Tokamak burn phase energy optimization with volumetric and wall interaction effects

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Virginia Polytechnic Institute and State University


The energy output during the burn phase will depend upon the ion temperatures and densities. The ion source rates and the plasma current can be varied to control the ion densities. The impurity concentration of the plasma can be controlled by incorporating a charged particle divertor.

A dynamic model of the burn cycle of a Tokamak is used to investigate the ion densities, temperatures and the plasma volume as a function of time. The total energy output per cycle is investigated as a function plasma current, and divertor efficiency. The ion source rates were varied automatically to hold the plasma volume within an operational range.

The point kinetics model of the plasma incorporates ions, energy and volume balance equations and explicitly accounts for the impurity ion buildup through the use of a particle-wall interaction model. The D-D, D-T, D-³He reactions are all considered in this model. The energy carried off by the neutrons in the D-D and D-T reactions is lost from the plasma. Impurities enter the plasma as a result of wall interactions with escaping ions and neutrons.

An equilibrium state vector was obtained using currently projected operating parameters. The total energy density for a burn cycle was found to be a monotonically increasing function of the plasma current. The energy density was found to be the largest for low-atomic-number first wall matteral and no divertor, due to the expansion of the plasma volume.