Time-resolved features of the electron beam emission from a neon plasma focus

The paper reports the results of an analysis directed towards the complete description of the temporal evolution of the electron beam emission and the identification of the phenomena involved in the electron emission processes in a 3 kJ/14 kV Mather-type plasma focus operated in Neon in the 1.5-5.5 mbar range. The electron beam was extracted through the anode and passed through a drift tube along which the electron current was measured using a fast derivative Rogowski coil coupled to an appropriate RC passive integrator. The X-ray emission in the 0.5-40 keV range was monitored using a soft X-ray spectrometer. A scintillator-photomultiplier detector was employed for photon energies above 70 keV. A computer-controlled CCD pinhole camera was used to capture X-ray images of the focusing area. Several electron emission periods and mechanisms corresponding to different plasma phenomena i.e. pre-focus emission, pinch emission, emission by instabilities and turbulence, secondary and late plasma compressions, etc. were identified and discussed. The study of the electron beam output with respect to the operating pressure showed that the electron beam production reaches an optimum (in terms of total current and shot-to-shot reproducibility) at 4 mbar neon pressure. (authors)