The improvement of potential confinement reported at the last IAEA Fusion E
nergy Conference in 1998 was attained by axisymmetrization of the heating p
attern of ECRH. It was experimentally shown that the axisymmetrization of E
CRH actually produced an axisymmetric potential profile. GAMMA 10 experimen
ts on potential confinement have advanced in the direction of longer sustai
nment and higher density. Experiments to achieve long sustainment of potent
ial confinement were carried out in order to study problems of steady state
operation of a tandem mirror reactor. A confining potential was sustained
for 150 ms by sequentially injecting two ECRH pulses into the plug region.
It had previously been difficult to increase the central cell density to hi
gher than about 2.5 x 10(12) cm(-3) with or without potential confinement,
owing to sonic density limiting mechanism. In order to overcome this proble
m, a new: higher frequency ICRF system (RF3: 36-76 MHz) has been installed.
A higher density plasma has been produced with RF3. In addition to RF3, NB
I in the anchor cells was recently made more effective through the reductio
n of neutral gas from the beam injectors. Potential confinement experiments
have advanced to higher central cell densities of up to 4 x 10(12) cm(-3)
with RF3 and NBI. A 35% density increase due to the potential confinement w
as obtained in the high density experiments.