Isotropic and anisotropic components of neutron emissions at the FN-II and PACO dense plasma focus devices

Abstract

The average angular distribution of neutron emissions has been measured in the Fuego Nuevo II (FN-II) dense plasma focus device (5 kJ) by means of CR-39 plastic nuclear track detectors. When pure deuterium is used as the filling gas, the data can be adjusted to a Gaussian function, related to anisotropic emission, superposed on a constant pedestal, related to isotropic emission. When deuterium-argon admixtures are used, the anisotropic contribution is best represented by a parabola. The same analysis is applied to previously reported results, for fewer shots, in pure deuterium from the PACO device, which is similar in size to the FN-II. In both devices the anisotropic component is smaller than the isotropic one, but with different features. In PACO the anisotropic component is concentrated on a large narrow beam around the axis, but its contribution to the total neutron yield is significantly smaller than in the FN-II, where the anisotropic component spreads over a wider range. The neutron flux per shot is monitored in both devices with calibrated silver activation detectors, at 20˚and at 90˚from the axis. The average values of the neutron flux at these two angles are used, along with the angular distributions obtained form the track detectors, in order to estimate the absolute neutron yield of both the isotropic and the anisotropic contributions. From examining different groups of shots, it is found that the shape of the angular distribution is important in the estimation of anisotropy, and that the value usually reported, as the ratio of neutron counts head-on and side-on, as measured by activation counters, may be misleading.

Research on pinch plasma focus devices of hundred of kilojoules to tens of joules

“…Also a characterization of the isotropic and anisotropic components of the neutron yield will be developed [25].…”

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

“…In particular, the neutron pulse duration (~100 ns) and the observed neutron anisotropy provide compelling evidence that supra-thermal mechanisms play an important role. However, in earlier work we found that there are both isotropic and anisotropic contributions in the neutron angular distribution, the former being the most important [4,5]. Although it has been established that there is more than one fusion mechanism, a detailed understanding of them is still lacking.…”

“…Earlier work on the diagnostics of fusion neutrons, using CR-39 nuclear track detectors, was done by Collopy et al [8], Frenje et al [11], and Castillo etal. [4]. Charged particles incident on a polymer track detector, such as CR-39, deposit their kinetic energy as dense trails of ionization and excitation resulting in numerous polymer chain scissions.…”

Neutron spectra from beam-target reactions in dense Z-pinches

“…We also note that it is common in the experimental literature to use anisotropy of the neutron yield as a signature of BT neutron production. [17][18][19] Less frequently, isotropy of the neutron yield has been used to infer a TN source. 20 However, in this work, we show that it is possible to get an isotropic neutron yield and spectra from a BT source due to magnetization of the accelerated ions.…”