[en] Experimental investigation of cathode erosion in atmospheric pressure hafnium-electrode plasma torches is reported under different plasma environments along with the results of numerical simulation. Air, nitrogen and oxygen are the plasma gases considered. Distinct differences in the erosion features in different plasmas are brought out. Cathode images exhibiting a degree of erosion and measured erosion rates are presented in detail as a function of time of arc operation and arc current. Physical erosion rates are determined using high precision balance. The changes in the surface microstructures are investigated through scanning electron microscopy (SEM). Evolution of cathode chemistry is determined using energy dispersive x-ray spectroscopy (EDX). Numerical simulation with proper consideration of the plasma effects is performed for all the plasma gases. The important role of electromagnetic body forces in shaping the flow field and the distribution of pressure in the region is explored. It is shown that the mutual interaction between fluid dynamic and electromagnetic body forces may self-consistently evolve a situation of an extremely low cathode erosion rate. (paper)

[en] Emissive probe diagnostics in saturated floating potential mode was carried out in RF plasmas of argon (Ar)–methane (CH₄) and Ar–CH₄–hexa methyl disiloxane (HMDSO). These plasmas are used for the deposition of diamond-like carbon (DLC) and SiO_x-containing DLC films, respectively. While performing the experiments it was found that the probe characteristics had two saturation regions instead of one. The same measurements when repeated in Ar and Ar–N₂ plasmas showed a single saturation as expected. The first experiments when repeated again showed the same anomaly. The experimental findings question the validity of emissive probe diagnostics in reactive plasmas. A possible model of dust formation inside the reactive plasma is predicted and the first saturation is linked to dust. The second saturation is credited as the actual plasma potential. The concept of dust was invoked after being sure that no effects of RF and reference electrode contamination are responsible for this behavior. The results indicate that we should remain cautious when using emissive probes in reactive plasmas as they may occasionally lead to erroneous results. (paper)

[en] Plasma enhanced chemical vapour deposition (PECVD) is one of the most favourable tools for deposition of different types of thin films. We have used this technique to deposit diamond like carbon - SiOx (DLC-SiOx) coating on Titanium Zirconium Molybdenum (TZM) alloy which is a design material for compact high temperature reactor (CHTR). However, the alloy has weakness against oxidation above 650°C and corrosive environment of Pb-Bi eutectic is also highly detrimental for it. It is seen that, deposited coating works as a protective layer on TZM and resists oxidation and corrosion of the alloy at elevated temperatures in Pb-Bi eutectic. (author)

[en] Diagnostics of downstream plasma generated in a microwave ECR plasma chemical vapour deposition (CVD) facility (a 2.45 GHz, 1.5 KW) is done using a Langmuir probe. The probe is inserted near the substrate location (640 mm away from main ECR zone). The objective is to see the extent of uniformity in the plasma parameters of generated plasma near the substrate location. For this purpose I-V probe characteristics were recorded at four different operating pressures for four different power levels for each pressure to cover the operating range of parameters that are used during thin film deposition. Data was analysed to obtain the radial electron energy distribution function (EEDF) and radial variation of plasma parameters such as electron number density (n_e), average electron energy (< E>), and plasma potential (V_p). Ion number density (n_i) was also estimated by Orbital Motion Limited Theory (OML) using a Graphical User Interface (GUI) developed for this purpose and compared with n_e calculated from electron energy distribution function (EEDF). The results obtained by the different methods are compared and observed differences are explained.

[en] This paper presents a heuristic approach-based design of a symmetric linear antenna array (LAA) and a non-uniformly excited single-ring circular antenna array (CAA) to improve the far-field radiation characteristics. The far-field radiation pattern improves with lower side lobe level (SLL) which is essential for the reduction in interference in the entire side lobe regions. A recently proposed evolutionary algorithm called social spider algorithm (SSA) is applied to determine the optimum sets of current excitation weights and the inter-element spacing among the array elements to reduce the SLL. In this context, 10-element and 16-element LAA and 8-element, 10-element and 12-element CAA design examples are presented by optimizing the array parameters. The simulation results obtained by using SSA-based approach confirm a considerable improvement in SLL and some restricted improvement in half-power beam width with respect to the uniform array pattern and those of the recently reported literature.

[en] The field emission properties of nano-structured materials have been the subject of extensive research for applications in field emission related device. Their low turn-on voltage and high emission current density make nano-structure based cold cathode an attractive method of generating an energetically clean, low power beam for electron gun. Accelerator and Pulse Power Division has taken initiative to study the feasibility of constructing field emission based electron gun for 3 MeV DC accelerator. The DC gun is required to generate 10 mA current, 5 KV DC electron beam. As a first step, a new set up has been designed and fabricated to study the field emission property of different samples. Three different samples of carbon nanotube directly grown on inconel substrate by plasma CVD under different conditions are studied for field emission property. The base pressure during the field emission measurement was kept at 2e-6 mbar and cathode anode distance was 1 mm. Maximum emission current density up to 19 mA/cm² is obtained at 1.6 KV DC Voltage for one of the sample. The same sample also exhibit low turn-on field i.e. 0.6 V/μm for another sample where CNTs were grown on unoxidised cathode, turn on field is 3.5 V/μm. Field emission current up to 64 micro-Ampere is obtained at 5 KV DC voltage. In this paper, we describe in details the experimental results obtained from different samples. (author)

[en] Carbon nanowalls (CNWs) have been synthesized by electron-cyclotron resonance chemical vapour deposition (ECR-CVD) method on Si substrates. During deposition, processing gas compositions were varied to improve growth rate and it was found that replacing inflammable H₂ by safer and cheaper N₂ improves growth rate of CNWs. Energy dispersive x-ray spectroscopy and Fourier transform Infra-red spectroscopy results showed that N₂ did not take part in bond formation. Emissive probe diagnostics showed that increasing precursor gas to 90% of total gas mixture increases impinging ions’ energy by 3.5 times leading to deposition of vertically oriented CNWs on Si substrate. (paper)

[en] We have designed and developed an APPJ device for solid nuclear waste removal Synthetic Plutonium samples were used as radioactive source and with the help of this device upto 92% decontamination was achieved under optimized condition inside glove box. A scaled up multi-electrode model APPJ reduced the operational time by 50% in comparison to single electrode device. Optimized Argon flow rate of 6 LPM ensured stable plasma jet and high decontamination. Portability, operational ease, high decontamination efficiency and very low secondary waste generation makes this technique a potential alternative to radioactive decontamination in nuclear waste management. (author)

[en] Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) are grown on inconel substrates under two different experimental conditions using atmospheric pressure glow discharge radio-frequency (RF) PECVD process. A specially designed hollow cathode is used for this plasma generation. The growth is carried out at 610 and 660 °C substrate temperatures on inconel substrates. Our results show that CNFs and CNTs could be synthesized at 610 and 660 °C respectively irrespective of pre-treatment methods in either set. HRTEM results indicate that a temperature-induced transformation of CNFs into CNTs occur when the growth temperature is raised from 610 to 660 °C. With the help of characterization results and a schematic model, it is shown how an increase in hydrogen diffusion (∼44% increase) plays a pivotal role in this transformation by providing a sink for hydrogen atoms. Field emission results show that most defective CNFs contribute to the maximum emission current density. This better field emission behavior is explained on the basis that the outer surfaces of CNFs are more defective due to the presence of the open edges of the graphene planes, which results in better field emission from the outer surfaces of the CNFs. (paper)

[en] The center of our disk galaxy, the Milky Way, is dominated by a boxy/peanut-shaped bulge. Numerous studies of the bulge based on stellar photometry have concluded that the bulge stars are exclusively old. The perceived lack of young stars in the bulge strongly constrains its likely formation scenarios, providing evidence that the bulge is a unique population that formed early and separately from the disk. However, recent studies of individual bulge stars using the microlensing technique have reported that they span a range of ages, emphasizing that the bulge may not be a monolithic structure. In this Letter we demonstrate that the presence of young stars that are located predominantly nearer to the plane is expected for a bulge that has formed from the disk via dynamical instabilities. Using an N-body+ smoothed particle hydrodynamics simulation of a disk galaxy forming out of gas cooling inside a dark matter halo and forming stars, we find a qualitative agreement between our model and the observations of younger metal-rich stars in the bulge. We are also able to partially resolve the apparent contradiction in the literature between results that argue for a purely old bulge population and those that show a population comprised of a range in ages; the key is where to look