Electron Cooling in a Magnetically Expanding Plasma

J. M. Little, E. Y. Choueiri

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Electron cooling in a magnetically expanding plasma, which is a fundamental process for plasma flow and detachment in magnetic nozzles, is experimentally investigated using a radio frequency plasma source and magnetic nozzle (MN). Probe measurements of the plasma density, potential, and electron temperature along the center line of the MN indicate that the expansion follows a polytropic law with exponent γe=1.15±0.03. This value contradicts isothermal electron expansion, γe=1, which is commonly assumed in MN models. The axial variation of the measured quantities can be described by a simple quasi-1D fluid model with classical electron thermal conduction, for which it has been previously shown that a value of γe≈1.19 is expected in the weakly collisional limit. A new criterion, derived from the model, ensures efficient ion acceleration when a critical value for the ratio of convected to conducted power is exceeded.

Original languageEnglish (US)
Article number225003
JournalPhysical review letters
Issue number22
StatePublished - Nov 23 2016

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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