Stable plasma at convex-concave field lines

Plasma in magnetic field configuration of alternating-sign curvature — with appropriate combination of the convex and concave field line parts, exhibits specific stability features against convective (flute-interchange) modes1,2. This results in the internally peaked stable pressure profiles that has been predicted from theory with taking into account necessary and sufficient ‘kinetic’ criterion of plasma convective stability. Simplest magnetic confinement system that is required for such a peaking — tandem of a mirror and cusp device, having minimum of second adiabatic invariant J = ∫ v dl in a middle of confinement volume. Compact magnetic confinement system Magnetor3,4 with 2.45 ECR plasma has been improved by adding additional current coil to satisfy alternating-sign curvature requirements for a plasma pressure peaking. First experimental measurements of the ion saturation current transverse profiles (see figure 1) demonstrate a maximum in ion saturation current at the region of low but alternating-sign curvature.