1 - Nuclear Sciences and Applications - IAEA

0 6 12 (Wall)
r(cm)
IAEA-CN-50/A-VH-8 441
0 6 12 (Wall)
r (cm)
FIG. 3. Density profiles through the transition of qs ~ 2,
qf plasma (constant current mode) is nearly constant during the discharge, except in
high density plasmas (ne > 3 X 10 20 m" 3 ). In the ramp-up current mode, when qf
passes through 2, the central density decreases rapidly to 2/3-1/2, mainly owing to
flattening of the density profile, then it stays constant. The relaxation of the density
profile suggests that it has a specific profile which mainly depends on the qf value.
The profile of the ion temperature from C V Doppler broadening gradually
becomes broad with time during the discharge. The profile of the electron temperature,
measured by Thomson scattering, also broadens gradually. Since the temperature
profile is steeper than the density profile, the pressure profile is not so flat as
the density profile.
4. ENERGY CONFINEMENT AND FLUCTUATIONS
The global energy confinement time TE is evaluated from rE = Wp/(Vp Ip -
dWp/dt). The plasma energy Wp is calculated from j8p. The relation of the global
energy confinement time TE to the electron density and the plasma current is found
to be close to the neoclassical scaling in the MHD region, that is, TE OC Ipn,., as is
shown in Figs 4(a) and (b) [4, 5, 10]. The radiation loss has been reduced to less than
one third of the total loss. However, confinement deteriorates when periodic, decaying
oscillations appear on the one-turn voltage, the soft X-ray emission, the visible
radiation, and the density. In particular, when q( approaches the lowest limit (qf ~
1.2), the density and q profiles become very flat, and a periodic, decaying oscillation
appears on the one-turn voltage, and the density of the peripheral region fluctuates
Time