1 - Nuclear Sciences and Applications - IAEA

IAEA-CN-50/A-V-4 309
uses the TRANSP code [2] to calculate the particle flux, F, as a function of
time and position by solving Eq. (1) using the measured time-dependent
density profile and an empirical model for the source function. Then using
data during the time the density wave propagates across the plasma, a linear
multiple regression of I7n = a + (p/nj (3nJdi) determines the transport
coefficient D and V at each radial position. This technique assumes that the
transport coefficients obtained are not a function of the size of the gas puff
itself. When compared, the two analysis techniques yield comparable
deduced transport coefficients.
Previous results [3] for a low density ohmic discharge indicated
that the radial diffusion is a minimum in the plasma core and rises to a
maximum in the periphery. The inward velocity has a similar shape to D,
and has values substantially greater than neoclassical. Recently four different
helium plasma conditions were examined with the density n l
e
= 1.6 x 10
and 3.1 x 10 V , and plasma current 1= 0.8 and 1.4 MA. At ng =
1.6 x 10 m' D with either current, the plasma global energy confinement
1Q O
time is in the linear regime. Forne = 3.1 x 10 m, the confinement
at 0.8 MA is in the saturated confinement regime while at 1.4 MA the
confinement is near the knee of the curve. In each case a small deuterium
puff of 1.33 Pa-rrr for 0.05 s was injected into an equilibrated helium plasma.
Figure 1 is a plot of the particle diffusivities obtained for these four ohmic
cases. The open and closed circles represent the high density cases; there is
no sign of a current dependence. The low density points (open and closed
triangles) also have no clear current dependence, but their values are
systematically higher than the high density points. When averaged over the
plasma radius the particle diffusivity for this case is a factor of two greater
than the high density cases, and thus the profile-averaged diffusivity is
roughly proportional to l/ne. All four conditions exhibit a radial dependence
that has a minimum at the plasma core and a maximum near the edge. The
profiles of the particle diffusivity De(r), and the equilibrium thermal
diffusivity X~(r), have the same shapes and their absolute values agree within
a factor of two across the full profile for the four plasma conditions
considered. Previous studies of particle transport using gas puffs on other