Iii. Confinement
نویسنده
چکیده
The problem of projecting the energy confinement properties of future devices is a long-standing one in toroidal confinement research. While substantial progress has been made in characterizing the transport properties of tokamaks and stellarators, no definitive understanding of the mechanism(s) of cross-field transport has been achieved. Thus, we are not in a position to perform “firstprinciples” calculations of the projected performance of BPX. On the other hand, a wide range of data has been accumulated from tokamak experiments covering a large space of experimental parameters. These data have been used to constrain (or “calibrate”) theory-based models and have also been fit with statistical regression models of varying degrees of sophistication, in order to perform projections to future devices. The BPX physics group, in collaboration with the Transport Task Force and the Doublet III-D (DIII-D) and Tokamak Fusion Test Reactor (TFTR) experimental teams, has recently begun to explore another avenue of approach, in which dimensionally scaled confinement (e.g., confinement time normalized by gyrofrequency n,r~) is expressed in terms of key dimensionless variables such as p, collisionality v,, and gyroradius divided by plasma half-width p/a. BPX-like values of /!? and V* can be achieved in present devices, so the problem of projecting BPX performance can be reduced to the simpler one of determining the variation of RcTE with p/a. Theoretical models suggest that this variation should be particularly simple, e.g., quadratic or cubic.
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