Review of the neutral-beam current requirements for the Mirror Fusion Test Facility (MFTF)

Abstract

The techniques used to evaluate the beam-current requirements for MFTF are similar to those in previous studies but incorporate some improvements. In particular, we have enlarged the radial code BUILDUP to allow for a smaller radial grid and to improve the numerical accuracy; we have also improved the model of the atomic physics processes and the particle-equilibrium calculations. Also, a model of plasma containment that conserves energy as well as particles but does not include any effect of the expected drift-cyclotron loss-cone (DCLC) turbulence has been incorporated into the previous studies. We show that the DCLC turbulence increases the average ion energy and decreases the particle confinement time. Because these effects cancel to first order, the beam-current requirements are independent of the turbulence. We find that 24 of the present LBL source modules would sustain a plasma with an average beta of 0.46. This figure is within 10% of the MFTF goal and is within our calculational accuracies. We further show that the beam-current requirements for the large-diameter plasma are consistent with those of experiments to study the buildup of a field-reversed plasma.