A method to determine the presence of hard X-ray emission processes from a dense plasma focus (205 J, 22 kV, 6.5 mbar H 2) using Ultra High Frequency (UHF) measurements and deep learning techniques is presented. Simultaneously, the electromagnetic UHF radiation emitted from the plasma focus was measured with a Vivaldi UHF antenna, while the hard X-ray emission was measured with a scintillator-photomultiplier system. A classification algorithm based on deep learning methods, using two-dimensional convolutional layers, was implemented to predict the hard X-ray signal standard deviation value using only the antenna signal measurement. Two independent datasets, consisting of 999 and 1761 data pairs each, were used in the analysis. Different realizations of the training/validation process using a deep learning model, obtained overall better results in comparison to other machine learning methods like kneighbors, decision trees, gradient boost, and random forest. The results of the deep learning algorithm, and even its comparison with other machine learning methods, indicate that a relationship between the electromagnetic UHF radiation and hard X-ray emission can be established, enabling the indirect detection of hard X-ray pulses only using the UHF antenna signal. This indirect detection presents the opportunity to have a simple and low-cost diagnostic, compared to the methods currently used to characterize the pulses of X-rays emitted from plasma focus discharges. INDEX TERMS Deep learning, Plasma focus, UHF antenna, X-ray pulse.

Plasma focus devices may arise as useful source to perform experiments aimed to study the effects of pulsed radiation on human cells in vitro. In the present work, a table top hundred joules plasma focus device, namely “PF-400J”, was adapted to irradiate colorectal cancer cell line, DLD-1. For pulsed x-rays, the doses (energy absorbed per unit mass, measured in Gy) were measured using thermoluminescence detectors (TLD-100 dosimeters). The neutron fluence and the average energy were used to estimate the pulsed neutron doses. Fifty pulses of x-rays (0.12 Gy) and fifty pulses of neutrons (3.5 μGy) were used to irradiate the cancer cells. Irradiation-induced DNA damage and cell death were assessed at different time points after irradiation. Cell death was observed using pulsed neutron irradiation, at ultralow doses. Our results indicate that the PF-400J can be used for in vitro assessment of the effect of pulsed radiation in cancer cell research.

We present experimental results on the characterization of a non-ablating fast pulsed capillary discharge, with a hollow cathode (HC) geometry, operating in argon below 1 Torr. Both the pre-breakdown and breakdown phase of the discharge are investigated with several diagnostics, which include electron beam monitoring, capacitive probe array and extreme ultraviolet (EUV) detector array. The pre-breakdown phase is found to be characterized by the emission of HC electron beams, which assist the propagation of a high speed ionization wave, with typical velocity in the 10 6 -10 7 m s −1 . Coinciding with electric breakdown a fast EUV radiation pulse is emitted. The leading edge of the radiation pulse is due to beam target emission by the HC electron beams. At the breakdown the radiation emission is mainly centered in the 5-15 nm spectral window, and is emitted from a capillary plasma which is being heated by a kiloampere level, 10 ns half-width current pulse.

Experimental observations of the hollow cathode effect (HCE) in an open end pulsed capillary discharge (PCD) are presented. In the HCE axial electron beams emitted from a pre-breakdown plasma produced spontaneously in the hollow cathode region (HCR) assist ionization growth in the interelectrode volume. The PCD operates in argon at 0.6-1.4 Torr, ∼10 kV applied voltage. Time resolved spectroscopic measurements, with 15 ns time resolution, are used in conjunction with photomultiplier observations of light emission from the capillary ends, and Faraday cup measurements of axial electron beams, to characterize the pre-and post-breakdown processes in the HCR of the discharge. The HCR emission is found to be dominated by Ar II lines. Comparison between measured and synthetic spectra indicates that the pre-breakdown HCR plasma is characteristic of a collisional low pressure, low density plasma, whereas the post-breakdown HCR plasma, tens of nanoseconds after breakdown, is due to plasma ejection from the capillary volume. Experimental evidence of a zippering effect in post-breakdown capillary plasma heating, due to an initial axial pressure gradient, as predicted by computer simulations, has been found.

Non-linear high-power devices produce electromagnetic noise (EMN) sources of great intensity that can disrupt and damage the surrounding electrical equipment and devices. This radiative phenomenon is very common at facilities where pulsed power generators are required, particularly those that are needed to produce dense transient plasma experiments. These conditions are found at the Chilean Nuclear Energy Commission (CCHEN), due to the presence of pulsed power generators that switch large currents (kA-MA) in short times (10-100 ns). In order to characterize and establish conditions to mitigate the effects of the EMN on nearby devices, a measurement system based on an ultra-high frequency (UHF) dipole antenna was developed. We evaluated the system measuring the EMN emanated from a plasma focus device, the PF-400J. Measurements at the place indicated broadband and intense electric fields that can couple to nearby cables and equipment (10-300 MHz bandwidth, up to 350 V/MHz spectral intensity, 100 V coupled voltage). Based on these measurements a compact and simple protection system was designed, built and tested, capable of effectively mitigating the high levels of EMN. The proper EMN impact mitigation indicates the correct operation of the suggested system. The developed system can be of interest to the energy community by facilitating EMN measurement produced by arc discharges.

A remote and non-invasive diagnostic of the plasma focus using antennas is presented in this work. The main motivation is the application of such diagnostic in a miniaturized plasma accelerator, based on the plasma focus architecture, as a cube satellite thruster. The evaluation of this proposal was carried out measuring a hundred of joules plasma focus operation simultaneously with the inductive measurement and antennas. Three different antennas tuned in the ultra high frequency range were tested: a monopole, Vivaldi and helical. The high frequency transients detected with the antennas were time correlated to the known inductive measurement features. The initial dielectric breakdown and later plasma pinch and subsequent disruption (i.e. the source of the propulsion) were identified to be the principal phenomena to be detected. Signal parameter correlations between the inductive sensor and the antennas showed that the pinch phenomena can be correlated with the antenna signals. Good correlation results were obtained with the monopole antenna when using peak value and signal energy parameter from the antenna transient. An improvement in the correlation results, for the helical and Vivaldi antennas, was obtained when calculating the frequency band energy. In this case, the Vivaldi antenna achieved the best results. The results of the monopole antenna make it an alternative remote sensor for plasma focus, but for the application of a miniaturized plasma focus as pulsed plasma thruster, the Vivaldi antenna is a more feasible design to replace the inductive diagnostic due to its compact design in comparison to the monopole. INDEX TERMS Inductive sensor, pulsed plasma thruster, plasma focus, ultra high frequency antennas.

The correct modelling of velocity distribution functions for particles in steady-state plasmas is a central element in the study of nuclear fusion and also in the description of space plasmas. In this work, a statistical mechanical formalism for the description of collisionless plasmas in a steady state is presented, based solely on the application of the rules of probability and not relying on the concept of entropy. Beck and Cohen's superstatistical framework is recovered as a limiting case, and a "microscopic" definition of inverse temperature β is given. Non-extensivity is not invoked a priori but enters the picture only through the analysis of correlations between parts of the system.

The temporal correlation between neutron and hard X-ray (HXR) emissions from a hundred joules plasma focus device (PF-400J) was studied. A method, time history analysis, to estimate the time of origin of neutrons with respect to HXRs is applied. In most of the discharges, it was found that neutrons are originated before HXRs in the axial direction and after HXRs in the radial direction. In some discharges, the time difference between HXRs and neutrons origin was found large enough, so that it can be interpreted that those neutrons would have been originated before the pinch. A qualitative discussion is conjectured to explain the experimental observations.