First microwave-heated helium plasmas in CNT

Photograph of a plasma in CNT, as seen through a viewport, consisting of helium with traces of nitrogen.
Photograph of a nitrogen plasma in CNT taken in the spring of 2013.

Microwave-heated helium plasmas have recently been been created in the CNT stellarator for the first time. The plasmas are expected to have some different properties from the plasmas made to date using air and nitrogen. This is due in large part to the fact that helium ions are seven times less massive than nitrogen (N2) ions, and that it takes 58% more energy to ionize a helium atom than is required for N2.


One readily apparent difference between nitrogen and helium plasmas is the color of their glow. The nitrogen plasmas made in CNT to date have a bright pink glow, whereas helium plasmas contain a cyan hue. The apparent color of the glow also depends on factors such as plasma temperature and the number of neutral particles present in the plasma. Work is now underway to more precisely characterize the differences between plasmas with different ion species.

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