Rawat, Rajdeep Singh

A 3 kJ plasma focus was operated with a 3He-D2 gas mixture, with partial pressures in the ratio of 2:1, corresponding to an atomic number ratio of 1:1 for 3He and D atoms. The fusion reactions D(3He,p)4He and D(d,p)3H were measured simultaneously using CR-39 polymer nuclear track detectors placed inside a pinhole camera positioned on the forward plasma focus axis. A sandwich arrangement of two 1000 μm thick CR-39 detectors enabled the simultaneous registration of two groups of protons with approximate energies of 16 MeV and 3 MeV arising from the D(3He,p)4He and D(d,p)3H reactions, respectively. Radial track density distributions were obtained from each CR-39 detector and per-shot average distributions were calculated for the two groups of protons. It is found that the D(3He,p)4He and D(d,p)3H proton yields are of similar magnitude. Comparing the experimental distributions with results from a Monte Carlo simulation, it was deduced that the D(3He,p)4He fusion is concentrated close to the plasma focus pinch column, while the D(d,p)3H fusion occurs relatively far from the pinch. The relative absence of D(d,p)3H fusion in the pinch is one significant reason for concluding that the D(3He,p)4He fusion occurring in the plasma focus pinch is not thermonuclear in origin. It is argued that the bulk of the D(3He,p)4He fusion is due to energetic 3He2+ ions incident on a deuterium target. Possible explanations for differing spatial distributions of D(3He,p)4He and D(d,p)3H fusion in the plasma focus are discussed.

The dense plasma focus (DPF) device is a coaxial plasma gun that uses a large electric current to heat and compress a gas to high temperatures (1-2 keV), densities (1025-26 m-3) and pressures (thousands of atmospheres). Under such extreme conditions, the gas radiates copious ultraviolet, X-rays and particle beams such as relativistic electrons and ion beams. At Plasma Radiation Sources Laboratory (PRSL), NIE, Singapore, our group has six plasma focus devices and our research efforts encompass a very wide range of topics covering various fundamental aspects of plasmas to the application of this device to lithography, soft and hard x-ray imaging, material modification and thin film deposition. This review paper reports the use of single shot and “repetitive” PF device for processing and deposition of thin films using plasma focus devices. To synthesize the magnetic thin films, the conventional hollow copper anode was substituted with an anode fitted with suitable material tip (FeCo or CoPt). Si wafer and copper mesh were placed axial down the anode axis at a suitable distance of about 25 cm above the anode top to improve the uniformity of deposited samples over bigger substrate size. The plasma focus device is operated at 1 Hz repetition rate at various combinations of charging voltage and filling pressure of hydrogen gas for different number of focus deposition shots. For the processing of thin films, the magnetic thin films of FePt were initially deposited using pulsed laser deposition and later exposed to energetic ions from hydrogen operated plasma focus device. The morphology, structure and magnetic properties of the synthesized and processed thin films are investigated using TEM, SEM, XRD and VSM, respectively. The paper will also discuss the fundamental of thin film deposition and irradiation mechanisms in plasma focus devices.

The NX2 device, a low energy plasma focus, at the Nanyang Technological University in Singapore, was used as a soft X-ray (SXR) source for micromachining. The gas used was neon which produced SXRs in a narrow spectral range of 0.9 - 1.6 keV. The SXR yield from repetitive operation of the NX2 device was monitored and measured using a cost effective multi-channel SXR spectrometric system. The system consists of filtered BPX65 PIN diodes, with the associated electronics --- an integrator, sample and peak holder, analogue switch, an A/D converter and a microcontroller. The system enables easy shot-to-shot statistical analysis under repetitive operation at adjustable preset trigger frequencies. A total of 4000 shots were fired at 0.5 Hz, using the same gas filling. The SXR production was at an average yield of 60 J/shot and a maximum single-shot yield of more than 100 J. The SXRs emitted by the NX2 device was used for contact micromachining, producing structures with an excellent aspect ratio of up to 20:1 on 25 μm SU-8 resist.

Tungsten (W) is considered as one of the promising candidates for plasma facing components in fusion reactors since it has high threshold energy, high melting point, low threshold shock resistance, and resistance against formation of co-deposits with tritium. Despite these commendable features, helium ions produced during fusion reaction are known to alter the microstructure of tungsten. In this work, dense plasma focus (DPF) device is used to study the effect of helium ion flux on double forged tungsten samples delivering a heat load of 6.27×104J/m2 per shot. The irradiation of virgin W samples is carried out at 5, 10, and 15 DPF helium shots. High heat loads resulted in blisters and micro-cracks on the sample surface. With an increase in the number of shots, the density of the blisters increased and craters on the W surface burst followed by re-solidification of the melted and sputtered surface. Surface nano-structurization, with nanoparticle formation, of W samples (nano-W) is realized by high-energy argon ion exposure of virgin samples in an argon filled DPF device. The average size of nanoparticles is found to increase with the number of shots and also leads to particle agglomeration. At 10 shots, uniformly distributed highly dense nanoparticles of 20–50 nm size have been synthesized. The nano-W samples are then irradiated by instability-accelerated high-energy helium ions in helium filled DPF device for 5, 10, and 15 shots to simulate fusion relevant conditions. The presence of the trapped helium bubbles in virgin-W and nano-W are examined by BSE imaging and XRD, respectively. The nanostructured tungsten shows improved structure and surface properties against Helium ion irradiation.

We report the facile synthesis of nanostructured polycrystalline nickel sulphide (NP-Ni₃S₂) on Ni foil at 750 and 800 °C by employing powder vapor transport technique. X-ray diffraction patterns(XRD) confirms the formation of polycrystalline Ni₃S₂ phase with rhombohedral structure. Raman spectroscopy and x-ray photo-electron spectroscopy (XPS)further confirms the formation of Ni₃S₂ phase. Scanning electron microscopy (SEM)reveals the formation of flower shaped nanostructures of NP-Ni₃S₂ material. As an electrode material of Li⁺ batteries, the initial discharge capacities for NP-Ni₃S₂ materials deposited at 750 and 800 °C are found to be∼2649 mAh g⁻¹ and∼1347 mAh g⁻¹, respectively with initial capacity loss of∼1067 mAh g⁻¹ and∼363 mAh g⁻¹ after first cycle and capacities of∼931 mAh g⁻¹ and∼818 mAh g⁻¹ after 30 cycles for a current density of 60 mA g⁻¹. An excellent capacity retention for NP-Ni₃S₂ material synthesized at 800 °C is due to its larger surface area and shorter diffusion length for mass and charge transport brought about by the flower-like porous nanostructures showing that the NP-Ni₃S₂ material synthesized at higher temperatures is more suitable as electrode material for Li⁺ batteries.

The oxidation behaviors of γ-TiAl and Mo-Si-Ti coating at 750 °C were investigated through controlling oxidation duration. Growth of Al₂O₃ and TiO₂ divided the oxidation process of substrate into four stages with increasing duration. (i) Al₂O₃ oxide film caused low initial oxidation weight gain. (ii) TiO₂ rod-like oxide particles destroyed the oxide film, causing increase of oxidation weight gain. (iii) Plate-like oxide particles caused by preferred orientation growth of Al₂O₃, hindered the rapid increase of oxidation weight gain. (ⅳ) Growth of TiO₂ rod-like oxide particles and flaking of oxide film led to rapid increase of oxidation weight gain. Mo-Si-Ti coating mainly composed of (Ti, Mo)₅Si₃ showed a gradient structure. A diffusion layer allowed the coating to show a compositional gradient. Grain size gradually decreased from substrate to coating, with equiaxed grains near substrate and columnar grains near coating surface. Columnar grains accelerated initial oxidation as well as the production and volatilization of MoO₃, causing holes in TiO₂/SiO₂ oxide film and higher initial oxidation weight gain than substrate. As the duration increased, oxide film became dense and fine grains and gradient structure prevented its flaking, accompanied by low oxidation weight gain. Mo-Si-Ti coating could enhance the oxidation resistance of substrate effectively.

The atmospheric microplasma in the gas-liquid phase technique serves as a new potential efficient and green catalyst preparation technique to fabricate nanomaterials. Due to the presence of diverse reactive species, this technique can promote rapid complex reactions in solutions, which are typically sluggish in traditional chemical processes. Here, atmospheric microplasma induced liquid chemistry (AMILC) is applied to fabricate three-dimensional (3D) binary Pt3Co nanoflowers. Nano-architectures of Pt3Co bimetals (2D nanosheets and 3D nanoflowers) can be formed by tuning the initial cobalt molar concentration in the solution. 3D nanoflowers show a 'nano-bouquet' like nanostructure with Co-oxide forming leaves and Pt3Co forming waxberries. 3D nanoflowers show promising electrocatalytic behavior towards ethanol and glucose sensing in alkaline condition. Additionally, AMILC takes less synthesis duration (~10 min) without hazardous chemicals for Pt3Co bimetal nanostructure preparation compared to conventional chemical approaches (>2 h), indicating that AMILC is a potential candidate with better energy efficiency, lower carbon footprint and green plasma chemistry process for 3D nanostructure material synthesis in catalyst applications.

The shaping and formation of the current sheath takes place in the breakdown phase of a plasma focus device. Achieving a clear understanding of the current sheath formation process is important because the plasma focus device performance depends on the quality of this sheath. In this paper, we created and successfully run an electromagnetic particle in cell code to simulate the breakdown phase. Magnetic effects are self-consistently incorporated in this formalism, allowing us to carry the simulation all the way to the point prior to breakdown.