Roberto Luis Moroso

Small plasma focus studied as a source of hard X-ray

An experimental study on hard X-ray pulses emitted by a small plasma focus is performed, regarding its application to biological radiographs in fast dynamic situations. It is found that the radiation intensity in a single shot is high enough to obtain fine resolution radiographs in very short exposures (about 10 ns). As an example, a radiograph on a live mouse is shown. It is found that the relation between responses of different detectors, i.e., thermoluminescence dosimeters and scintillator-photomultiplier, is linear.

Filaments in the Sheath Evolution of the Dense Plasma Focus as Applied to Intense Auroral Observations

This paper investigates the dense plasma focus (DPF) for applications in space-plasma physics. The plasma focus (a variant of Z-pinch) generates plasmas from fast high-voltage electrical discharges on coaxial electrodes suitable for very different studies: from fusion up to plasma-space modeling. In particular, the plasma sheath of the DPF is studied here and measured in some detail as a possible model for auroral observations. Deuterium gas was used in the experiments, and many helpful techniques were used, such as ultrafast photograph and neutron detection from nuclear-fusion reactions. In this paper, we show the different phases of the plasma focus correlated with discharge-current characteristics and neutron and X-ray production. Filamentary formations in the current sheath are shown, and its correlation with neutron production is done. The same number of filaments (about 60) reported in auroral observations are detected in plasma-focus discharges.

Portable Neutron Probe for Soil Humidity Measurements

A very small dense plasma focus (142 J) was designed and constructed with the aim to be used as portable pulsed fast neutron source (2.45 MeV in a pulse of 90 ns). The characteristics of this device make it suitable for underground use. The soil humidity can be determined through the detection of thermalized neutrons. In this work we show results of the several prototypes developed in laboratory research to find the best geometric and dynamic parameters for optimize the neutron yield. The diagnostic measurements performed in each discharge include bank current derivative and both time‐integrated and time‐resolved detection of neutrons emitted by the apparatus. The best neutron yield reached is of the order of 107 in 4 π sr. flux per pulse. This result introduces a new point in an unexplored range of the neutron yield vs. focus current scaling law.

Spatial structure and energy spectrum of ion beams studied with CN detectors within a small PF device

Abstract The paper reports the application of Solid-State Nuclear Track Detectors to study the pulsed plasma-ion streams emitted from plasma-focus (PF) type discharges, which were performed within a low-energy PACO device constructed at Instituto de Fisica Arroyo Seco. The PACO device was operated under static initial gas conditions or with dynamic gas puffing. Studies of the structure of the fast deuteron beams were carried out within an energy range from 80 keV to about 2 MeV . Studies of ion energy and an ion angular distribution were also performed. The measurements showed that the fast deuterons are emitted in many “narrow” micro-beams, as in other larger PF devices. The anisotropy of the deuteron angular distribution was explained by the stochastic character of the formation of local ion sources within the PF discharge column.

Dynamics of the ionizing and magnetic fronts in the radial compression stage of a DPF current sheath

Further results regarding the sudden drop of dense plasma focus (DPF) neutron yield at low pressure are presented. Experimental measurements of temporal evolution of magnetic piston MP (interface plasma-magnetic field) and current sheath ionizing front IF (interface plasma-neutral gas) are performed in the radial compression stage of DPF discharges. At the optimum deuterium pressure for neutron yield (1.5 mb), MP and IF have similar r(t) functions, so that the thickness of the sheath remains practically constant ( approximately 0.2 cm) in the whole stage. At the lower pressure limit for neutron yield (1 mb) the sheath begins the radial compression stage with a smaller thickness ( approximately 0.1 cm) and in the last 35 ns the IF moves forward (relatively to the MP) with a velocity of 7.5E+7 cm/s and the thickness in the layer reaches a value of approximately 0.5 cm. This sudden acceleration of the IF is interpreted as the main cause of the lower pressure limit in the neutron yield. >

The first stages of the discharge in a low-energy dense plasma focus

The very beginning of the discharge has been studied in the PACO dense plasma focus (DPF) device. Electrical and optical diagnostics (ultra-fast photographs of emitting light) have been employed to describe the plasma in the breakdown and also when the plasma sheath (or current sheath) did part of its coaxial travel. The plasma shape in its earliest stage and in more advanced stages are related between them for characteristic working pressure regimes. Using other diagnostics such as neutron emission detection, the breakdown features and the apparatus performance were correlated.

Fast valve and nozzle for gas-puff operation of dense plasma focus

A simple and reliable valve and nozzle system for a very fast injection of gas has been designed and constructed for its use in gas-puff mode of dense plasma focus experiments. It delivers a very quick rise time: 55μs. The pressure measured in our setup at a distance of 15 mm from the nozzle output is about 0.285 mbar, with a plenum pressure of 3 bars (absolute). The time between the valve aperture and pressure front arrival is 360μs. This result comes up as an average of about a hundred measurements. The energy input is 95 J (270 V on a 3000μF capacitor bank). The typical dimensions of the valve are 52 mm in diameter and 80 mm in length. The entire volume of the valve is, then, very small. The relative low pressure and voltage operation are significant advantages of this development. The performance of the valve satisfactorily fulfills the objectives of gas-puff plasma focus operation.

The Plasma Focus Current Sheath in a Squirrel Cage Gun

A study on the current sheath (CS) evolution of the small dense plasma focus PACO is performed through images of the visible light emitted. They show that the outer electrode, made in bars, is reached by the CS after the final pinch stage.

Images of a Plasma Focus Current Sheath With a Continuous Cylindrical Outer Electrode

Images of the roll-off, radial compression, final pinch, and after pinch stages of the current sheath (CS) of the dense plasma focus PACO (plasma autoconfinado) whose outer electrode is a brass cylindrical shell are shown. The different stages of the current sheath were measured with an image converter camera, 5-ns exposure time. The images of the CS evolution look similar to those previously obtained with an array of bars as cathode, as well as neutron yields and working pressures.

Images of the dense plasma focus phenomenon in the 2-kJ PACO device

Ultra-speed images of visible light emitted by dense plasma focus discharges of the plasma auto-confined (PACO) device are presented. Representative moments, from the very initial stage to the final one, for different operating conditions, are shown here. Qualitative differences between plasma sheaths in different pressure regimes can be observed, even if the stage is the same. Apart from the interesting scientific observations, the beauty of this phenomenon shown in the photographs must be remarked.