In the Uragan‐3M (U‐3M) and Uragan‐2M (U‐2M) torsatrons possibilities and prospects of Alfvén method utilization for wall conditioning, plasma production and heating are studied. In U‐3M the effect of fast ion loss on H‐like mode formation is investigated. In U‐2M the wall conditioning associated with the chemical reactivity of the atomic hydrogen to create volatile substances is used. A compact four‐strap antenna is proposed for Alfvén resonance heating in U‐2M (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spontaneous changes in confined plasma parameters have been observed recently in the l = 3/m = 9 Uragan-3M torsatron with an RF produced and heated plasma, these being interpreted as transition to an improved confinement mode due to ITB formation near the ι = 1/4 rational magnetic surface. In the work presented joint studies are carried out of changes in some edge and diverted plasma characteristics that accompany ITB formation. It is shown that ITB formation induces a hard E r bifurcation at the boundary presumably driven by the ion orbit loss. As a result, E r becomes more negative, and an E r shear layer occurs, where the low-frequency microturbulence and the turbulenceinduced anomalous transport are suppressed, i.e. an ETB is formed. At the pre-bifurcation phase of transition a reduction of fast ion loss takes place. The bifurcation results in an improvement of electron confinement, while the ion loss increases.

No abstract

No abstract

In the l = 3 Uragan-3M torsatron with RF-produced and heated plasmas (ω ω ci ), a two-temperature ion distribution with a suprathermal tail is formed. Faster ions (FIs) can be the characteristic of reactor-size stellarators in the long mean free path regime. The presence of the helical divertor offers new opportunities for studying FI loss by measuring ion fluxes and energies in the divertor plasma.Ion energy distributions were measured in divertor flows in two symmetric poloidal cross-sections in several field periods. It is shown that FI flows out to the divertor mainly on the ion B × ∇B drift side in accordance with the assumptions of a determinative FI contribution to the plasma divertor flow vertical asymmetry inherent to torsatrons/heliotrons.Strong toroidal non-uniformities in flows and energies of ions outflowing into the divertor are observed. The island structure of the U-3M magnetic configuration and locality of RF power injection are considered as possible reasons for these non-uniformities.