Search

Kappa-distributed velocities in plasmas are common in a wide variety of settings, from low-density to high-density plasmas, and appear in both space and laboratory plasmas. Despite being widely used as a model, the origin of the kappa distribution remains, to this day, unclear. For instance, deviations from the Maxwell-Boltzmann distribution are sometimes regarded as a signature of the non-additivity of the thermodynamic entropy, although there are alternative frameworks such as superstatistics where such an assumption is not needed. In this work we recover the kappa distribution for particle velocities in a non-equilibrium, steady-state plasma from the theory of superstatistics, assuming only a single requirement on the dependence between the kinetic energy of a test particle and that of its immediate environment. Most importantly, unlike previous derivations based on superstatistics, we do not make any assumption about temperature or its statistical distribution, instead obtaining them from the requirement on kinetic energies. Our results suggest that a description of kappa-distributed plasma is simpler in terms of features of the inverse temperature distribution rather than the traditional parameters $\kappa$ and the thermal velocity $v_{\text{th}}$.

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France); As a way to investigate the minimum energy to produce a pinch plasma focus discharge, an ultra miniature device has been designed and constructed (nanofocus NF: 5nF, 5-10kV, 5-10kA, 60-250 mJ, 16 ns ns time to peak current). Sub-millimetric anode radius covered by a coaxial insulator were used for experiments in hydrogen. Evidence of pinch was observed in electrical signals in discharges operating at 60 mJ. A single-frame image converter camera (4ns exposure) was used to obtain plasma images in the visible range. The dynamics observed from the photographs is consistent with: a) formation of a plasma sheath close to the insulator surface, b) fast axial motion of the plasma sheath, c) radial compression over the anode, and d) finally the plasma is detached from the anode in the axial direction. The total time since stage a) to d) was observed in ~30 ns. X ray and neutron emission is being studied. Neutron yield of the order of 103 neutron per shot is expected for discharges operating in deuterium at 10kA.

This paper introduces in full detail a methodology for the measurement of neutron yield and the necessary efficiency calibration, to be applied to the intensity measurement of neutron bursts where individual neutrons are not resolved in time, for any given moderated neutron proportional counter array. The method allows efficiency calibration employing the detection neutrons arising from an isotopic neutron source. Full statistical study of the procedure is descripted, taking into account contributions arising from counting statistics, piling-up statistics of real detector pulse-height spectra and background fluctuations. The useful information is extracted from the net waveform area of the signal arising from the electric charge accumulated inside the detector tube. Improvement of detection limit is gained, therefore this detection system can be used in detection of low emission neutron pulsed sources with pulses of duration from nanoseconds to up. The application of the methodology to detection systems to be applied for D-D fusion neutrons from plasma focus devices is described. The present work is also of interest to the nuclear community working on fusion by magnetic confinement and lasers, and working on neutron production by accelerators or similar devices., Submitted to Rev. Sci. Instruments

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France); As first stage of a program to design a repetitive pulsed radiation generator for industrial applications two miniature plasma foci have been designed and constructed at the Comisión Chilena de Energía Nuclear. The devices operate at an energy level of the order of tens of joules (PF-50J, 160 nF capacitor bank, 20-35 kV, 32-100 J, ~150 ns time to peak current) and hundred of joules (PF-400J, 880 nF, 20-35 kV, 176-539 J, ~300 ns time to peak current). Hard X-rays are being studied in these devices operating in hydrogen. Images of metallic plates with different thickness were obtained on commercial radiographic film, Agfa Curix ST-G2, in order to characterize the energy of the hard X-ray outside of the discharge chamber of PF-400J. An effective energy of the order of 90keV was measured under those conditions. X ray images of different metallic objects also have been obtained.

SPEED2 is a generator based on Marx technology and was designed in the University of Dusseldorf. SPEED2 consists on 40 +/- Marx modules connected in parallel (4.1 mF equivalent Marx generator capacity, 300 kV, 4 MA in short circuit, 187 kJ, 400 ns rise time, dI/dt~1013 A/s). Currently the SPEED2 is operating at the Comision Chilena de Energia Nuclear, CCHEN, Chile, being the most powerful and energetic device for dense transient plasma in the Southern Hemisphere. Most of the previous works developed in SPEED2 at Dusseldorf were done in a plasma focus configuration for soft X-ray emission and the neutron emission from SPEED2 was not completely studied. The research program at CCHEN considers experiments in different pinch configurations (plasma focus, gas puffed plasma focus, gas embedded Z-pinch, wire arrays) at current of hundred of kiloamperes to mega-amperes, using the SPEED2 generator. The Chilean operation has begun implementing and developing diagnostics in a conventional plasma focus configuration operating in deuterium in order to characterize the neutron emission and the hard X-ray production. Silver activation counters, plastics CR39 and scintillator-photomultiplier detectors are used to characterize the neutron emission. Images of metallic plates with different thickness are obtained on commercial radiographic film, Agfa Curix ST-G2, in order to characterize an effective energy of the hard X-ray outside of the discharge ., Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France); As first step of a program to design a repetitive pulsed neutron generator for applications two miniature plasma foci have been designed and constructed at the Comisión Chilena de Energía Nuclear. The devices operate at an energy level of the order of tens of joules (PF-50J, 160 nF capacitor bank, 20-35 kV, 32-100 J, ~150 ns time to peak current) and hundred of joules (PF-400J, 880 nF, 20-35 kV, 176-539 J, ~300 ns time to peak current). Neutron emission has been obtained in both devices operating in deuterium. An especial techniques was necessary to develop in order to detect neutron pulsed of 104 neutrons per shot. The maximum total neutron yield measured was of the order of 106 and 104 neutrons per shot in the PF-400J and PF-50J respectively. Axial and radial measurements of the neutron emission are presented and the anisotropy is evaluated in this work. The neutrons are measured by pairs of silver activation counters, 3He detectors and scintillator-photomultiplier detectors.