# Plasma Expansion Characterization of a Vacuum Arc Thruster with Stereo Imaging
## 3 Results
The front view of the plume together with the PJP is shown in (e), while (d) represents the isometric view of the left direction of observation and (f) shows the corresponding right view with the 3D  
Figure 14: Results for all measurements without magnetic nozzle: (**a**) left direction of observation 10 ns; (**b**) recording 10 ns; (**c**) right direction of observation 10 ns; (**d**) left direction of observation 500 ns; (**e**) recording 500 ns; (**f**) right direction of observation 500 ns; (**g**) left direction of observation 750 ns; (**h**) recording 750 ns; (i) right direction of observation 750 ns; (j) left direction of observation 10 \(\upmu\)s; (**k**) recording 10 \(\upmu\)s; (**l**) right direction of observation 10 \(\upmu\)s.  
PJP model, respectively. Considering the recording of the two perspectives, the shape can be recognized in the corresponding reconstructed 3D model. As the recordings and the models show, the shape of the plasma plume is not uniform, because of the clearly different expansion shape observed from the two perspectives. In Figure 13, the corresponding results of the evaluation from measurements 1 \(\upmu\)s after ignition with a magnetic nozzle are illustrated. The arrangement of the images is identical to that in Figure 12. Here, the model of the thruster with the magnetic nozzle is also displayed. An isometric view of the reconstructed model is also shown in (d) and (f) to offer a spatial impression of the result. Here, the more uniform shape of the plasma plume  
Figure 15: Results for all measurements with magnetic nozzle: (**a**) left direction of observation 10 ns; (**b**) recording 10 ns; (**c**) right direction of observation 10 ns; (**d**) left direction of observation 500 ns; (**e**) recording 500 ns; (**f**) right direction of observation 500 ns; (**g**) left direction of observation 750 ns; (**h**) recording 750 ns; (**i**) right direction of observation 750 ns; (**j**) left direction of observation 10 \(\upmu\)s; (**k**) recording 10 \(\upmu\)s; (**l**) right direction of observation 10 \(\upmu\)s.  
can be detected. By comparing the results from Figures 12 and 13, it can also be seen that the plasma shows greater expansion along the nozzle exit when using the magnetic nozzle. To detect the plume expansion at several points in time, the camera recorded images with a set delay according to Table 1. For all recordings, a 3D model was computed. Figure 14 shows the recorded images and the corresponding reconstructed 3D models for the other measurements--10 ns, 500 ns, 750 ns and 10 \(\upmu\)s after ignition--and without a magnetic nozzle. In this figure, the 3D model of the PJP is omitted for clarity. The formation of the plasma plume is very irregular. This can be seen from the recordings (b), (e), (h) and (k). They do not show the homogeneous and uniform formation of the plasma plume. Rather, clear irregularities and incisions are visible on the contour of the plume. The calculated three-dimensional models reproduce these obvious features well. It can be seen that the discharge spreads preferably horizontally at the beginning. Only after a longer time interval from ignition does the plume expand increasingly vertically. The corresponding 3D models using the magnetic nozzle for the different points in time were also calculated. In Figure 15, the results for the measurements with a magnetic nozzle are listed. The arrangement is identical to that in Figure 14. The gap in the images and the 3D models presents the magnetic nozzle, as can be seen in Figure 13. The recordings (b), (e) and (h) and the reconstructed models show that the formation of the plume is more homogeneous than for the measurements without a magnetic nozzle. It can also be recognized that the plume expands preferentially vertically and spreads further with an increasing time interval to the ignition in comparison to the case using no magnetic nozzle. Looking at all calculated 3D models, it can be said that the shape and features of the plasma plume can be reconstructed from both directions of observation.