Intermittent transport in the plasma periphery of the T-10 tokamak

Abstract

Plasma periphery investigation performed in the T-10 tokamak has shown an essential increase of the perpendicular anomalous particle flux in the scrape-off layer (SOL) with an average plasma density rise. The strengthening of the radial transport is found to occur at an average electron density above a threshold level, which depends on a plasma current Ip. The value of the threshold level is about 0.3 times the Greenwald density. Langmuir probe measurements of SOL plasma parameters indicate that intermittent events can play a significant role in the cross-field transport. Intermittent behaviour of the plasma parameters is associated with formation and propagation of the plasma regions (or structures) with high density. The structures move in radial and poloidal directions. Radial movement is predominantly directed to the vacuum vessel wall in the SOL. The radial velocity of the high density plasma structures reduces from 1000 m s−1 near the last closed flux surface to 200 m s−1 at the wall of the vacuum chamber. The radial size of the structures also decreases with minor radius from 3 to 0.5 cm. The poloidal velocity is equal to 1000–1300 m s−1 and is directed towards an ion diamagnetic velocity; the poloidal size of the plasma structures is 2–3 cm. The observed plasma structures can be responsible for more than 50% of the total radial turbulent particle flux. T-10 results support the hypothesis that intermittent convection rather than diffusion can define the cross-field transport.