The hybrid extension of Vortex Confinement and the gap effect of potential biasing

Plasma in axisymmetric mirror traps is unstable versus flute-like modes if no stabilising measures are taken. Instead of stability it is also possible to aim at suppressing the convective transverse transport generated by unstable modes. A ‘vortex confinement’ scheme of this type is utilised in current operation regimes of the Gas-Dynamic Trap in Novosibirsk Bagryansky et al. (2011 Fusion Sci. Technol. , vol. 59, pp. 31–35). The relevant model Beklemishev et al . (2010 Fusion Sci. Technol. , vol. 57, pp. 351–360) describes the effect as due to nonlinear interaction of the flute modes with the background sheared rotation induced by plasma biasing via end plates and limiters. The rigid $m=1$ mode is saturated only due to current dissipation at the end plates, i.e. the partial line tying. The original model assumes flat radial profiles of plasma density and electron temperature, neglecting possible centrifugal and electron-temperature effects. These sources of instability are added to the original framework using a single scalar forming its hybrid extension. Efficiency of the biasing scheme for nonlinear suppression of flute-like convection is shown to depend primarely on spatial positions of biased facility elements, rather than on additional sources of instability.