Model-based Current Profile Control at DIII-D
Symposium on Fusion Technology
Warsaw, Poland, September 11-15, 2006
| Abstract |
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There is consensus in the fusion community that control of the radial
profiles of various plasma quantities (current, pressure, rotation,
etc.) will be key to the optimization of burning plasma scenarios. It
has been suggested, for instance, that global current profile control,
eventually combined with pressure profile control, can be an effective
mechanism for neoclassical tearing mode (NTM) control and avoidance.
It has been also suggested that simultaneous real-time control of the
current and pressure profiles could lead to the steady state
sustainment of an internal transport barrier (ITB) and so to a
stationary optimized plasma regime.
A key goal in control of an advanced tokamak (AT) discharge is to
maintain safety factor (q) and pressure profiles that are compatible
with both MHD stability at high toroidal beta and a high fraction of
the self-generated bootstrap current. This will enable high fusion
gain and noninductive sustainment of 100% of the plasma current for
steady-state operation. Active feedback control of the q profile
evolution at DIII-D has been already demonstrated [1]. In this work we
report progress towards enabling model-based active control of the
current profile during both plasma current ramp-up and flattop phases.
Initial results on modeling and simulation of the dynamic evolution of
the poloidal flux profile are presented. Dynamic models will allow the
exploitation of recent developments in the field of (nonlinear) control
of distributed-parameter systems to solve present profile control
problems in magnetic fusion energy.
[1] J.R. Ferron, et al., "Control of DIII-D Advanced Tokamak
Discharges," 32nd EPS Conference on Plasma Physics, Tarragona,
27 June – 1 July 2005, ECA vol. 29C, p. 1,069 (2005).