Plasma Focus Research Articles

Damage and Deformation Effects in the Surface Layers of Copper and Copper–Gallium Alloy under Pulsed Irradiation in a Plasma Focus Unit

Damage and Deformation Effects in the Surface Layers of Copper and Copper–Gallium Alloy under Pulsed Irradiation in a Plasma Focus Unit

Coulomb expansion of a cold non-neutral rubidium plasma

We study the expansion of a strongly coupled, non-neutral, and cylindrically arranged ion plasma into the vacuum. The plasma is made from cold rubidium atoms in a magneto-optical trap (MOT) and is formed via ultraviolet photoionization. Higher-density and lower-density plasmas are studied to exhibit different aspects indicative of strong coupling. In a higher-density regime, we report on the formation and persistence of plasma shock fronts, as well as external-field-induced plasma focusing effects. In the lower-density regime, conditions are ideal to observe the development and evolution of nearest-neighbor ion correlations, as well as geometry-induced asymmetries in the pair correlation function. Simulated results from a trajectory model and a fluid model are in good agreement with the measurements.

Novel panorama “anode cathodes assembly” run-away hydrogen ion image studies in 4π plasma focus device space at different gas pressures

From many parameters affecting ion emission angular distributions in a plasma focus device (PFD), gas pressure is a parameter highly affecting ion emissions, the mechanisms of which have yet to be further understood. In this research, effects of hydrogen gas pressure up to 100 mbar were studied on angular distributions of run-away hydrogen ions generated directly from the “anode cathodes assembly”. In order to demonstrate further the emission of such ions and study the effect of gas pressure on the ion emissions, a novel self-invented panorama mega-size polycarbonate cylindrical ion image detector was used for wide-angle panorama image detection of run-away hydrogen ions from the “anode cathodes assembly”. The mega-size detectors were processed in our novel single-cell panorama electrochemical etching ion image processing system constructed for this study. The studies confirmed effective detection of images of high intensity run-away hydrogen ions; observation of 6 “hydrogen ion cathode shadowgrams” by the unaided eyes; estimation of total hydrogen ion tracks under different gas pressures and in particular a high proof of strong source of ion emission from the “anode cathodes assembly” partially responsible for formation of cathode shadowgrams formed on the detectors.

BASINÇ VE VOLTAJIN KÜRESEL PLAZMA ODAK CİHAZI DİNAMİ ÜZERİNE ETKİSİ

A spherical plasma focus device with two concentric electrodes is simulated using equal amount of deuterium and tritium mixture as a working gas. The developed model is used to investigate 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 pulse vacuum-arc plasma generator for nanoengineering application

In paper described the results of work on the application of vacuum-arc machine in nanoengineering area. Researches were carried out to optimize the operation of this machine for the synthesis of nanomaterials in low-pressure arc-discharge plasma, plasma diagnosis and production of nanopowders. An electrode system based on the grounded cathode with impulse ignition has been developed. The anode current was measured and the mass output of the product was calculated. Experimental data on energy density were obtained, confirming the presence of plasma focusing on the electrode system axis due to its own magnetic field, the focus value of which reaches about 18 kJ/m2. Powder samples were also obtained in the form of clusters containing the copper particles (up to 98%) and spherical powder with size from 116 nm to 1.2 µm. Homogeneity and dispersion of powder depended on the time of the processes accompanying the deposition.

A New Application of Sohrabi Albedo Neutron Dosimeters around a Plasma Focus Device.

A new application of the Sohrabi albedo neutron dosimeters is reported for the first time for determination of very low-level neutron ambient dose equivalents on and around a 3.5 kJ plasma focus device (PFD). The Sohrabi dosimeters basically use a polycarbonate track detector as bare and/or in contact with B convertor(s) under special cadmium cover arrangements. Its sensitivity was improved by using enriched B under new cadmium arrangements in order to detect epithermal neutrons in addition to fast and thermal neutrons. Results of 12 dosimeters installed externally around the PFD at different azimuthal (φ) and polar (θ) angles showed that azimuthal (φ) fast, epithermal, thermal, and total neutron ambient dose equivalents were symmetric and isotropic, respectively, with values 55.15 ± 8.36, 1.36 ± 02, 0.53 ± 03, and 57.04 ± 8.62 μSv/shot at ~25 cm from anode top. Polar (θ) neutron ambient dose equivalent values on z-axis relative to 90 angle were relatively higher. Results of 38 dosimeters placed on PFD facility walls for workplace monitoring and on a BOMAB phantom at operator's location for personal dose equivalent determination showed values below minimum detection limits after exposure to 130 PFD shots. However, an operator's personal dose equivalents at ~1.0 and ~3.0 m from the anode top were estimated to be, respectively, ~13.7 and ~1.52 mSv y using azimuthal angle (φ) values if the PFD operates, for example, up to 20 shots per day for 200 d y. Even under such an extreme assumption, annual personal dose equivalent is still much below 20 mSv, the annual ICRP dose limit for workers.

Backwards extrapolation activation diagnostics and their dynamic range for pulsed neutron source measurements

Activation materials implanted within radiation detectors can be used to measure pulsed neutron fields. This work develops an instrument concept with the aim to maximise sensitivity to pulsed fusion neutron fields and, using a data-rejection algorithm combined with backwards extrapolation, enable neutron fluence estimates to be made over a large dynamic range. Through high-fidelity modelling of residual temporal emissions, and a parameterised approach, we study the sensitivity to neutrons of a plastic scintillator–Ag foil layer detector concept. For an optimal design we apply paralysable and non-paralysable deadtime models to the predicted response to D–D fusion neutron fields at various neutron field intensities. In high neutron fluence irradiation scenarios, where deadtime effects are strongly evident, we use our approach to make estimates of the fluence from instrument response data. We discuss the practical applications of such diagnostics used for plasma focus (PF) fusion experiments, such as at the PF-1000U facility in IPPLM, Poland, inertial confinement fusion and pulsed tokamak experiments, for example at MAST-U, where such diagnostics could complement fission counter-based neutron diagnostics in the future. Finally, we show that the calibration of such detection systems may be achieved using relatively low emission rate, steady state neutron sources, with calibration factors that are straightforward to apply to pulsed neutron field measurements.

MHD Simulation of Hemisphere Plasma Focus Using Snowplow Model

The Hemisphere Plasma Focus (HSPF) device is a new construction of plasma focus (PF) devices wherein the discharge takes place between the inner and outer concentric hemispherical electrodes with total energy up to 3.4 kJ. The pinch effect appears in the shape of a sharp crevice in the discharge current signal. HSPF is simulated by utilizing the Snowplow Model depending on the circuit equation incorporated with the momentum equation. Some modifications were added to the model to improve the theoretical data in order to be consistent with the experimental results. The code includes a rundown phase starting from the equator point toward the antipodal point and the reflected shock phase at the axis. The model results are compared with experimental results, and the effect of discharge parameters such as the discharge voltage and helium gas pressure on the plasma parameters is studied. The total system inductance is about 285 nH with a resistance of about 23 mΩ. Furthermore, the plasma inductance has a maximum value at the pinch time, which is decreased by increasing the charging voltage or decreasing the gas pressure. The mass factor in the HSPF device is found to be relatively low compared to that of the coaxial PF device. The shock front and current sheath velocities are increased by increasing the drive factor while the pinch time is decreased. Also, the minimum pinch radius and the plasma inductance have a reverse trend as a function of the drive factor.

Tomographic Reconstruction of the Neutron Time–Energy Spectrum From a Dense Plasma Focus

A dense plasma focus (DPF) nuclear fusion device is an attractive pulsed neutron source in many applications, due to its relatively large neutron yield, produced in a short time duration. To design a DPF that generates neutrons within a specified time profile, or that generates a neutron energy spectrum with specific properties, it is necessary to characterize and model the results of the fusion process releasing the neutrons. The time–energy spectrum of fusion neutrons is an ideal quantity used in validating multiphysics codes that simulate the pinch and fusion processes, because it is a quantity that requires physics of each of the stages leading up to and ending in the fusion reaction to be simulated correctly. In particular, since DPF fusion neutrons are not monoenergetic—and there can often be several fusion pinches creating neutrons—a computer simulation matching high quality neutron spectrum measurements provides confidence in the fidelity of the simulation. In order to make such a comparison, it is first necessary to have quality measurements from which to infer the spectrum. In this work, we project neutron spectroscopy as the classical tomographic inverse problem from neutron time-of-flight data at multiple distances, but enhanced by using an additional measurement of the time profile of the fusion pinch near its source and by using detector pairs set up in a geometry that allows for scatter background subtraction. The detector pairs enhance the quality of the time-of-flight measurements, and the additional constraint posed by the measured time profile allows for reconstructions discretized as finely as the time measurements and in energy as finely as 100 keV, without the problem being underdetermined. We present results from a deuterium-fueled DPF at the U.S. Department of Energy’s Nevada National Security Site and show that we can infer the time–energy spectrum from our measurements for both single and multi-pinch fusion reactions with equal fidelity.

Development of a neural network method for measuring the energy spectrum of a pulsed electron beam, based on Bremsstrahlung X-Ray

In the pulsed electron beam generators, such as plasma focus devices and linear induction accelerators whose electron pulse width is in the range of nanosecond and less, as well as in cases where there is no direct access to electron beam, like runaway electrons in Tokamaks, measurement of the electron energy spectrum is a technical challenge. In such cases, the indirect measurement of the electron spectrum by using the bremsstrahlung radiation spectrum associated with it, is an appropriate solution. The problem with this method is that the matrix equation between the two spectrums is an ill-conditioned equation, which results in errors of the measured X-ray spectrum to be propagated with a large coefficient in the estimated electron spectrum. In this study, a method based on the neural network and the MCNP code is presented and evaluated to recover the electron spectrum from the X-ray generated by collision of the electron beam with a target. Multilayer perceptron network showed good accuracy in electron spectrum recovery, so that for the X-ray spectrum with errors of 3% and 10%, the network estimated the electron spectrum with an average standard error of 8% and 11%, on all of the energy intervals.

Influence of Multiple Short Highly Energetic X-ray Pulses on the Biosynthetic and Physiological Activity of the Strain Trichoderma reesei M7

In order to increase the biosynthetic capacity of the Trichoderma reesei-M7 strain – a notorious cellulase enzyme producer – the experimental biological object to be studied was exposed to the impact of the highly energetic X-ray pulses, produced by the dense plasma focus device (DPF). The X-ray pulses thus produced can have exceptionally high density of the flow of X-photons. The pulsed mode of irradiation fundamentally differs from the continuous when considering its effect on biological objects – they can rapidly absorb great amounts of radiation in a glimpse, leading to a qualitatively different interaction with their matter. In the experiments done the survivability was determined, as well as the vegetative biomass, four types of cellulase activity and the quantity of total protein after the treatment of the spores suspension (2.105 CFU/ml) of Trichoderma reesei M7 with this pulsed X-radiation. The absorbed doses were in the range of 7 to 45000 mSv. It was noticed that the survivability of the strain, if compared with the control samples, drops, reaching 57% of the initial value (of the untreated spores) for the sample with 45010 mSv of absorbed dose. From the data presented below it can be concluded that three of the samples with high absorbed doses, namely with 11754, 19439 and 42917 mSv, demonstrated increases their cellulase activities. In the case of 42917 mSv the increment of the endoglucanase activity, compared to the control, reaches 41,1%, FPA rises with 30,3%, and the β-glucosidase activity nearly doubles – and increase of 92,7%.

Experimental Study of the Effect of External Inductance on Pinch Characteristics and Neon Soft X-Ray Yield in Filippov-Type Plasma Focus Device

So far, the detailed experimental effect of the inductance on the X-ray yield in the Filippov-type plasma focus devices has not been documented in literature. In this paper, a 90 kJ Filippov-type plasma focus device is used to investigate the effect of three different external inductances (20, 40, and 60 nH) on the pinch current and neon soft X-ray (SXR) yield experimentally. The obtained results for the three inductances show that the 60 nH inductance produces maximum pinch current for high voltages (12–13 kV). The results also show that with using 60 nH external inductance, a larger fraction of maximum current is transferred into the plasma column. Experimental results show that the ratio of pinch to maximum currents for 60 nH is larger than for the two other external inductances. The effect of external inductance on the neon soft X-ray emission at constant pressure (0.25 Torr) and different voltages (10–13 kV) is investigated with a five-channel diode X‑ray spectrometer. Of the three external inductances, the average neon SXR yield has a maximum value at 11 kV for 40 and 60 nH, and 12 kV for 20 nH. The maximum neon SXR yield energy is 24.87 ± 2.52 J for the external inductance 20 nH at 12 kV and it is 23.62 ± 3.10 J for the external inductance 40 nH at 11 kV and 5.23 ± 1.15 J for external inductance 60 nH at 11 kV. Experimental results show that with increasing of external inductance, the maximum neon SXR decreases.

Scenario of a magnetic dynamo and magnetic reconnection in a plasma focus discharge

The paper discusses a possible energy transformation that leads to the acceleration of fast ions and electrons. In plasma-focus discharges that occur during deuterium filling, which have a maximum current of about 1 MA, the accelerated deuterons produce fast fusion neutrons and fast electrons hard X-ray emissions. Their total energy, which is of the order of several kilojoules, can be delivered by the discharge through a magnetic dynamo and self-organization to the ordered plasma structures that are formed in a pinch during the several hundreds of nanoseconds of the pinch implosion, stagnation, and evolution of instabilities. This energy is finally released during the decay of the ordered plasma structures in the volume between the anode face and the umbrella front of the plasma and current sheath in the form of induced electric fields that accelerate fast electrons and ions.

Internal Structure of the Jets from Young Stars Simulated at Plasma Focus Facilities

The laboratory simulations of jets from young stars that have been carried out for many years at plasma focus facilities allow the internal structure of the active regions emerging during the interaction of the jet with the surrounding plasma to be studied in detail. We have found a new wide class of solutions for the equations of ideal magnetohydrodynamics describing the closed axisymmetric stationary flows that are apparently realized in the active regions. Such flows are shown to well reproduce the internal structure of the plasma structures observed in laboratory simulations of astrophysical jets.

Influence of mechanical and plasma shockwaves on the structure and properties of superconductors

The article presents the results of studying the critical temperature, critical current, and field dependencies of superconducting Bi-2223 and MgB2 multilayer tapes after them being subjected to the influence of shock waves generated at the Plasma Focus test bench and mechanical impacts of various intensities. The influence of the specific energy, the number of impacts, the distance of the samples from the plasma anode, the energy of the falling shock mechanism, and the step of moving the impacts was studied. Studies have shown that the critical current Jc can be increased by 50 % in magnetic fields of 2–3 T. In this case, the grains are crushed, compacted, homogenized, and the impurity content changes. The results of microanalysis of superconducting interlayers in the initial state and after influence of shock-wave of plasma show an improvement in the homogeneity of the distribution of the main components (Mg and B) and impurities (C and O).

Damage study and comparison the effects of high-energy pulsed-protons of plasma focus device with low-energy protons of glow discharge plasma of tokamak

This work investigates and compares the effects of high-energy, short-pulsed proton irradiation with low-energy, continuous proton beam on tungsten (W) surface. For this purpose, a W specimen was irradiated in 20 shots of plasma focus device with fluence of 5.2 × 1019 ions m−2, while another specimen was exposed to glow discharge (GD) plasma for 2.5 h with fluence of 2 × 1022 ions m−2. Lee Code was used to obtain the ion beam characteristics produced in the plasma focus device. SEM image was taken from the irradiated specimens before and after irradiation. Small blisters were detected on the surface of W irradiated with high-energy proton pulses, covering the entire surface of W. Larger blisters created by merging the small blisters were also observed. Small cracks were also created at the surface of W irradiated with high-energy ions. At the surface of W irradiated with the GD plasma, very large blisters were observed in the order of a few micrometers. In addition, fuzzy nanostructures can be seen on the W surface, which are grown in the island form. The XRD analysis was used to investigate the effects of radiation on the W crystal structure. Raw samples and samples irradiated with high-energy protons and low-energy protons were analyzed by the XRD. The results showed that the peaks in the XRD pattern of W samples irradiated with high energy protons were shifted to higher angles than those irradiated with low-energy protons. The peak intensity of the samples irradiated with high energy ions has significantly decreased.

Application of dense plasma focus devices and lasers in the radiation material sciences for the goals of inertial fusion beyond ignition

Specimens of materials for prospective use in chambers of nuclear fusion reactors with inertial plasma confinement, namely, W, ODS steels, Eurofer 97 steel, a number of ceramics, etc., have been irradiated by dense plasma focus devices and a laser in the Q-switched mode of operation with a wide range of parameters, including some that noticeably exceeded those expected in reactors. By means of 1-ns laser interferometry and neutron measurements, the characteristics of plasma streams and fast ion beams, as well as the dynamics of their interaction with solid-state targets, have been investigated. 3D profilometry, optical and scanning electron microscopy, atomic emission spectroscopy, X-ray elemental and structural analyses, and precise weighing of specimens before and after irradiation have provided data on the roughening threshold and the susceptibility to damage of the materials under investigation. Analysis of the results, together with numerical modeling, has revealed the important role of shock waves in the damage processes. It has been shown that a so-called integral damage factor may be used only within restricted ranges of the irradiation parameters. It has also been found that in the irradiation regime with well-developed gasdynamic motion of secondary plasma, the overall amount of radiation energy is spent preferentially either on removing large masses of cool matter from the material surface or on heating a small amount of plasma to high temperature (and, consequently, imparting to it a high velocity), depending on the power flux density and characteristics of the pulsed irradiation.

Sensitivity analysis via adjoint Monte Carlo calculations of plasma focus irradiation of micro-silica beads in phantoms

One of the main issues in the analysis of the performances of radiation detectors via Monte Carlo methods is their sensitivity with respect to the various irradiation parameters: source intensity and position, detector effectiveness and sensitivity, etc. In the present work, the capability of a quite new Trueinvivo© micro-silica beads TLD has been analyzed from the point of view of the Monte Carlo modeling of the irradiation process and the possibility of a speed up of the calculations using accurate bias techniques based on the adjoint solution of the transport process. The source considered is a Plasma Focus device explicitly designed for cell cultures or “in vivo” tests. The experimental data and the pure analogic Monte Carlo simulation previously obtained results coming from dosimeters at different depth and positions in a PMMA phantom composed by slabs and built for hosting the TLDs, have been benchmarked with respect to the adjoint bias approach. The results obtained through different biasing techniques, backward particle transport analysis, Weight Windows and a discrete ordinate model solution, show how it is possible to optimize the Monte Carlo calculations with great effectiveness.

The cathode array effects on features and reproducibility of emitted hard x-rays, and anode erosion in a small plasma focus device

Using a small (450 J) Mather-type plasma focus device, this research investigates the effects of cathode rod removal from the cathode array in two steps on hard x-ray emission, both in total and specifically from the plasmoid. The effect on anode rod erosion is also measured. Six hard x-ray detectors were placed around the chamber to measure the emitted hard x-rays. By reducing the number of cathode rods, some features of these hard x-rays such as peak intensity and pulse yield decreased and were deteriorated. Besides, the capability of the device for producing and reproducing the hard x-rays with roughly similar and repeatable characteristics diminished. Moreover, the anode erosion took place during the breakdown phase and by using the detectors around the chamber, similar features were obtained both for the total and the plasmoid hard x-rays, but with different scales. The cathode rod removal could violate the symmetry and uniform formation of the current sheath layer during the breakdown phase and could weaken and change the direction of the Lorentz force vector acting on the current sheath layer during the axial phase. It also causes discharge delay and decreases the axial and radial velocities of the current sheath layer which would result in a weak pinch effect and reduced number of energetic runaway electrons inside the plasma column during the pinch phase. These electrons, by colliding the anode surface, are mainly responsible for producing the great portion of the emitted hard x-ray. On the contrary and based on a different mechanism, the cathode rod removal enhances the number of the runaway electrons during the breakdown phase which increases the anode erosion and enhances the impurities that eventually leads to a weak emission of low intensity hard x-rays.

Study of Soft X-ray Emission from Sahand as Filippov Type Plasma Focus Using Different Cathode Type

Study of Soft X-ray Emission from Sahand as Filippov Type Plasma Focus Using Different Cathode Type