No abstract

It is important to understand how the plasma with unparalleled heat (~10MWm-2) and ion (~1024 m-2s-1) flux will interact with the tungsten walls in the ITER tokamak, more specifically at the Divertor region of the fusion machine. Several linear magnetized plasma devices have been developed worldwide that reproduced ITER Divertor like extreme conditions for studies on relevant plasma surface interaction (PSI) issues under simulated plasma conditions. The "CPP-IPR Magnetized linear Divertor Plasma Experiment for Plasma Surface Interaction" or CIMPLE-PSI is one of the few Tokamak Divertor simulator devices that successfully reproduces both ITER-like ion and heat flux values, whose design, development and recent commissioning will be presented in this paper. A segmented plasma torch produced high-density plasma jet collimated with a maximum 0.45 Tesla axial magnetic field propagates at few Pascal chamber pressure that is maintained by four numbers of roots vacuum pumps with 14,000 m-3/h pumping capacity that interacts with a remotely placed tungsten target under controlled experimental conditions. The paper will report detailed diagnostics of the plasma jet through optical emission spectroscopic techniques (1.33 m McPherson spectrometer), a retractable Langmuir probe and water calorimeters while operating the plasma with helium and hydrogen mixture of gases. During recent PSI experiments in this device under irradiation of pure helium plasma (exposed for 1800 seconds under 0.3T magnetic field, target biased to-45 V), we had witnessed (FESEM, HRTEM) formation of surface nanotendrils in profuse amounts, recent characterization results from which also will be presented here.

Floating potential fluctuations from a direct current magnetron sputtering plasma have been analysed using time series analysis techniques like phase space plots, power spectra, frequency bifurcation plot, etc. The system exhibits quasiperiodic-chaotic-quasiperiodic-chaotic transitions as the discharge voltage was increased. The transitions of the fluctuations, quantified using the largest Lyapunov exponent, have been corroborated by Hurst exponent and the Shannon entropy. The Shannon entropy is high for quasiperiodic and low for chaotic oscillations.

A single-step, thermal plasma-assisted technique is reported for size-controlled synthesis of silver-carbon (Ag-C) nanocomposites, to be used for antibacterial applications. Silver nanoparticles of sizes less than 10 nm can directly penetrate into the core of the bacteria, while stiff, nanocrystalline carbon may rupture the microorganisms with their sharp edges. Experiments demonstrated that silver nanoparticles nucleate anchoring tightly on carbon sheets, which can inhibit their aggregation and growth in size and becomes more effective as crystallinity of the carbon enhances further. Nanocomposite samples were synthesized using a hot graphite nozzle and with variation of ambient pressure in the sample collection chamber. The Ag-C sample synthesized at 190 mbar chamber pressure demonstrated the best antibacterial activities. The zone of inhibition was measured for this sample as 18 mm for the gram-positive E. hirae and 15 mm for the gram-negative E. coli bacteria at their corresponding minimum inhibitory values of 0.54 mg ml−1 and 0.9 mg ml−1 respectively. The crystallinity of the carbon nanosheets was measured to be the best for this particular sample and the average size of the silver nanoparticles remaining entangled on them was measured as 4.6 nm, which to our knowledge is the smallest ever synthesized by a plasma-assisted method. The gas temperature at the injection section was measured using the C2 Swan band system, (0, 0) vibrational transition located at 516.5 nm, which confirms temperature enhanced substantially in presence of the graphite nozzle, which had led to the enhanced material crystallinity and synthesis of particles with the smallest sizes.

No abstract