Three dimensional simulation study of spheromak injection into magnetized plasmas

The three dimensional dynamics of a spheromak-like compact toroid (SCT) pla smoid, which is injected into a magnetized target plasma region, is investi gated by using MHD numerical simulations. It is found that the process of S CT penetration into this region is much more complicated than that which ha s been analysed so far by using a conducting sphere (CS) model. The injecte d SCT suffers from a tilting instability, which grows with a similar timesc ale to that of the SCT penetration. The instability is accompanied by magne tic reconnection between the SCT magnetic field and the target magnetic fie ld, which disrupts the magnetic configuration of the SCT. Magnetic reconnec tion plays a role in supplying the high density plasma, initially confined in the SCT magnetic field, to the target region. The penetration depth of t he SCT high density plasma is also examined. It is shown to be shorter than that estimated from the CS model. The SCT high density plasma is decelerat ed mainly by the Lorentz force of the target magnetic field, which includes not only the magnetic pressure force but also the magnetic tension force. Furthermore, by comparing the SCT plasmoid injection with the bare plasmoid injection, magnetic reconnection is considered to relax the magnetic tensi on force, i.e. the deceleration of the SCT plasmoid.