Tokamak Plasma Equilibrium Controllability Limitations Due to Delays
D. Sondak, E. Schuster, M.L. Walker
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Orlando, Florida, November 12-16, 2007
Abstract
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When designing the control loops for tokamaks, it is important to
acknowledge the effects of time delays. An assumption which is
sometimes made is that if the system open loop response is
intrinsically slow, due for example to substantial vessel shielding or
to the imposition of limits on rate of change of control currents,
then extra time delays which are individually shorter than these will
not have significant undesirable effects on control. However, because
delays and phase lags are in general cumulative in effect, this
assumption is typically incorrect. This study examines and quantifies
these effects in the axisymmetric control loop in superconducting
tokamaks, for the case of plasma current control, radial and vertical
position control, and plasma boundary control. Delays in the power
supplies, data acquisition, and vessel structure are taken into
account. Methods for remediating the negative effects due to time
delays are also presented.