Mather-type Plasma Focus Device Research Articles

Experimental investigation and simulation of penetration depth of nitrogen ions emitted by plasma focus device inside titanium samples

The plasma focus device is a simple, inexpensive, and precious device that can be considered as a source of high-energy ions for researches relevant to interactions of ions with widely used materials such as titanium. Regarding exclusive properties such as a high degree of hardness and resistance to corrosion, titanium nitride alloy is considered to be one of the most essential materials with a wide range of industrial applications. In the present study, the characteristics of titanium nitride alloys were studied using a 1.5 kJ Mather-type plasma focus device. To do this, a Faraday cup detector is used to measure the current density of the ion beam in order to determine the energy spectrum of nitrogen ions using time of flight approach. The optimal operational condition of the device for nitrogen ions emission, in terms of gas pressure and voltage of discharge were also determined. Titanium samples were situated on the top of the anode of the device and were exposed to nitrogen ion radiation considering 5, 10, and 20 shots of the device. To simulate the penetration depth of nitrogen ions inside the titanium samples, the SRIM code is used. The obtained energy of ions from the time of flight technique was set as input of the SRIM code, and it was found that nitrogen ions, with an average energy of 50 keV can penetrate about 110 nm inside the titanium sample. It was understood that the finding results of the penetration depth are in good agreement with the SEM micrographs of the titanium samples. The sputtering yield of titanium atoms was determined using the SRIM simulation code, and it was found that the yield of the surface of the samples is less than 0.2 atoms per individual nitrogen atom.

Angular distribution of ion beams energy and flux in a plasma focus device operated with argon gas

Energy and flux of ion beams in a Mather type (5 kJ) plasma focus device was investigated. The experiments were performed with argon as the chamber gas at the optimum pressure of 0.3 mbar and the charging voltage of 15 kV. Six identical Faraday cups located at angular positions 0, 15, 30, 45, 60 and 75° with respect to the anode axis were exploited to collect ion signals. The Faraday cups were mounted on a quadrant holder so that all Faraday cups have the same radial distance of 7 cm from the anode tip. In order to gain knowledge of target ions, when the plasma focus device is used for thin film deposition, three different targets of copper, graphite and tungsten were inserted on top of the anode tip. The ion signals registered by Faraday cups showed three main peaks relating to X-ray, argon gas and target ions, respectively. Plots of ion flux as a function of ions energy were obtained for argon gas and different targets separately. Energy spectra obtained from the Faraday cups revealed different anisotropies for argon gas and targets ions.

Characterization of carbonized magnesium formed in a low energy plasma focus device

Carbon-ion deposition on magnesium substrate was performed using a low energy Mather-type plasma focus device. Deposition process was carried out at 0, 15, 30 and 45° angular position with respect to the device anode axis. X-ray diffraction (XRD) confirmed presence of Mg2C3, Mg (OH)2 and graphite crystals on the produced films. Field emission scanning electron microscope (FE-SEM) coupled to elemental mapping analysis from surface and cross section of the samples was performed. The analysis showed the formation of a multi-layer thin film, in which carbon nano particles (CNPs) covered the composite layer. The CNPs were formed by graphite crystals while the composite layer formed by combination of Mg2C3 and Mg (OH)2 crystals. The band gap energy of indirect transition (⁓1.75 eV) of Mg2C3 was extracted from optical measurements of UV–Visible spectrum. XRD and Raman spectroscopy were used to investigate the graphite crystal structure of CNPs at each deposition angle. The study indicates that the graphite crystal structure of the samples is consisted of nano-crystalline and reduced nano-crystalline graphite structures. X-ray photoelectron spectroscopy (XPS) was used to characterize the elemental composition of the surface structure. The presence of Mg2C3 and Mg (OH)2 in composite layer, nano-crystalline, and reduced nano-crystalline graphite in CNPs was identified by high resolution transmission electron microscopy (HR-TEM). Potentio-dynamic polarization test was used to analyze the corrosion resistance of the prepared thin films with respect to un-deposited substrate. The findings indicate that the thickness and the size of Mg2C3 crystals have direct effect on corrosion resistance parameters.

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 surface damage and hydrogen distribution in irradiated tungsten by protons in plasma focus device

Abstracts In this paper, tungsten samples were exposed by H ions under 5, 10 and 20 PF discharges in a Mather-type plasma focus device. The hydrogen retention and the produced damage in the tungsten surface were studied. The tungsten samples were analyzed by SEM, XRD and ERDA after irradiation. The SEM micrographs showed the blisters, cracks and open bubbles on the surface of the irradiated samples. The size of the blisters increased by enhancing the number of PF discharges. The XRD pattern revealed the crack formation and propagation at the surface of the samples. The hardening and softening behavior of the exposed samples were figured out from the X-ray diffraction pattern. The ERDA was used to obtain the depth profile of hydrogen in tungsten. Ions range and the depth profile of the damage rate in the tungsten target were calculated using the SRIM code. ERDA illustrated that the highest H concentrations occurs in the target depth range of 20–60 nm whereas the SRIM simulation showed that the highest number of H ions can pierce about 60–120 nm into the tungsten sample. This discrepancy is due to the erosion. The damage rate decreases by increasing the penetrating depth.

Results of the Preliminary Experiments with a Miniaturized Plasma Focus Device

In this article, a miniaturized Mather-type Plasma Focus (PF) device is presented. This device operates at a very low energy range (0.3–3 J). Here, the results of the first experiments with it at different working conditions (different gases, initial pressures and discharge voltages) have been investigated.

Plasma Current Sheath Dynamics and Energy Dissipation in a Low-Energy Plasma Focus Device

This paper reports the measurements of plasma current sheath (PCS) dynamics, the energy dissipation processes, and the plasma focus (PF) electrical characteristics, particularly during the axial phase discharge in a Mather-type PF device (EAEA-PF1) energized with a 30 µF capacitor bank charged with 8, 10 and 12 kV. All these works are carried out under discharge conditions where the optimal PF action is achieved. At each charging voltage (Vch), 8 kV, 10 kV and 12 kV, the optimal PF action is studied for different Argon gas pressures (P) ranging from 0.4 to 1.2 Torr. The results show that the best PF is formed at Vch = 8 kV and P = 0.6 Torr, Vch = 10 kV and P = 0.8 Torr, and Vch = 12 kV and P = 0.8 Torr. The implosion velocity (Vz) results of PCS show that the maximum value of Vz (4.48 cm/µs) occurs at the end of the axial phase (i.e., at the coaxial electrode muzzle), which is detected at Vch = 12 kV and P = 0.8 Torr. Moreover, a less inefficient snowplow action is observed under these discharge conditions. The energy dissipation process data indicate that at Vch = 12 kV and P = 0.8 Torr, the ratio between the total energy dissipation and the input energy has a maximum value of ≅ 90%, and the minimum residual energy left on the condenser bank (175.39 J) is also achieved under these discharge conditions.

Analysis of the pinch characteristics in a miniaturized repetitive plasma focus device

In this article, the experimental results of pinch characteristics in a miniaturized (20 J) repetitive Mather-type plasma focus device (SORENA-1) have been presented. Argon, neon and deuterium were used as working gases, and variations of pinch characteristics such as pinch time tp, negative spike height hp, pinch duration dt with working conditions (different gases, initial pressures and discharge voltages) were described and analyzed.

Effects of deposition angle on synthesis of amorphous carbon nitride thin films prepared by plasma focus device

Amorphous carbon nitride (a-CNx) thin films were deposited on graphite substrate at different angular positions using a low energy (up to 4.9 kJ) Mather-type plasma focus device. The deposition processes were carried out during 20 focus shots at optimum nitrogen gas pressure of 0.4 mbar. The formation of amorphous carbon nitride was confirmed by Raman Spectroscopy, SEM, EDX, FTIR, and XRD analyses. The intensity ratio of D and G peaks (ID/IG) recorded by Raman Spectroscopy showed two distinct trends at various angular positions. The sample deposited at 30° had the highest ID/IG ratio and correspondingly the highest sp3 CHx content in FTIR spectrum. Samples with lower ID/IG ratio appeared with smaller grain size and more smooth surfaces in SEM images. The highest CN intensities in FTIR spectrum belonged to those samples deposited at 30 and 75° angular positions.

Retraction Note to: A Review on Nanoporous Gallium Nitride (NPGaN) Formation on P-Type Silicon Substrate with the Mather-type Plasma Focus Device (MPFD)

The Editor-in-Chief is retracting this article [1] because it has been previously published [2]. M. Habibi, who is listed as an author on the previous publication, is not listed as an author on this version. The authors have not responded to any correspondence from the publisher about this retraction.

Improvement of the radiographic method for measurement of effective energy of pulsed X-ray emission from a PF device for different anode's insert materials

In this paper, effective energy of pulsed X-Ray emitted from a Mather-type plasma focus device in stored energy of 2.5 kJ with six different anode's insert materials was measured using radiographic method with attenuation filters. Since intensity and energy of X-ray beam were considerably changed with changing the insert material, the method was improved by using different filters simultaneously in all the experiments and selection of the best filter in each experiment according to the appropriate criteria. Effective energy of pulsed X-ray beam was measured 16, 28, 50, 51, 34 and 44 keV when aluminum, copper, zinc, tin, tungsten and lead were used as insert materials, and aluminum, copper, silver, silver, copper and lead were used as filters, respectively.

Study of Plasma Flows Generated in Plasma Focus Discharge in Different Regimes of Working Gas Filling

Results are presented from experimental studies of the plasma flows generated in the KPF-4 Phoenix Mather-type plasma focus device (Sukhum Physical Technical Institute). In order to study how the formation and dynamics of the plasma flow depend on the initial distribution of the working gas, a system of pulsed gas puffing into the discharge volume was developed. The system allows one to create profiled gas distributions, including those with a reduced gas density in the region of plasma flow propagation. Results of measurements of the magnetic field, flow profile, and flow deceleration dynamics at different initial distributions of the gas pressure are presented.

Time-to-Pinch Investigation of 5 kJ Mather-Type Plasma Focus Device

The Egyptian Atomic Energy Authority-Plasma focus (EAEA-PF2) has been upgraded to a 5 kJ plasma focus device. Its characteristics have been investigated at various pressures and different voltages in a 5 kJ Mather-type plasma focus device for Ar gas. Its time-to-pinch has been measured, simulated and analyzed at different operating conditions. It is observed from the results that, the time-to-pinch decreased when either the charging voltage increased or the gas pressure decreased. In addition, the time-to-pinch is estimated theoretically using Lee model RADPF5.15. A comparison between the experimental and theoretical time-to-pinch is discussed. Also, the drive factor of plasma focus is analyzed at different pressures and charging voltages. It is noticed that, the mass and current factors are affected by changing the pressure and voltage. Finally, it is observed that, the drive factor is proportional inversely to the pressure and directly to the charging voltage.

The effects of the cathode array on emitted hard x-ray from a small plasma focus device

In this study, the effects of the cathode array variations on emitted hard x-rays from a small Mather type plasma focus device (450 J) were investigated. The gradual elimination of the cathode rods inside the cathode array of the device lowered the quality and quantity of the emitted hard x-rays at different pressure values of argon gas. We theorized that the variations of the cathode array were able to change some discharge parameters that could vary the number of the energetic runaway electrons generated during the pinch phase which were responsible for the created features of the emitted hard x-rays. On the other hand, we hypothesized that the removal of the cathode rods could influence the current sheath dynamics during all the phases of a shot including its average axial velocity which was demonstrated by using two axial magnetic probes. We also theorized that cathode rod omission from the cathode array could also increase the initial inductance and the impedance of the system, and the impurities inside the plasma during the pinch phase which could lead to the growth of the instabilities. Moreover, by using the wavelet technique and studying the Mirnov signals, it was shown that the decrease of the cathode rod number increased the plasma magnetic field fluctuations or instabilities (MHD activities) that adversely affected the pinch quality, and reduced the emitted hard x-rays.

The effects of pre-ionization using a shunt resistor on reproducibility of the x-ray emission in a dense plasma focus device

In this research, the effects of pre-ionization using a shunt resistor on reproducibility of x-ray emission in a Mather type plasma focus device have been studied. This technique increased the intensities of the emitted x-rays from argon as the filling gas of the device and made the x-ray yields with similar intensities reproducible. A Mirnov coil was also used to record the variations of the plasma's magnetic field, and the wavelet spectrums of these recorded signals showed the reduced instabilities due to the application of the pre-ionization technique. Moreover, it was demonstrated that this technique was capable of reducing the number of initial runaway electrons that could increase the impurities and instabilities inside the plasma. In addition to the above-mentioned features, this technique could improve the uniform formation of the current sheath during the breakdown phase that might later lead to a high quality pinch and high intensity emitted x-rays.

Ion acceleration mechanism in plasma focus devices

AbstractPlasma focus is one type of ion source with energy up to few MeV. While some efforts have been made to understand the physics of ion beam acceleration in plasma focus devices (PFD), an acceptable clarification does not exist yet. In this work, the procedure of ions) electrons) acceleration in PFDs to the MeV energy is investigated theoretically. Moreover, the trajectory of electrons (ions) and their angular distribution are studied. The simulations are carried out by COMSOL Multiphysics version 5.2 for a 4.5 kJ Mather type PFD. The results of simulations and calculations show that trapped ions in the negative potential of electrons, their movement toward the top of the anode and the drift motion due to electrical and magnetic fields near the top of the anode are the main causes of high energy electrons (ions) production and acceleration.

Characteristics of X-ray Hot Spots in a 3.5 kJ Plasma Focus Device at Different Pressures of Argon and Air

The present study examined the formation of hot spots in the plasma column of a 3.5 kJ Mather-type plasma focus device. Experiments were performed with air and argon as operating gases at 0.2–1.5 mbar of pressures. X-ray source images were obtained using a pinhole camera with dental X-ray film as X-ray detector. The objective was to investigate the effect of the operating conditions and gas type on formation and characteristics of the hot spots. Results showed that when using air in comparison to argon, the total X-ray emission is increased and therefore, the hot spots are covered by this high intensity emission and would be observed less frequently in the image. Using metal filters to attenuate the low-energy X-rays revealed that the most energetic or the most intense radiation was emitted from the hot spots region. The images of the X-ray source obtained using argon at the middle pressures (0.4–0.6 mbar) showed both the plasma column and the photons emitted from the anode surface. A pressure of 0.8–1.5 mbar using argon was most likely to observe the hot spots. For argon gas, the 0.9 mbar was the pressure in which the hot spots were more frequently observed with high reproducibility of location and number. Measurements revealed that the typical size of a hot spot was 10–300 µm and the distance from the anode surface was 0.5–20 mm.

Measurement of the effective energy of pulsed X-rays emitted from a Mather-type plasma focus device

The current study examined the effective energy of pulsed x-rays emitted from a Mather-type plasma focus device with copper anodes at an energy range of 2–3kJ using x-ray transmission radiography. Aluminum filters of different thicknesses and dental x-ray film were used. When air gas was used at a constant voltage of 21kV at 0.3, 0.6, 0.9 and 1.2 mbar, the effective energy of pulsed the x-ray was 10.9, 10.7, 17.3 and 15.8keV, respectively. At 0.6 mbar of air, as the operating voltage increased to 19, 21 and 23kV, the effective energy of the x-ray radiation was 10.6, 10.7 and 12.4keV, respectively. Comprehensive investigation of the characteristics of x-ray emission from plasma focus devices makes it feasible to use this device as an intensive x-ray generator for medical and industrial purposes. The present study is a part of a program which is planned to realize these applications.

RETRACTED ARTICLE: A Review on Nanoporous Gallium Nitride (NPGaN) Formation on P-Type Silicon Substrate with the Mather-type Plasma Focus Device (MPFD)

The Editor-in-Chief is retracting this article [1] because it has been previously published [2]. M. Habibi, who is listed as an author on the previous publication, is not listed as an author on this version. The authors have not responded to any correspondence from the publisher about this retraction.

A novel technique based on a plasma focus device for nano-porous gallium nitride formation on P-type silicon

A new deposition formation was observed with a Mather-type Plasma Focus Device (MPFD). MPFD was unitized to fabricate porous Gallium Nitride (GaN) on p-type Silicon (Si) substrate with a (100) crystal orientation for the first time in a deposition process. GaN was deposited on Si with 4 and 7 shots. The samples were subjected to a 3 phase annealing procedure. First, the semiconductors were annealed in the PFD with nitrogen plasma shots after their deposition. Second, a thermal chemical vapor deposition annealed the samples for 1 h at 1050 °C by nitrogen gas at a pressure of 1 Pa. Finally, an electric furnace annealed the samples for 1 h at 1150 °C with continuous flow of nitrogen. Porous GaN structures were observed by Field emission scanning electron microscopy and atomic force microscopy. Furthermore, X-Ray diffraction analysis was carried out to determine the crystallinity of GaN after the samples were annealed. Energy-Dispersive X-Ray Spectroscopy indicated the amount of gallium, nitrogen, and oxygen due to the self-oxidation of the samples. Photoluminescence spectroscopy revealed emissions at 2.94 eV and 3.39 eV, which shows that hexagonal wurtzite crystal structures were formed.