Experimental Demonstration of Improved Neoclassical Transport with Quasihelical Symmetry

Differences in the electron particle and thermal transport are reported between plasmas produced in a quasihelically symmetric (QHS) magnetic field and a configuration with the symmetry broken. The thermal diffusivity is reduced in the QHS configuration, resulting in higher electron temperatures than in the nonsymmetric configuration for a fixed power input. The density profile in QHS plasmas is centrally peaked, and in the nonsymmetric configuration the core density profile is hollow. The hollow profile is due to neoclassical thermodiffusion, which is reduced in the QHS configuration.

Figure 1

Profiles of (a) electron temperature and (b) density for a QHS plasma with 26 kW of injected power and a Mirror plasma with 67 kW of power.

Figure 2

Profiles of experimental and neoclassical particle fluxes for the (a) Mirror and (b) QHS discharges shown in Fig. 1. The neoclassical flux is broken into the components driven by the density and temperature gradients and the radial electric field.

Figure 3

Profiles of the (a) electron temperature and (b) density profile for a Mirror plasma in which the power is deposited off axis.

Figure 4

Experimental and neoclassical thermal diffusivities for QHS and Mirror plasmas.