Low Energy Mather-type Plasma Focus Research Articles

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.

Energy spectrum of multi-radiation of X-rays in a low energy Mather-type plasma focus device

The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a Mather-type plasma focus device (operated with argon gas). The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300 ± 50 ns. The significant contribution of Cu—Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu—Kα and Cu—Kβ was around 0.14 ± 0.02 (J/Sr) and 0.04 ± 0.01 (J/Sr), respectively. The total energy of the emitted hard X-ray (> 15 keV) was around 0.12 ± 0.02 (J/Sr).

Post-pinch generation of electron beam in a low energy Mather-type plasma focus device

AbstractThe post-pinch generation of electron beam in a low energy Mather-type plasma focus (PF) device has been investigated. A fast-calibrated Rogowski coil was used to monitor the emission of electron beam. A two-channel diode X-ray spectrometer along with suitable filters provided the records of energy spectrum of X-ray radiation. Single time-period emissions of electron beam with duration of 100 to 20 ns were recorded in the high range of the device operating pressure (0.8–2 mbar). However, in the low range regime (0.2–0.8 mbar), occurrence of single spike electron beam with duration of 150 ± 50 ns, as well as multi-emission of electrons with duration of 400 ± 50 ns, was visible. A multi-peak of tube voltage along with multi-time-period radiation of X-rays dominated by copper lines (Cukα and Cukβ) was noticeable in the low-pressure range. The generated electron beam during the post-pinch phase of anomalous resistances is suspected to be the main source of X-ray radiation. This can also be related to the turbulence of the plasma column during the occurrence of anomalous resistances.

Correlation of current drop, filling gas pressure, and ion beam emission in a low energy Mather-type plasma focus device

The behavior of current drop and its correlation with ion beam emission during the radial phase of a high inductance low energy Mather type plasma focus device have been studied. The study includes two ranges of filling gas pressure, namely the low range of 0.2–0.8 mbar and the high range of 0.8–1.5 mbar. Two different current simulation processes were performed to aid the interpretation of the experimental results. Within the low range of operating pressure, an acceptable match between the computed and experimental current signals was achieved when the effects of anomalous resistances were contemplated. While in the high range of pressure, the computed and experimental current traces were in line even without considering the effects of anomalous resistances. The analysis shows that by decreasing the filling gas pressure the effects of instabilities are intensified. The computed and experimental current traces, along with ion beam signals gathered from a faraday cup, show that there is a strong correlation between the intensity of ion beam and its duration with the current drop during the radial phase.

Current sheath behavior and its velocity enhancement in a low energy Mather-type plasma focus device

The dynamics of the plasma sheath layer and its velocity enhancement have been studied in a low energy (4.9 kJ) Mather-type plasma focus device. Experiments were performed to study the effect of the Lorentz force variation on the current sheath expansion and movement, as well as the existence of traction between all parts of the sheath layer. Two different shape of anodes (cylindrical and step) along with an axial magnetic probe were used to investigate the effects of various experimental conditions, namely different charging voltages and gas pressures. In order to explore the upper limit of the current sheath velocity, a comparison has been made between the experimental data gathered by the probe and the Lee’s computational model. The limitations governing the enhancement of the current sheath velocity that can lead to the deterioration of a good focusing phenomenon were also investigated. The increase of the current sheath velocity due to the usage of the step anode on ion generation and hard x-ray emissions have been demonstrated by means of an ion collector and a hard x-ray detector.

Generation of titanium K-radiation in a 1 kJ plasma focus

Titanium K-series line radiation emission from a low energy Mather-type plasma focus operated with hydrogen was investigated by employing Quantrad Si pin diodes as time resolved X-ray detectors. It has the highest value of 1.6 ± 0.1 J in 4π-geometry, and the corresponding machine efficiency is about 0.16 ± 0.01%. The total X-ray emission is about 3.2 ± 0.2 J, and the corresponding machine efficiency is about 0.32 ± 0.02%. The Ti K-line radiation emission may result from the interaction of energetic electron beam emitted from the focus region, and the energetic electrons in the current sheath, with the anode tip.

Electron Temperature Measurement Using PIN Diodes as Detectors to Record the x-ray Pulses from a Low-Energy Mather-Type Plasma Focus

In the experiment to determine the plasma electron temperature, a modified multi-channel PIN diodes assembly is used as detectors to record the x-ray pulses from a low-energy Mather-type plasma focus device energized by a 32 μF, 15 kV (3.6 kJ) single capacitor, with deuterium as a filling gas. The ratio of the integrated bremsstrahlung emission transmitting through foils to the total incident flux as a function of foil thickness at various temperatures is obtained for foil absorbers of material. Using 3 μm, 6 μm, 9 μm, 12 μm, 15 μm and 18 μm thick aluminium absorbers, the transmitted x-ray flux is detected. By comparing the experimental and theoretical curves through a computer program, the plasma electron temperature is determined. Results show that the deuterium focus plasma electron temperature is about 800 eV.

X-ray emission from a plasma focus with high-Z inserts at the anode tip

X-ray emission in different energy windows, from a low energy Mather-type plasma focus by employing high Z inserts at the anode tip is investigated. Quantrad Si pin diodes with differential filtering are employed as time-resolved x-ray detectors, whereas a pinhole camera is used for time-integrated analysis. The x-ray flux from the focus region is found to be measurable within the pressure range 0.25–3.5 mbar of hydrogen. The maximum emission in 4π-geometry is found to be 29.4±0.2 J, 3.43±0.05 J and 4.00±0.02 J with Pb, W and Mo inserted anodes, respectively, and corresponding wall plug efficiencies for x-ray generation are 1.28%, 0.15% and 0.2%. The x-ray emission is found predominantly as a result of electron beam activity on the anode tip, which is confirmed by the images recorded by the pinhole camera.

Study of molybdenum K-series line radiation emission from a low energy plasma focus

K-series line radiation emission of Mo and Cu from a low energy Mather-type plasma focus is investigated. Quantrad Si pin diodes are employed as time resolved X-ray detectors, where as a pin hole camera is used for time integrated analysis. The measurable X-ray flux for hydrogen is observed in the pressure range of 0.5–3.5 mbar. Mo and Cu K-line radiation emission in this geometry has the highest values of about 0.05 J/sr and 0.17 J/sr, respectively at a filling pressure of 2.0 mbar. The corresponding efficiencies are 0.03% and 0.09%, respectively. Total X-ray emission and efficiency in 4 π-geometry are also obtained with values 4.12 J and 0.18% at 2.0 mbar. The Mo K-line radiation emission may result due to interaction of energetic electron beam emitted from the focus region with the molybdenum insert.

Nitrogen ion spectrum from a low energy plasma focus device

The nitrogen ion spectrum generated from a low energy Mather-type Plasma Focus device is reported. The main species of ions present are N/sup +1/, N/sup +2/, and N/sup +3/. It is found that its relative concentrations at a distance of several cm from the ion source are in agreement with those predicted for an equilibrium charge-state of the beam, and hence the spectrum of the neutral nitrogen is also derived. By taking into account the lateral spread of the beam due to multiple elastic scattering with the background gas, the derivation of absolute values for the total ion spectrum within the investigated energy range (>170 keV), the total number and total energy of the fast particles has been obtained.

Effects of anode shape on plasma focus operation with argon

X-ray and ion beam emission from a low-energy Mather-type plasma focus energized by a single , 12 kV (2.3 kJ) capacitor is investigated employing three different anode shapes and using argon as filling gas. The radiation yield and the filling gas pressure for good focus are found to be strongly dependent on the anode shape. An appropriate tapering of the anode end enhances the emission threefold for both x-rays and ions. The intensities of the signals are also found to be correlated mutually as well as with the high-voltage probe signal intensity. Furthermore, time-integrated pinhole images reveal that the x-rays originate predominantly from the anode end surface. In other words, an appropriate shaping of the anode end switches the device to a high-emission mode for both x-rays and a charged particle beam.

Neutron and x-ray emission studies in a low energy plasma focus

In a low energy Mather-type plasma focus energized by a single 32 μF capacitor, the x-ray and neutron emission is investigated using time-integrated and time-resolved detectors. The x-ray emission profile has a width (FWHM) of 40–50 ns. The neutron emission profile is broader compared to the x-ray emission profile and also delayed by 30–40 ns. To identify different regimes of x-ray emission, an x-ray pin-hole camera along with different absorption filters is employed. While the x-ray emission is high within a narrow pressure range of 2.0–2.5 mbar, the neutron emission is intense for a wider range of 1.0–4.5 mbar. The intense x-ray emission seems to originate from the axially moving shock wave. These results also indicate rather different production mechanisms for x-ray and neutron emission. Also on comparing the x-ray images with Al(2 μm), Al(5 μm), Al(9 μm) filters, we find that the bulk of x-rays from the focus filament have energies less than 2 keV.

USE OF SOLID STATE NUCLEAR TRACK DETECTORS CR-39 TO STUDY CHARGED PARTICLES EMISSION FROM A 3 kJ PLASMA FOCUS

The CR-39 solid state nuclear track detectors are employed to investigate the fluence anisotropy of charged particles (protons, deuterons and tritons) emitted from the focus region of a low energy Mather-type plasma focus energized by a single 32 μF, 15 kV (3.6 kJ) capacitor. The charged particle flux is the highest in the axial direction, and decreases towards the radial direction. The radial charged particles flux is six times smaller than the flux in the axial direction.

Comparative study of low energy Mather-type plasma focus devices

The characteristics of three different low energy Mather-type plasma focus devices are investigated and compared. The effects of anode length and insulator sleeve length on neutron yield and on fluence anisotropy are studied. It is found that proper tuning of the focus tube inductance with that of the driver enhances the neutron emission from the focus region, increases the neutron pulse width and broadens the deuterium pressure range for high neutron yield. The insulator contamination which occurs due to Cu evaporated from the electrodes drastically changes the device characteristic. The possibility of using the device as a multi-pulse neutron generator is also examined.

Delayed hot spots in a low energy plasma focus

In a low energy Mather-type plasma focus device, hot spots having temperature in the range of few KeV have been observed even 1 µs after the pinch disintegration and in regions away from the pinch area. These hot spots are perhaps created by the thermal runway due to temperature fluctuations in the background gas.