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A study of energy transfer in a small plasma focus device has been carried out during its axial phase. The snow-plough model has been used in the simulation as a basic model for the calculation of plasma dynamics. The energy trans...
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A study of energy transfer in a small plasma focus device has been carried out during its axial phase. The snow-plough model has been used in the simulation as a basic model for the calculation of plasma dynamics. The energy transferred to the plasma is calculated by considering the work done by the electromagnetic piston during the axial phase. It was found that the plasma energy calculated by this model agrees well with the experimental data within the pressure range of 1 mbar to 4 mbar if the mass shedding effect is included in the model. According to the present computation, the energy transferred into the plasma, in the case of a plasma focus with 2.3 kJ initial energy operated with nitrogen gas within the pressure range of 1 to 4 mbar, is between 224 J to 250 J. This corresponds to energy transfer efficiency of 9.6% to 10.7%. The mass shedding factor decreases from 0.23 to 0.069 with increasing pressure. Correspondingly, the energy transfer efficiency changes slightly at a higher pressure.
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Existing conventional megajoule plasma focus machines with 2-3 MA are producing fusion neutron yields of several times 10(11) in deuterium operation, the fusion yields predominantly being the beam-gas target. Increasing the curren...
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Existing conventional megajoule plasma focus machines with 2-3 MA are producing fusion neutron yields of several times 10(11) in deuterium operation, the fusion yields predominantly being the beam-gas target. Increasing the current to 10 MA and using 50%-50% D-T mixture will scale the neutron yield towards 10(16) D-T fusion neutrons. In this work, we derive the Lawson criterion for plasma focus devices with a beam-target fusion neutron mechanism, so that we may glimpse what future technological advancements are needed for a break-even Q = 1 plasma focus. We perform numerical experiments with a present-day feasible 0.9 MV, 8.1 MJ, 11 MA machine operating in 100 Torr in 50%-50% D-T mixture. The Lee Code simulation gives a detailed description of the plasma focus dynamics through each phase, and provides plasma and yield parameters which show that out of 1.1 x 10(19) fast beam ions produced in the plasma focus pinch, only 1.24 x 10(14) ions take part in beam-target fusion reactions within the pinch, producing the same number of D-T neutrons. The remnant beam ions, numbering at least 10(19), exit the focus pinch at 1.9 MeV, which is far above the 115 keV ion energy necessary for an optimum beam-target cross-section. We propose to regain the lost fusion rates by using a high-pressure D-T-filled drift-tube to attenuate the energy of the remnant beam ions until they reach the energy for the optimum fusion cross-section. Such a fusion enhancement tube would further harvest beam-target fusion reactions by increasing the interaction path length (1 m) at increased interaction density (6 atm). A gain factor of 300 is conservatively estimated, with a final yield of 3.7 x 10(16) D-T neutrons carrying kinetic energy of 83.6 kJ, demonstrating Q = 0.01.
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The results of the development of a two-dimensional MHD code for carrying out computational studies of the dynamics of plasma current sheath in spherical chambers with a plasma focus are presented. Equations of magnetohydrodynamic...
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The results of the development of a two-dimensional MHD code for carrying out computational studies of the dynamics of plasma current sheath in spherical chambers with a plasma focus are presented. Equations of magnetohydrodynamics with allowance for magnetic field diffusion, thermal conductivity and plasma radiation are used in this work. An implicit scheme is used in the calculation of the magnetic field, which makes it possible to describe the motion of plasma in a low-density region behind the plasma sheath. The formulas that take into account the possible appearance of anomalous resistance in the plasma are used to calculate the plasma conductivity. The neutron yield is calculated with allowance for thermonuclear and beam-target neutron generation mechanisms. The effect of the minimum residual gas density behind the plasma sheath on the cumulation of the plasma sheath is studied. The effects of magnetic field diffusion, thermal conductivity and anomalous plasma resistance on the plasma sheath dynamics are considered. The calculations are performed for two spherical plasma-focus chambers operating with currents up to 1 and 2 MA and neutron yields to 10(12)and 1.5 x 10(13)DT neutrons, respectively. The comparison of the calculated dependences with experimental data on the current, voltage and neutron yield made it possible to refine the parameters used in the calculations and achieve a satisfactory agreement between the simulation and experiment.
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The paper is devoted to the study of the plasma flows generated in the plasma focus discharge at the PF-3 facility at its propagation in the ambient medium up to distances of 100 cm and, in particular, the study of the dynamics of...
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The paper is devoted to the study of the plasma flows generated in the plasma focus discharge at the PF-3 facility at its propagation in the ambient medium up to distances of 100 cm and, in particular, the study of the dynamics of such important parameters as velocity, total energy, and momentum. Momentum and energy measurements were made using a ballistic pendulum, which could be used simultaneously in the calorimeter mode. Optical collimators are used to measure the flow velocity. It is shown that, in experiments with argon at a distance of 65 cm, the energy density of the incident flow of >= 10 J/cm(2) is observed. The total number of particles in the flow and the total mass of the flow are calculated.
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Experimental studies of discharges in the plasma focus facility with neon filling and respective numerical simulations employing the radiative Lee code are reported. The pinch currents exceed the Pease-Braginskii current, which in...
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Experimental studies of discharges in the plasma focus facility with neon filling and respective numerical simulations employing the radiative Lee code are reported. The pinch currents exceed the Pease-Braginskii current, which indicates that radiative losses are larger than heating and that contraction of the formed plasma should occur. Both of these effects were indeed observed. Parallel numerical simulations were crucial for the identification of such an effect.
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We present the results of laboratory simulation of jets from young stars at the PF-3 plasma focus facility at the NRC "Kurchatov Institute." The objective of research question was to determine factors making the spatial structure ...
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We present the results of laboratory simulation of jets from young stars at the PF-3 plasma focus facility at the NRC "Kurchatov Institute." The objective of research question was to determine factors making the spatial structure of plasma jets in discharges in gases of different chemical compositions, namely, neon, helium, and helium with admixtures of neon, different. It was found that the plasma flow in the case of pure neon is the most structured: the head of the ejection consisted of numerous clumps, which makes is very similar to clumps in the jets from young stars, the so-called Herbig-Haro objects. The ejection in the case of pure helium was the least structured. However, the shape of the ejection head substantially changes upon admixing merely 1% of neon into helium, revealing a noticeable small-scale structure. Estimates show that these specific features can be related to the difference in the cooling efficiency of the studied gases both in the plasma ejection itself and in the shock wave generated upon jet propagation through the background gas. It is suggested that the main reason for the appearance of inhomogeneities in the plasma blob are different types of instabilities that develop in the presence of efficient radiative cooling, as is the case of the Herbig-Haro objects. In addition, it was established that, in some cases, plasma ejections can consist of several blobs propagating nearly parallel to each other that appear as early as at the stage of plasma pinching. Collision of shock waves generated by each of the blobs leads to the appearance of clumps, which facilitates formation of the lace-like structure of plasma ejection.
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На примере струйных выбросов из молодых звёзд показано, как лабораторное моделирование позволяет существенно продвинуться в...
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На примере струйных выбросов из молодых звёзд показано, как лабораторное моделирование позволяет существенно продвинуться в понuмании основных физических процессов, ответственных за образование и устойчивость этих удивительных объектов. В частности, обсуждается возможность моделирования струйных выбросов в лабораторном эксперименте на установке ПФ-3 в Национальном исследовательском центре "Курчатовский институт". Многие свойства течений, полученных на экспериментальной установке, согласуются с основными характеристиками струйных выбросов, наблюдаемых в окрестности молодых звёзд.
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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 sepa...
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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 x 10(13) (higher than the measured neutron yield of 1.26 x 10(13) at 25 kV), it increases to 1.32 x 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)).
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The results of studying the propagation of plasma flows in the surrounding medium performed on the PF-3 plasma focus facility in the laboratory simulation of astrophysical jets from young stellar objects are presented. The modes w...
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The results of studying the propagation of plasma flows in the surrounding medium performed on the PF-3 plasma focus facility in the laboratory simulation of astrophysical jets from young stellar objects are presented. The modes with the plasma formations which retain their compactness when propagated over significant distances are obtained. The decrement of the flow's deceleration as a result of its interaction with the background gas is determined. A technique is developed for estimating the plasma temperature by the ratio of radiation intensities from various parts of the spectrum. It is shown that the background gas is heated by the flow radiation, which leads to a change in its ionization state. Thus, the plasma flow propagates not in a neutral gas but in a weakly ionized plasma.
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This paper reports on a two-dimensional computer simulation of the breakdown phase performed for a plasma focus (PF) device. The spatial and temporal development of the electron density and the potential of the electric field are ...
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This paper reports on a two-dimensional computer simulation of the breakdown phase performed for a plasma focus (PF) device. The spatial and temporal development of the electron density and the potential of the electric field are calculated by numerically solving the continuity equations for electrons and ions together with the Poisson equation. This model has been used to study the evolution of a discharge and its different characters depending on the applied gas pressure.
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