Evolution of the structure of the dense plasma near the cross point in exploding wire X pinches

Abstract

The dynamics of the dense plasma near the cross point of an X pinch has been investigated using 1 ns x-ray backlighting images at different moments relative to the start of 100 ns [full width at half maximum (FWHM)] 200 kA current pulses. If the two metal wires are fine enough (e.g., 10 μm W or 17.5 μm Mo) to form a pinch at the cross point, accompanied by an x-ray burst, with the available current pulse, then the images show three stages of development: a radial explosion/expansion phase; an implosion during which a dense Z pinch of 200–300 μm length forms at the cross point together with plasma jets which move axially away from that point; and a breaking up of the Z pinch, coincident in time with one or two x-ray bursts, after which a 300 μm gap opens up. For W, the backlighter minimum sensitivity is 1017/cm2 areal density, and the dense Z pinch is estimated to have a volume density close to 1021/cm3. Shock waves appear to be expanding at about 50 μm/ns from the end points of the collapsing Z pinch, where the plasma was the most dense.

Cross-point coronal plasma dynamics in two- and four-wire x-pinches

“…8,9 These hot spots are of great interest for their high energy density conditions and are used as a source for high energy radiography. 7,[10][11][12][13][14][15] Following the x-ray burst, plasma is rapidly evacuated from the central region, leaving a gap in the axial density profile which continually expands late in time. 7,13,16 Much of the research on x-pinches has been to characterize the implosion dynamics at the cross point, in order to more fully understand the x-ray generation mechanics.…”

“…7,[10][11][12][13][14][15] Following the x-ray burst, plasma is rapidly evacuated from the central region, leaving a gap in the axial density profile which continually expands late in time. 7,13,16 Much of the research on x-pinches has been to characterize the implosion dynamics at the cross point, in order to more fully understand the x-ray generation mechanics. 7,13 A substantial amount of work on the examination of x-pinch dynamics has been carried out with the use of x-ray backlighters, using x-pinches in parallel load configurations ͑us-ing the x-ray burst from one to image the other͒.…”

“…[4][5][6] At the same time, the self-generated magnetic field from the flow of current combines at the cross point to create a strong global field that compresses the plasma to near solid densities, forming a z-pinch that is a few hundreds of micrometers in length, often referred to as a micro z-pinch. 7 Magnetohydrodynamic instabilities lead to pinching of the plasma at multiple points along the micro z-pinch. Some of these pinching points develop into "hot spots" of high density and temperature plasma that emit intense bursts of soft x-ray radiation, in the 1 -10 keV range, that can have subnanosecond duration.…”

“…7,13,16 Much of the research on x-pinches has been to characterize the implosion dynamics at the cross point, in order to more fully understand the x-ray generation mechanics. 7,13 A substantial amount of work on the examination of x-pinch dynamics has been carried out with the use of x-ray backlighters, using x-pinches in parallel load configurations ͑us-ing the x-ray burst from one to image the other͒. 7,13,[17][18][19] Radiography has also been used in conjunction with selfemission soft x-ray imaging to examine differences in the dynamics and output of two-and four-wire x-pinch configurations.…”

Correlation of Neutron and X-ray Emission from Plasma Focus with Pre-ionization

“…Plasma focus (PF) is among the low-priced available neutron and ions generators, with unique features of extremely short pulses (hundreds of ns) that suit it for different interesting applications [3][4][5][6]. Similarly, the soft X-rays emitted from PF have attracted the many researchers due to large numbers of application such as high brightness source for lithography in order to fabricate the electronic devices, X-ray laser pumping, X-ray Microscopy, X-ray backlighting and radiography [7][8][9][10][11][12].…”