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This term came up pretty quickly when reading about plasmas, and although it’s somewhat frequent in terms of use, I couldn’t find a clear explanation of what it is, so I figured it’d be useful, both for me and other students who find themselves in this situation.

FizzKicks
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  • You may find the following useful: https://physics.stackexchange.com/a/268594/59023 and https://physics.stackexchange.com/a/535896/59023 – honeste_vivere Aug 27 '21 at 13:35

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"Tenuous" means the density of the plasma is less than 1 particle/cm^3.

In contrast "dense" plasma is on the order of thousands of particles/cm^3.

See p. 38 of NASA-HDBK-4002B https://standards.nasa.gov/sites/default/files/standards/NASA/B/0/2022-06-07-NASA-HDBK-4002B-Approved.pdf

oogieoogieful
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    These terms only make sense in astrophysics. Air has about 10^18 particles/cm^3. Even the ion density inside a plasma globe's streamers is far more (despite ions only being a tiny fraction of the air molecules in the globe). – Kevin Kostlan Mar 29 '23 at 18:39
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    Page 38 says "A tenuous plasma of less than 1 particle/cm³ will charge the spacecraft and its surfaces more slowly than a dense plasma of thousands of particles/cm³." This doesn't seem to be a definition. It suggests that <1 particle/cm³ is tenuous, but not the converse. I think that "tenuous" just means "not dense", and "dense" is rather vaguely defined. As Kevin Kostlan said, thousands of particles/cm³ is not at all dense in other contexts. – benrg Mar 29 '23 at 19:03