Dense Plasma Focus Device Research Articles

A pulsed neutron source with a sealed dense plasma focus chamber

Compared with other pulsed neutron sources, dense plasma focus (DPF) devices have the advantages of simple in construction, extremely compact and cost-effective. In this paper, a DPF device was developed for used as pulsed neutron source. The Mather-type sealed chamber was adopted for long duration and multishot operations without vacuum system, which is convenient for transport, use and storage. The maximum D-D neutron yield of the device is approximately 1.1 × 109 n/pulse when the storage capacitors are charged with 22 kV and the deuterium gas filling pressure is 750 Pa. The neutron pulse width (FWHM) was measured to be 45 ns ± 10 ns.

Symmetry and structure in the “Generalized Plasma Focus problem”

The “Generalized Plasma Focus problem” refers to a generic class of plasma propagation phenomena that share many features of a dense plasma focus device. Its recent theoretical development has been shown to predict some features of the pinch phase in PF-1000 and POSEIDON. The theory attempts to decompose the plasma propagation problem into two weakly interdependent subproblems. This is achieved by expressing every physical variable of an applicable continuum model of the plasma as the product of a scaling parameter, which contains device-related information and represents its numerical magnitude, and a scaled variable that is devoid of device-related information, is of order unity, and represents the spatiotemporal structure of that variable. The first subproblem seeks a traveling surface of revolution whose local normal velocity equals the scaling parameter for velocity and is aligned with the magnetic force density. Spatiotemporal distributions of all the scaled variables must move along with this reference surface by definition. This paper explores the resulting scaling theory and its symmetry properties. A new coordinate transformation results in a formula for the spatiotemporal distribution of the magnetic field of the curved and non-steady plasma sheath. New insights into the snowplow effect are obtained. A current sheath with a rear boundary exists only when the current is decreasing and only when the current carrying plasma is less dense than the fill gas. The current sheath thickness is the same for small and large devices. The geomagnetic flux compression problem has an exact solution.

The Investigation of Pre-ionization Effect on the Improvement of Pinch Quality and Increased Hard X-ray Radiation in a Dense Plasma Focus (DPF) Device

The Investigation of Pre-ionization Effect on the Improvement of Pinch Quality and Increased Hard X-ray Radiation in a Dense Plasma Focus (DPF) Device

Total neutron emission from deuteron fusion and plasma pinch compression in a medium-sized plasma focus operating with D2 and D2 + Ne gas mixtures—Experimental results

Newly obtained results on hot and dense deuterium and deuterium-neon plasma compression in a z-pinch electrical discharge configuration are presented. The investigated plasma was generated and compressed using 269 high-current discharges in a medium-sized (dense) plasma focus device. The experimental chamber of the device was filled with deuterium and deuterium-neon gas mixtures under constant total mass/density conditions. Magnetic and electric probes, beryllium neutron activation counter, and high-speed four-frame vacuum ultraviolet/soft x-ray pinhole camera were used to study the plasma dynamics and radiation emission. The results obtained experimentally for the first time confirmed clearly a decrease in the minimum radius of plasma columns with an increase in initial neon fraction. Simultaneously, a decrease in the total neutron emission from deuteron fusion was found. The observed plasma/discharge evolution revealed that the classical description of plasma-focus discharges can be approximately correct up to the moment of maximum compression. Including, existence of quasi-equilibrium plasma compression is probable. It is also possible that the homogeneity of plasma columns during the slow compression phase and maximum compression moment increases with the increase in initial neon fraction. The effect of higher stabilization (repeatability) of discharges was confirmed, for higher initial neon fractions. The dependency of the total neutron emission yield on the parameters describing the full discharge dynamics and the maximum discharge voltage was confirmed. The existence of this type of dependency, for a minimum pinch radius is also possible. In contrast, there was little dependency to the total discharge current parameters measured in the collector area.

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.

Focus Fusion: Overview of Progress Towards p-B11 Fusion with the Dense Plasma Focus

LPPFusion is developing a source of fusion energy using the dense plasma focus device and p-B11 fuel, a combination we call Focus Fusion. So far, this project has led to the achievement of the highest confined ion energies of any fusion experiment (> 200 keV) as well as, recently, the lowest impurities of any fusion plasma. Among privately-funded fusion efforts, our experiments have achieved the highest ratio of fusion energy generation to device energy input (wall-plug efficiency) and the highest nτT product of 3.4 × 1020 keV-s/m3. Our calculations and simulations indicate that the quantum magnetic field effect will allow a great reduction in bremsstrahlung radiation with p-B11 fuel. For commercial fusion, this approach has several major advantages. The small size and simplicity of design of the DPF can lead to 5 MW generators that are much cheaper than any existing energy source, that can be manufactured by mass production and that can be located close to loads. It shares with other p-B11 approaches a lack of neutron damage and radioactive waste. Direct energy conversion of the ion beam and x-rays produced by the device avoids the high costs associated with thermal cycles. With adequate, but still modest, financial resources we anticipate working prototype generators could be ready for production by 2026–2030.

Effect of insulator length and fill pressure on filamentation and neutron production in a 4.6 kJ dense plasma focus

Optimization of neutron yields from dense plasma focus devices is a complex multi-faceted challenge that necessitates the prudent selection of mechanical constraints such as the electrode and insulator geometries. Here, the neutron yield is found to significantly depend on the insulator length. As the length of the insulator increases, the exposed anode length traveled by the sheath during the run-down phase decreases. This suggests an increase in the optimal fill pressure with increasing insulator length to maintain the pinch time near peak current. However, in the present study, the opposite trend is observed—the optimal fill pressure for neutron production decreases with increasing insulator length. Optical probing of the sheath from run-down to the pinch reveals significant plasma filamentation with increasing pressure and a dependence of insulator length on filamentation onset. A direct consequence of increased filamentation is a reduction in mass sweeping efficiency, directly quantified as a function of fill pressure for the first time.

Deposition of molybdenum carbide thin films by dense plasma focus device

This work was motivated by the promising physiochemical properties and catalytic activity of molybdenum carbide. Thin films of molybdenum carbide were deposited on the mono-crystalline cubic Si (400) substrate by utilizing a 3.6 kJ dense plasma focus device (Mather-type) with multiple shots. The structure of the films was examined by X-ray diffraction (XRD). XRD results indicated the absence of crystalline film for 5 focus shots, while for increased numbers of focus shots, the emergence of Mo-C peaks in the orientations (120), (014) and (232) confirmed the formation of orthorhombic β-Mo2C polycrystalline films. Moreover, a small variation in the crystallite size was observed by increasing the number of focus shots. The presence of molybdenum and carbon was confirmed by energy-dispersive X-ray (EDX) analysis. Surface morphology was studied under scanning electron microscope (SEM). SEM micrographs revealed non-uniform films with some surface defects such as cracks and craters of micron size, and rough surface. Revealed by the ellipsometry technique, the film thickness increased by increasing the number of focus shots. The electric conductivity, measured by the four-point probe technique, was the highest for 10 focus shots. However, the films have some structural defects, low conductivity and impurities like silicon and silicon carbide, but it was the first ever successful attempt to deposit molybdenum-carbide (Mo2C) thin films using the dense plasma focus device.

Study The Effect of Anode Length on Nitrogen Plasma Pinch Dimensions in NX2 and UNU / ICTP PFF Dense Plasma Focus Devices

Study The Effect of Anode Length on Nitrogen Plasma Pinch Dimensions in NX2 and UNU / ICTP PFF Dense Plasma Focus Devices

Angular Distribution of Ion Beam Emission From Dense Plasma Focus Device: An Investigation by the Vlasov–Maxwell Equations

The Vlasov–Maxwell (VM) equations have been solved by the forward semi-Lagrangian (FSL) method to calculate the argon ion beam angular distribution in the dense plasma focus (DPF) device. The validity of the VM employment was investigated through the Dreicer field, the mean free path, and the Debye length of the plasma pinch. The simulations have shown that the ion beams were emitted in a direct way at the initial pressures of 10 and 20 Pa. The ion beam angular distribution expanded for pressures bigger than 20 Pa. It has been shown that this was because the radial component of the electric field inside the pinch was increased and the axial component of the electric field was decreased by increasing the initial pressure of the working gas. The places of the ion beam micro-sources (hotspots) have been illustrated by means of the ion and electron density profiles.

High energy density pulsed argon plasma synthesized nanostructured tungsten for damage mitigation under fusion relevant energetic he ion irradiation

Tungsten (W) is considered as one of the promising candidates for plasma facing components in fusion reactors since it has high threshold energy, high melting point, low threshold shock resistance, and resistance against formation of co-deposits with tritium. Despite these commendable features, helium ions produced during fusion reaction are known to alter the microstructure of tungsten. In this work, dense plasma focus (DPF) device is used to study the effect of helium ion flux on double forged tungsten samples delivering a heat load of 6.27×104J/m2 per shot. The irradiation of virgin W samples is carried out at 5, 10, and 15 DPF helium shots. High heat loads resulted in blisters and micro-cracks on the sample surface. With an increase in the number of shots, the density of the blisters increased and craters on the W surface burst followed by re-solidification of the melted and sputtered surface. Surface nano-structurization, with nanoparticle formation, of W samples (nano-W) is realized by high-energy argon ion exposure of virgin samples in an argon filled DPF device. The average size of nanoparticles is found to increase with the number of shots and also leads to particle agglomeration. At 10 shots, uniformly distributed highly dense nanoparticles of 20–50 nm size have been synthesized. The nano-W samples are then irradiated by instability-accelerated high-energy helium ions in helium filled DPF device for 5, 10, and 15 shots to simulate fusion relevant conditions. The presence of the trapped helium bubbles in virgin-W and nano-W are examined by BSE imaging and XRD, respectively. The nanostructured tungsten shows improved structure and surface properties against Helium ion irradiation.

Computation of Impurity Effects on Argon Pinch Soft X-Ray Emission Using the Nonrelativistic 4-D Vlasov–Maxwell Approach

In this article, the Vlasov–Maxwell equations have been integrated by the forward semi-Lagrangian method to compute the soft X-ray (SXR) emission from a dense plasma focus device filled with pure and impure argon. The impurity has been assumed as copper of which the electrodes were made. The results have shown that, in the case of pure argon, the emission power reached up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5 \times 10^{9}{\mathrm {W}}$ </tex-math></inline-formula> . However, for the impurity with a 10% volumetric fraction and with the effective charge number of 10, the emission power reduced to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 10^{5}{\mathrm {W}}$ </tex-math></inline-formula> . With the further increase in the impurity amount, the emission power reduced again. However, if the impurity charge number is close to the pure gas charge number, the attenuation of the SXR emission decreases.

Effect of Atomic Number on Plasma Pinch Properties and Radiative Emissions

The aim of the research is to examine the dependence of plasma pinch properties and radiation emissions on the atomic number of the operating gas within the dense plasma focus device (NX2) when using hydrogen and argon gases. Simulation was performed with Lee’s code on an NX2 dense plasma focus at a constant gas pressure value ( P 0 = 0.5 torr ). The results showed that the minimum radius of the plasma focus in the case of the hydrogen plasma pinch was 0.30 cm and in the case of the argon plasma pinch 0.17 cm, and this affected the value of the radiation emission as it was 7.8 × 10 − 6 J and 11 J for the hydrogen and argon pinch, respectively. The energy of the ion beam released by the breakdown of the plasma pinch was found as E n = 23.8 J in the state of hydrogen and E n = 105 J in the state of argon.

Bilayer of zirconium oxide/lanthanum oxide high-κ dielectric fabricated for metal-oxide-semiconductor nano-electronic device applications

This study reports the fabrication of zirconium oxide (ZrO2)/lanthanum oxide (La2O3) bilayer on silicon substrates using the ions generated in a modified dense plasma focus device. Both ZrO2 and La2O3 are fabricated using one burst of focused plasma each on substrates kept at a distance of 4.0 cm from top of the anode. The as-deposited bilayer is further annealed to study the effect of annealing on the characteristics of the bilayer. The bilayer is found to have uniform morphology as obtained in scanning electron microscopy and atomic force microscopy results. The uniformity of bilayer is found to improve upon annealing. These as-deposited and annealed bilayers are electrically characterized through current-voltage and capacitance-voltage measurements in a metal–oxide-semiconductor (MOS) capacitor configuration. The leakage current density and capacitance density of MOS capacitors fabricated on as-deposited and annealed bilayers, respectively are ~2.89 × 10−10 A/cm2 and ~7.23 × 10−12 A/cm2 at 1 V and ~2.18 µF/cm2 and ~2.72 µF/cm2. Conduction mechanism of MOS capacitor is field/tunnel emission and Schottky emission at low and high electric field, respectively. The annealed bilayers are found to possess improved morphological and electrical properties making them suitable candidate for future nano-electronic device applications.

A Theoretical Verification to Enhancing Effect of Ferrites on Magnetic Field and Line Radiation of a Dense Plasma Focus Device

In this work, the effects of ferrites on the generated magnetic field as well as the emitted line radiation in a dense plasma focus device have been theoretically investigated. The computations have been performed using a magnetic field calculation method represented in the modified Lee model. The results have shown that the ferrite magnetization contributes to the uniformity of the total magnetic field. The derived equations showed linear dependence of the average magnetic field on the ferrite susceptibility. Also, with including the maximum inductance of the device in the line radiation formula, it has been seen that the line power relates to the susceptibility in a linear manner.

Broad-energy oxygen ion implantation controlled magnetization dynamics in CoFeTaZr

In this paper, a novel pulsed broad energy spectrum ion-implantation technique, using the dense plasma focus device (DPF), for uniform oxygen-ion doping along the thickness of a ~250 nm thick magnetic CoFeTaZr layer is investigated. A new operational regime of the dense plasma focus – the off-focus mode – is explored to avoid the surface damage of the exposed sample by the high energy plasma streams/jets and instability accelerated ions, typically observed in conventional efficient-focus mode operation. The faraday cup measurements shows the increase in ion fluence from 3.83 × 1013 ion/cm2 for efficient-focus mode to 8.76 × 1013 ion/cm2 for off-focused mode operation in the broad-ion-energy range of 1–100 keV. The x-ray photoelectron spectroscopy (XPS) of the unexposed sample shows the presence of Co in Co0, Co2+ and Co3+, Fe in Fe0, Fe2+ and Fe3+, and Ta in Ta0 and Ta2+ oxidation states while Zr was observed with only metallic Zr binding energy peaks indicating the surface oxidation of the unexposed sample. The exposure to oxygen plasma in DPF device led to the increase in the higher oxidation states of Co, Fe and Ta with reduction in metallic binding energy peak and the deconvolution of oxygen XPS spectrum confirmed the bonding of oxygen to Co, Fe and Ta. The magnetization dynamics of unexposed and oxygen-ion doped samples was studied using magnetoimpedance measurements in the 1–2.5 GHz frequency range. Gilbert’s damping factor, in-plane anisotropy and effective magnetization of the magnetic substrate were calculated and it is found that these properties can be modulated with a lighter ion dosage using this novel pulsed broad-energy-ion implantation technique. It is concluded that the off-focus mode DPF operation can provide the ions of required energy and fluence to implant oxygen ions across the thickness of the CoFeTaZr magnetic thin film to modulate its magnetic properties.

Plasma processed tungsten for fusion reactor first-wall material

Tungsten is one of the prime candidates for a first-wall material near the divertor area due to its high temperature strength, high thermal conductivity, low erosion rate and low tritium retention. The erosion resistance of tungsten to the edge plasmas and transient events are carefully investigated in a simulated fusion environment. Here, we use the dense plasma focus (DPF) device operated in a D2 as a source for pulsed fusion plasma. The tungsten (α-W) substrates with a preferential growth direction along (110) plane were used. These pristine-W samples were nanostructurized using a (i) low-temperature continuous nitrogen RF plasma system and (ii) coated with 60 nm tungsten film, using high-temperature argon plasma in a dense plasma focus (DPF) device. The low- temperature plasma treatment created mesh-like porous nanostructure on the surface of pristine-W with change in crystalline orientation to (200), while the DPF-based deposition resulted in a nanocrystal (30–50 nm) decorated surface with enhanced (200) orientation. The crack propagation and bubble formation during DPF D2 plasma exposure were significantly controlled by the surface modification of tungsten. The mesh-like structure was modified to form loosely bound spherical nanoparticles, while the nanocrystals remained tightly bound and grew in size with D2 plasma exposure. The better adhesion of the nanocrystals and controlled growth along the (200) direction resulted in least change in hardness measurements for the nanocrystal decorated samples. Thus, nanocrystal decoration of tungsten with a preferential growth direction of (200) can help reduce the fusion-induced damage in first-wall materials.

Dynamics of ion beam emission in a low pressure plasma focus device

The plasma that accelerates and compresses in the formation of the pinch in dense plasma focus devices has been found to be an abundant source of multiple radiations like ion beams and x-rays. In this work, the ion beam and x-ray emissions from a 2.7 kJ (13.5 kV, 30 µF) plasma focus device operated at pressure below 1 mbar were investigated. The time profile of the ion beam emission was analysed from the simultaneously measured ion beam, soft and hard x-ray signals using biased ion collectors, BPX 65 silicon PIN diode and a scintillator-photomultiplier tube assembly. Time resolved analysis of the emissions revealed that the emission of the ion beam corresponded to several different pinching instances. Two components of the ion beam were identified. An ion beam of lower energy but higher intensity was emitted followed by an ion beam of higher energy but lower intensity in the first plasma pinch. The ion beam emitted from the first plasma pinch also has higher energy than subsequent plasma pinches. The emission was found to be associated with the amplitude of voltage spike. The results from ion beam and electron beams suggest that they were emitted by the same localized electric field induced in the pinched plasma. The strongest plasma focus discharge indicated by sharp voltage spike of high amplitude and highest ion beam energy were both observed at 0.2 mbar. The average energy of the ion beam obtained is (53 ± 13) keV. At this optimum condition, the ions beam with the highest energy also led to the highest hard x-ray emission.

A Theoretical Study of the Possibility of Obtaining the Radioisotope 13N for Medical Applications Using Dense Plasma Focus Device

The aim of this research is to study the possibility of obtaining the short-lived radioisotope 13N by colliding with a deuterium ion beam emitted by an NX2 dense plasma focus device with a graphite target, as a technique alternative to the traditional technique for getting short-lived radioisotope (SLR) accelerators. Lee code was used to study the properties of the plasma pinch, which is the source of deuterium ion beams. Then, a function of distributing the beam energy and stopping power was found within the graphite using SRIM program. The reaction cross-section was also found from an EXFOR database and the radiative yield of the reaction was calculated. The radioactivity of 13N was calculated and found to be equal to A = 4.14×103 Bq. The effect of the change in deuterium gas pressure on the radioactivity was studied and it was found that the best value for the pressure is 3 Torr, where the number of deuterium ions is the greatest amounting to 3.12×1011 ions and thus the radioactivity increased to 5.616 ×103 Bq. The effects of repetition rate of the studied dense plasma focus device and the exposure time of the graphite target to deuterium ions were studied. The radioactivity was calculated at repetition rates (1,5,10,16 ) Hz and exposure times (30,60,600) sec., where we noticed an increase in the value of radioactivity at a repetition rate of 16 Hz and an exposure time of 600 sec., reaching to 28791 × 103 Bq. To obtain a radioactivity value for 13N suitable for use in PET technique, the radioactivity value was calculated at high repetition rates (50,100,500) Hz and exposure times (30,60,600) sec. We obtained the value of radioactivity 527 ×106 Bq at a repetition rate of 500 Hz and an exposure time of 300 sec. and this value is suitable for use in PET technique. However, there are technical difficulties in the studied dense plasma focus device to obtain a high repetition rate of this value. The radioactivity of 13N was calculated at very high times of exposure of the graphite target to deuterium ions (1000, 1500, 2000, 2500, 3000) sec. at the repetition rates of the device studied. The highest radioactivity value obtained was 55.79 ×106 Bq at an exposure time of 3000 sec. and this value is less than the required value for the required use in PET technique. Keywords: Dense plasma focus device NX2, Lee code, Radioactivity.

Charged particles and x-ray emission studies on a dense plasma focus device

The emission of charged particles, electron and ion beams, and radiation, soft and hard x-rays, from the pinching plasma have been investigated in the UofS-I dense plasma focus (DPF) device. The UofS-I DPF is in a Mather-type configuration, powered by a 2 kJ, 25 kV-charged capacitor bank, operated with 10–20 mTorr argon gas. The charged particles have been recorded using a Faraday cup for ion beam collection, and a charge collector and a Rogowski coil for the electron beam measurement. Moreover, the soft and hard x-rays have been detected using a BPX-65, filtered silicon PIN photodiode and a scintillator, respectively. The time delays of signals with respect to the pinch time have been compared. Strong correlations of the charged particles and the x-ray emission intensities with the voltage peak and current dip have been observed, and consequently indicate their dependence on the anode voltage and strength of pinching of plasma.