ON THE DENSITY LIMIT OF TOKAMAKS
Under the conditions of so far performed quasi-steady Tokamak experiments near the density limit, the plasma pressure gradient in the outer layers of the plasma body becomes mainly determined by the plasma - neutral gas balance. An earlier analysis of ballooning instabilities driven by this gradient in regions of "bad" curvature has been extended to deduce an explicit stability criterion which determines the density limit. This criterion is closely related to the empirical Murakami limit. At relevant Tokamak data, the deduced limit becomes proportional to j-z square root (R) where j-z is the average current density and R the major plasma radius. It is further found to be independent of the toroidal magnetic field strength and anomalous transport, as well as to be a slow function of the outer layer temperature and the mass number. The deduced stability criterion is consistent with so far performed experiments. Provided that the present analysis can be extrapolated to a wider range of parameter data and be combined with Alcator scaling, conditions near ignition appear to become realizable in small Tokamaks by ohmic heating alone. These conditions can be satisfied at relevant magnetic field strengths and plasma currents, by imposing a high plasma current density.
Bibliographic Reference: WRITE TO DEPARTMENT OF PLASMA PHYSICS AND FUSION RESEARCH, ROYAL INSTITUTE OF TECHNOLOGY, S-100 44 STOCKHOLM 70 (SWEDEN), MENTIONING REPORT TRITA-PFU-82-13, 1982
Record Number: 1989122052800 / Last updated on: 1987-01-01
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