Conical Anode Research Articles

Modification of Child-Langmuir Law for Electrodes of Different Materials and Shapes Using Nitrogen Gas

A dc glow discharge plasma between the planar electrode and planar, conical, and hemispherical electrodes was studied. The electrode materials made of aluminum, graphite, and stainless steel (SS) were used. The experimental results showed a deviation in the traditional Child-Langmuir (CL) law as a result of the use of different shapes and materials of anodes and cathodes. The new parameters of the modified CL law as a function in the surface areas of electrodes, their work function materials, and their contributions to the electrical discharge. The lowest discharge characteristics were for the aluminum planar electrode (anode or cathode) with the aluminum and graphite hemispherical one. The planar aluminum cathode with the conical SS anode gave the highest discharge characteristics. The planar aluminum anode with conical SS cathode had the lowest Paschen curve values. In Paschen curves, the highest values were discovered to be for the planar cathode in a comparison with different cathodes. The hemispherical aluminum anode had the highest Paschen values compared with different anodes. Moreover, the contribution ratio of the anode to the cathode in the discharge for the aluminum planar diode was equal to the ratio between their surface areas and the ratio between their work function materials. In contrast, this contribution ratio for the other discharge cases was equal to the multiplication of the surface areas ratio of the anode to cathode and the ratio of their materials’ work functions. The modified CL law and its coefficient were generalized for the electrodes of different shapes, materials, and used gases.

Effect of Annealing and Ion Beam Irradiation on AC Electrical Properties for Gold Sputtered PM-355

Deposition of different gold thickness on PM-355 cleaned by ethanol forming thin films using magnetron sputtering. Gold layer with thickness 300, 400, 500, 700, 1000, 1300, and 1500 nm were deposited to prepare Au / PM-355 thin films. Then, ac electrical properties response of thin films for a wide frequency range 20Hz - 5MHz were measured at roomtemperature. Meanwhile, the measurements of ac conductivity, dielectric constant, and dielectric loss factor were plotted at different frequencies to determine the optimum thickness. Hence, the comparison was done between optimum Au thickness thin films cleaned by two organic solvents and ethanol before annealing at different frequencies. Also, study the effect of annealing and ion beam that extracted radially from conical anode and disc cathode ion source on optimum Au thickness thin film electrical properties. It is found that the annealing increases both dielectric constant, dielectric loss, and ac conductivity of optimum Au thin film at different frequencies. Despite, the nitrogen ion beam effected on these thin films by decreasing the dielectric constant and ac conductivity for all thin films except the chloroform one. Finally, study the comparison between the annealing and followed by ion irradiation thin films. It is noticed the decrease in ac electrical conductivity and dielectric constant at different frequencies.

Modeling of Electron Sources for High Voltage Glow Discharge Forming Profiled Electron Beams

The methodology of simulation of high voltage glow discharge electrodes’ systems with anode plasma, formed the profile electron beams with the ring-like focus, is considered in the article. The universality of proposed model is confirmed by the fact, that the slope angle of generatrix line of conic anode surface correspond to the axis of the electrodes system have been chosen as one of model parameters. Such novel solution has led to simulating the different types of electrodes’ systems, which form the profiled electron beams. The position of plasma boundary in considered high voltage glow discharge electrodes’ systems is firstly calculated on the basis of one-dimensional model of discharge gap, and after that recalculated with taking into account the real geometry of electrodes’ system. Such approach allows to significantly simplify the proposed mathematical model and to avoid using the sophisticated iteration numerical methods for defining plasma boundary form and position without decreasing the accuracy of simulation results. The results of simulation of plasma boundary position are compared with obtained experimental data and disagreement between simulation and experimental results is nearly 10–15%. The results of simulation of distribution of electric field in the cathode-fall region as well as results of simulation of distribution of beam current density in the ring-like focus of formed hollow electron beam are presented in the article. The simplicity and universality are the main advantages of the proposed model.

The Effect of the Shape of the Anode Head on the Nitrogen Soft X-Ray Emission from a Dense Plasma Focus Device: a Numerical Investigation Using the Modified Lee Model Code Accompanied by Experiments

An alternative way for calculating the magnetic field in the Lee Model Code has been used. The effects of the various anode-tip shapes on the DPF behavior have been studied. The current and impedance calculations have been employed for these investigations. For the conical anode tip, the best pinch current and soft x-ray radiation have been seen in simulations which was in good agreement with the empirical results. The investigations were carried out for the voltages of 11, 12, and 13 kV and the pressure range of 1–6 Torrs. The asymmetry in the discharging current has been investigated through three arbitrarily defined cathode current distribution patterns. The simulations showed that asymmetry in the axial discharge current increased the plasma Impedance and consequently reduced the soft x-ray emission.

Investigation of conical anode – disc cathode ion source

An axial direct-current conical anode – disc cathode ion source has been designed, constructed, and operated. The electrical discharge and the output ion beam characteristics are measured using nitrogen gas. It is found that at the optimum dimensions, pressure equal to 4.5 × 10−5 mm Hg and discharge current equal to 250 μA, a maximum output ion beam current equal to 91 μA can be obtained. A comparison between the experimental results and theoretical calculations of the output ion beam current values at the optimum dimensions and operating parameters for different discharge current of conical anode and disc cathode ion source using nitrogen gas is determined. It is found that a good agreement exists between the experimental results and theoretical calculations.

ВИЗНАЧЕННЯ ЕНЕРГЕТИЧНОЇ ЕФЕКТИВНОСТІ ТРІОДНИХ ЕЛЕКТРОННИХ ГАРМАТ ВИСОКОВОЛЬТНОГО ТЛІЮЧОГО РОЗРЯДУ ІЗ ПЛОСКИМ ДОПОМІЖНИМ ЕЛЕКТРОДОМ

У статі описується математична модель тріодних електродних систем високовольтного тліючого розряду із плоским допоміжним електродом. Такі електронні гармати знаходять широке впровадження у промисловості для виконання технологічних операцій зварювання, паяння, відпалювання виробів, нанесення композитних керамічних покриттів та для переплавлення тугоплавких металів з метою їх очищення від шкідливих домішок. Запропонована математична модель базується на визначенні положення плазмової межі через аналітичне розв’язування кубічного рівняння з використанням формул Кордано з урахуванням реальної геометрії електродів. Задача пошуку положення плазмової межі в електродній системі високовольтного тліючого розряду вирішується через розв’язок рівняння балаансу заряджених часток у розрядному проміжку. Спочатку задача визначення положення плазмової межі відносно катода була розв’язана для аксиально-симетричної системи із лінійною геометрією електродів. У статті розглянута структурна схема такої електродної системи та визначені базові параметри сформованої математичної моделі. Після цього, також через аналітичне розв’язування кубічного рівняння з використанням формул Кордано, отримана формула для перерахунку положення плазмової межі з одномірної системи до системи із конусним анодом. У статті також отримані формули для разрахунку енергетичної ефективності тріодної електронної гармати із конусним анодом та пламтинчатим електродом. Наведені та проаналізовані результати розрахунку енергетичної ефективності реальної електронної гармати. Розрахункові результати порівнюються з експериментальними даними. Всі експерименти були проведені в лабораторії електронно-променевих технологічних пристроїв Національного технічного університета України «Київський політехнічний інститут імені Ігоря Сікорського». Отримана точність розрахунків, порівняно із експериментальними даними, складає біля 10 – 15%. Отримані в статті наукові результати є вкрай цікавими та важливими для науковців та інженерів, які займаються розробкою електронно-променевого технологічного обладнання та його впровадженням у сучасне виробництво.

Моделирование триодных источников электронов высоковольтного тлеющего разряда с пластинчатым управляющим электродом и коническим анодом.

Моделирование триодных источников электронов высоковольтного тлеющего разряда с пластинчатым управляющим электродом и коническим анодом.

Increase in the neutron yield from a dense plasma-focus experiment performed with a conical tip placed in the centre of the anode end

The paper describes the evolution of self-organized structures inside a pinched plasma column during the phase of the effective production of fusion neutrons, as observed in the mega-ampere plasma focus experiment performed with a conical tip placed in the centre of the anode face. In a comparison with the plane anode face configuration, the described anode shape facilitated transformations in the pinch column during the neutron production and increased the neutron yield several times. Simultaneously, it decreased the minimal diameter and the length of the pinched column, and it depressed the first neutron pulse. It also induced shorter pulses of X-rays and neutrons, which enabled the determination of a temporal difference between the emission of electron and deuteron beams. The fast electrons were produced mainly during a disruption of the pinch constriction, while the fast deuterons – during the formation and explosion of plasmoids. The paper also presents the temporal evolution of a current distribution in the plasmoid during the neutron production, as well as the appearance and stable positions of current filaments traces upon the surface of the conical anode tip.

Study of the secondary electron emission coefficient using disc and conical electrodes

In this work, glow discharge is formed by similar disc and conical electrode shapes from aluminum material at constant anode–cathode gap distance equal to 10 cm. The breakdown voltage and discharge current against the pressure × distance are measured at different pressures. The secondary electron emission coefficient is calculated using Townsend’s secondary ionization coefficient equation. A comparison is made between the breakdown voltage, discharge current, and secondary electron emission coefficient using disc and conical anode–cathode electrodes. Hence with a product of pressure and distance equal to 6 Torr cm, the secondary electron emission coefficient value of conical shape is higher than for the disc shape.

Monte Carlo Simulations of a Scanning System Based on a Panoramic X-Ray Tube with a Conical Anode

Monte Carlo simulations were used to study photon production in a panoramic X-ray tube with a conical tungsten target to determine the optimal characteristics of the target shape and electron beam configuration. Several simulations were performed for accelerating potentials equal to 250 kV, 300 kV, and 500 kV with electron beams of various radii and anode sizes. The angular distribution of the photon intensity was analysed by numerical calculations for an assembly composed of an X-ray tube and an external collimator with a cylindrical hole to simulate a panoramic scanning system with an X-ray pencil beam.

Enhancing Neutron Emission From a 500-J Plasma Focus by Altering the Anode Geometry and Gas Composition

The plasma focus (PF) could be a valuable neutron source for Homeland Security applications if high repetition rate with reproducible output is demonstrated. Increasing the neutron yield from a small PF device would contribute to producing a PF neutron source than can compete with other electronic neutron generators for Homeland Security applications and neutron radiography. Two approaches to increase the neutron yield were examined. The first was to alter the anode geometry from a conventional cylinder (20-mm diameter) to a cone (20-5 mm) over a 20-mm length. The neutron-yield increase was 5× in pure D2. The second was to mix inert gases with the deuterium. When 2%, 4%, and 8% Ar and Kr were added to D2, the cylindrical anode showed a maximum 3.6× increase in neutron yield while the conical anode did not show any improvement in neutron yield. However, the operating mass density (pressure) range was increased for the conical anode when inert gases were added.

Experimental Observation of Hot Spots in a Filippov-Type Plasma Focus Device

In this paper we have presented the experimental results of hot spots observation in different working conditions in Filippov-type Plasma Focus Device “Dena” (90 kJ, 25 kV), analyzing of these results have shown that the working conditions have great influence on hot spots formation. In using the pure gases like D2, Ar, Kr and Ne the formation of hot spots has been seen rarely, and it can be related to impurities like vapoured metal from the anode surface, also in using the light impurities hot spots were not formed, and only for the heavy impurities like Kr the formation of hot spots have been observed. The discharge voltage also plays an important role in hot spots formation, for voltages less than 16 kV, hot spots have not been observed. Also, using the conic insert anode leads to more and distinct hot spots than the case of flat one. The best results of hot spot observation in these experiments have been achieved by using a conic insert anode and D2 + 1% Kr as working gas.

Velocity and texture of a plasma jet created in a plasma torch with fixed minimal arc length

A new plasma jet (PJ-100) plasma spraying torch with a fixed minimal arc length was tested and the basic working parameters were measured and evaluated. The velocity of the plasma exiting both the cylindrical and the conical anode nozzles was assessed by measuring the thrust generated by the plasma jet and by photographing the translation of plasma clouds (parts with different brightnesses) in the last third of the length of the plasma plume. The basic characteristics of the argon/hydrogen plasma jets (enthalpy, mean temperature, mean plasma velocity and effective exhaust thrust velocity) were determined for different working regimes, for both the cylindrical and the conical nozzles. The thermal efficiency of the new plasma torch is between 70% and 74% for the plasma generation power up to 90 kW. The plasma plume generated in the cylindrical nozzle has a homogeneous radial temperature (and velocity) distribution with a full laminar flow.

Electrolytic magnesium production and its hydrodynamics by using an Mg–Pb alloy cathode

Physical interaction of magnesium and chlorine was minimized by collecting magnesium in a molten Pb cathode at the bottom of the electrolyte and placing anode at the top where the chlorine gas was evolved. Thus the magnesium losses associated with the formation of suspending droplets and fine magnesium particles were eliminated and current losses were mainly due to the recombination reaction of dissolved magnesium and chlorine. Current yield changed by changing the tip angle of the conical anode. It was due to the fact that the amount of chlorine diffused into the melt was proportional to the chlorine bubble area in contact with the electrolyte per unit time. Therefore, correlation of experimentally measured electrolysis data requires the knowledge of the size and the total residence time of the chlorine bubbles in inter-electrode region. Average diameter and total residence time of the bubbles were determined for anode tip angles that were used in electrolysis experiments by a room temperature hydrodynamic model. Amount of magnesium that was lost as a result of reaction with the dissolved chlorine was calculated by assuming the dissolution of chlorine gas as the rate determining step. Theoretical magnesium losses calculated by using the data from the room temperature hydrodynamic model were in good agreement with the electrolysis experiments. Furthermore, calculated cell voltages that use the sum of theoretical decomposition potential and IR drop obtained from the composite resistance due to the electrolyte and chlorine bubbles were also in agreement with the experimental data.

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.

Characteristics of moderate current vacuum discharge triggered by multipicosecond and nanosecond duration laser pulses

A comparative study of the characteristics of moderate-current (∼10kA), low-energy (⩽20J) vacuum discharge triggered by multipicosecond and nanosecond duration laser pulses is performed. Temporal profiles of the x-ray emission, discharge current, and anode voltage measured in vacuum discharge created between a planar titanium cathode and a conical point-tip anode are observed to be quite different for the two regimes of the laser pulse duration. While cathode plasma jet pinching is clearly observed in the discharge created by low-energy (∼5mJ), 27 ps full width at half-maximum (FWHM) laser pulses, a feeble pinching occurred for 4 ns (FWHM) laser pulses only above a threshold energy of ∼250mJ. In addition to the multiple K-shell x-ray pulses emitted from the titanium anode up to 100 ns, evidence of a much harder x-ray component (hν>100keV) is also seen in the discharge triggered by picosecond laser pulses.

X-ray and neutron emission studies in a new Filippov type plasma focus

We have performed experimental comparative studies of the x-ray and neutron emission generated by the new Filippov-type plasma focus Dena, (90 kJ, 25 kV, 288mF) in the pressure range of 0.6-1 torr. Time-integrated and time-resolved detectors, together with an x-ray pin-hole camera, along with a Be filter of 10mm thickness have been used. For a working gas of neon and a at insert anode, the maximum soft and hard x-rays (SXR-HXR) yield obtained was 16 V and 1.5 V/shot over a 4p solid angle, respectively, for a charging voltage range of 16-20 kV. As for the argon gas, the similar results such as 3.5 and 2 V/shot have been found, leading to a total conversion eAciency of x-ray emission of 0.09 % (for neon) and 0.03 % (for argon) of the stored energy. These efficiencies have been improved by the employment of a conic insert anode up to 0.4% and 0.1%. With deuterium puffing gas and a at insert anode, the maximum emission yield has been found to be 2.5 V for SXR and 1 V for HXR/shot which produce an ultimate emission profile width (FWHM) of 70-90 ns for x-rays and neutrons, giving rise to a maximum neutron yield of 1.2 × 109. Nevertheless, the maximum yield has been increased up to 5.5 times with the conic insert anode. In order to increase the neutron yield, we have introduced a krypton admixture to the deuterium filling gas and found that, for a krypton pressure of about 0.1 torr, the neutron yield increases by a factor of 3.5 for the flat insert and 1.5 for the conic insert anodes.

Explosive cathode gyrotron experiments

Experiments have investigated the behavior of explosive emission cathode gyrotrons using cylindrically symmetric coaxial diodes with centrally located knife-edged cathode and conical anode. Voltage probes and current shunts were exploited to monitor the diode electrical behavior when driven by a 3 /spl mu/s 1/e time Marx power supply (up to 150 kV). Temporal reference signals permitted comparison of the diode's electrical evolution with the simultaneously measured microwave output signal from the gyrotron. The microwave output pulse duration was found to depend on the diode gap spacing (in the range 16-27 mm), the cavity magnetic field (range 1.3-3.3 T) and the cathode material, the termination being caused by the decay of the accelerating potential across the diode and the disruption of the diode geometry. The ratios of the cathode flare expansion velocities for graphite, copper and stainless steel cathodes were estimated as (1:(1.3/spl plusmn/0.2):(2.2/spl plusmn/0.5)) with a corresponding change in the duration of the microwave output signal [((590/spl plusmn/17):(414/spl plusmn/25):(325/spl plusmn/10)) ns at 2.6 T]. Preliminary results are reported of recent experiments which have compared the optical emissions from the diode region during pulsed gyrotron operation with the simultaneously recorded diode electrical behavior and the gyrotron microwave output.

Characterization of field emitter structures by means of modeling electron trajectories in vacuum

A typical vacuum microelectronic structure with a conical field emitter tip, gate and anode is simulated by computer. The electric field is calculated as a function of the applied voltage using the finite element method, and the emission current density on the surface of the emitter is evaluated applying Fowler–Nordheim theory. By solving Newton’s equations of motion, the electron trajectories are found. The solution of Poisson’s equation shows that the influence of space charge on the electric field is negligible. Field distributions and electron trajectories which permit a more precise understanding of the operation mode of the structure are presented. Based on these results, the current–voltage characteristics and some derived parameters (transconductance, low-signal-gain, corner frequency) are shown, including guidelines for the design.

Simulation of field emission microtriodes

Vacuum microtriode RF amplifier performance, based upon a unit cell with a conical field emitter tip, gate, and anode, was evaluated using computer simulation. Electron emission was calculated from the Fowler-Nordheim equation. The dependence of emitted current, transconductance, and field enhancement upon geometrical factors, e.g., tip sharpness, tip height, cone half-angle, and gate hole radius, is shown. The device design parameters of transconductance, cutoff frequency, small signal gain, and efficiency have been calculated. Electron streamlines and current flux are shown for time-dependent RF input. Because a compact electron beam source has wide application, the normalized beam emittance, brightness, and beam quality are calculated for a typical case. Potential difficulties with anode power deposition are noted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>