New plasma-focus experiments without and with additional targets

Abstract

Summary form only given. The paper reports on results of recent Plasma Focus (PF) experiments performed with medium-scale machines operated at 60-180 kJ. The first series of PF discharges was carried out within a PF-150 machine at 60 W, 28 kV. The device was equipped with Mather-type electrodes of 100 mm and 50 mm in diameter, and 200 mm in length. Attention was paid to current-sheath (CS) and PF pinch dynamics, which was investigated with a high-speed framing camera, consisted of two VR channels and two soft X-ray modules. Exposure of VR frames was about 1 ns, and that of X-ray frames was about 0.8 ns. Synchronization was realized with fast photodiodes registering the CS radiation. Electrical signals were stored with a TDS784A digital oscilloscope, and all the frames were elaborated with an image capturing and processing system (AICPS). Measurements were also performed with X-ray pinhole cameras and neutron counters. Comparison of the VR pictures and corresponding X-ray images revealed correlation between fine structures formed inside the pinch column. The second series of experiments within PF-150 machine was carried out with solid targets made of thin metal- or carbon-wires, fixed on the z-axis at the electrode outlet. Using the same diagnostic equipment, it was observed that the interaction of the low-mass CS layer with the wire target produces an almost homogenous plasma column, which does not expand considerably during the CS collapse process. At the same time the X-ray emission along the z-axis is considerably higher that that emitted in the radial directions. The third series of PF experiments was performed within a PF-360 machine equipped with the Mather-type electrodes of 170 mm and 120 mm in diameter, and 300 mm in length. The system was operated at 110 kJ, 30 kV, or 176 kJ, 35 kV. Several additional diagnostic techniques were applied to study time-integrated and time-resolved characteristics of the charged particle emissions. To increase a neutron yield from fusion reactions the use was made of cryogenic targets in the form of heavy-ice (D/sub 2/O) layers deposited upon special cryogenic targets. Considerable differences in the neutron yield have been observed in dependence on the experimental conditions applied. These new experiments are described, and the results are compared with those of previous PF studies.