Studies of the spatial and temporal evolution of a dense plasma focus in the X-ray region

Abstract

The dynamics of the plasma evolution in a dense plasma focus has been studied using a streak camera system in the soft X-ray region. The experiments were performed on a medium energy plasma focus operating with a hydrogen-argon admixture. The streak camera system employed provides nanosecond resolution and allows the plasma to be viewed simultaneously through two different filters to achieve energy resolution. Observations are made in the radial direction and along the pinch axis. Collimated X-ray PIN diodes suitably filtered were used to provide additional information on the structure of the X-ray emitting regions of the plasma. The plasma focus is observed to be totally dynamical and continuously evolving in nanosecond time scale. Hot spots are observed to form among the moving plasma at various times. Such continuous nanosecond time scale evolution of the focus pinch in the X-ray region have not been reported previously. IntroductionThe plasma focus device has long been the favorite device for investigation owing to the anomalously high neutron yield and the favorable neutron scaling with discharge current (Decker et al. 1980). The exact mechanism for neutron production is still under discussion. On large machines with W 0 >250kJ, the results indicate that, for properly optimized electrode dimensions, the neutron emission starts at the beginning of or during maximum compression (Pecorella et al. 1977;Jerzykiewicz et al. 1985;Herold et al. 1985). These reports have dispelled the concept that most neutrons are generated by beam-target interaction resulting from the much quoted m = 0 instability as originally suggested by Anderson (1958) in a conventional Z-pinch. Some early measurements on smaller machines suggested that the neutron production is due to the m = 0 instabilities (Schonbach et al. 1974). These machines were operating mainly in the 15-30 kV region, with capacitor bank energy W o below 20 kJ. More recent experiments on small machines, but operating at voltage of 60 kV or higher, indicate that a first period of neutron production which is independent of the m = 0 instabilities is also present (Hirano et al. 1985;Herold et al. 1988). The spatial and temporal evolution of the hot dense plasma is therefore of great importance in the quest to understand the basic mechanisms responsible for the neutron yield observed in these devices.In this paper, we report on experiments to study the evolution of the hot plasma with

Study of Neutron From a Dense Plasma Focus Paco Instrument by Means of Nuclear Tracks Detectors

“…It normally operates as follows: a relatively fast discharge of high voltage (31 kV) and current (250 kA) is realized on a pair of coaxial electrodes under an atmosphere of 92 D 2 at low pressure (1−3 mbar). As a result of self-compression of the deuterium plasma, a zone of high density and temperature (focus) is formed where very energetic deuteron and electron beams, hard and soft X-ray pulses [7], and nuclear fusion reactions are generated. Therefore, a neutron flux of 2.45 MeV is produced in pulsed form, with variable duration (shot to shot) between about 80 and 150 ns (FWHM) and a total average irradiance of about 2 × 10 8 neutrons per pulse distributed in 4π sr. Figure 2, shows typical waveforms, simultaneously recorded, of the temporal evolution of hard X-rays and fusion neutrons (lower trace), anodecathode voltage at the top of the coaxial gun (middle trace), and discharge current derivative (upper trace).…”

Radiolysis of Serine in High Radiation Field

“…It normally operates as follows: a relatively fast discharge of high voltage (31 kV) and current (250 kA) is realized on a pair of coaxial electrodes under an atmosphere of D 2 at low pressure (1−3 mbar). As a result of self-compression of the deuterium plasma, a zone of high density and temperature (focus) is formed where very energetic deuteron and electron beams, hard and soft X-ray pulses [7], and nuclear fusion reactions are generated. Therefore, a neutron flux of 2.45 MeV is produced in pulsed form, with variable duration (shot to shot) between about 80 and 150 ns (FWHM) and a total average irradiance of about 2 × 10 8 neutrons per pulse distributed in 4π sr. Figure 2, shows typical waveforms, simultaneously recorded, of the temporal evolution of hard X-rays and fusion neutrons (lower trace), anodecathode voltage at the top of the coaxial gun (middle trace), and discharge current derivative (upper trace).…”

Small plasma focus as neutron pulsed source for nuclides identification

“…It normally operates as follows: a relatively fast discharge of high voltage (31 kV) and current (250 kA) is realized on a pair of coaxial electrodes under an atmosphere of D 2 at low pressure (1.2-1.8 mbar). As a result of selfcompression of the deuterium plasma, a zone of high density and temperature (focus) is formed where very energetic deuteron and electron beams, hard and soft x-ray pulses, 9 and nuclear fusion reactions are generated. Therefore, a neutron flux of 2.45 MeV is produced in pulsed form, with variable duration (shot to shot) between about 80 and 150 ns (FWHM) and a total average irradiance of about 2 × 10 8 neutrons per pulse distributed in 4π sr. Fig.…”

“…Neutron sources for irradiation normally are constituted by radioisotopes of relatively high activity (A) and medium and long decay lifetime (τ ), such as the actinide 252 Cf (A = 170 × 10 6 (n/min)/μg and τ = 2.64 yr), or mixtures of α particles' emitter such as 241 Am or 226 Ra with 9 Be powder. a) Author to whom correspondence should be addressed.…”