Abstract
In the Engineering Test Facility (ETF), the plasma pulse duration is expected to be hundreds
of seconds, which is comparable to the resistive time scale that governs the resistive diffusion
of the equifibrium. The resistive evolution of the safety factor q profile may, for MHD
stability reasons, limit the duration of the plasma burn in a tokamak reactor. It may be
possible to control this evolution and extend the plasma burn time through proper profile
tailoring. We study the evolution of the q profile on the resistive time scale numerically using
a one-and-one-half-dimensional (1ı89 single fluid transport code. Two high beta (~r-
7-16%) cases are considered: (a) a beam-driven hydrogen plasma with no nuclear alpha
heating for which the beam energy is used as a device to control the temperature profile, and
(b) an ignited D-T plasma in which the neutral injection has been turned off. For the
beam-driven plasma, it is shown that low beam energy heating profiles lead to resistive steady
states having broad temperature profiles and flat q profiles, while high beam energy heating
profiles lead to resistive steady states having peaked temperature profiles and deep q profiles.
The centralized nuclear heating in an ignited D-T plasma causes the evolution of the q profile
for this case to behave much like that in the high energy, beam-driven case: namely, the q
values near the plasma center decrease on the resistive time scale until a deep, resistive,
steady-state q profile is reached.