Plasma Focus Research Articles

On the failure of neutron yield scaling in the dense plasma focus

The observed scaling of neutron yield in the dense plasma focus (DPF) as the fourth power of the current in the plasma was the principal driver of the growth of DPF research in its early days. Subsequent discovery of failure of this scaling law was also the principal reason for its abandonment by major laboratories. Attempts to understand this failure of scaling have so far been inconclusive. This Letter looks at this failure in the context of the recently introduced the Generalized Plasma Focus problem and suggests a possible reason that can be experimentally examined using small plasma focus devices. This involves restrictions placed on the drive parameter by conservation laws for mass, momentum, and energy. A suggested empirical workaround to the problem of neutron yield scaling failure could also be configured as a method for increasing the pressure range for neutron emission in small DPF devices.

First exploratory survey of poloidal magnetic flux emission from a dense plasma focus

Studies of neutron emission from a dense plasma focus suggest that a significant fraction of neutron emission in some shots is caused by fast deuterons that have a prominent azimuthal component of motion. Recent examples are observations of long-lasting neutron emission in the side-on direction in PF-1000 and of neutron flux asymmetry (end/side) less than unity in Gemini. Such azimuthal motion of deuterons indicates the presence of an azimuthal electric field that accelerates them and a poloidal magnetic field that keeps them within the zone of acceleration. This in turn must be accompanied by poloidal magnetic flux emission (PMFE) from the plasma focus. Recently, a diagnostic technique for detection of PMFE has been proposed and demonstrated. This paper presents results of its successful replication and the first ever exploratory survey of PMFE emission using the UNU-ICTP plasma focus at the Nanyang Technological University, Singapore.

Effect of anode shape on neutron and x-ray emission in dense plasma focus

The neutron and x-ray production is investigated in various pulse-power devices for a deeper understanding of the ion and electron acceleration mechanisms and the application of pulsed neutron sources. We present the extensive results from an anode shape experiment carried out on the PFZ-200 plasma focus device. The various shapes of anodes were tested, including cylinders, tapers, or rounded tips. The experimental shots with a peak current above 200 kA were performed in pure deuterium working gas at 280–600 Pa pressure to obtain maximal neutron yield for each anode shape. The average neutron yields are in the range of (1–2) ×108 neutrons/shot. Outstanding findings about x-ray emission were obtained with the group of tapered anode tips. Using the scintillation detectors shielded by 5 cm thick lead bricks, we obtained the hard x-ray signals with photons exceeding 600 keV energy. Such relatively high x-ray energy indicates the optimized conditions for electron and ion acceleration. At the same time, the individual shots have been well reproducible. Therefore, we were able to study plasma dynamics with the schlieren images taken at different times at different shots.

Investigation of the Plasma Current Sheath Dynamics in the Run Down Phase of the Hemispherical Plasma Focus Devices Using Two-Dimensional Time Dependent Modeling

Investigation of the Plasma Current Sheath Dynamics in the Run Down Phase of the Hemispherical Plasma Focus Devices Using Two-Dimensional Time Dependent Modeling

Role of surface morphological parameters on wettability of obliquely deposited Cu thin films in a plasma focus device

Role of surface morphological parameters on wettability of obliquely deposited Cu thin films in a plasma focus device

Filamentary-like structures of plasma in a small 3-kJ dense plasma-focus discharge in pure deuterium

Filament-like structures were observed during discharges in a small 3-kJ plasma focus device operated with pure deuterium. These structures were recorded by means of two different laser diagnostic techniques: a schlieren system and a differential laser interferometry. They present the novel fine-scale (submillimeter) plasma structures recorded during the radial implosion, at the pinch stagnation, at the development of instabilities, and during a decay of the dense plasma column, when hard x-rays and fusion-produced neutrons were generated. The temporal uncertainty of these observations was about 2 ns, and the spatial one amounted to 40 μm. The filamentation seems be a natural and spontaneous process which occurs in high-current, hot, and dense plasmas produced in plasma focus devices. The observed filaments have usually longitudinal and/or azimuthal orientations. Their higher plasma density and appearance in regions of the measured and assumed current flows can be interpreted as the formation of plasma-current filaments with concentrated magnetic energy. These filamentary effects should be studied due to their possible role during the evolution of instabilities and the formation of small sources emitting fast electrons and ions.

Measurement of Ion Energy Distribution Function of Fast Plasma Flow Driven by Plasma Focus Device Using Retarding Field Energy Analyzer

To understand the mechanism of particle acceleration in collisionless shocks, generating a collisionless plasma flowing through dilute gas is required. We have proposed a compact plasma focus (CPF) device to generate collisionless plasma by using pulsed-power discharge. To discuss a particle acceleration process in collisionless shocks, it is necessary to evaluate an ion energy distribution function (IEDF) of the plasma. In this study, we measured the IEDF of the plasma flow using a retarding field energy analyzer (RFA). The experimental results measured by the RFA showed that ions with a few eV are dominant in the plasma flow generated by the CPF device. The IEDF could be fitted with the shifted Maxwellian distribution. The plasma parameters were estimated to be the ion number density ni = 4.6+−00..28 × 1019 m−3, the ion temperature Ti = 0.8+−00..64 eV, and the drift velocity vd = 11+−03..55 km/s. The estimated velocity approximately agreed with the result of a time-of-flight method calculated by the ion current waveform.

Deposition of tungsten in methane atmosphere using a low energy plasma focus device

Deposition of tungsten in methane atmosphere was performed using a low energy plasma focus device. The resulting compounds were synthesized and investigated during the deposition process. Carbon-rich contamination was identified as an organic viscous liquid crystal defect. Tungsten carbide (W2C) and dark-black oxygen-deficient tungsten trioxide (WO3-x) thin films were synthesized by plasma focus device using different number of focused shots. The synthesis of each thin film, which was dependent upon operation of plasma focus device was verified and discussed. Tungsten carbide W2C was synthesized during the deposition process while the dark-black WO3-x was created after the deposition process in atmosphere. All compounds were investigated by spectroscopy, crystalline, and microscopy methods. Nano indentation test disclosed higher value of hardness for the film containing tungsten carbide compound (10.01 GPa) compared to both pure tungsten (5.72 GPa) and the dark-black WO3-x thin film (6.83 GPa). The verified band gap energy of dark-black WO3-x was around 1.475 eV.

Sn/Pb ratio variation in spherical structures deposited on silicon surface using plasma focus

The deposition of Sn and Pb elements on top of Si surface was realized using plasma focus device. Due to the special characteristic of this type of plasma, the silicon substrate is heated by the bombardment of plasma ions, before the deposition of these elements sputtered from the anode. The deposition of the two elements was found to be influenced by substrate-anode distance as a consequence of surface heating. It was found that the relative amounts between the two deposited elements was not the same as their original ratio in the anode before sputtering. The ratio between Sn and Pb varies with increasing depth into the SnPb deposited on the Si substrate. Additionally, the size of micro spherical structures formed on the surface affected the ratio of the two deposited elements. The variation of the ratio is explained as result of deposition/evaporation competition influenced by the surface heating.

Formation of Surface Microcracks and Ejection of Particles into a Vacuum under Irradiation of an Aluminum–Magnesium Alloy in the Vikhr’ Plasma Focus Setup

Formation of Surface Microcracks and Ejection of Particles into a Vacuum under Irradiation of an Aluminum–Magnesium Alloy in the Vikhr’ Plasma Focus Setup

Focusing and reduction of correlated energy spread of chirped electron beams in passive plasma lens

All-optical compact plasma focusing and transportation of electron beams, in the passive mode of a plasma lens, is studied via real geometry particle-in-cell simulations for its suitability for the laser wakefield acceleration technique. The focusing of an electron beam by a passive plasma lens is a non-linear and dynamic process, which strongly depends on the space charge induced evacuation of the plasma electrons in the vicinity of the propagating electron beam. Effects of such focusing on the energy spread, divergence, and emittance of laser-driven electron beams are analyzed numerically for different plasma densities. An initially negative chirp in electron beam energy is shown to be instrumental in suppressing the unwanted growth in the relative energy spread of the electron beam during the passive lensing. Usefulness of such a passive plasma element for a single and multi-stage laser wakefield acceleration configuration is demonstrated.

Dependence of Soft X-Ray Yield on Plasma Focus Parameters and Its Kinetic and Magnetic Pressures

Dependence of Soft X-Ray Yield on Plasma Focus Parameters and Its Kinetic and Magnetic Pressures

Operation of Plasma Focus Chamber as a Part of a Subkilojoule Pulsed Neutron Generator

Operation of Plasma Focus Chamber as a Part of a Subkilojoule Pulsed Neutron Generator

Liquid biopsy-informed precision oncology study to evaluate utility of plasma genomic profiling for therapy selection.

TPS1616 Background: Liquid biopsies have enabled a transformation in the management of patients with cancer as they have the potential to detect, characterize, and monitor tumor burden. However, the increasing complexity involved in the integration of genomic data into clinical practice has presented challenges with the practical implementation of liquid biopsies in clinical cancer care. To address these challenges, multidisciplinary teams comprised of experts within oncology, genetics, pathology, and informatics have created Molecular Tumor Boards (MTBs), which can improve clinical outcomes for cancer patients by efficiently utilizing the technologies created by the rapidly expanding precision oncology industry. Nevertheless, there remains a gap in the optimal implementation and interpretation of these diagnostic findings to maximize patient outcomes and access to standard of care therapies and clinical trials. Methods: We instigated a prospective observational liquid biopsy-informed precision oncology study, in which patients with metastatic solid tumors will be matched with genotype-driven therapies via serial liquid biopsies (NCT05585684). Liquid biopsy-derived genotypes will be generated through a clinical NGS assay (PGDX Plasma Focus) and will be annotated by an automated ensemble approach for variant actionability assessment, developed by the Johns Hopkins MTB, followed by a treatment recommendation. Key eligibility criteria include patients ≥18 years old, with ECOG performance status of 0-1 and with metastatic disease that have relapsed or progressed after standard of care first-line therapies or patients for which first-line standard of care therapeutic options are not expected to yield a clinical response. The primary objectives of the trial focus on feasibility of the approach and evaluating the fraction of patients with actionable mutations, for which the MTB recommendation is enacted upon. Unique to this study, a recommendation to not pursue genotype-targeted therapy is equally considered for personalized clinical decision making. Secondary objectives are to investigate whether enacting upon MTB recommendations improves progression-free and overall survival and perform a comparative analysis with tumor-based NGS. Exploratory objectives are to determine if serial molecular profiling after initiation of systemic treatment is sufficient to determine therapeutic response, compare with RECIST radiographic response and determine whether changes in liquid biopsy dynamics correlate with progression-free and overall survival. This study will enroll 150 patients with solid tumors, including lung, esophageal, breast, and head and neck cancer and mesothelioma to evaluate the clinical utility of liquid biopsy genomic profiling. Patient accrual for this study initiated in February 2023. Clinical trial information: NCT05585684 .

Development of a portable pulsed fast ⩾106 neutron generator based on a flexible miniature plasma focus tube

A plasma focus device is a laboratory fusion device that is used to produce pulsed neutrons for a few tens of ns duration. A compact plasma focus tube (volume ≈ 130 cm3) has been developed, and this was connected to a newly developed capacitor bank using 24 coaxial cables, each 10 m long. The capacitor bank was of compact size and consisted of four energy storage capacitors (each 6 µF, 20 kV, size: 20 cm × 20 cm × 30 cm). The peak discharge current of the capacitor bank was estimated to be 176 kA with a rise time of around 3.6 µs at maximum 4.8 kJ operation energy. The average neutron yield was observed to be maximum (3.1 ± 1.0) × 106 neutrons/pulse with a pulse duration of 15–25 ns at an operating energy of 2.7 kJ (15 kV) and deuterium gas filling pressure of 4 mbar. Long coaxial cables allow only the plasma focus head (neutron source) to be moved as per need, making this a portable pulsed neutron source that is useful in many applications, including in extreme conditions, such as in borehole logging applications for oil and mineral mapping. This report describes the various components of this portable neutron generator together with its neutron emission characteristics.

Ion beam analysis of W irradiated with deuterium-based plasma discharges at PF-1000U

Plasma focus devices generate discharges with dense hot plasma (HP) flows and fast ion streams (FIS) with energies up to several MeV, enabling their use to test materials for nuclear fusion applications. Tungsten plates were exposed to deuterium and to mixed deuterium-helium plasmas at distinct power flux densities at the large PF-1000U device. Elemental modifications as the induced deuterium retention and co-deposition of impurities at the target surfaces were studied by scanning electron microscopy and, particularly, by ion beam analysis (IBA). The results evidence that typically, deuterium retention is enhanced during the first discharges and may decreases afterwards due to surface erosion. Additionally, by adding helium to the working gas to generate the plasmas, deuterium retention increase. Similar results may be achieved by decreasing incident flux densities. The experiment highlights the role of the use of IBA to quantify elemental modifications imposed by irradiation of materials in plasma focus facilities.

Decomposition of SF6 by a plasma focus device

Decomposition of SF6 by a low energy plasma focus (PF) device has been investigated. The PF device performance in SF6 atmosphere was weaker than other gases such as argon, methane and nitrogen. Tungsten and vanadium anode tips were employed to generate thin layers of deposited products on substrates with different number of focused shots in SF6 atmosphere. The proper choice of the anode tip and substrate material has a direct effect on SF6 decomposition and generation of desire products. Free fluorine atoms and ions are produced during discharges that react with housing chamber and corrode the device materials such as Pyrex insulator, 304 stainless steel chamber and many more. Field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX), grazing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS) were utilized to identify the deposited solid film products.

DPF-produced TiN coatings on NiTi: biological and mechanical properties

One of the best ways to obtain TiN coatings is through the nitriding process by efficient methods such as dense plasma focus (DPF). The gas composition of the nitrogen environment is a crucial factor affecting the properties of the coating. In this study, three different atmospheres of 100%N2, 50%N2–50%O2, and 75%N2–25%Ar were used to investigate their impact on the mechanical and biological properties of TiN coatings on NiTi substrate. The operating condition that yielded the coating with the highest hardness, as well as the lowest contact angle and Ni ion release, was chosen as the optimum condition. According to the XRD results, TiN was recognized as the dominant phase which causes high hardness and prevents Ni ion release. Moreover, surface analyses determined that the sample coated in 50%N2 composition possessed higher hardness and as a result displayed better mechanical properties. Also, the improved microstructural properties lead to an enhanced coating/substrate adhesion strength. On the other hand, the reaction of TiO2 and TiN lead to the formation of TiN0.6O0.4 ternary compound and for this reason, the 50%N2–50%O2 sample exhibited better performance in preventing the release of the toxic nickel ion compared to the other samples. Finally, due to the presence of TiO2 and TiN0.6O0.4 in the sample surface treated at 50%N2–50%O2, better hydrophilicity was observed compared to other samples. Results confirm that the applied surface modification method is effective in increasing the mechanical and biological properties of the NiTi, where it may open numerous possibilities for efficient use in orthopedic applications.

Erratum: “The generalized plasma focus problem and its application to space propulsion” [Phys. Plasmas 30, 043109 (2023)

Erratum: “The generalized plasma focus problem and its application to space propulsion” [Phys. Plasmas 30, 043109 (2023)

Use of a plasma focus device to study pulsed x-ray effects on peripheral blood lymphocytes: Analysis of chromosome aberrations

X-ray pulses (full width at half maximum ∼ 90 ns, dose rate ∼ 107 Gy s−1) were used to irradiate the monolayer of peripheral blood mononucleated cells using the PF-2kJ kilojoule plasma focus device. Four different exposure conditions were evaluated using 5, 10, 20, and 40 pulses, with the mean dose measured by TLD-100 being 0.12 ± 0.02 mGy, 0.14 ± 0.03 mGy, 0.22 ± 0.06 mGy, and 0.47 ± 0.09 mGy, respectively. Cytogenetic analysis showed an increase in all types of chromosomal aberrations following exposure to x-ray pulses. The distribution of dicentrics and centric rings was overdispersed after 5, 10, 20, and 40 pulses. Additionally, after 20 and 40 pulses, the presence of tricentric chromosomes is detected. Chromosome aberration frequencies found in this study were always higher than the estimated frequencies of chromosome aberrations using published dose–effect curves for conventional radiation sources. The overdispersion observed, the elevated maximum relative biological effectiveness (RBEM) and the presence of tricentric chromosomes at the relatively low doses of exposure (<0.5 Gy) seem to indicate that low doses of pulsed x-rays of low energy show similar biological effects as those observed for high-LET radiation. X-ray pulses emitted by PF-2kJ were found to be more efficient in inducing chromosome aberrations, even more than α particles.