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Experimental observations of the plasma dynamics in a vacuum spark are presented which permit measurements of the electron density and temperature during a large part of the compression phase of the pinch. The vacuum spark is generated by a low-impedance pulse forming line with a maximum current in excess of 100 kA. The discharge is operated in the hybrid mode in a titanium plasma. A laser focused onto the cathode provides the preionizing source. Soft x-ray emission from the current sheath is observed with an x-ray framing camera well before maximum compression. These observations are compared with holographic interferograms, both showing the formation of an axisymmetric rhombic boundary to the plasma sheath. The temperature and density of both the sheath and the internal plasma are observed until the formation of hot spots at the time of maximum compression. The temperature evolution of the hot spots is presented, showing a repeatable behavior that depends on the axial position.

Experimental studies on a fast pulsed capillary discharge are presented. The discharge operates in a 0.8 mm inner diameter capillary, at 12 kV applied voltage. On axis discharge initiation is achieved by means of the hollow cathode effect. A short, less than 10 ns, XUV pulse is produced. Preliminary time resolved spectroscopic studies indicate that a hot, fast evolving short duration capillary plasma is produced.

We report on experimental observations in PFP-I, a small 3.8 kJ plasma focus, which is operated in Hydrogen-Argon mixtures to investigate the effect of parameter modifications on the overall performance of the device. An extensive array of diagnostics is been used, which includes voltage and current probes in the external circuit, a novel small magnetic probes array located along the cathode rods, filtered PIN diodes located side and end on, and filtered multi-pinhole and slit-wire X-ray camera. Extended operating range from below 0.2 Torr upwards has been achieved. Hot spot formation has been investigated as a function of H2-Ar mixing ratio. Hot spot sizes around 150 μm in the soft X-ray region, have been inferred from the slit-wire measurements. Pin-hole time integrated X-ray pictures and time resolved PIN diode measurements have been used to determine characteristic hot-spot temperatures in the 350 to 450 eV range.

Summary form only given. The Vacuum Spark is a small scale device which allows the achievement of plasma conditions leading to radiative collapse on a nanosecond timescale. We report on the plasma formations in a Vacuum Spark operated in the hybrid mode when driven from a 1.5 Ohm coaxial pulse forming line with a maximum current of 140 kA in a 120 ns pulse. A comparatively low power Nd:YAG laser pulse incident onto the cathode initiates the discharge. The evolution of the titanium plasma electron density and temperature is followed both in the visible and the soft X-ray part of the spectrum. The plasma electron density dynamics are followed using a novel micro holographic interferometric technique, based on the Mach-Zehnder interferometer, permitting a spatial resolution better than 20 /spl mu/m. This technique is compared with simultaneous results from image plane interferometric holograms. The probing beam is a 1 ns frequency doubled Nd:YAG laser.

In this work we present experimental observations of the XUV and electron beam emission properties of an ultrafast pulsed capillary discharge, which combines the features of a transient hollow cathode discharge with the inherent characteristics of the capillary discharge.

The recording of the spatial structure of a high temperature plasma in the hard X-ray region is limited by the problem of shine-through associated with a thin aperture material, when fine resolution is required, as well as the low-emission flux from the plasma in the high energy spectral region. In this paper, the design and performance of a hard X-ray camera is presented to monitor plasma radiation structure emitting in a spectral region above 12 keV, using the slit-wire camera design. In a series of experiments on GIT-4, the camera was used successfully to identify the spatial structure of the hard X-ray emission from the plasma and demonstrated the existence of a sub-100 /spl mu/m diameter, cm long plasma column emitting in the 18-30 keV region.

Experiments on the GIT-4 pulsed power generator have been performed in order to find out more about the composite pinch formation, stability and performances [1,2]. Different fibre materials and different external shell masses were tried out, in order to study their influence on the pinch behavior [3]. We present here results obtained from space resolved multi-pinhole, multi-filter X-ray camera under a variety of load conditions. The analysis was performed using a filter analysis [4] code with a full simulated spectra from the high Z materials. The temperature distribution along the composite pinch in those different experimental situations has been estimated, in different spectral regions. The influence of shell mass loading on the pinch uniformity will be discussed.

The capillary discharge is of great interest as a high brightness, short pulse XUV and soft X-ray source. Intense light emission from the visible to the soft X-ray region can be produced with very high brightness due to the high aspect ratio. Both broadband continuum and narrow band line radiation can be produced. Lasing gain in long capillary discharges have been demonstrated in a number of experiments. To increase the plasma temperature the pressure has to be decreased. The difficulties at low pressure are the tendency for the discharge to be formed on the surface of the wall and long build-up time of the discharge. This introduces significant materials from the wall discharge which is not directly under external control. To overcome these problems we have developed a device for intense XUV production which combines the features of a transient hollow cathode discharge with the characteristics of the capillary discharge. In this paper, some of the pulsed power aspects of this pulsed hollow cathode capillary discharge are presented together with some of the results obtained. The potential underlying the understanding, as well as the control, of the operating regime of a high temperature capillary discharge open up several areas of innovative research. The implication of the successful realization of a table-top X-ray laser in both research and application could not be over emphasized. (3 pages)

Preliminary experimental results on the investigation of hotspot formation in a small 3.8 kJ Plasma Focus device operating at constant mass density in Hydrogen-Argon and Hydrogen-Nitrogen mixtures are presented, at pressures from below 0.2 Torr upward, with relative percentages of Hydrogen ranging from 80% to 100%. The diagnostics includes voltage and current measurements, multi pinhole and slit-wire X-ray photography, filtered PIN diode array, and an array of small magnetic probes located along the cathode rods to study the current sheath structure during the run down phase of the discharge. A measurement of the hot-spot characteristic size in different spectral regions is obtained from the slit-wire images, whereas the time resolved information from the PIN diodes is used to infer the temperature evolution of the plasma points. Typical results show more reproducible hotspot formation in H2-Ar then in H2-N2 mixtures, with characteristic temperature in the 300 to 570 eV range, and hotspot size between 130...

A series of collaborative experiments on complex plasma loads have been carried out on the large inductive energy storage (IES) generator, GIT-4, over the last three years. The aim of the experiments is to explore the different configurations for the formation of ultra-high energy density plasmas in high voltage pulsed power systems by direct electromagnetic energy coupling. In this paper, the authors present some of the underlying philosophy on these experiments and the results obtained. Particular emphasis is placed on the pulsed power aspects and the effect of source-load coupling.

The possibility of attaining high temperature density plasma by passing a high current through a thin wire or fibre has long been recognized. In the paper experiment, another concept is prosed to produce the composite pinch configuration. Rather than the external injection of an additional plasma cylinder, an additional surface coating on the thin fibre is used. By the application of a controlled preheat current, this surface coating is then vaporised to form the additional plasma jacket over the fibre. Different coating methodologies were explored and the resulting plasma structure studied. (AIP)