Overview of the latest HT-7 experiments

Abstract

An overview of the progress with experiments in the HT-7 during 2003-4 is presented. The H-mode, negative reversed shear and high l i operational scenarios were investigated for quasi-steady-state high performance plasma discharges. Ion Bernstein wave (IBW) heating at 30 MHz produced a typical edge H-mode plasma. Transport in both electron and ion channels were reduced in the outer half portion of the plasma. H-mode was produced in off-axis lower hybrid current drive (LHCD) plasmas by launching a lower hybrid wave (LHW) with a greater parallel refractive index, N peak || , of 3.1. The improved confinement status in such plasma discharges could be sustained for more than 400τ E . A high inductance, l i , plasma was created using a fast plasma current ramp down and sustained by central LHCD and IBW heating for a duration of >1 s with a strongly peaked electron temperature profile. The highest central electron temperature obtained was 4.5 keV. An increase in the energy confinement time with l i was observed. It was found that the IBW heating could improve the plasma confinement at the same l i if part of the LHW power was replaced by IBW. Stationary internal transport barriers with normalized performance H 89 β N > 1-3 were obtained with combined injection of LHW and IBW for a duration of several hundred energy confinement times in the weak negative magnetic shear (RS). Increasing the total injection power to 1 MW did not degrade the plasma confinement significantly in the RS operational scenario. Long pulse discharges were performed, using three feedback controls for the plasma current and position, the central line-averaged electron density and the magnetic swing flux of the transformer. The longest plasma discharge, with a duration of 240 s, T e (0) ∼ 1 keV and the central electron density >0.8 × 10 19 m −3 was achieved in 2004. The wall saturation and refreshment (wall pumping) were first observed in such long pulse discharges. A fully LHW current driven plasma without using ohmic current in the central solenoid coils was sustained for 80 s. The main limitation for the pulse length was due to the recycling, which caused an uncontrollable rise in the electron density.

Investigation ofZeffand impurity behaviour in lithium coating experiments with full metallic first wall in HT-7 tokamak

“…The HT-7 is a medium-sized superconducting tokamak with circular poloidal cross-section operated in limiter configuration aimed at high-performance plasma and steady-state operation, and has a major radius R = 1.22 m, a minor radius a = 0.27 m and a toroidal magnetic field B T ~ 2.0 T [15]. Deuterium (D 2 ) serves as the major working gas.…”

Recent experiments in the EAST and HT-7 superconducting tokamaks

“…Significant progress has been achieved in EAST construction/operation and HT-7 experiments with many contributions from broad international collaboration. In the last two years, HT-7 experiments were strongly oriented to support the EAST project both physically and technically [3,4]. HT-7 is used for specific physics investigation, in particular long pulse discharges, edge plasma turbulence, etc.…”

Conceptual design of the lower hybrid current drive system for the T-15 tokamak

“…[11] [7] (η LH ≈ 0.3× 10 20 A W −1 m −2 ). In the FTU tokamak, the current drive was observed at a plasma density above 10 20 m −3 [3].…”