retooled with additional helium puffing. The edge diagnostics show a strong change of a radial electric field and plasma parameters near LCFS. The alteration at the plasma edge is generated by high LH ion heating. It was found that the L-H transition is accompanied by a noticeable reconstruction of the poloidal and radial plasma parameters profiles in the SOL and in the limiter shadow region.

Investigation of small-scale tokamak plasma turbulence by correlative UHR backscattering diagnostics

“…The difference, according to expression (1), may be attributed to the contribution of the negative ion diamagnetic drift velocity V di to the long-scale fluctuation velocity shown by the upper broken line in figure 4(a). The plasma rotation profile provided by the UHR BS technique was benchmarked as well against the visible light impurity spectroscopy [20] data. For this purpose the measurements were performed during the He-puffing into the optical diagnostic cross section, which resulted in the spectral lines emission growth.…”

Poloidal inhomogenity of the particle fluctuation induced fluxes near the LCFS at lower hybrid heating and improved confinement transition at the FT-2 tokamak

“…is the correlation coefficient [1,11]. To obtain the quasi-steady-state Г 0 (t) flux the low frequency governed not only by radial heat fluxes, but also by other factors (e.g., poloidal particle fluxes) [8].…”

“…B ϕ , (angular brackets indicate averaging with respect to time). Here C n(~)E(~) is the correlation coefficient [1,11]. To obtain the quasi-steady-state Г 0 (t) flux the low frequency (smoothing) probe signal component was used.…”