Current Sheath Dynamics and its Evolution Studies in Sahand Filippov Type Plasma Focus

One of the most important factors for optimizing the plasma focus device operation is the dynamics of the plasma. In this paper, we investigated the profile and dynamics of the current sheath by measuring the velocity and distribution of current sheath in Sahand as a Filippov type plasma focus device. For this purpose, the discharge is produced in pure neon gas with capacitor bank stored energies in the range of 14–50 kJ. The current sheath is monitored using two sets of magnetic probes, one with four and other with three equi-distant probe coils. These probes, installed in both radial and axial directions near the edge of the interior electrode (anode), are used for monitoring the distributions and dynamics of the current sheath. The maximum current sheath velocities at radial and axial phase are 4 ± 0.13 and 3.51 ± 0.22 (cm/μs) respectively for 0.25 Torr. The decreasing of CS velocities in going move away from anode surface is one of the our results in this paper. In this paper we conclude that the current sheath velocity at radial phase in Sahand is greater than axial phase. The effect of the neon working gas pressure and working voltage on the current sheath dynamics and its spatial evolution is investigated and presented.     

Studies of the Hard X-ray Emission from the Filippov Type Plasma Focus Device, Dena

This article is about the characteristics of the hard X-ray (HXR) emission from the Filippov type plasma focus (PF) device, Dena. The article begins with a brief presentation of Dena, and the mechanism of the HXR production in PF devices. Then using the differential absorption spectrometry, the energy resolved spectrum of the HXR emission from a 37 kJ discharge in Dena, is estimated. The energy flux density and the energy fluence of this emission have also been calculated to be 1.9 kJ cm⁻² s⁻¹ and 9.4 × 10⁻⁵ J cm⁻². In the end, after presentation of radiography of sheep bones and calf ribs, the medical application of the PF devices has been discussed.     

Preparation of Titanium Carbide Thin Film Using Plasma Focus Device

In this work, we report titanium carbide (TiC) formation on the stainless steel—304 substrates by using a low energy (2 kJ) Mather-type plasma focus (PF) device. The argon–acetylene admixture (in 3:1 ratio) was used as the filling gas at a pressure of 1 torr. The thin films were deposited with different number of focus deposition shots (5, 15 and 25 shots), at 0° angular position with respect to the anode axis and at constant distance from the anode tip (10 cm). Deposited thin films have been investigated for their structure by X-Ray diffractometry (XRD) and surface morphology by scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. The average size of crystallites (from XRD), crystalline growth of structures (from SEM), and size of grains and surface roughness (from AFM) were investigated, which increase by increasing the number of focus deposition shots.     

Study of Lateral Spread of Ions Emitted from 2.3 kJ Plasma Focus with Hydrogen and Nitrogen Gases

The characteristics of ion beams of hydrogen and nitrogen with different filling pressures emitted from the plasma focus device of 2.3 kJ energy are investigated. CR-39 SSNTDs are employed for the registration of tracks of ions. The exposed detectors are etched in 6N NaOH solution at 70°C and then examined with an optical microscope. The ion flux is estimated to be of the order of 10^5–6 tracks/cm². The flux with the radial position does not exhibit any regular pattern of variation.     

Properties of Ion Beams Generated by Nitrogen Plasma Focus

Numerical experiments have been systematically carried out using the modified Lee model code on various plasma focus devices operated with nitrogen gas. The ion beam properties (ion beam energy, ion beam flux, ion beam fluence, beam ion number, ion beam current, power flow density, and damage factor) of the plasma focus have been studied versus gas pressure for each plasma focus device. The results show that, for these studied plasma focus devices, the mean ion energies decrease with increasing gas pressure, while the beam ion number increases with higher pressure. The fluence, flux, ion current, power flow density and damage factor have maximum values at the optimum pressure. It is shown that, the maximum power flow densities range from 10¹² to 10¹⁴ W m^?2 and the damage factor values reach almost 10⁹–10¹¹ W m^?2 s^0.5. The obtained results provide much needed benchmark reference values and scaling trends for ion beams of a plasma focus operated in nitrogen gas. These results could be used as an indicator for ion properties emitted from nitrogen plasma focus for various applications including material processing.     

Experimental Study of the Variation of Neutron Emission Anisotropy in a Filippov-type Plasma Focus Facility

This paper presents the results of experimental studies of the variation of spatial anisotropy in neutron emission with working conditions in a 90 kJ Filippov-type plasma focus device. The working gases are D₂ and D₂ + 1%Kr. The results of our experiments have shown that the anisotropy factor decreases with increasing the initial pressure and/or discharge energy. Furthermore, it has been observed that by using D₂ + 1%Kr as working gas, the variation in anisotropy factor with initial pressure and/or discharge energy is relatively high, but by using D₂ it changes slowly. The highest neutron yield has been achieved by using D₂ + 1%Kr and a conic insert anode. Thus, we have studied the correlation between neutron yield and anisotropy factor for this case at fixed working conditions from shot to shot. At 16 kV discharge voltage and pressures around optimum, the behavior of anisotropy factor is generally increasing with neutron yield, whereas at low and high pressures, the anisotropy factor does not change significantly with yield.     

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 multichannel 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 32μF, 15 kV (3.6 k J) 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 3μm, 6μm, 9μm,12μm,15μm and 18μm 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.     

An Electron-Cyclotron-Resonance Plasma as a Source of Multiply Charged Ions

The properties of an electron-cyclotron-resonance (ECR) plasma (3 cm microwaves up to 2.4 kW) have been investigated. A total of 80 ?A noble gas ion current has been extracted from a 1 mm dia. hole so far. The charge state distributions show a maximum above the 1+ state, indicating that multiple impact ionization is a dominant process. X-ray spectra, sheath potential and microwave reflection were measured to gain some physical understanding of the discharge. The applicability of our device as an ion source is discussed.     

Detection of X-ray Radiations from Low Energy Focus Plasma Using Thermoluminescence Dosimeter TLD-500A

The present plasma focus device (0.1 kJ Mather type) is powered by a capacitor bank of 1 μF at 15 kV maximum charging voltage. The radiations emission was investigated using time-integrated thermoluminescence TLD-500. These detectors have been calibrated against standard X-ray machine (VIC model 4000M⁺) as well as standard gamma sources (Co⁶⁰ and Cs¹³⁷⁾ to identify the dose from X-ray delivered to the dosimeter. It is found that from the results of time-integrated detectors, the maximum radiation dose obtained at 0.1 Torr pressure and charging voltage 15 kV for different gases. At this pressure, the device favours a proper discharge dynamics so as to form a strong pinching i.e. transferring maximum energy into plasma.     

Plasma Focus as a High Intensity Flash X-Ray Source for Biological Radiography

A study on X-ray emission from a low energy (3.3 kJ) plasma focus (PF) device operated with hydrogen is reported. X-ray are detected by using an X-ray detector consisting of three Quantrad Si PIN-diodes with differential filtering and with a pinhole camera. The X-ray yield in different energy windows is measured as a function of hydrogen filling pressure. The maximum yield in 4-geometry is found to be 46.6 J and corresponding wall plug efficiency for X-ray generation is 1.40%. In particular, to demonstrate feasibility of the present PF as a high intensity flash X-ray source for good contrast biological radiography, an X-ray radiogram of a fish, is presented. The fine structure of the specimen can be seen in different parts. The PF, because of its high X-ray yield and good reproducibility is particularly suited for this application.     

Deuterium Plasma Focus as a Tool for Testing Materials of Plasma Facing Walls in Thermonuclear Fusion Reactors

This paper presents the first verification of the fast ion beam (FIB) and fast plasma stream (FPS) properties computed using the Lee code. Recent estimates of FIB and FPS properties in PF-400J from interferometric images are compared to our computed results. Reasonable agreement is found in the comparison of several quantities. Our computed power flow density (energy flux) and integral damage factor are 2.45 × 10¹² Wm^?2 (2 times of experimental value) and 1.78 × 10⁸ Wm^?2 s^0.5 (~almost the same as experimental value) respectively, for target placed at 1.5 cm from the anode top of PF-400J. This verification gives us confidence to proceed to systematic numerical calculations on the PF-400J and similar small plasma focus devices (PF50, NX2, NX3, FMPF-3, INTI PF) to obtain FIB properties (ion beam energy, ion beam flux, ion beam fluence, beam ion number, ion beam current, power flow density, and damage factor). These results confirm that the plasma focus, including small ones, could be useful to study the effects of cumulative pulses on target materials being considered for plasma facing walls in future tokamak or laser-implosion fusion reactors.     

Soft X-Ray Emission in the Water Window Region with Nitrogen Filling in a Low Energy Plasma Focus

For operation of the plasma focus in nitrogen, a focus pinch compression temperature range of 74–173 eV (0.86 × 10⁶–2 × 10⁶ K) is found to be suitable for good yield of nitrogen soft X-rays in the water window region. Using this temperature window, numerical experiments using five phase Lee model have been investigated on UNU/ICTP PFF and APF plasma focus devices with nitrogen filling gas. The Lee model was applied to characterize and optimize these two plasma focus devices. The optimum nitrogen soft X-ray yield was found to be Y_sxr = 2.73 J, with the corresponding efficiency of 0.13 % for UNU/ICTP PFF device, while for APF device it was Y_sxr = 4.84 J, with the corresponding efficiency of 0.19 % without changing the capacitor bank, merely by changing the electrode configuration and operating pressure. The Lee model code was also used to run numerical experiments for optimizing soft X-ray yield with reducing L₀, varying z₀ and ‘a’. From these numerical experiments we expect to increase the nitrogen soft X-ray yield of low energy plasma focus devices to maximum value of near 8 J, with the corresponding efficiency of 0.4 %, at an achievable L₀ = 10 nH.     

Comprehensive Study on Soft X-Ray Emission from Admixtures of Nitrogen and Neon Gases in the APF Plasma Focus Device

The present work is an investigation on the effect of working gas composition as well as applied voltage and operating pressure on the behavior of SXR emitted from the APF device. Three volumetric ratios(90:10), (75:25), and (50:50) of nitrogen:neon (N₂:Ne) admixture were used with operating conditions at applied voltages of 11, 12, and 13 kV and operating pressures of 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5 torr. Using (N₂:Ne) gas mixture ratios of (90:10) and (75:25) and at applied voltage of 11 kV, the optimum pressure for maximum intensity of SXR was 3.5 torr. However, for the percentage of (50:50), it shifts to higher pressure of 4 torr. At higher applied voltages of 12 and 13 kV, the optimum pressures shift to higher values, 4 torr for both volumetric ratios (90:10) and (75:25), and 4.5 torr for the ratio of (50:50). It was found that the intensity of SXR increases with the increase of neon (Ne) percentage in the admixture of (N₂:Ne) and applied voltage. The highest intensity was for the volumetric ratio of (50:50) operating at the voltage of 13 kV. Our results illustrated that mixing neon (Ne) with nitrogen (N₂) as the working gas in the PF is a power source of SXR emission.     

Studies on Ion Emission from the Plasma Focus Device by Using Ion Collector and Track Detector

Ion beam emission from a neon gas filled plasma focus device has been studied by using ion collector and solid state nuclear track detector. The neon ion beam emission is found to be highly pressure dependant and it is maximum at a pressure of 0.3 Torr. The maximum ion energy at 0.3 Torr is estimated to be 1 MeV. Preliminary results on solid state nuclear track detector indicate the formation of tracks in CR-39 due to exposure of neon ions. The average rim diameter of tracks is measured to be 4.35 μm and the number of track is of the order of 10¹⁰ track/m².     

Plasma Focus Device as a Breeder of 14.66 MeV Protons to Produce Short-Lived Radioisotopes

In plasma focus devices filled deuterium gas with low pressure admixture gas, ³He, the deuterium creates high energy protons of 14.66 MeV through the ³He(d, p) ⁴He(Q = 18.35 MeV) fusion reaction. This reaction takes place due to the thermal and non-thermal (beam-target) mechanisms. The proton yield production for deuterium filling gas is determined by using the beam-target character of the pinched plasma and moving boiler model. If we use a low pressure admixture gas like ¹¹B, these high energy protons in turn, could generate short-lived radioisotopes like ¹¹C (used in positron emission tomography) via the ¹¹B(p, n)¹¹C reaction. Calculations indicate the influence of drive parameter to the final yield for a Mather type device.     

Deposition of Chromium Thin Films on Stainless Steel-304 Substrates Using a Low Energy Plasma Focus Device

In this paper, we study thin films of chromium deposited on stainless steel-304 substrates using a low energy (1.6 kJ) plasma focus device. The films of chromium are likewise deposited with 25 focus shots each at various axial distances from the top of the anode (3, 5, 7, 9 and 11 cm). We also consider different angular positions with respect to the anode axis (0°, 15° and 30°) at a distance of 5 cm from the anode tip to deposit the chromium films on the stainless steel substrates. To characterize the structural properties of the films, we benefit from X-ray diffraction (XRD) analysis. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are applied as well to study the surface morphology of these deposited films. Furthermore, we make use of Vicker’s micro-hardness measurements to investigate the mechanical properties of chromium thin films. The XRD results show that the degree of crystallinity of chromium thin films depends on the substrate axial and angular positions. The AFM images illustrate that the film deposited at the distance of 5 cm and the angular position of 0° has quite a uniform surface with homogeneous distribution of grains on the film surface. From the hardness results, we observe that the sample deposited at the axial distance of 5 cm from the anode tip and at the angle of 0° with respect to the anode axis, is harder than the other deposited films.     

Radiation Emission Correlated with the Evolution of Current Sheath from a Deuterium Plasma Focus

The time resolved emission of neutrons and X-rays (both soft and hard) is correlated with the current sheath evolution during the radial phase of a 3.2 kJ Mather-type plasma focus device operated in deuterium at an optimised pressure of 4 mbar. A three-frame computer-controlled laser shadowgraphy system was incorporated in the experiment to investigate the time evolution of the radial phase of the plasma focus. The dynamics of the sheath was then correlated with the time resolved X-rays and neutron emission. The time-resolved neuron and hard X-ray emission was detected by a Scintillator-photomultiplier system while the time resolved soft X-rays were detected employing filtered PIN photo diodes. The observations were recorded with a temporal accuracy of a few ns. For the reference, the total neutron yield was also monitored by an Indium Foil activation detector. The correlation with the High Voltage Probe signal of the discharge, together with the X-ray and neutron emission regimes enabled to identify the important periods of the sheath evolution i.e. the radial compression (pre focus), minimum pinch radius (focus) and the post focus phenomena. During the initial stage of the radial phase, velocities of 10–23 cm/μs, while at the later stage of the radial phase (up till the compression), velocities up to 32–42 cm/μs were measured in our experiment. For the discharges with the lower neutron yield (lower than the average value ~1 × 10⁸ n/discharge), the current sheath appears to be disturbed and neutron and hard X-ray signal profiles do not carry much information whereas the soft X-ray emission is significant. For the discharges with high neutron yield (higher than the average value), the current sheath has a smooth structure until the maximum compression occurs. Hard X-ray emission is maximum for the discharges with high neutron yield, especially whenever there is development of m = 0 instability compressing the column to very high densities. The neutron are emitted long after the maximum compression supporting the beam target fusion. For the discharges with High neutron yield, the soft X-ray production is less as compared to the discharges with low neutron yield.     

Temporal Variation of the Current Sheet Inductance from PACO Plasma Focus Device

The temporal variation of the current sheet (CS) inductance in a plasma focus device can be calculated using the current derivative and the voltage signal acquired on the anode electrode, which are very common measurements in this type of device. The value of that inductance contains important information about the discharge performed including the CS lift-off from the insulator, voltage between the pinch extremes, maximum energy of the X-ray, energy delivered to the pinch and information about the actuating fusion mechanisms if the filling pressure is deuterium. This work discusses the values of the CS inductance extracted from several discharges of the Plasma Auto Confinado (PACO) plasma focus, installed in the National University of the Center of Buenos Aires—Argentina (2 kJ total energy, capacitor bank of 4 μF charged to 31 kV and a maximum current of 250 kA).     

Study of Neutron Yield Degradation in a Low Energy Plasma Focus

The neutron emission degradation from a low energy (1 kJ) plasma focus (PF) system designed to develop as a sealed neutron source is investigated. The yield decreases from 4 × l0⁶ to 2 × l0⁶neutrons per shot, after 40 discharges. Analyzing the gas using the mass spectrograph, nitrogen, carbon monoxide and hydrogen are found the dominant impurities added in the working gas. The addition of impurities depends on the number of discharges and not the time after the gas filling.