Stable plasma at convex-concave field lines

Summary form only given. 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.