Laser shadowgraphic study of plasma sheath in dense plasma focus in the presence of external axial magnetic field

The Dense Plasma Focus (DFP) is a device for the production of plasma of very high density (≅1025-26 m-3) and temperature in the range of 1-2 keV. This device can be used as a source of neutrons, X-rays, and particle beams by filling the plasma chamber with suitable gas. If we use suitable diagnostics it may be possible to study the dynamics of the plasma sheath. This is achieved with the help of laser-shadowgraphy by Lee et al. It may be further noted that the application of axial dc magnetic field (Bz) may influence the various parameters of neutrons, X-rays, and particle beams and also the dynamics of focus formation. Mather et al. found with the help of soft X-ray pin hole photographic analysis that Bz provided the spatial stability to the focused plasma column. Material erosion from the centre electrode and X-ray emission from the electrode face as a result of electron bombardment was also found to be reduced. Beckner and Smith investigated that the neutron yield is decreased by a factor of 40 in the presence of Bz. Bernstein and Hai also measured the energy of the neutrons and found that the average energy of the neutrons decreased. However, no study has so far been made about the influence of such Bz on plasma sheath dynamics. We have therefore studied in the present paper the dynamics of plasma sheath in the presence of Bz with the help of N2-laser shadowgraphic method. (author) 6 refs., 5 figs