Mapping the Local Electron Density of a Laboratory Hydrogen Plasma via the Investigation of Stark Broadening

The Caltech MHD Plasma Jet experiment generates a relatively low temperature plasma of approximately 2eV and density of approximately 10^21m-3, and yet has been observed to emit X-rays with energies averaging around 7keV. How a modest temperature plasma generates electrons energetic enough to produce these X-rays is an open question. The local electron density is to be investigated with the use of a two-color optical diagnostic tool which allows for the capture of side-by-side monochromatic images at different wavelengths. Using two ultra-narrowband optical filters placed at 484.7nm and 485.6nm, the Stark broadening of the Hβ spectral line can be investigated. Using a fast framing camera, measurements of this broadening may be resolved with a higher degree of spatial and temporal resolution than simple spectrometry, which has already been used to demonstrate significant stark broadening. Specific attention will be given to a hydrogen plasma undergoing the kink instability and a secondary Rayleigh-Taylor instability (RTI), for which temperature and density maps are to be generated. A preliminary goal is to measure the correlation between local electron density reduction, temperature fluctuation, and overall dimming of the plasma in the region of the RTI. This measurement is expected to provide information relevant to how a low temperature plasma can generate electrons greatly exceeding the average thermal velocity.