Integration of LHCD and IBW heating for high-performance discharges under steady-state operation in the HT-7 tokamak

Abstract

Significant progress in obtaining high-performance discharges under quasi-steady-states in the HT-7 superconducting tokamak has been realized since the last IAEA meeting. In relation to the previous experiments, various features of the non-inductive current driven, heating, profile control, MHD stabilization and edge physics are integrated and optimized to achieve steady-state high-performance discharges. Both on-axis and off-axis electron heating with global peaked and locally steepened electron pressure profiles were realized with improved confinement if the ion Bernstein wave (IBW) resonant layer was properly selected. Stabilization of MHD instabilities was demonstrated by off-axis IBW heating. The internal transport barrier structure was formed by off-axis lower hybrid current drive (LHCD). Long-pulse discharges with T e ∼ 1 keV and central density ∼1 × 10 19 m −3 were obtained with a duration of 10-20 s. A combination of IBW heating and LHCD produced a broadened current density profile, which may be a signature of the synergy effect between two waves. Experimental results show that features of IBW in controlling electron pressure profile can be integrated into LHCD target plasmas. HT-7 has produced a variety of discharges with β N × H 89 >1-4 for durations of several to several tens of energy confinement times with a non-inductive driven current of 50-80% by optimizing the IBW heating and LHCD and avoiding MHD activities.

Internal collapse of the plasma during the long pulse plasma discharge and its influence on the plasma performance

“…In the long-sustained high-performance discharge by synergy of LHCD and IBW, it is very important to utilize the IBW local heating to increase the high-confinement volume [8,9]. Two operation scenarios of off-axis IBW with on-axis LHCD or off-axis LHCD are routinely employed.…”

Long-pulse discharges by synergy of LHW and IBW heating in the HT-7 tokamak

“…High-performance plasma is produced by the synergy between IBW and LHCD with a broadened current profile and broadened ITB on electron density and temperature profiles in the HT-7 [3,4]. The key issue for achieving high-performance discharge by using LHCD and IBW is to increase the high confinement volume.…”

“…It was found that the hard X-ray bremsstrahlung emission from suprathermal electrons, generated with lower hybrid current drive, was enhanced during ion Bernstein wave power injection. By means of the improvement of heating system and hard X-ray diagnostics in the HT-7, the optimal profile of hard X-ray intensity has been achieved by the synergy effect [3,4]. High-performance plasma is produced with a broadened current profile and broadened ITB (internal transport barrier) on electron density and temperature profiles in the HT-7 [3,4].…”

“…By means of the improvement of heating system and hard X-ray diagnostics in the HT-7, the optimal profile of hard X-ray intensity has been achieved by the synergy effect [3,4]. High-performance plasma is produced with a broadened current profile and broadened ITB (internal transport barrier) on electron density and temperature profiles in the HT-7 [3,4]. This high-performance mode utilizing synergy effect of IBW and LHCD provides a new way to obtain steady-state operation in the advanced tokamak scenario [3].…”

Progress in technology and experiment of superconducting tokamaks in ASIPP

“…Significant progress in developing the technologic and scientific basis for steady-state operation modes of high performance plasmas has been achieved in the last few years [2][3][4]. Experiments in the HT-7 tokamak were focused on investigating different scenarios for the confinement improved operation modes under quasi-steady-state condition and long pulse discharges.…”