Plasma Focus

The effect of gas pressure on the neutron yield and ion properties is investigated in this article by using the developed model. The gas pressure range is from 1 to 40 Torr with 1-Torr increment in the spherical plasma focus device using an equal amount deuterium-tritium gas mixture. The beam-target neutron yield, beam-ion speed, beam-ion energy, plasma column ion density, beam-ion density, and plasma temperature are calculated with respect to gas pressure variation. Increasing the gas pressure leads to an increase in the neutron yield until 26-Torr gas pressure. But, beyond 26 Torr, increasing gas pressure results in decreasing neutron yield. This result indicates that the optimum gas pressure for neutron yield in the spherical plasma focus device is 26 Torr with 1.42 × 10 13 neutrons for used operating parameters, which are 25-kV charging voltage, 36-nH external inductance, and 432-µF capacitor bank. This device has an 8cm inner electrode radius and a 14.5-cm outer electrode radius. While beam-ion and plasma-ion densities increase with the gas pressure, the beam-ion speed and energy decrease. It is also found that the plasma loses less energy for higher gas pressures through radiation emissions compared to lower gas pressures. Since there is not enough published experimental data about spherical plasma focus devices, this article is conducted with the simulation of the spherical plasma focus device.

A spherical plasma focus device with two concentric electrodes is simulated using deuterium and tritium mixture (50:50) as a working gas. The developed model is used to study the effect of gas pressure and charging voltage on dynamics of current sheath in spherical plasma focus. While charging voltage is varied from 15 kV to 30 kV to see the effect of voltage, gas pressure is increased from 1 Torr to 20 Torr for gas pressure study. In this work, it is found that there is a strong correlation between current sheath dynamics and investigated parameters which are gas pressure and charging voltage.

The developed spherical plasma focus model is used in this study to investigate the optimum neutron yield in terms of the gas pressure, cathode radius and external inductance. The optimum values for these parameters are found separately. Then, the charging voltage is varied from 25 kV to 35 kV with 1 kV increment by using these separately found optimum values to see the rate of increase in neutron yield. While the used gas pressure range is 1-40 Torr with 1 Torr increment, cathode radius range is 11.5-17 cm with 0.5 cm increment. External inductance is varied from 10 nH to 150 nH with 5 nH increment. The optimum values for gas pressure, cathode radius and external inductance are found to be 26 Torr, 15 cm and 75 nH, respectively. Even though combining these separately found optimum values of pressure, cathode radius and external inductance does not necessarily form an optimized set of operational conditions for the SPF, they lead to a higher neutron yield in that while neutron yield with these separately found optimum values at 25 kV charging voltage is 2.82 × 10 13 (higher than the measured neutron yield of 1.26 × 10 13 at 25 kV), it increases to 1.32 × 10 14 , when charging voltage is increased to 35 kV. Using these values shows that spherical plasma focus device can be used as a neutron source with high neutron yield (on the order of 10 14).

We have performed an experimental analysis on the investigation of high energy ion beam irradiation on Si (100) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beams are characterized using standard surface science diagnostic tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive X-ray (EDX) analysis and atomic force microscope (AFM) and the results are ...

We report the investigation of high energy ion beam irradiation on titanium (Ti) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The surface modifications induced by the ion beam using two different anode materials, graphite and copper, are characterized using standard surface science diagnostic tools, such as x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray analysis, Raman spectroscopy and Auger electron spectroscopy. It has been found that the interaction of the pulsed PF ion beams, with characteristic energy in the 15–300 keV range, with the Ti surface, results in the formation of nanocomposite carbon structures. It is observed that the resulting ion irradiated surface morphologies are different, depending on the different anode materials, under otherwise identical operational conditions. In the case of the graphite anode the interaction of PF ion beams followed by the anode vapour with the Ti surface results in the formation of gradient layers of TiC with embedded carbon nanostructures.

A spherical plasma focus device with two concentric electrodes is simulated using deuterium and tritium mixture (50:50) as a working gas. The developed model is used to study the effect of gas pressure and charging voltage on dynamics of current sheath in spherical plasma focus. While charging voltage is varied from 15 kV to 30 kV to see the effect of voltage, gas pressure is increased from 1 Torr to 20 Torr for gas pressure study. In this work, it is found that there is a strong correlation between current sheath dynamics and investigated parameters which are gas pressure and charging voltage.

We have investigated, with time and space resolution, the ion beam emission from a plasma focus (PF) device, operating in methane, at 20 kV, with 1.8 kJ stored energy. A detector array is used to measure simultaneously the ion beams at five different angular directions with respect to the PF axis (0 • , 10 • , 15 • , 20 • and 90 •), at a distance of 77 cm from the ion source. Ion beam energy correlations for operation in methane indicate that the dominant charge states on the detector are H + , C +4 and C +5 , irrespective of the angular positions. The time integrated ion beam signal and the energy-dispersive x-ray analysis of a carbon films deposited on silicon surface shows the impurity emission from the PF electrode surface. Measured ion fluxes are maximum for the energy range of 15–40 keV, 50–100 keV and 100–300 keV, for H + , C +4 , and C +5 , respectively. Measurements of the angular distribution of hydrogen and carbon ions reveal a strong angular anisotropy. It is argued that the observed angular anisotropy of the ion beam emission can be explained in terms of ion Larmor radius effects during the z-pinch like plasma formation phase, which is characteristic of PF discharges.

Se estudio la emision de Iones para 5 disparos(25/10/2005) de un Plasma Focus de baja enegia (1.8 kJ) tipo Mather operado a 20 kV en Metano. Se monitoreo el voltaje entre electrodos, deriva de corriente, emision de rayos X y emision de Iones, a traves de un divisor resistivo, un rogowski coil, un diodo BPX65 y un arreglo de detectores angularmente distribuidos, respectivamente. Cada disparo entregó información sobre el tipo de Foco, la energia aprovechada y distribucion angular del flujo de iones. A traves de un arreglo de detectores ubicados a 77 cm de la fuente de iones para 5 angulos diferentes(0°, 10°, 15°, 20° y 90°) respecto al eje del PF, se analizo la distribucion angular del Flujo de Iones en funcion de la Energia. Usando la tecnica de tiempo de vuelo (TOF) se determino que las especies dominates en la descarga son H + , C +4 y C +5. Se observo una fuerte anisotropia de la emision de iones generado por el campo electromagnetico en la implosion de la ultima fase(Plasma Denso) de la descarga de PF. A pesar de esta anisotropia los estados de carga dominantes son para las especies de H + , C +4 y C +5 .

A comprehensive analysis of scaling laws for plasma focus devices producing neutrons is presented. Similarities and differences in plasma focus devices working with stored energies ranging from 1 MJ to 0.1 J are found. First, a brief review listing the most important results achieved by the Thermonuclear Plasma Department of the Chilean Nuclear Energy Commission, CCHEN, is presented. The aim of the work at CCHEN has been to characterize the physics of dense plasma foci and also to carry out the design and construction of smaller devices—in terms of both input energy and size—capable of providing dense hot plasmas. Certain scaling rules have been found from this research. These rules combined with other scaling laws have been applied to design and construct plasma focus devices with storage energy in a region never explored before (tens of joules and less than 1 J). Thus, a comprehensive analysis also including results from other groups is presented. In particular, all the devices, from the largest to the smallest, maintain the same value of ion density, magnetic field, plasma sheath velocity, Alfvén speed and the quantity of energy per particle. Therefore, fusion reactions are even possible to obtain in ultraminiature devices (driven by generators of 0.1 J for example), as they are in the larger devices (driven by generators of 1 MJ). However, the stability of the plasma pinch highly depends on the size and energy of the device.

A spherical plasma focus device with two concentric electrodes is simulated using deuterium and tritium mixture (50:50) as a working gas. The developed model is used to study the effect of gas pressure and charging voltage on dynamics of current sheath in spherical plasma focus. While charging voltage is varied from 15 kV to 30 kV to see the effect of voltage, gas pressure is increased from 1 Torr to 20 Torr for gas pressure study. In this work, it is found that there is a strong correlation between current sheath dynamics and investigated parameters which are gas pressure and charging voltage.

The effect of the cathode radius variation (from 11.5 cm to 17 cm) on neutron yield, discharge current, plasma temperature, and ion properties (velocity, energy, and density) are investigated in this study using the developed spherical plasma focus model and the results are reported in this paper. Peak discharge current and peak beam-ion properties decrease with increasing the cathode radius. Maximum plasma temperature (22.34 eV) and maximum beam-target neutron yield (1.18×10 13) are achieved using the cathode with 15 cm radius. The longest pinch duration for all calculations is also achieved using 15 cm cathode radius. It is found that the optimum cathode radius is 15 cm in terms of the neutron yield, plasma temperature and beam-ion properties in spherical plasma focus device.

In this work, the developed spherical plasma focus model is used to investigate the effect of the cathode radius on the plasma dynamics and radiation emissions. The cathode radius is varied from 11.5 cm to 17 cm with 0.5 cm increment, and the results are reported in this paper for the spherical plasma focus with 8 cm inner electrode (anode) radius. While discharge current and voltage, plasma and shock velocities, and radiation emissions are found to be higher for short cathode radius, plasma resistance increases with increasing cathode radius. This study also shows that the optimum cathode radius for plasma dynamics and radiation emissions is 15 cm for the used spherical plasma focus device.

We report the investigation of high energy ion beam irradiation on Si (1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The unexposed and ion exposed substrates were characterized by x-ray diffraction, scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive x-ray analysis and atomic force microscopy (AFM) and the results are reported. The interaction of the pulsed PF ion beams, with characteristic energy in the 60–450 keV range, with the Si surface, results in the formation of a surface layer of hexagonal silicon carbide. The SEM and AFM analyses indicate clear step bunching on the silicon carbide surface with an average step height of 50 nm and a terrace width of 800 nm.

Dynamical discharge characteristics and their relation with the total neutron yield emitted from a 400 J plasma focus operating in deuterium gas are presented. The dynamical nature of the plasma focus is obtained merely from the analysis of the voltage and current electrical signals without considering any particular geometry for the plasma sheath. It is calculated that large neutron yields are obtained when plasma inductance, mechanical energy and plasma voltage at pinching time have larger values. In contrast, no correlations are found among neutron yields either with plasma propagation velocities or quantities at the beginning of the radial phase. There is also found that the current sheath geometry changes according to the gas pressure, having larger curvature for lower pressures. The calculations also provide estimations of sheath thicknesses at the detachment from the insulator in the range of 0.5–1 mm, being thicker for larger neutron yield.

A comprehensive analysis of scaling laws for plasma focus devices producing neutrons is presented. Similarities and differences in plasma focus devices working with stored energies ranging from 1 MJ to 0.1 J are found. First, a brief review listing the most important results achieved by the Thermonuclear Plasma Department of the Chilean Nuclear Energy Commission, CCHEN, is presented. The aim of the work at CCHEN has been to characterize the physics of dense plasma foci and also to carry out the design and construction of smaller devices—in terms of both input energy and size—capable of providing dense hot plasmas. Certain scaling rules have been found from this research. These rules combined with other scaling laws have been applied to design and construct plasma focus devices with storage energy in a region never explored before (tens of joules and less than 1 J). Thus, a comprehensive analysis also including results from other groups is presented. In particular, all the devices, from the largest to the smallest, maintain the same value of ion density, magnetic field, plasma sheath velocity, Alfvén speed and the quantity of energy per particle. Therefore, fusion reactions are even possible to obtain in ultraminiature devices (driven by generators of 0.1 J for example), as they are in the larger devices (driven by generators of 1 MJ). However, the stability of the plasma pinch highly depends on the size and energy of the device.

A planar-piston model of the hard x-ray production in Plasma-Focus devices is presented. The model applies Von Karman approximations to represent the inner structure of
the pinch. The hard x-ray emission is calculated assuming Bremsstrahlung from the collision on the anode base of an electron current running away from the pinch.. The model was applied to analyse the experimental data of a small Plasma Focus without surrounding cathode, founding good agreement.

A maximum entropy production principle (MEPP) has been postulated to be a criterion of stability for steady states of open systems [Martyushev et al., Phys. Rep. 426, 1 (2006)]. We find a necessary condition for stability of steady solutions of the complex Ginzburg-Landau equation. This condition violates MEPP.

In this work, the applied voltage effect on neutron yield and ion production are studied by varying the charging voltage between 15 kV and 30 kV with 1 kV increment to investigate neutron yield, radiation emissions and ion properties using the developed MHD model. While Joule heating, radiative recombination, bremsstrahlung and line radiation are calculated as radiation terms, beam-ion speed, energy and density are calculated as ion properties. The dominant neutron production mechanism is beam-target which results from the accelerated energetic ions under the diode voltage which is calculated along with neutron yield. In this study, while maximum neutron yield is 2.63 10 13 for 30 kV charging voltage, beamion energy and speed reach 61 keV and 240 cm/µs, respectively.

A spherical plasma focus device with two concentric electrodes is simulated using deuterium and tritium mixture (50:50) as a working gas. The developed model is used to study the effect of gas pressure and charging voltage on dynamics of current sheath in spherical plasma focus. While charging voltage is varied from 15 kV to 30 kV to see the effect of voltage, gas pressure is increased from 1 Torr to 20 Torr for gas pressure study. In this work, it is found that there is a strong correlation between current sheath dynamics and investigated parameters which are gas pressure and charging voltage.

... Author Contact Information , E-mail The Corresponding Author , Domiziano Mostacci a , Federico Rocchi a , Michele Frignani a , Agostino Tartari b ... The problem is highly non-linear, since the external RLC circuit discharge influences the Lorentz force acting on the plasma sheath ...