Spectroscopic study of the magnetic field, ion dynamics and electron density evolution in a plasma opening switch

Spatially resolved measurements in a planar microsecond POS, using spectroscopy of dopants in the plasma together with charge-exchange spectroscopy, are presented. Measurements of the axial ion velocities together with the B-field and the plasma density evolution show pushing of the protons ahead of the magnetic field together with field penetration into the carbon plasma. A plasma density drop, which leads to the switch opening, was observed during the field penetration into the carbon plasma. The pushing of protons causes plasma flow into the vacuum region between the POS and the load and influences the energy coupling to the load. These results demonstrate the great importance of the effects associated with a multicomponet plasma and makes the plasma composition an important parameters influencing the POS operation. Measurements with a reversed polarity of the POS do not show any significant difference in the magnetic field and the electron density evolution, as predicted by the electron magnetohydrodynamic theory, implying the field penetration is not dominated by Hall penetration. Alternatively, the observed penetration could also be associated with an anomalous collisionality, which would also explain the observed broad current channel. However, so far, no mechanism predicting such a high collisionality has been demonstrated.