On the Bursting of Filaments in the Plasma Focus
Photographs of the current sheath of (low energy) plasma focus show a disruption of the filaments. We interpret this phenomenon as a vortex breakdown. Physical parameters which support this hypothesis are obtained from measurements, from the theoretical thickness of the current sheath given by Nardi and from some models of the plasma flow. The widening of a vortex due to axial velocity increase is analyzed by means of magnetohydrodynamic collinear models. The main results are: i) the existence of a limit separating. supercritical from subcritical regimes (their character changes with the ratio between kinetic and magnetic energy); ii) the existence of flow regimes where the vortex radius remains approximately constant for moderate increments of the external velocity; iii) the structure of the vortex may change substantially for a sufficiently large increment of the external velocity, even in subcritical states; iv) the possibility that a burst of the vortex may occur when the external velocity suffers a slowdown.
KeywordsAxial Velocity Vortex Ring Plasma Focus Central Electrode Subcritical State
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