Instabilities in the plasma focus

This review paper starts with a description of the compression stage of the focusing plasma, using a snow-plough model. It is shown that sophisticated MHD calculations substantiate the snowplough theory, however are not suited to describe the phenomena in the final compressed stage. For this purpose, a particle-in-cell calculation is employed, yielding a beam-beam collision model for the neutron production. Experimental evidence indicates that neutron production is associated with the appearance of m=0 instabilities and is the direct result of collisions between anomalously accelerated ions. One of the mechanisms of ion acceleration are strong local electric fields. Another possible mechanism can be seen in beam-plasma instabilites caused by runaway electrons. The analytical derivation of the dispersion relation for plasma focus conditions including runaway effect is discussed. (Auth.)