EMERGING TRENDS IN WALL-FREE HALL THRUSTERS DEVELOPMENT

2D-hybrid model was created for the proposed new type accelerator with a virtual cathode which allows to avoid sputtering of the cathode surface and to preserve the dynamics of accelerated ions. In the framework of the model, it was shown that ions first form a positive space charge in the system center, and eventually, under an ac-tion of created own electric field, emerge from both ends of the system.

Validation of evaporation-determined model of arc-cathode coupling in the peak current phase in pulsed GMA welding

A first experimental validation of the EDACC (evaporation-determined arc-cathode coupling) model is performend by comparing the experimental and simulated current in the peak current phase of a pulsed GMAW (gas metal arc welding) process. For this, the EDACC model was extended to limit the cathode surface temperature to a realistic value of <2400K. The information on the plasma for the EDACC model was gathered from literature and extrapolated and extended according to qualitative reasoning. The information on the cathode surface of the EDACC model was derived from a steady-state simulation of the weld pool, using an averaging approach over time for the energy and current. The weld pool surface temperature was compared to pyrometric measurements, that were performed for this work, and the agreement was found to be fair. The observed agreement between the modelled and experimentally determined current was within 10%. As strong assumptions were made for the comparison, the validation cannot be considered as final, but the assumptions are thoroughly analyzed and discussed. However the critical link between surface temperature, plasma temperature and total current transmitted could be reconstructed.

Use of Biochar-Based Cathodes and Increase in the Electron Flow by Pseudomonas aeruginosa to Improve Waste Treatment in Microbial Fuel Cells

In this paper, we tested the combined use of a biochar-based material at the cathode and of Pseudomonas aeruginosa strain in a single chamber, air cathode microbial fuel cells (MFCs) fed with a mix of shredded vegetable and phosphate buffer solution (PBS) in a 30% solid/liquid ratio. As a control system, we set up and tested MFCs provided with a composite cathode made up of a nickel mesh current collector, activated carbon and a single porous poly tetra fluoro ethylene (PTFE) diffusion layer. At the end of the experiments, we compared the performance of the two systems, in the presence and absence of P. aeruginosa, in terms of electric outputs. We also explored the potential reutilization of cathodes. Unlike composite material, biochar showed a life span of up to 3 cycles of 15 days each, with a pH of the feedstock kept in a range of neutrality. In order to relate the electric performance to the amount of solid substrates used as source of carbon and energy, besides of cathode surface, we referred power density (PD) and current density (CD) to kg of biomass used. The maximum outputs obtained when using the sole microflora were, on average, respectively 0.19 Wm−2kg−1 and 2.67 Wm−2kg−1, with peaks of 0.32 Wm−2kg−1 and 4.87 Wm−2kg−1 of cathode surface and mass of treated biomass in MFCs with biochar and PTFE cathodes respectively. As to current outputs, the maximum values were 7.5 Am−2 kg−1 and 35.6 Am−2kg−1 in MFCs with biochar-based material and a composite cathode. If compared to the utilization of the sole acidogenic/acetogenic microflora in vegetable residues, we observed an increment of the power outputs of about 16.5 folds in both systems when we added P. aeruginosa to the shredded vegetables. Even though the MFCs with PTFE-cathode achieved the highest performance in terms of PD and CD, they underwent a fouling episode after about 10 days of operation, with a dramatic decrease in pH and both PD and CD. Our results confirm the potentialities of the utilization of biochar-based materials in waste treatment and bioenergy production.

INCREASING THE ENERGY EFFICIENCY OF THERMOCATHODES OPERATION

The paper presents the results of experimental research on modifying the active area of cathode surfaces applied in the construction of electronic guns and increasing their operating efciency. The intensity of the thermo-electronic emission current is directly proportional to the area of the active surface of the cathodes used for this purpose. To change the micro-geometry of the metal cathode surface, the method of pulsed electric discharge machining (PEDM) was applied. As a result of the application of the discharge plasma on the surface of the cathodes, Taylor cones with heights ranging from 50 to 100 µm were extracted. The analysis of the obtained current-voltage characteristics allows us to compare the values of the saturation current intensities for unprocessed cathodes and those processed by the proposed technology. The increase of the active area of the cathodes with conical asperities causes the increase of the electronic thermoemission current by 10^4. A comparing to the cathodes whose active surfaces have not been processed by this method.