Dynamics of Plasma Phenomena in "Plasma Focus" Under the Action of Powerful Laser Radiation

Abstract

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Update on the Scientific Status of the Plasma Focus

“…Although the existence of B z in the pinch phase can be ascribed to helical deformation of the plasma boundary (see Figure 89), this is not possible for the radial implosion phase where very symmetric plasma shells are routinely seen. The evidence from PF-1000 is based on magnetic probe measurements [212] and is supported by the observations on contactless compression of a laser-plasma plume by an imploding plasma focus sheath [169][170][171] and magnetic probe measurements [174] in POSEIDON (see Section 2.4.1).…”

“…The resulting copper plasma plume was observed to emerge with negligible radial expansion, using time integrated soft X-ray pinhole photography and 5 frame pulsed ruby laser interferometry. In a subsequent experiment [170], the plume was generated in an off-axis location and was seen to be pushed towards the axis and then to expand axially with negligible radial expansion (see Figure 1 of [171]). Since the DPF plasma sheath and its associated azimuthal magnetic field had not yet reached the vicinity of the copper plume, the authors concluded that this behavior could be caused only by an axial magnetic field filling the space between the still-imploding plasma focus sheath and the plasma plume.…”

“…In 1979, Gribkov et al [169] inferred the existence of an axial component of magnetic field associated with the implosion phase of the plasma focus. A laser pulse ablated the center of the copper anode of the Filippov type DPF at the Lebedev Physical Institute in Moscow much before the plasma focus sheath collapsed to form a pinch column.…”

Axial magnetic field and toroidally streaming fast ions in the dense plasma focus are natural consequences of conservation laws in the curved axisymmetric geometry of the current sheath

“…Time integrated soft x-ray pinhole photography and 5 frame pulsed ruby laser interferometry revealed that the resulting copper plasma plume emerged with negligible radial expansion. In a subsequent experiment [28], the plume was generated in an offaxis location and was seen to be pushed towards the axis and then to expand axially with negligible radial expansion (see Fig.1). Since the DPF plasma sheath and its associated azimuthal magnetic field had not yet reached the vicinity of the copper plume, the authors suggested that this behavior could be caused only by an axial magnetic field.…”

“…Because their azimuthal motion keeps them confined within the plasma, these energetic ions, mixed with shock wave reflected from the axis, could be expected to lead to the much-higherthan-thermal fusion reaction rate [3]. The observation [28] of ~100 keV deuterons circulating around the axis in Frascati DPF thus has a natural explanation in terms of conservation laws without invoking any m=0 instability, anomalous resistivity or reconfiguration of the magnetized plasma. Indeed, there is evidence from three large facilities about neutron emission being unaffected by absence of m=0 instability [50][51][52].…”