Better helium plasma

The previous movie only showed the plasma at low voltages before the feedthough broke.
We made a new feedthrough, fused quartz, should be able to handle 50kV.
This time we go beyond sparks, a stable plasma can be seen, it's clearly red (helium), and near the end (around 7.5 kV, about 3.5 mA) some Xray spots can be seen.