Tendency of MHD Forces to Create Localized, Collimated Plasma-filled Flux Tubes & Ion Orbit Instability in a Flux Tube

Electrostatic helicity injection involves the injection of new azimuthal magnetic flux to link the existing axial flux of an open magnetic field. Since magnetic flux is frozen into plasma, this injection of new flux requires the injection of new plasma as well. This associated plasma injection means that helicity injection involves an increase of the density in the flux tube comprised by the initial open magnetic field lines. The injection of plasma and its embedded magnetic flux results in a collimation of the open flux tube when the embedded magnetic flux becomes compressed due to flow stagnation. Plasma injection occurs in the form of jets originating from biased electrodes having plasma sources. These jets can originate from both cathodes and anodes. An ion orbit instability may occur for cathode-originating jets. In cathode-originating jets the ions move opposite to the direction of the conventional current and so experience an anti-pinch force which can be strong enough to overwhelm the usual magnetic force responsible for cyclotron orbit motion.