H Bruzzone

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

At present the Plasma Physics and Plasma Technology Group of the Comision Chilena de Energia Nuclear (CCHEN) has the experimental facilities in order to study fast dense transient discharges in a wide range of energy and current, namely: I) energy from hundred of kilojoules to tens of joules, II) current from megaamperes to tens of kiloamperes. Also several diagnostics have been implemented. An overview of the work being carried out on dense pinch plasma focus discharges at the Comision Chilena de Energia Nuclear is presented. The plasma energy density and scaling laws for the neutron yield are discussed. Possible applications of the radiation emitted are also discussed.

Experimental study of the hard x-ray emissions in a plasma focus of hundreds of Joules

An experimental study on hard x-ray production in a small plasma focus device operating in a few hundreds of Joule range is presented. A threshold in the voltage drop on the pinch was observed for x-ray emission. A comparison with Dreicer theory for electrons runaway in plasmas yields significant agreement. The study was performed at a constant pressure (1.8 mbar) of deuterium with three different anode lengths.

The initial phase in plasma focus devices

A discussion of the initial phase in plasma focus devices is given, in the light of the available experimental and theoretical knowledge on this subject. The influence of this phase on the focus phase is also discussed.

Characterization of the axial plasma shock in a table top plasma focus after the pinch and its possible application to testing materials for fusion reactors

The characterization of plasma bursts produced after the pinch phase in a plasma focus of hundreds of joules, using pulsed optical refractive techniques, is presented. A pulsed Nd-YAG laser at 532 nm and 8 ns FWHM pulse duration was used to obtain Schlieren images at different times of the plasma dynamics. The energy, interaction time with a target, and power flux of the plasma burst were assessed, providing useful information for the application of plasma focus devices for studying the effects of fusion-relevant pulses on material targets. In particular, it was found that damage factors on targets of the order of 104 (W/cm2)s1/2 can be obtained with a small plasma focus operating at hundred joules.

A simple plasma diagnostic based on processing the electrical signals from coaxial discharges

A technique for the determination of the inductance evolution in coaxial discharges based on measurements of the voltage between the electrodes and of the discharge current time derivative is presented and discussed. The technique is applied to measurements performed in a 5.7 kJ plasma focus device operating with deuterium filling in the 1–6 mbar range (which is the neutron yield range) and the obtained results are in good agreement with the expected evolution of a current sheet within the electrodes system.

Neutron Correlations with Electrical Measurements in a Plasma Focus Device

The measurement of the voltage between electrodes and the discharge current time derivative in Plasma Focus devices can be used to obtain important information on the neutron-producing pinch stage of the mentioned devices. The analysis of a 60-shots experimental run in a 5.7 kJ Mather-type device results in correlations suggesting that the neutron yield depends mostly on the average energy per particle delivered to the plasma during the pinch stage.

The lift-off stage of plasma focus discharges

A simple model describing the lift-off of the current sheet in the initial stage of plasma focus (PF) discharges is presented. The model results are supported by measurements performed on a low energy PF device and also with other experimental results found in the literature. The ideas used in the model have a sufficient general validity so that they can be applied to essentially all existing PF devices.

Effect of the external outer electrode in plasma-focus discharges

The pinching efficiency of a plasma focus operating with an open cathode was studied by reconstructing the temporal evolution of the inductance of the plasma-electrodes system. It was found that the performance as a neuron generator is substantially reduced compared with the same device configured with a surrounding cage-like cathode. In particular, no pinching occurred in 30 shots performed at 1, 2 and 3?mbar without outer electrode.

Radiative collapses in Z-pinches with axial mass losses

The possibility of producing radiative collapses in pinches is studied using a 1/2D numerical model with pure bremsstrahlung as the source of radiation, including anomalous resistivities and axial mass losses. The results of the model show the existence of both a lower and an upper limit value of the pinch current to produce collapses. It is also shown that a minimum initial pinch radius (which depends on the initial particle density) is required in order to obtain radiative collapses. The inclusion of axial mass losses makes the production of the collapse more difficult, because it enhances the anomalous resistivity heating.

Numerical Simulation of the Inductance Variation of a Plasma Focus Based in a Two-Dimensional Model

A numerical model for the calculation of the variable inductance during the current-sheet (CS) evolution in plasma-focus (PF) devices is presented. The model represents the CS by an articulated surface of many coaxial conical elements accelerated by the Lorentz force while collecting the mass swept in their paths. The numerical results are validated against the measurements of the time-varying inductance in a 6-kJ PF device, showing good agreement.