1 - Nuclear Sciences and Applications - IAEA

IAEA-CN-50/A-I-4 71
A pneumatic pellet injector was installed in early 1988. This injector produced
three hydrogen pellets with a velocity of 1.5 km-s" 1 and with cylindrical sizes of
2.7 mm (diameter) X 2.7 mm (length) to 3.8 mm (diameter) x 3.8 mm (length).
3. DISCHARGE CONTROL AND OPERATIONAL REGIME
Experiments on JT-60 have been conducted in different configurations: limiter
and divertor with outside or lower single null. Various heating methods have been
used, ranging from Ohmic heating alone to combinations of Ohmic, NBI, ICRF and
LHRF. Fuel has been supplied by gas puffing and/or pellet injection.
Various techniques have been introduced into the discharge control for obtaining
high density and high current (low q) plasmas as shown in Fig. 2. The LH current
drive (f = 2 GHz, No = 1.7, PLH = 1.5 MW) was used in the current ramp-up
phase to save the flux swing of the Ohmic power supply. Subsequently, a long pulse
NBI was necessary to suppress a serious, m = 3/n = 1 locked mode [5]. This mode
grew at qeff = 2.8-3.0 and a required NBI power of more than 13-15 MW for
stabilization. After passing through the dangerous unstable zone of the locked mode,
a density increase by additional gas puffing became possible with the aid of high
power NBI. The plasma current and the line averaged electron density reached
Ip = 3.2 MA (qeff = 2.2) and n^ = 1.0 x 10 20 nr 3 , respectively, in the flat-top
phase. The NBI was required still in the current termination phase to prevent hard
disruptions.
The operation regime of JT-60 is shown in Fig. 3. In limiter discharges with
graphite wall, a high density (n