Table of contents

A compact microwave plasma has been employed as an ion source for focused ion beam applications, that can provide non-toxic ions and facilitate rapid processing of materials without introducing any metallic contamination. A variety of microstructures with high aspect ratio (line width/depth) (∼100–1000) relevant to the energy and current regimes, are created on copper thin films using 26 keV Ne, Ar and Kr ion beams. A mathematical formulation is developed to calculate the impact of the ion beams, which act as energetic projectiles falling onto the target sample, by defining a new parameter called 'current normalized force' which is the total momentum transferred per unit time, normalized with the beam current. Capillary guiding of the plasma ion beams has demonstrated beam self-focusing which can be employed to further reduce the beam source size (plasma electrode aperture) for demagnification. Particle-in-cell (PIC) simulations are performed to interpret the experimental results of self-focusing. Hysteresis in beam current with extraction voltage (ion energy) is observed and the hysteresis area is used to calculate the dissipated charge from the beam during capillary transmission. The effect of plasma and beam parameters on focal dimensions has been investigated, and a unique feature of enhanced nonlinear demagnification is observed when the aperture size of the plasma electrode is reduced to below the Debye length. Submicron focusing of plasma ion beams is observed by minimizing the space charge effects and reducing the plasma electrode aperture (source size).

The dielectric material is one of the important influencing factors for the dielectric barrier discharge (DBD) characteristics and its application effects. The glass, quartz, polycarbonate (PC), and polytetrafluoroethylene (PTFE) materials are selected as dielectric materials of a coaxial DBD reactor. A nanosecond (ns) pulse power supply is used to drive the coaxial DBD reactors and the influences of dielectric materials on the optical, electrical, and temperature characteristics of DBDs are recorded. The mechanisms of the effects of the dielectric materials on the DBD characteristics are analysed by equivalent electrical model and heat conduct model. From the observation of the discharge, all of the discharges are in the diffuse mode without filament and the coaxial DBD with glass dielectric barrier are more homogenous. With the electrical analysis, it is found that the glass dielectric barrier with larger relative permittivity compared with the other materials leads to a better discharge uniformity and a higher power deposition in gap. At the same applied voltage, the coaxial DBD reactor with glass dielectric barrier also has the highest energy efficiency, which can reach 70.8% at 24 kV peak applied voltage. The operation temperatures of the coaxial DBD reactors after 900 s discharge with different dielectric materials are compared. The coaxial DBD reactor with glass dielectric barrier has the highest outside wall temperature at 78.0 °C. The reactor with PTFE dielectric barrier has the lowest operation temperature at 58.2 °C. With the heat conduct analysis, the results show that the coaxial DBD reactor with glass dielectric barrier has the highest the inner barrier tube temperature at 137.9 °C and has the lowest heat loss power rate at 29.2% under thermal balance. The reported work provides important reference for the selection of dielectric materials for DBD reactors and for the optimization in the industrial application.

This work investigates and compares the effects of high-energy, short-pulsed proton irradiation with low-energy, continuous proton beam on tungsten (W) surface. For this purpose, a W specimen was irradiated in 20 shots of plasma focus device with fluence of 5.2 × 10¹⁹ ions m⁻², while another specimen was exposed to glow discharge (GD) plasma for 2.5 h with fluence of 2 × 10²² ions m⁻². Lee Code was used to obtain the ion beam characteristics produced in the plasma focus device. SEM image was taken from the irradiated specimens before and after irradiation. Small blisters were detected on the surface of W irradiated with high-energy proton pulses, covering the entire surface of W. Larger blisters created by merging the small blisters were also observed. Small cracks were also created at the surface of W irradiated with high-energy ions. At the surface of W irradiated with the GD plasma, very large blisters were observed in the order of a few micrometers. In addition, fuzzy nanostructures can be seen on the W surface, which are grown in the island form. The XRD analysis was used to investigate the effects of radiation on the W crystal structure. Raw samples and samples irradiated with high-energy protons and low-energy protons were analyzed by the XRD. The results showed that the peaks in the XRD pattern of W samples irradiated with high energy protons were shifted to higher angles than those irradiated with low-energy protons. The peak intensity of the samples irradiated with high energy ions has significantly decreased.

Characteristics of ultraviolet (UV) radiation (254 nm) sources employing ferrite-free inductively-coupled low pressure mercury discharge excited in the closed-loop quartz tube with the inner diameter (ID), d_t = 16,6 mm and the length, Λ_pl = 815 mm were experimentally studied. Discharge was maintained at a frequency of 1,7 MHz and RF powers, P_lamp = 95–170 W, in the mixture of mercury vapor (~7–8 mTorr) and buffer gas fill (Ar, 30%Ne + 70%Ar) at pressures of 0,7 and 1,0 Torr. A 3-turn induction coil made from low loss Litz wire (resistivity, ρ_w = 1,4 × 10^–4 Ω cm⁻¹, wire diameter, d_w = 1,5 mm) was disposed on the lamp surface along the closed-loop tube perimeter. As lamp RF power increased from 95 to 170 W, induction coil power losses, P_coil, decreased from 7–9 to 3–4 W while coil power efficiency, η_coil = 1- (P_coil/P_lamp), grew from 92 to 98%. Lamps with buffer gas at pressure of 1,0 Torr, operated at plasma RF power, P_pl =  105–150 W, had high plasma UV radiation generation efficiency, η_{254pl, max} = Φ₂₅₄/P_pl = 67%–68%, while lamp UV radiation generation maximal efficiency, η_{254, max} = η_coilη_{254pl, max}, had slightly lower values of 63%–66%.

The avalanche waiting time behaviour of the Chapman sandpile model (Chapman et al, 2001 Phys. Rev. Lett.86, 2814), compared to the ELM waiting time behaviour of a JET fusion plasma, has been considered by (Bowie et al, 2016 Phys. Plasmas23, 100 703). Here we extend the analysis of the Chapman sandpile model, by considering cases in which the combinations of variables chosen give rise to three distinct waiting times. It is observed that the short and medium waiting times sum to the long waiting time, suggesting a relationship between all three. Further, it is observed that each of the short, medium, and long waiting times occur independently. We conject that if the short and medium waiting times sum to the long waiting time in a fusion plasma, that may suggest that the Chapman model and the fusion plasma share an underlying common dynamical behaviour, and further, that each of the three waiting times may arise from the same underlying cause. By contrast, if the short and medium waiting times do not sum to the long waiting time, that suggests that the Chapman model would be inappropriate. We remark that the relationship between the short, medium, and long waiting times bears a resemblance to the relationship between the terms of the Fibonacci sequence, and is also consistent with frequency coupling.

GLAST is a small spherical tokamak with an insulating vacuum vessel of pyrex. It has major and minor radii of 20 and 10 cm, respectively. Magnetic measurements play a fundamental role in plasma breakdown and start-up studies. This paper presents the development, fabrication, calibration, and installation of magnetic diagnostics on GLAST III Tokamak. Magnetic diagnostics consist of the flux loops, magnetic field pickup sensors, and Rogowski coil. The signals obtained from various coils are integrated with passive analog integrators. The experimental results obtained from these magnetic diagnostics are presented and discussed.

Although the fuse is one of oldest components of electrical engineering, its operating remains very complex because of the extreme rapidity of the phenomena and the fact that they take place in an opaque environment. Until now, engineers and researchers have only studied the fuse operation by indirect method, simulation or post mortem fuse state. But, a collaboration between mixed research units with the European Synchrotron for Research Facilities allowed filming the fuse operating by x-ray imaging. The method specification is to record the sequence with 5 million frames per second. The conductive material is thus observed to pass from a solid-liquid phase to an initiation of the plasma, thereby establishing the initial conditions of the arcing phase. The high speed films also permit to observe the lengthening of the arc in a few microseconds. The images can be synchronized with the voltage and the current, which makes it possible to return to the calculation of the electric field in function of time. Data analysis has been compared with simulation models and the separation of the curves prove the lack of knowledge of arc ignition phase due to the plasma which is out of its thermodynamic equilibrium.

In large area sputter coating of glass, the consumption of electric power is one of the major cost drivers. This applies especially to dielectric transparent coatings which are relatively thick and for which sputter yields and rates can be rather low. These materials are usually sputtered from dual magnetrons using medium frequency (sine wave) or bipolar (square wave) power supplies at frequencies up to 100 kHz. Frequencies at 50 kHz or higher are beneficial for suppressing arcing on the target surface, and the power required to achieve viable sputter rates is often high, making the power consumption a significant cost contribution. In this study we look at the effect of the power supply technology and frequency on the sputter rate and the sputtered layer thickness per electrical energy input. The tests were carried out with aluminum dual planar targets and with TiOx dual rotary targets. At low frequencies around 20 kHz, the bipolar generator can yield about 10% higher sputtering rates at the same input power. At about 40 kHz, which is often chosen to minimize arcing, the rates from the two power supplies are about equal.

The analytical solution of dust-ion-acoustic-solitary waves (DIASWs)with the influence of external periodic force are reported in a dusty plasma model which consists of dust-ion collisions. Using reduction perturbation technique (RPT) damped modified forced Korteweg-de-Vries-Burger (DMFKdVB)equation in some critical composition is obtained. Various physical parameters i.e. dust ion collision frequency (ν_id0), the entropic index (q), the velocity of travelling wave (M₀) ,the ratio of the densities between electrons and ions (μ), viscosity coefficient (η), frequency (w) of the external perturbation and the strength(f₀) of the perturbation are observed. This study may be helpful to interpret the characteristics of DIASWs in astrophysical rings, interstellar clouds and comet tails.

This work investigates the reliability of the function called 'regionprops' which is used for measuring the 2D length of the plasma discharge. Work was conducted in a Rotating Gliding Arc (RGA) reactor, using air as plasma forming gas. Arc rotational images at three different gas flow rates i.e. 5, 25 and 50 litres per minute $\left({LPM}\right)$ were captured using high speed camera with an exposure of 100 μs. A total of 6799 images from all the three flow rates were considered for analysis. The 2D length of the discharge was measured by two methods namely, (a) 'regionprops' function (Python) and (b) manual tracing (ImageJ). The 2D arclength measured using 'regionprops' function matched very closely to that measured by manual hand tracing technique using ImageJ tool. A linear relation between both the methods was observed for all the three flow rates, with the coefficient of determination i.e. R² > 0.9 . The validation of 'regionprops' function shown in this work marks an important step as the function is simple to use and adapt compared to any other techniques such as shortest–path algorithm.

Negative hydrogen ion sources for NBI systems at fusion devices rely on the surface conversion of hydrogen atoms and positive ions to negative hydrogen ions. In these sources the surface work function is decreased by adsorption of caesium (work function of 2.1 eV), enhancing consequently the negative ion yield. However, the performance of the ion source decreases during plasma pulses up to one hour, suggesting a deterioration of the work function. Fundamental investigations are performed in a laboratory experiment in order to study the impact of the plasma on the work function of a freshly caesiated stainless steel surface. A work function of 2.1 eV is achieved in the first 10 s of plasma, while further plasma exposure leads to the removal of Cs from the surface and to the change of the work function: a value of around 1.8–1.9 eV is measured after 10–15 min of plasma exposure and then the work function increases, approaching the work function of the substrate (≥4.2 eV) after 5 h. The Cs removal must be counteracted by continuous Cs evaporation, and investigations performed varying the Cs flux towards the surface have shown that a Cs flux of at least 1.5 × 10¹⁶ m⁻²s⁻¹ is required to maintain a work function of 2.1 eV during long plasma exposure at the laboratory experiment.

Atmospheric non-thermal plasma is gaining increasing attention for various applications including food, medical and healthcare technologies because of its unique capability in producing reactive species. In spite of its promising potential, generating non-thermal plasma over large and complex geometries such as the human body or a narrow channel is still challenging and is limiting the use of atmospheric non-thermal plasma. In this study, we propose two new electrode systems, printed and knitted electrodes, to enhance scalability and flexibility of a conventional atmospheric non-thermal plasma source. The flexibilities of both electrode systems are quantified for varying curvatures to generate non-thermal plasma over complex geometries. Moreover, both electrode systems are assessed for varying system size to assess the ability of large scale plasma geometries. Electrical and optical diagnostics including Optical Emission Spectroscopy (OES), are used to monitor the property of plasma generated by these systems. The present study shows that both printed and knitted electrodes can produce non-thermal plasma, however both have certain limitations. Concluding from these findings, a schematic of new hybrid electrode system for the treatment of large surfaces or narrow long channels is proposed to eradicate these limitations.

A sinusoidally-excited Venturi-DBD operating in neon has been investigated. The Ne(1s₅) metastable density has been quantified spatially resolved using laser atomic absorption spectroscopy for different pressure levels. Density values of up to 7 · 10¹⁶ m⁻³ could be determined at atmospheric pressure and up to 3 · 10¹⁶ m⁻³ at 100 mbar. For all investigated parameters, the Ne(1s₅) density was found to be distinctly higher in the proximity of the cathode than in the anode region. Complementary investigations of the discharge development using phase-resolved optical emission spectroscopy complete the characterization of the device. The discharge was found to show typical properties of a glow-like discharge regarding current waveform and luminosity distribution. In addition, the influence of nitrogen and oxygen impurities and admixtures in the process gas has been determined. A substantial impact was found on both the Ne(1s₅) concentration and the current waveform.

Programmable control of the inductive electric field enables advanced operations of reversed-field pinch (RFP) plasmas in the Madison Symmetric Torus (MST) device and further develops the technical basis for ohmically heated fusion RFP plasmas. MST's poloidal and toroidal magnetic fields (B_p and B_t) can be sourced by programmable power supplies (PPSs) based on integrated-gate bipolar transistors (IGBT). In order to provide real-time simultaneous control of both B_p and B_t circuits, a time-independent integrated model is developed. The actuators considered for the control are the B_p and B_t primary currents produced by the PPSs. The control system goal will be tracking two particular demand quantities that can be measured at the plasma surface (r = a): the plasma current, I_p ∼ B_p(a), and the RFP reversal parameter, F ∼ B_t(a)/Φ, where Φ is the toroidal flux in the plasma. The edge safety factor, q(a) ∝ B_t(a), tends to track F but not identically. To understand the responses of I_p and F to the actuators and to enable systematic design of control algorithms, dedicated experiments are run in which the actuators are modulated, and a linearized dynamic data-driven model is generated using a system identification method. We perform a series of initial real-time experiments to test the designed feedback controllers and validate the derived model predictions. The feedback controllers show systematic improvements over simpler feedforward controllers.

We model electron acceleration using paraxial approximation (PA) and seventh order correction description (O7) of a laser field in vacuum in the presence of an axial magnetic field. The effect of initial momentum, laser intensity, spot size, and initial position of electron on optimum value of magnetic field and electron energy for linearly and circularly polarized laser pulse has been investigated. We show that PA fails to obtain correct values of optimum magnetic field and electron energy. The amplitude of oscillations of the electron increases with time in the presence of axial magnetic field and PA fails to correctly take into account focusing and defocusing of laser and obtain correct results.

Experimental examination of possibility to affect the shapes of flames under combustion of the liquified petroleum gas (LPG) were performed by several non-conventional cold atmospheric plasma arrangements. The lateral fused hollow cathode, the microwave surface wave plasma jet and the combination of these systems confirmed possibility of an efficient control of the flame shapes, increasing stability of flames and broadening of their front parts.

This work attempts to correlate the plasma density and RF harmonic profiles with respect to the pressure (at 13.56, 27.12 and 40.68 MHz) with the stochastic and ohmic power absorption mechanisms in a Capacitively Coupled Discharge (CCD), over a wide pressure range (0.6–1000 mTorr). Diagnostics include calibrated capacitive probe, compensated Langmuir Probe (LP) and uncompensated floating LP for measuring plasma parameters and RF signals. Pressure profiles of stochastic and ohmic powers, P_Stoch and P_Ohm (at 13.56 MHz) are obtained from their ratio (ξ) and the power absorbed by the electrons. Normalized profiles of an effective power (∼${P}_{{\rm{Stoch}}}^{\rho }\times {P}_{{\rm{Ohm}}}^{1-\rho };$ρ : pressure dependent parameter) are tuned to reproduce closely the normalized plasma density profiles from which relative contributions of stochastic/ohmic mechanisms are determined. It is shown that up to ≈30 mTorr, plasma production is stochastic while beyond that both methods contribute jointly. The RF harmonic profiles can be analysed similarly. Higher harmonics produced by the intrinsic nonlinearity of the stochastic process should appear most clearly in the plasma at low pressures where the latter operates alone. On the other hand, the fundamental RF voltage that is always present in the plasma, can also produce higher harmonics at the probe tip by driving the nonlinear probe sheath. Thus, the harmonics produced directly by the stochastic nonlinearity are inextricably mixed up with those arising due to the probe sheath. Significantly, one may conclude therefore that it is not possible to investigate the stochastic mechanism of power absorption by a study of its harmonics when the latter are measured using invasive probes.