The feedback control system to control plasma current and
position on the HT-7 superconducting tokamak was greatly improved in early
1998. Lower hybrid current drive (LHCD) experiments with the
improved control system were performed to sustain long pulse
discharges and to improve plasma confinement. Partial non-inductive
current drive and full non-inductive current drive for several seconds by
means of LHCD were demonstrated. It was observed that plasma confinement
could be considerably improved by LHCD. Experimental
evidence suggests that this improvement during the LHCD
phase could be due to the modification of the current profile in
the outer region of the plasma. MHD modes (especially m = 2) seem
unstable with such a current profile. The EFIT code was modified
for the reconstruction of the magnetic surfaces in HT-7 and a test computation
was performed.
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