FP techniques have been successfully applied to 3-D equilibrium
reconstruction on W7-AS using a database of NEMEC equilibria
in terms of very compact set of input parameters: 3 ratios of the 4
external coil currents to describe the vacuum field, a physical
limiter position to identify the location of the boundary flux surface
and PC's of the equilibrium pressure profile as a function of
normalized toroidal flux. Recovery accuracy is good, due in part to
the selection of the information-rich pressure profile PC's as FP
predictors describing the finite-
deformation of the vacuum
field of the stellarator.
We have demonstrated that, based on these rapid FP reconstructions, interpretive equilibrium identification can be practically applied on W7-AS and can be performed in under ten seconds on a 300 MHz UltraSPARC workstation. This is some 3 orders of magnitude faster than was previously possible for standard equilibrium reconstructions on W7-AS using NEMEC on a Cray J-90. Moreover, our scheme follows a systematic least-squares minimization algorithm and requires no user intervention such as that required by the standard method. Results from our method are at least as good or better than those from the standard calculation, but are often superior, yielding less residual asymmetry in the electron pressure profile. Modifying the procedure to match any additional global or profile data is straightforward since this requires only alteration of the cost function.
This work could form the basis of routine equilibrium reconstructions accompanying the W7-AS experiment on a shot-to-shot basis, for the single time-point at which the Thomson scattering diagnostic is triggered.