Plasma dynamics and neutron production of the POSEIDON plasma focus

The correlation between plasma dynamics and neutron and X-ray emission was investigated on the plasma focus POSEIDON for various operational modes and for several electrode geometries. Qualitatively the plasma dynamics at high pinch currents is similar to that of smaller devices: after compression the plasma remains relatively stable, contained in a cylindrical pinch configuration for 100 nsec (pinch phase). During this phase a surface rippling of small amplitude occurs (flute instability). Later the plasma configuration is destroyed by one or more successive m = 0 instabilities. Pinch dimensions are larger than those of smaller devices. The neutron signal clearly exhibits a double-humped structure. The first pulse is emitted during the pinch phase. The high neutron yield cannot be explained by a thermonuclear model. Therefore, ion acceleration or anomalous ion heating must take place in this phase. Neutron emission in the pinch phase was not observed on smaller devices. The m = 0 breakup leads to a second neutron pulse. The neutron emission in this phase lasts up to a time at which the coarse plasma structures have already decayed. This long lasting emission is explained by the existence of long living turbulence structures. The schlieren pictures give evidence of substructures in the decaying plasma. The dimensions of these structures are larger than expected from the theory.