Plasma potential profiles and oscillations in ECRH and NBI plasmas in the TJ-II stellarator

摘要

The direct measurements of an electric potential and its fluctuations in a core plasma are of a primary importance for the understanding the confinement improvement mechanisms and the role of electric field E_r in toroidal plasma confinement. Heavy Ion Beam Probe (HIBP) diagnostics is used in TJ-II (four-period flexible heliac, B_0= 1 T, = 1.5 m, a = 0.22 m) to study directly the plasma potential Φ with fine spatial (< 1 cm) and temporal (1 μs) resolution. Cs+ ions with energies up to 150 keV are used to probe ECRH and NBI heated plasmas (P_(ECRH)≤ 600 kW, P_(NBI) < 900 kW (port through), E_(NBI) = 30 kV) from the edge to the core. Poloidally resolved potential measurements provide poloidal electric field E_(pol)= (Φ1-Φ2)/χ,χ~1 cm, so the turbulent particle flux: Г_r = Г_(EpolxBtor) = < n_e~v_r~> [1].