Overview of recent results from HSX and the planned experimental program

Up to now HSX has demonstrated that the quasihelical symmetry (QHS) does indeed improve single-particle confinement over a non-optimized 3-D configuration, as predicted. Some neoclassical differences have been observed under the present operating conditions. Using flows induced with a biased electrode we have demonstrated that quasisymmetry leads to reduced parallel viscous damping. The flow in the QHS configuration rises and damps more slowly than in the Mirror (quasihelical symmetry intentionally broken) and attains approximately twice the flow velocity for the same drive. This work is being extended to look at flow damping in the presence of islands that locally break the quasihelical symmetry. The density profile is broader and not as peaked in the Mirror compared to the QHS configuration. We have concluded, by making comparisons of on-axis to off-axis heating, that thermodiffusion may account for the difference, with low thermodiffusion in the QHS case. We do not yet see large, conclusive differences in the temperature profiles between the two configurations consistent with the expected dominant role for anomalous transport under present operating conditions. We have used the 1-D transport code, ASTRA to help point the way to understand the relative role of anomalous versus neoclassical transport so that we can move to a regime where the neoclassical differences would be emphasized. Our goals are to increase the density, the magnetic field and heating power. By this fall we will raise the magnetic field to 1.0 T. Ordinary-mode heating with our 28 GHz gyrotron will be employed using a new quasioptical transmission line to deliver the full 200kW (minus losses in the line) to the torus. This will allow us to raise the density by a factor of 2, decrease anomalous transport, reduce the contribution of the nonthermal population to the global stored energy and raise the confinement time. Over the next 1 or more years, another 200 kW gyrotron will be brought into operation, making available 400 kW total microwave power. Power modulation of the 2nd gyrotron will permit a determination of the thermal conductivity by heat wave analysis that can be compared to steady-state measurements. A steerable launcher will give some control over Te profiles for thermal conductivity and thermodiffusion studies. Empirical stellarator database studies suggest that global confinement improves with decreasing effective ripple, even when the plasma collisionality is relatively high. By energizing all of the main HSX coils except for those of Type 3 (of 6 types), a magnetic configuration is made which has a high effective ripple (nearly a factor of four over our Mirror mode), but similar volume, transform and well depth to the QHS configuration. Variation of the coil-3 current with respect to the rest of the modular coils will allow comparisons of confinement over a wide range of effective ripple in a single device. (author)