Important issues from x-ray studies of high-current pulse discharges of the plasma-focus type

Summary form only given. The paper reports on recent measurements of the X-ray emission from a large plasma-focus PF-1000U facility [1] and compares them with results from the old Poseidon device [2]. The most important results of time-integrated measurements, which were performed by means of an X-ray pinhole camera, are presented and analyzed. Attention is paid to studies of a fine structure of the collapsing current sheath and dense pinch column. Observations of plasma filaments and so-called “hot spots” are discussed. The first observation of plasma filaments inside the PF pinch column [3] was later confirmed by some small-scale PF experiments, but in the large PF-1000U facility plasma filaments have for the first time been recorded recently. Other new results are time-integrated X-ray images of PF-1000U discharges with the gas puffing, which in some cases show very distinct “hot spots” formed outside the dense pinch core. They are explained by local neckings of spiral current filaments which surround the central pinch column.The paper reports also on time-resolved X-ray measurements, which were carried out by means of scintillation detectors coupled with fast photomultipliers, and by means of PINdiodes shielded with different absorption filters. Particular attention is paid to correlations of time-integrated X-ray images and time-resolved X-ray signals recorded during the recent PF-1000U experiments. Using collimators, which look at different parts of the PF pinch column, it has been possible to observe some delayed X-ray signals. Comparing these signals with time-integrated X-ray images it was possible to determine X-ray sources, and identify “hot spots” which have been formed later than others. It enabled dynamics of the “hot spots” formation to be investigated. A ratio of X-ray signals behind different filters has been used to estimate an electron temperature. The reported X-ray measurements are- of importance not only for learning about physical phenomena in PF discharges, but also for possible applications of intense X-ray pulses.