kJ Mather-type Plasma Focus Research Articles

Effect of anode shape on correlation of neutron emission with pinch energy for a 2.7kJ Mather-type plasma focus device

Correlation of neutron emission with pinch energy for a Mather-type plasma focus energized by a single capacitor 12.5μF, 21kV (2.7kJ) is investigated by employing time resolved and time integrated detectors for two different anode shapes. The maximum average neutron yield of about 1.3×108 per shot is recorded with cylindrical anode, that increases to 1.6×108 per shot for tapered anode. At optimum pressure the input energy converted to pinch energy is about 24% for cylindrical anode as compared to 36% for tapered anode. It is found that the tapered anode enhances neutron flux about 25±5% both in axial and radial directions and also broadens the pressure range for neutron emission as well as pinch energy. The neutron yield and optimum gas filling pressures are found strongly dependent on the anode shape.

Preparation of silicon carbide film by a plasma focus device

Silicon carbide (SiC) films were grown on the silicon (100) substrate by a 20 kJ Mather-type dense plasma focus device. The preparation method and characterization data are presented. X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (SEM) and nano-indentor were employed for the characterization of the samples obtained at different axial position of 50 mm, 90 mm, 130 mm and 170 mm, respectively. Polycrystalline 3C SiC were obtained at the position of 90 mm and 130 mm from XRD and FTIR spectra. SEM image showed that the silicon carbide films obtained at the position of 90 mm are porous on surface layer. Nano-indentor indicates that the film obtained at the position of 130 mm has the highest mechanical hardness.

Deposition of titanium nitride on AISI-304 in a plasma focus environment

Polycrystalline, smooth, and hard thin films of TiN are successfully deposited on AISI-304 substrates using a 1.5 kJ Mather-type dense plasma focus device charged at 18 kV. The purpose of this study is to investigate the structural and mechanical properties of the TiN thin films in terms of ion dose and substrate position to establish the optimum deposition conditions. The films are analyzed using XRD, SEM, electron microprobe and micro-hardness testing. XRD confirms the deposition of a polycrystalline TiN thin film together with the emergence of an iron chromium nickel phase. The surface hardness-in comparison to the unexposed substrate-is found to increase up to 250% when a film is deposited using 30 focus shots at an axial distance of 6 cm. SEM micrographs show that the quality of the film is improved with an increasing number of focus shots. The constituent elements of the film are also confirmed by electron microprobe.

The correlation of x-ray emission with pinch energy in a 1.5 kJ plasma focus

Correlation of x-ray emission with pinch energy from a 1.5 kJ Mather-type plasma focus device for Ag and Sn inserts at the Cu tapered anode tip is reported. The space and time resolved x-ray emission characteristics are investigated by using a simple pinhole camera with appropriate filters and a multichannel pin-diode spectrometer. High voltage probe and Rogowski coil signals are used to estimate the pinch energy. At optimum conditions, the maximum x-ray yield in 4π-geometry is found to be 9 and 8 J/shot with efficiency of 0.6% and 0.5% for Sn and Ag inserted anodes. This is despite the fact that input energy converted to pinch energy is lower at 8% for Sn insert compared with 15% for the Ag insert. An increase in x-ray yield with an increase in pinch energy is observed for Sn as well as Ag. Pinhole images reveal that x-rays of energy less than 5 keV are emitted from the focus region and the high-energy x-rays are emanated from the anode tip.

X-ray emission scaling law from a plasma focus with different anode tip materials (Cu, Mo, and W)

X-ray emission from a 2.3–5.3kJ Mather-type plasma focus [Phys. Fluids 7, 5 (1964)] employing copper, molybdenum, and tungsten anode tip is studied. Argon is used as a working gas. Characteristic CuKα and Mo K-series emission and their ratio to the continuous x-rays are determined. From the variation of the x-ray yield data with filling pressure at different charging voltages, scaling laws are obtained. X-ray pinhole images demonstrate that a significant amount of x-ray emission is from the anode tip. The comparison of the ratio of characteristic to continuum radiation for copper anode with typical x-ray tube data reveals that the contribution of very high energy electron beam from the focus region for x-ray generation through thick target bremsstrahlung mechanism is not significant. Rather, electrons with energy of the order of, or even less than, the charging voltage are responsible for bulk of the x-ray emission.

Short circuit tests on a 150 kJ, 1 Hz repetitive Plasma Focus

This work presents the results of short circuit tests recently conducted on PFMA1 [1], a 150 kJ Mather-type Plasma Focus [2] designed to run at a repetition rate of 1 Hz for two hours at a time. PFMA1 is operated at 30 kV, with a 350 µF capacitor bank of 32 parallel capacitors. It is equipped with a custom designed fast high-voltage capacitive probe, a Rogowski coil [3] to monitor the total current flowing from the capacitor bank, and a breakdown time jitter analyzer. The short-circuit tests are conducted at 12 ÷ 13 kV. Snowplow-type 2D simulations [4] predict a peak of approximately 1.5 MA for the total current at a filling pressure of 10 Torr of deuterium. In this work a description of PFMA1 will be given, together with analytical computations of the inductance of the device; these computations will be compared with the results from a 2D finite element model in cylindrical symmetry. A full description of the electrical diagnostics used in the experiments will be provided. Experimental results will be presented and discussed, and will be compared with those obtained theoretically. Agreement is found to be very good.

Characteristics of FeCo nano-particles synthesized using plasma focus

In our recent investigation, a 3.3 kJ Mather type plasma focus was used to synthesize FeCo nano-particles. The tops of the anodes normally used were replaced by the materials to be synthesized using different numbers of focus shots. It is observed that the characteristics of the nano-particles depend not only on the numbers of focus shots but also on the angular position of the mounted sample. SEM results show that the size of the nano-particles is smaller when the sample is mounted at a bigger angular position. The size of the particles increases linearly with the increase in the number of focus shots. EDX shows that the FeCo nano-particles are stoichiometric. The magnetic properties measured using a vibrating sample magnetometer identify the soft magnetic nature of the FeCo nano-particles. The saturation magnetization has been found to increase in samples prepared with a higher number of focus shots using repetitive plasma focus NX2.

Nano-structured Fe thin film deposition using plasma focus device

This paper reports the deposition of nano-structured Fe thin films using 3.3 kJ Mather-type plasma focus. The conventional hollow copper anode was replaced by anode fitted with solid Fe top and the deposition was done using different numbers of deposition shots at two different angular positions. Scanning Electron Microscopy shows that the size of nano-phase agglomerate is smaller when the sample is deposited using either lesser number of deposition shots or at higher angular position with respect to anode axis. X-ray Diffraction shows that crystal structure characteristics change with increase in number of deposition shots. Measurements of magnetic properties using Vibrating Sample Magnetometer identify intermediate magnetization and coercivity in Fe thin films deposited at smaller angular position with respect to anode axis. It is concluded that the morphological, structural and magnetic characteristics of Fe thin films deposited using plasma focus device depend not only on the number of focus deposition shots but also on the angular position of the sample.

Enhancement of X-ray emission in the side on direction in a Mather-type plasma focus

A 1.8 kJ Mather-type plasma focus (PF) for argon and hydrogen filling is examined. Two anode configurations are used. One is tapered towards the anode face, and the other is cylindrical but the face is cut at different angles. At optimum conditions, the system is found to emit Cu–Kα X-rays of about 1.6±0.1 J/sr in the side-on direction for argon filling, which is about 32% of the total X-ray emission. In 4π-geometry, maximum total X-ray yield and wall plug efficiency found are 26.4±1.3 J and 1.5± 0.1% respectively. The modified geometry may help to use the PF as a radiation source for X-ray diffraction.

The heating of plasma focus electrodes

Plasma focus (PF) technology development today is strictly related to the possibility of a high frequency repetitive working regime. One of the more relevant obstacles to this goal is the heating of structural components due to direct interaction with plasma. In this paper, temperature decay measurements of the inner electrode of a 7 kJ Mather type PF are presented. Data from several series of shots at different bank energies are analysed and compared with theoretical and numerical models. Two possible scale laws are derived from the experimental data to correlate thermal deposition with bank energy. It is found that a fraction of about 10% of total energy is released to the inner electrode. Finally, after some considerations about the cooling and heating mechanisms, an analysis on maximum temperature sustained by materials is presented.

Generation of Deuteron Beam from the Plasma Focus

The generation of deuteron beam from a 3 kJ Mather type plasma focus is studied. Two simple ion collectors made of copper plates are employed and are placed at the axis of the electrodes to detect the ion beam. The deuteron beam intensity at various deuterium gas pressures is determined together with ion beam energy using the time of flight method. For a series of discharges of the present plasma focus system operated at 15 kV discharge voltage, ion beams of energies ranging from 50 to 200 keV have been measured. The suitable deuterium filling pressure for ion beam production for electrodes lengths of 16 cm, 22 cm and 27 cm are 1 mbar, 0.7 mbar and 0.5 mbar respectively.

Spectral study of the electron beam emitted from a 3 kJ plasma focus

In a 3 kJ Mather-type plasma focus device operated in neon, the electron beam emission is investigated using both a magnetic electron energy analyser (in the 30–660 keV range) and a Rogowski coil (coupled with an appropriate RC passive integrator). Several electron emission features are identified and correlated with the x-ray emission in different energy ranges. The electron beam output shows very strong correlation with the general plasma dynamics (breakdown, axial and radial acceleration, pinch and post-pinch phases). The electrons' energy spectra showed most of the electron emission concentrating below 200 keV and negligible emission with energy above 350 keV. At 4 mbar neon, the electron emission, as well as the beam energy, is the highest and has a good shot-to-shot reproducibility.

Carbon ion implantation on titanium for TiC formation using a dense plasma focus device

In this paper, we report titanium carbide formation on a titanium metal substrate by using a 3.3 kJ Mather-type dense plasma focus (DPF) device equipped with a graphite carbon source. The titanium substrate is inserted from the top of the plasma chamber and is irradiated by argon and carbon ions produced in multiple shots of DPF. X-ray diffraction spectra of the layer formed on the titanium substrate with 10, 15, 20, 25 and 30 shots at a typical distance of 2.5 cm from the top of the anode show peaks corresponding mostly to titanium carbide. The surface morphology and hardness of the layer formed have been investigated using a scanning electron microscope and a Knoop microhardness tester, respectively.

Comparative study of soft x-ray emission characteristics in a low energy dense plasma focus device

An investigation on the soft x rays emitted in a 2.2 kJ Mather-type dense plasma focus device using a multichannel diode spectrometer and a simple pinhole camera is reported. Emitted x rays associated with different shapes (hollow, solid, and hemispherical) of anode and in hydrogen/nitrogen gas medium are compared. The structure of x-ray emitting sites as well as x-ray yields were found to be strongly influenced by the shape of the anode and the filling gas pressure. The maximum yield of 2.2 J into 4π sr was obtained in the case of hemispherical anode in hydrogen gas medium. The x-ray pinhole images of the collapsed plasma with the hemispherical anode indicated spot-like structure having 500–800 μm in diameter. On the contrary, other anode shapes showed columnar pinched structure of 8–10 mm in length and 1–2 mm in diameter. Results indicated that an appropriate design of the anode could enhance the x-ray yield by more than tenfold in a conventional low energy dense plasma focus device.

Energy Dissipation in Run-Down Phase of Mather-Type Plasma Focus Discharges

The influence of the cathode structure on the focus discharges in a 7 kJ Mather-type plasma focus device was investigated by using two types of cathode electrodes, 1) bar and 2) tubular cathodes. I...

Measurement of Argon Ion Beam and x-ray Energies in a Plasma Focus Discharge

We investigated the characteristics of ion beam emission in a small 1.9 kJ Mather-type plasma focus device filled with argon gas, and obtained the energy spectra of argon ion beams using a time-of-flight (TOF) method with a capacitive current monitor and a well-designed Faraday cup. We also observed x-ray emissions, and obtained the time correlation between the x-ray emissions and the ion emissions. The maximum energy of the argon ions was over 800 keV, and the most common ion energy was 200 keV. Ion emission started before the x-ray emission, and was also observed when no x-ray emission was detected; however stronger ion emissions were observed when x-ray emissions were detected. The energy of soft x-rays was determined to be about 2.96 keV of Ar Kα line using a mass absorption method, and hard x-ray emissions of Cu Kα line was also observed. We compare our experimental results with several existing models of the charged particle acceleration in a plasma focus discharge.

Room temperature deposition of titanium carbide thin films using dense plasma focus device

Thin films of titanium carbide (TiC) were deposited on 304-stainless steel substrates using a dense plasma focus device. The conventional hollow copper anode of the 3.3 kJ Mather type plasma focus device was replaced by solid titanium anode for deposition of TiC thin films. The argon–acetylene admixture (in 7:3 ratio) was used as the filling gas at a pressure of 1.5 mbar. Substrates were placed along the anode axis at a distance of 11.5 cm from the top of the anode. Thin films of TiC were deposited using different numbers of focus shots, like 10, 20 and 30, at room temperature substrates. Deposited films were analyzed for their structure, surface morphology, surface profile, elemental composition and distribution using X-ray diffraction (XRD), scanning electron microscopy (SEM), surface profiling and energy dispersive X-ray spectroscopy (EDX). XRD patterns in all three cases are found to have diffraction peaks for (111), (200), (220), (311) and (222) TiC crystalline planes. Scanning electron micrographs show a smooth film surface with increasing clustering of TiC grains with the increase in number of focus deposition shots. EDX spectra confirm the presence of expected constituent elements with the gradual increase in TiK α peak (of the TiC thin film) relative to FeK α peak (of the substrate) with increasing numbers of focus deposition shots due to increasing film thickness. EDX mapping reveals a uniform distribution of TiC over the substrate surface. These results confirm the first ever deposition of TiC thin films using a dense plasma focus device.

A COST EFFECTIVE X-RAY DETECTOR FOR PLASMA FOCUS DIAGNOSTICS

A time-resolved rugged X-ray detector (XRD) which may be used in intense radiation environment is developed. The detector is used to study the X-ray emission from a low-energy (2.3 kJ) Mather-type plasma focus energized by a 32 μF single capacitor, using hydrogen and argon (3:2) mixture as gas filling. In the detector, the electron emitter is made of nickel and aluminum. The sensitivity of the detector with nickel cathode is found to be very low. No signal could be recorded by masking the detector with even the 2 μm thick Al foil. When Al cathode is used in the XRD, the sensitivity of the detector increases abruptly. To stop the optical/ultraviolet radiation from approaching the active area, it is masked with 6 μm Al filter. It is found that an XRD with nickel cathode is not useful for X-ray detection in a low-energy plasma focus. However, due to its excellent response to vacuum ultraviolet radiation (≤600 Å), it may find application in the study of the axial rundown of current sheath, and its velocity. The X-ray emission from focus plasma is the highest at 0.5 mbar. With increase in pressure, the emission is dropped. At filling pressures of 2.0–2.5 mbar, the X-ray emission increases again. High X-ray emission at 0.5 mbar is due to interaction of energetic electrons in the current sheath with the anode surface, whereas moderately high emission at 2.0–2.5 mbar is caused by an axially moving shockwave.

ROLE OF ANODE LENGTH IN A MATHER-TYPE PLASMA FOCUS

Neutron emission from a 3 KJ Mather-type plasma focus is studied. Specifically, the behavior of system with the change in anode length is investigated. Anode lengths of high and low fluence anisotropy as well as for high neutron yield are identified. Experiment also suggests the possibility of ion beam generation leading to neutron production via beam-plasma interaction.

Monochromatic x-ray emission of a fully ionized hydrogen plasma

Subnanosecond emission phenomena have been studied at a modified 1 kJ Mather type plasma focus device. High energy particle beams, nonthermal infrared and microwave emission as well as anisotropic soft X-rays are observed. In the plasma a hydrodynamic instability leads to a final radius of r ⋍ 50 μ m and a length of l = 500 μm through which a current of l = 200 kA is driven. Induced by the high power density, microinstabilities modulate the plasma density periodically. Due to particle-wave interaction, electrons and ions are accelerated to energies beyond 1 MeV. The electron beam is emitted in pulses with a pulse period of about 10–30 ps and a pulse width in the range of 1–3 ps. Simultaneously, anisotropic emission of soft X-rays at a wavelength of about λ = 1 nm into a cone with a half angle θ = 0.2 rad is observed. The relative line width Δλ λ = 2×10 −3 , indicates a temporal coherent emission of X-radiation by the fully ionized hydrogen plasma. Assuming an FEL-like process as generation mechanism of the soft X-rays, the periods length of the density structure and the relativistic factor γ of the electron beam are determined as λ ⋍ 17 nm and γ ⋍ 3 . The observed phenomena in the plasma can be theoretically described as a self-organization process in terms of a three-wave-coupling model of a beam-plasma system.