Plasma confinement modification and convective transport suppression in the scrape-off layer using additional gas puffing in the STOR-M tokamak

Abstract

The influence of short gas puffing (GP) pulses on the scrape-off layer (SOL) transport is studied. Similar responses of ion saturation current and floating potential measured near the GP injection valve and in the 90 • toroidally separated cross-section suggest that the GP influence on the SOL region should be global. A drop in plasma temperature and a decrease in the rotational velocity of the plasma are observed in the SOL region immediately after the GP pulse; however, an unexpected increase in electron and ion temperatures is observed in the second stage of the plasma response. The decrease in floating potential fluctuations indicates that the turbulent transport is dumped immediately after the GP pulse. The GP-induced modification of turbulence properties in the SOL points to a convective transport suppression in the STOR-M tokamak. A substantial decrease in the skewness and kurtosis of ion saturation current fluctuations is observed in the SOL region resulting in the probability distribution function (PDF) getting closer to the Gaussian distribution. The plasma potential reduction, the change in plasma rotation and the suppression of turbulent transport in the SOL region indicate that the plasma confinement is modified after the GP injection. Some features of the H-mode-like confinement in the plasma bulk also accompany the SOL observations after application of the additional sharp GP pulse.

Modification of plasma rotation with resonant magnetic perturbations in the STOR-M tokamak

“…As pointed out before, the toroidal flow velocities measured at plasma core region (as in the case of O V and C VI ions) tend to rotate in the counter-current direction. The toroidal flow velocity changes its direction towards the cocurrent direction for the case of C III (r = 7 cm) and increases further at radial locations further outward [56], creating a toroidal flow shear across the plasma.…”

Effect of a deuterium gas puff on the edge plasma in NSTX

“…As mentioned in the Introduction, previous deuterium gas puffing experiments on the PBX-M [5], ADITYA [8,9] and STOR-M [10] produced significant perturbations in the edge plasma and the edge turbulence. However, gas puffing done for the GPI measurements on Alcator C-Mod [11,12], EAST [13] and TEXTOR [14] reported no significant perturbations of the gas puff on the edge turbulence, and the present paper basically confirms those results.…”

“…These gas puffs also reduced the edge poloidal flow speed, and caused reversal in the toroidal flow speed due to the local edge particle source [9]. Gas puff effects in non-diverted hydrogen Ohmic discharges were also studied on the small STOR-M tokamak [10], where the lineaveraged density was doubled by these gas puffs, but the loop voltage decreased, indicating an increase in the core electron temperature and global confinement. The scrape-off layer (SOL) density increased and electron temperature decreased ∼1-3 ms after the puff, along with a reduction in the floating potential fluctuations, as in ADITYA [8].…”

Intermittent convective transport suppressed by supersonic molecular beam injection on the HL-2A tokamak

“…On the TEXTOR tokamak [15], by using resonant magnetic perturbation (RMP) in ohmic discharge, the blob size and radial velocity can be reduced, which may be related to an increase in sheath dissipation due to the decrease of effective field-line connection length. On ADITYA [16] and STOR-M [17] the suppression of intermittent fluctuation using gas puffing (GP) in L-mode was observed. On ADITYA, they found that the suppression was not due to the effect of Reynolds stress or velocity shear, but due to the attenuation of interchange instability caused by the reduction of the floating potential gradient and a local flattening of the density profile.…”