1,721,045 research outputs found
Gabriel Stephen Kurniawan's Quick Files
No full textThe Quick Files feature was discontinued and it’s files were migrated into this Project on March 11, 2022. The file URL’s will still resolve properly, and the Quick Files logs are available in the Project’s Recent Activity
Gabriel Stephen Kurniawan's Quick Files
No full textThe Quick Files feature was discontinued and it’s files were migrated into this Project on March 11, 2022. The file URL’s will still resolve properly, and the Quick Files logs are available in the Project’s Recent Activity
Hollow cathode thrusters for all-electric spacecraft
No full textThis paper characterizes thrust performance of a variant of the T6 hollow cathode modified for improved operational characteristics. The device displays promising performance and highlights the potential for application as a microthruster. The T6 cathode is able to produce specific impulse of over 1050s with xenon and argon; however the dominant acceleration mechanism at low flow rates is shown to be almost entirely electromagnetic effectively constituting a low power, magneto-plasma-dynamic thruster. The modified cathode also displayed very low discharge voltages ~12V and stable operation while carrying currents as high as 30-Amps on flow rates of less than 0.1mgs-1 down to 0.04mgs-1 with xenon. This investigation also highlights the importance of electrode geometry in hollow cathode thruster design and indeed in all other applications of hollow cathode where flow rates should be minimize
A model for low work function compound deposition on hollow cathode insert surface
No full textThe chemistry of the low work function compounds on tungsten emitter surface has been presented qualitatively giving a possible explanation of the 4:1:1 ratio commonly used. The processes involved in BaO deposition and desorption have been described and quantified as well as possible given the chemical data present in the literature producing a simple model for deposition and desorption. The model has then been tested with the ELT NSTAR cathode. The results obtained from the model have been found to be very conservative as expected and a possible explanation has been given stressing the need of a coupled deposition-desorption-plasma model
A model for barium oxide depletion from hollow cathode inserts
No full textIn this paper, a chemical model to predict barium oxide depletion from hollow cathode insert will be developed.This model is based on the knowledge of the ternary diagramthat describes the BaO?CaO?Al2O3 system and takes also intoaccount the diffusive motion of barium oxide inside the insert. A comparison between numerical and experimental data is made to determine the diffusion coefficient inside the insert. The diffusion coefficient found presents an Arrhenius trend with activation energy similar to the one of barium oxide evaporation. A 2-D model is used to demonstrate how the temperature profile along the insert is a key parameter to calculate barium depletion. This is the first model the authors are aware of that includes boththe complex chemistry of the BaO?CaO?Al2O3 system and thediffusion motion of BaO from the insert core to the surface.<br/
Hollow cathode life time model
No full textIn this paper the latest advances in the hollow cathode lifetime modeling carried out at the University of Southampton will be presented. A barium oxide insert depletion model and a surface low work function compounds deposition/depletion model have been already developed by the authors. Here a procedure to update the plasma parameters relatively to changes of the hollow cathode surface work function and an end-of-life criterion will be presented. The procedure has been validated with experimental results and then coupled with the deposition/desorption model already developed by the authors. The evolution of the surface of the cathode tested for 28,000 hours by Sarver-Verhey has been simulated and from the data obtained an end of life criterion has been developed. Then using this criterion the ELT NSTAR discharge cathode has been simulated under the throttling conditions used during the Deep Space 1 Spare Ion Engine. The lifetimes found are in agreement with the theoretical expectation
Assessment of the T5 and T6 hollow cathodes as reaction control thrusters
No full textHollow cathodes have been proposed as reaction control thrusters for all-electric and small spacecraft. This paper makes an assessment of modified T5 and T6 hollow cathodes for use as millinewton range thrusters. The influence of terminal parameters such as discharge current, mass flow rate, and cathode/anode geometry on thrust production is discussed. The data indicate that the T5 cathode may be able to develop specific impulses in the range of 150–250 s with argon at reasonable thrust efficiencies of up to 14%. As such, hollow-cathode thrusters may meet some limited applications. However, it is unlikely that this type of thruster could be improved significantly or could compete with similar thrusters in the same operating range. High specific impulse operation is also shown to develop large discharge voltage fluctuations, which may significantly limit the lifetime of such a device.<br/
Barium oxide depletion from hollow cathode insert, modelling and comparison with experiments
No full textIn this paper, the results of a barium oxide depletion model are compared with some experimental results. Themodel is used to simulate the T5 and T6 cathodes and the NSTAR discharge cathode. A comparison with the experimental data is performed. For the T5 and T6 cathodes, good qualitative agreement is found, but for theNSTAR cathode, the agreement is not as good. In both cases, the agreement is improved when the boundary conditions are modified to better reflect the experimental conditions. The model presented is the first three-dimensional axisymmetric insert model that includes the dependency of BaO depletion from both the impregnant chemistry and the diffusive motion inside the insert
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