Electrode Configuration Effect on the Performance of a Two-Dimensional Magnetoplasmadynamic Arcjet

Thrust performance and internal plasma flowfield of a 1-MW class self-field magnetoplasmadynamic (MPD) arcjet were measured to evaluate their dependence on the cross-sectional geometry of the electrodes. A multichannel two-dimensional MPD arcjet in quasisteady operation was used to visualize the two-dimensional flowfield and reveal the correlation between the internal flowfield and the thrust performance. The experimental results for six different electrode configurations show that the thrust performance strongly depends on the thruster chamber cross-sectional geometries for the I sub(sp) range of interest, 1000-3000 s. The cathode length determined the engine performance, regardless of the anode geometry. In particular, the convergent-divergent anode with a short cathode showed the best performance. The superior acceleration mechanism of the short cathode was explained on the basis of two-dimensional plasma distributions such as discharge current contours and plasma density obtained by Mach-Zehnder interferometry. A dense plasma region near the tip of the short cathode was observed and subsequent expansion guided by the diverging nozzle can enhance aerodynamic acceleration, which contributes to large thrust generation.