Dynamics of cold pulses induced by super-sonic molecular beam injection in the EAST tokamak

TL;DR

This study investigates the propagation of cold pulses induced by super-sonic molecular beam injection in the EAST tokamak, revealing non-local heat transport, density fluctuation dynamics, and turbulence behavior in ohmic plasmas.

Contribution

It provides detailed high-resolution measurements of cold pulse dynamics and turbulence response, offering new insights into plasma transport mechanisms during SMBI in tokamaks.

Findings

Non-local heat transport occurs at specific plasma currents and densities.

Electron density fluctuations increase promptly after SMBI.

Turbulence velocity changes sign near the temperature inversion point.

Abstract

Evolution of electron temperature, electron density and its fluctuation with high spatial and temporal resolutions are presented for the cold pulse propagation induced by super-sonic molecular beam injection (SMBI) in ohmic plasmas in the EAST tokamak. The non-local heat transport occurs for discharges with plasma current $I_p$=450 kA ($q_{95}\sim5.55$), and electron density $n_{e0}$ below a critical value of $(1.35\pm0.25)\times10^{19}~\mathrm{m^{-3}}$. In contrary to the response of core electron temperature and electron density (roughly 10 ms after SMBI), the electron density fluctuation in the plasma core increases promptly after SMBI and reaches its maximum around 15 ms after SMBI. The electron density fluctuation in the plasma core begins to decrease before the core electron temperature reaches its maximum (roughly 30 ms). It was also observed that the turbulence perpendicular velocity close to the inversion point of the temperature perturbation changes sign after SMBI.