C. Moreno

Hard x-ray source for flash radiography based on a 2.5kJ plasma focus

A compact tabletop plasma focus suitable for hard x-ray imaging applications is presented. The hard x-ray emission was characterized by means of an effective energy analysis, based on images obtained with a single shot. The effective energy of the radiation was estimated to be around 83keV from radiographic images of metallic pieces. Numerical calculations, based on validated codes, are presented to give a quantitative interpretation of the experimental results. Experimental demonstration of the suitability of this device for introspective imaging of metallic pieces is also given.

Plasma focus based repetitive source of fusion neutrons and hard x-rays

A plasma focus device capable of operating at 0.2 pulses per second during several minutes is used as a source of hard x-rays and fast neutrons. An experimental demonstration of the use of the neutrons emissions for radiation probing of hydrogenated substances is presented, showing a particular application in detecting water concentrations differences in the proximity of the device by elastic scattering. Moreover, the device produces ultrashort hard x-rays pulses useful for introspective images of small objects, static or in fast motion, suitable for the identification of internal submillimetric defects. Clear images of metallic objects shielded by several millimeters iron walls are shown.PACS Codes: 29.25.Dz,52.59.Px

Compact Repetitive Plasma Focus as a Powerful Source for Hard-X-Ray and Neutron Scanning

In this communication a tabletop version of medium energy Plasma Focus is presented. It was designed for x- ray and neutron based applications, has a 5.6 muF bank formed by 8 capacitors, operates at 30 kV, delivers 250 kA in a quarter-period of 1.3 mus, and produces 3 107 neutrons per pulse at a repetition rate of 1 Hz. The hard x- ray output of this device is used for introspective imaging of metallic pieces, whereas the neutron yield is used for substance interrogation. A simplified model for the design engineering of this device is discussed, providing both the expected neutron yield and the x-ray characteristic energy. The hard x-ray output characteristics are evaluated from the acceleration voltage induced in the pinch, which is around 100 kV. Experiments conducted to validate the model are presented, showing a good agreement between the theoretical results and the experimental data.

0.2 Hz Plasma-Focus-based source of fast neutrons and hard x rays for applications

A small chamber Plasma Focus that operates at 0.2 Hz for several minutes is used as a source of hard x rays and fast neutrons. The device is powered by a microprocessor controlled capacitor charging power supply. The x rays are used for introspective imaging of metallic pieces, static and in motion, that allows for the detection of internal defects as small as 1 mm. The x ray radiation is able to produce clear images of objects placed behind several millimeters of iron and steel. The fast neutrons allow for the detection of hydrogenated substances and can discriminate between different concentrations of water located near the device.

A 1-D MHD Model for the Axial Induced Electric Field During the Self Compression of a Cylindrical Plasma Column

Summary form only given. The radial compression of cylindrical plasmas induces acceleration voltages considerably higher than those used to charge the capacitor bank employed in the discharge. These phenomena typically occur in Z-pinches and plasma focus devices, where 100 keV X-rays are commonly observed in machines operated with charging voltages of 50 kV or less. Several accelerating mechanisms were discussed in the literature to explain this peculiarity and its effect on the discharge behavior. In this communication, a 1D MHD model for the time evolution of the plasma column dynamics is proposed to evaluate the accelerating potential along the symmetry axis, taking into account the plasma resistivity as well as the inverse skin effect. The total current circulating through the plasma column is calculated in a self consistent manner with the external circuit evolution. The numerical results of the model, which predicts electric fields of 100 kV/cm; convergent radial velocities of about 20 cm/mus for deuterium plasma columns of 2 mm in diameter; are satisfactorily compared with experimental results about the characteristic energy of the hard-X-rays generated by electron impact on the anode base

Experimental Determination of the Current Sheath Structure in a Plasma Focus

Summary form only given. The current density profile associated to the current sheath produced in a 5.6 muF Mather type plasma focus operated at 20 kV was studied by means of a magnetic probe placed in the interelectrodic space at different axial positions along the gun. From the probe signal, both, the arrival time and the temporal width of the current sheath, were measured during the run down phase. The discharge initiation time, as well as the pinching time were determined using a Rogowski coil. A slightly increasing velocity for the traveling sheath along the gun, reaching Mach numbers of about 200 for nitrogen and 100 for hydrogen, were inferred from the data. Ultrafast images of the visible radiation emitted by the plasma obtained with an image converter (10 ns exposure time) show that the luminosity as well as the shape of the visible radiation emitted by the sheath depends on the filling gas type. It was also observed that the temporal width of the current distribution diminishes as it travels along the gun. The measurements indicate that the current distribution is spatially compressed during its evolution. A theoretical model considering the perturbing effect that the probes encasing body causes on the measurement itself, as well as the time-dependent nature of the problem due to the temporal variation of total discharge current, is presented. Using this model, the magnetic signals are used to infer the current density profile in the current sheath