The feedback control system to control plasma current and position on the H
T-7 superconducting tokamak was greatly improved in early 1998. Lower hybri
d current drive (LHCD) experiments with the improved control system were pe
rformed to sustain long pulse discharges and to improve plasma confinement.
Partial non-inductive current drive and full non-inductive current drive f
or several seconds by means of LHCD were demonstrated. It was observed that
plasma confinement could be considerably improved by LHCD. Experimental ev
idence 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. Th
e EFIT code was modified for the reconstruction of the magnetic surfaces in
HT-7 and a test computation was performed.