Plasma Focus Research Articles

High energy ion beams from the plasma focus

Instability development in the pinch induces a locally enhanced electric field that accelerates the charged particles to extraordinary high energies. Rapid discharge is the singular state of the ion source confirming high plasma impedance. High energy ion beam is correlated to the electrical discharge parameters and consequently the ion acceleration potential is directly related to the mean ion energy. Multi−MeV ions have been measured by magnetic spectrometry and nuclear activation yield-ratio to obtain the ion energy spectra and critically analyze the ion spectrum. A set of magnetic lens arranged in an optimized coil configuration results in medical grade radioactivity of 0.5GBq for a low energy plasma focus. High energy proton beams enables evaluating the sensitivity of link-board components and the error structure identification, with a significant probability of 0.1perproton.

Pressure change dynamics of plasma focus chambers as a part of the pulse neutron generators

The dynamics of working gas pressure changes in the plasma focus (PF) chambers were studied by using the chamber with a built-in manometer as part of the ING-102 neutron generator (2.5 MeV neutron yield 106÷107 neutrons/pulse). Investigations were carried out during high-voltage training and neutron emission operation mode. The studies were executed while filling the chamber with various gas mixtures. For operation with a deuterium-tritium mixture, a sealed-off chamber with a built-in gas generator was used. After the primary filling of the PF chambers with a gas mixture, there is a systematic decrease in pressure by Δp = (5 ÷ 50) ·10−3 Torr (∼0,7 ÷ 7 Pa) after each shot of the chamber.The change in the shape of breakdown curves Ubr(p) in the interelectrode gap of the chamber after each series of shots was studied. That made it possible to assess the optimal number of shots during high-voltage training of the PF chamber.

On the Generation of Plasma Jets in the Kilojoule Plasma Focus Device

—Laser–optic methods were used to study the properties of plasma jets generated in the KJ Plasma Focus device. Measurements of the plasma jet velocity were conducted immediately after its appearance. During the first 10 ns, the average velocity is about 5 × 107 cm/s, which corresponds to energy of 18 keV for the ions of nitrogen, which was the working gas of the PF setup. The jet density and velocity decrease manifold over distance of 2–3 cm from its generation point. The experiments confirm that the main reason of jet generation is the necking of the pinch. It was found that after the pinch decay, a new plasma column appears, which propagates in the axial direction.

Features of Damageability and Modification of Surface Layers of Al and Its Alloys by Powerful Energy Fluxes in a Plasma Focus Facility

Features of Damageability and Modification of Surface Layers of Al and Its Alloys by Powerful Energy Fluxes in a Plasma Focus Facility

Features of Pinch Plasma, Electron, and Ion Beams That Originated in the AECS PF-1 Plasma Focus Device

The measured current traces of alow energy AECS PF-1 plasma focus device are used for studying of the formed plasma, and the produced ion and electron beams. Anadapted version of the Lee model (RADPFV5.15FIB&REB) is applied, taking into account the fitting procedures between the measured and computed current waveforms for each shot. The experiments on AECSPF-1 were performed with three different gases—helium, nitrogen, and argon—for studying the effect of the atomic number on the properties of the generated beams. For numerical experiments using the Lee model, 36 successful shots for each gas were selected. The peak values of the total discharge current Ipeak were 50–55 kA, the pinch currents Ipinchwere34–36 kA, and the final pinch radius reached a minimum value of 0.03 cm for argon. The ion mean energy ranged from 35 keV (for He) to 223 keV (for Ar). The beam energy also had an extreme value of 1.34 J (0.05%E0) for argon. The results presented the highest values of 2.4 × 1014Wm−2 for the power flow density, and adamage factor of around 3.1 × 1010 Wm−2s0.5 for argon. For electron beams, the results also showed that the fluence and flux increased with the higher atomic number and reached a peak of 9.7 × 1022 m−2 and 5.9 × 1030 m−2 s−1 for argon, respectively. The results presented the highest values of 2.2 × 1016Wm−2 for the power flow density (heat flux), and adamage factor of around 3 × 1012 Wm−2s0.5 for argon. The kinetic energy of the relativistic electrons was found to be within the range of 18–23 keV. The results show that the ion and electron beam properties (energy, flux, fluence, ion and electron numbers, current, power flow density, and damage factor) emitted from the plasma focus had wide ranges based on the operational plasma focus parameters. Thus, these results could be used for selection of the suitable plasma focus parameters for desired material processing applications.

Self-sustainability and energy-balance in a fast Fusion–Fission Hybrid Reactor (FFHR) based on Dense Plasma Focus (DPF) and multiplicative cascade

A Fusion–Fission Hybrid Reactor (FFHR) is made of a subcritical reactor driven by the neutrons generated in a nuclear fusion device. The fast neutron spectrum produced by this system could be able to burn actinides from the spent nuclear fuel. Unfortunately, current fusion devices are unable to provide an adequate neutron yield with reasonable spending of energy. However, it is possible to design the subcritical set to multiply considerably the neutron flux by using the so-called multiplying cascades. In addition, given its simplicity, the Dense Plasma Focus (DPF) is an interesting candidate as a neutron source. In this work, we analyze a concept of a metallic-fuel hybrid reactor based on a subcritical set and driven by a DPF as a neutron source. Their spectra are evaluated to determine if they are compatible with the operation of a fast reactor. The energy balance is also studied to find its ability to be self-sufficient when using an existing DPF. Finally, its capability to generate tritium from its lithium blanket is also analyzed. The system is self-sustainable.

On filamentation in the dense plasma focus

Striking pictures showing filamentary structures in the plasma focus have intrigued researchers from the early days of plasma focus research. A definitive understanding of their occurrence, origin, structure, and role in plasma focus physics is still not in sight as summarized in a recent comprehensive review. This is because they are often not observed in a “standard mode” of plasma focus operation with pure deuterium, particularly in large installations, but are found in smaller experiments or those with gaseous admixtures. This has led to the suspicion that filaments are not a native feature of the plasma focus phenomenon. Recent success in observation of filaments in PF-1000 in pure deuterium operation by novel modification of the interferometer system that allows simultaneous interferometry and schlieren photography changes this situation. This Letter looks at the implications of this development in the larger context of plasma focus physics. Conceptualization of filamentation as a native feature of the traveling current distribution behind an ionizing strong shock wave is shown to be a feasible paradigm that can be formulated as a computable model for filamentation in the plasma focus.

Discovery of Third Possible Ion Generating Source in 4π Plasma Focus Device Space.

Discovery of a possible third source of ion generation in 4π Plasma Focus Device (PFD) space is reported. Unexpected observation of dense ion tracks, called "On Shadow Ion Tracks" (OSIT), on the "ion cathode shadows" (ICS) was discovered. These ions were formed on panorama mega-size cylindrical polycarbonate ion image detectors placed behind the cathodes in the PFD space on PFD wall, where no ion tracks are expected to exist. Such unexpected ion tracks were observed when different gases were used, in particular hydrogen, deuterium, and helium. An ICS is formed on the detector when each cathode shadows and removes all ions bombarding it from the "anode top" and "anode cathodes assembly." Such ion tracks forming the OSITs seem to be generated not from the "anode top" and "a node cathodes assembly" but also from a third possible ion source in PFD space bombarding the detector.

Time-domain study of the synchrotron radiation emitted from electron beams in plasma focusing channels.

This paper sheds light on the time structure of betatron radiation, emitted by electrons that undergo betatron oscillations as they accelerate under the action of plasma wakefields. It is a common practice to assume that the betatron pulses are as short as the electron bunch length, however we show that this is not a general rule. Indeed, the betatron pulse length is affected by the betatron motion, which stretches and modulates the radiation pulses already at the source level. Propagation in a vacuum, therefore, can greatly lengthen the betatron pulses by orders of magnitude. In the wake of the above, the coherent emission of betatron radiation is studied. Coherent betatron radiation has been found to propagate in an underdense region created by ponderomotive forces, thus not suppressed by the overdense plasma absorption. This could be observed experimentally, revealing information on the acceleration process and on key beam parameters.

Особенности повреждаемости ниобия импульсным лазерным излучением в сравнении с пучково-плазменным воздействием

The features of damageability of niobium by pulsed fluxes of laser radiation (LR) in the free-running modes (power density qFR = 105 – 106 W/cm2 with pulse duration τFR = 700 μs) and Q-switch mode (q = 108 – 109 W/cm2, τMD = 80 ns) in comparison with the pulsed effects of helium ion (HI) and helium plasma (HP) fluxes in the Plasma Focus (PF) setup at a flux power density qi ~ 108 W/cm2 and qp ~ 107 W/cm2, respectively and pulse durations τi ≈ 30 – 50 ns and τp ≈ 100 ns. LR fluxes were exposed to Nb in air; the working gas in the PF chamber was helium. It is shown that, in contrast to the effect of IG and HP fluxes on niobium in the PF installation, which contribute to the erosion of the material, the irradiation of niobium by pulsed LR in air fluxes under the conditions implemented does not cause noticeable surface erosion. When Nb is exposed to pulsed LR in the FR mode, the melt interacts with the air and forms on the irradiated surface of a thin film of elements of the liquid and gas phases. A similar nature of damage to Nb under the conditions of laser and beam-plasma treatment was found: a wavy relief of the irradiated surface with the presence of drop-like fragments on it, extended wave crests and microcracks. Irradiation of Nb by pulsed LR fluxes in the FR mode leads to the formation in the surface layer (SL) of sections with block and cellular structures, which are also formed after experiments in the PF chamber. It was found that after laser treatment in the FR and Q-switch modes, bubbles (blisters) are not formed in the SL of niobium, which are always present on the irradiated surface when exposed to pulsed fluxes of HI and HP in the PF chamber due to the implantation of helium ions in Nb. It is noted that in laser experiments there is no possibility of implanting working gas ions into the material, which is characteristic of beam-plasma impacts in PF devices, which affects the parameters of damageability and modification of the structure of the irradiated SL.

Occurrence of microstructures on steel surface under the influence of plasma focus discharge

The surface of metals after irradiation by intense streams of argon plasma arising in the plasma focus was studied. Metal samples of steel, copper, tungsten and molybdenum were investigated. Different types of microstructures were recorded. The surfaces of steel samples contain micropores with sizes of 0.1-3 μm with a shape close to circular. On copper and tungsten plates the appearance of fine-dispersed structures with sizes of 0.5-20 μm is observed. The possible mechanisms of the appearance of these microstructures are discussed. Keywords: plasma focus, intense plasma flows, micropores, filamentous discharge structure.

Comparison of the Effects of Fusion Plasma Ions on Aluminum and Tungsten Using a Plasma Focus Device

Comparison of the Effects of Fusion Plasma Ions on Aluminum and Tungsten Using a Plasma Focus Device

The effect of neon ion irradiation on tungsten for next generation fusion reactor

Tungsten exhibits robust thermo-physical and mechanical properties in ion material interaction. It is considered as an important material of the plasma facing component for next generation fusion reactor. This material could be one of the candidates to use in the divertor region of the tokamak. With this motivation a series of experiments have been performed with a plasma focus device to study the effect of neon irradiation on tungsten in various experimental conditions like with angular variation and with number of plasma focus shots. Exposed and unirrdiated tungsten samples were analyzed subjecting to surface morphological and structural studies namely using optical microscope, scanning electron microscope, atomic force microscope, grazing incidence X-ray diffraction, Vickers hardness measurement. OM photographs are analyzed quantitatively in terms of holes and pores with angular variation and number of PF shots. Surface analyses verifies the formation of micro-cracks, bubbles, blisters, holes. X-ray diffraction pattern shows the development of compressive stress on the sample due to thermal load and formation of other phases or expanded phases.

Возникновение микроструктур на поверхности стали под воздействием разряда плазменного фокуса

The surface of metals after irradiation by intense streams of argon plasma arising in the plasma focus was studied. Metal samples of steel, copper, tungsten and molybdenum were investigated. Different types of microstructures were recorded. The surfaces of steel samples contain micropores with sizes of 0.1-3 μm with a shape close to circular. On copper and tungsten plates the appearance of fine-dispersed structures with sizes of 0.5-20 μm is observed. The possible mechanisms of the appearance of these microstructures are discussed.

Имитационное облучение ДУО стали 16Cr – 4Al – 2W – 0,3Ti – 0,3Y2O3, перспективной для термоядерных реакторов, в установке Плазменный фокус “Вихрь”

A study of the radiation-thermal resistance of ferritic steel 16Cr – 4Al – 2W – 0.3Ti – 0.3Y2O3 was made. This ODS (oxide dispersion strengthened) steel is perspective for fusion applications. The “Vikhr” Plasma Focus installation was used to introduse of powerful pulsed flows of helium ions and helium plasma. The power density of a beam of fast helium ions and high-temperature helium plasma flows was ~ 108 and 107 W/cm2 at exposure times of ~ 50 and 100 ns, respectively. The number of pulses N varied in the range from 10 to 30. The rate of evaporation and radiaсtive sputtering changed slightly with an increase in the number of pulses of energy flows acting on the material and amounted to h ≈ 0.01 – 0.02 μm/puls. The irradiated surface after repeated melting under the action of a pulsed radiation-thermal load with powerful energy flows acquired a wave-like character with inclusions of dispersed micro particles of the second phase, containing mainly yttrium, oxygen, aluminum, iron, and titanium. At the same time, in contrast to the refractory metals (W, Mo, Ti) earlier under similar radiation conditions studied, no micro- and macro cracks were formed on the surface of the material facing the plasma. “Vikhr” Plasma Focus setup proved to be an effective tool for simulation testing of candidate materials with magnetic and inertial plasma confinement.

Генерация мощных пучков ионов металлов субмиллисекундной длительности

The possibility of using one grid electrode in the form of a part of a sphere for extraction from a free plasma boundary and focusing of metal ions is shown for the first time using titanium ions as an example to form a pulsed beam with a duration of 500 µs and a power density reaching 105 W/cm2. The results of studying the influence of the amplitude of the accelerating voltage in the range of 9–30 kV and the size of the grid cells on the efficiency of space charge neutralization and ion beam focusing are presented.

Generation of high-power submillisecond metal ion beams

The possibility of using one grid electrode in the form of a part of a sphere for extraction from a free plasma boundary and focusing of metal ions is shown for the first time using titanium ions as an example to form a pulsed beam with a duration of 500 μs and a power density reaching 105 W/cm2. The results of studying the influence of the amplitude of the accelerating voltage in the range of 9-30 kV and the size of the grid cells on the efficiency of space charge neutralization and ion beam focusing are presented. Keywords: metal ions, vacuum arc plasma, submillisecond beams, high power density.

Synthesis of hydrocarbon-vanadium thin films by a low energy plasma focus device

Synthesis of hydrocarbon-vanadium thin films by a low energy plasma focus device is reported. The thin films have organometallic structure and organometallic trovacenyl carboxylic acid anhydride (C26H22O3V2) is formed. The vanadium deposition process was achieved in methane atmosphere using different number (10, 20, and 30) of focused shots. Prior to deposition process, surface of pure vanadium substrate and the anode tip were exposed to atmosphere to allow the formation of vanadium trioxide (V2O3) and hydrogen vanadium bronze (HxV2O5) structures. During deposition process, HxV2O5 reacts with methane molecules and C26H22O3V2 molecular structure in nano-grain scale is created. The findings of present study indicates that C26H22O3V2 can be categorized as a semiconductor with band gap energy in the range of 1.20–1.35 eV. Furthermore, it is demonstrated that C26H22O3V2 molecular structure is not Raman active. Characteristics of the V2O3, HxV2O5 and C26H22O3V2 structures are investigated by crystalline, spectroscopy and microscopy methods. The average crystallite size of C26H22O3V2 was roughly 6 nm with almost 16% carbon deposited in the thin films. The Raman results are independent of the number of focused shots.

Correlation of Pinch Properties with Minimum Pinch Radius in UNU/ICTP PFF for Different Pressure of Argon Gas

In this present work, numerical experiments are performed using the Lee code to examine the correlation of minimum pinch radius(rmin) with pinch energy density(PED),ion number density (Ni),induced voltage(Vmax), total radiation power (Prad),and Joule heating power (Pjoule)in UNU/ICTP PFF device when using argon gas at different pressure. The computed results show that at the optimum pressure of 1.0 Torr argon, PED (338 × 109Jm-3), Ni (123 × 1023/m3), Vmax (245 kV), Pjoule(114.48 × 108W),and Prad (173 × 108W) reach to their maximum values whilst the rmin reaches to its lowest value of 0.01 cm. At this optimum condition, the strong radiation cooling effect is found and the excess (Pjoule-Prad) in radiative power of -58.51× 108W(negative singe indicates the energy going out from pinch plasma) which is sufficiently enough to cause the radiative collapse in heavier argon pinch plasma. Hence, the excess radiation power would be another reason for the occurrence of radiative collapse beside the critical (Pease-Braginskii) current. The variation nature of pinch properties of this studies are compared with those of PF1000 plasma focus device that makes the consistent of the present research work.

Образование поверхностных микротрещин и выброс частиц в вакуум при облучении сплава системы алюминий – магний в установке Плазменный фокус “Вихрь”

It was found that particles of the metal are ejected in vacuum during the formation of microcracks in a film on the surface of a model alloy of the aluminum-magnesium system (AMG type) under the influence of pulsed beam-plasma flows with a power density q ~ (106 – 5·107 W/cm2) in a plasma focus setup. The formation of microcracks in the surface film of refractory aluminum oxide (Al2O3) occurs due to the processes of its sputtering, mechanical action of pulsed energy flows and thermal stresses arising in the surface layer. Ejection of alloy particles through microcracks in the oxide film is observed after melting of the surface layer of the alloy at q > 107 W/cm2. The possible influence of such effect on the process of ejection of dust particles in thermonuclear fusion facilities is noted.