Improved Mode by Lower Hybrid Current Drive on HT-7 Tokamak

A transition from low confinement mode (L-mode) to high confinement mode (H- mode) is realized by lower hybrid current drive (LHCD) on HT-7 superconducting Tokamak. The energy confinem ent time increases from 14.6ms (Ohmic phase) to 24.5m s (LHCD phase), which is consistent with calculation using the H-mode scaling law of ITER93ELM free. By using LHCD, an internal transport barrier (ITB) is form ed and the confinement factor H up to 2.11 is obtained. Results indicate that plasma confinement is improved greatly. 1. Intr oduction Nuclear fusion experiments have made a rapid progress since 1980's in many toka maks by using lower hybrid wave (LHW). Recently , m any results on im proved confinement in JT-60U and Tore-Supra have been reported(1, 2). In 2001 campaign with high plasma parameters on HT-7, improved confinements are obtained by means of LHCD. In LHCD experiment on HT-7, the plasma current is built up firstly by Ohm ic (OH) discharge, then LHW is switched on to sustain the plasm a current. The experiments are performed with a feedback control system adjusting the input power from the OH transformer to keep plasmas current Ip as a cons tant(3). The energy confinem ent time is defined as tot E P W ?