The dynamics of the DPF as determined from an analysis of laser scattering spectra



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Time resolved scattering spectra have been observed from a dense plasma focus (DPF) illuminated by a pulse of laser light, for two axial positions, 0.6 cm and 1.3 cm from the face of the center electrode. Scattering was observable from 10 nsec prior to the arrival of the collapse on axis until the visible light bremsstrahlung fell below the background illumination of the plasma sheath (~50 nsec). Tlie frequency spectrum is markedly asymmetric about the laser frequency, a feature which is inconsistent with spectral expectations based on thermal particle distributions even if particle drifts or wave excitations are included. A model is postulated which attributes the asymmetry to a non-isotropic velocity distribution and to a lateral displacement of the scattering region from the central axis of the focus. Analysis based on this model yields radial collapse velocity, density, and ion temperatures. Noteworthy features are the absence of radial bounce and indications of axial jetting with ~10[raised 8]cm/sec implied axial velocities.