Modification of plasma flows with gas puff in the scrape-off layer of ADITYA tokamak

Abstract

The parallel Mach numbers are measured at three locations in the scrape-off layer (SOL) plasma of ADITYA tokamak by using Mach probes. The flow pattern is constructed from these measurements and the modification of flow pattern is observed by introducing a small puff of working gas. In the normal discharge, there is an indication of shell structure in the SOL plasma flows, which is removed during the gas puff. The plasma parameters, particle flux and Reynolds stress are also measured in the normal discharge and in the discharge with gas puff. It is observed that Reynolds stress and Mach number are coupled in the near SOL region and decoupled in the far SOL region. The coupling in the near SOL region gets washed away during the gas puff.

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

“…On the TEXTOR tokamak, there was no significant perturbation in the plasma or edge turbulence at their deuterium GPI puff rate of up to ∼4.6 × 10 20 atoms/s for ∼0.5 s. 46 On the other hand, some small tokamaks such as ADITYA have reported changes in the edge turbulence with gas puffs of ∼2 × 10 21 atoms/s correlated with a decreases in the edge electron temperature due to radiative cooling. 158,159 On other devices such as Alcator C-Mod when operating at low densities n e 0.8 × 10 20 m 3 or EAST, 87 the normal helium GPI puff of ∼10 20 atoms/s for ∼0.2 s caused a significant (≥20%) rise in plasma electron density, probably due to the recycling of helium. A similar or larger rise in density is caused when a deuterium puff is used for GPI in C-Mod.…”

Flow structure and shear generation in the 3D SOL of a circular tokamak plasma in Aditya

“…The typical plasma discharges that are considered for simulations in this study are selected from the examples where the flow and potential probe measurements in the SOL are already reported in the earlier studies [17,18,22]. For example, Mach number measurements were made in the discharges with plasma current, I p ∼ 25 kA, plasma duration ∼ 25 ms, core electron temperature ∼ 100 eV, center chord averaged plasma density 5 × 10 12 cm −3 , SOL plasma density 5 × 10 11 cm −3 using hydrogen as working gas [17].…”

“…The simulated M profiles could be compared with the usual measurements of the Mach number [17,18], as in and from the fit to data in Ref. [17] obtained from the probe measurements (triangles) at the first probe location.…”

“…Behavior of plasma transport, flows, drifts and their associated fluctuations are studied routinely in the edge and SOL region of tokamak Aditya by analyzing the data from Mach probes and Langmuir probes [17,18,22].…”

“…While this approach has been successful in analyzing many aspects of the observations, the underlying assumptions need to be substantiated and improved further in order to cover the areas where the ambiguity still exists. An improved estimate requires data which is global in nature and allows to correlate the local behavior of the measurements to the global features of the parameter variations modeled by approximate means, e.g., using a schematic slab model as done in the recent data analysis [18,22].…”