10^10 J/m^3 For All Plasma?

[Agnaa]

Our Calculations page currently has this to say at the end of the Plasma section...

For example plasma, for which high energy density physics applies, is defined to have at least an energy density of 10^10 J/m^3.

That line implies that any matter in the plasma state would have an energy density of 10^10 J/m^3. But when you read the link that's just not what it says.

It instead says that high energy density physics begins there. For stuff heated to 10,000 K and over. This appears to not include all plasma; especially because the previous chapter in the book is titled "Low-Temperature Plasma Science and Engineering", and is about plasma at lower temperatures than that.

And on a more fundamental level, it sounds strange for physicists to define a state of matter this way. All other states of matter are based on the way the particles behave, which is why objects melt and boil at different temperatures. I would not expect them to define a plasma as just a certain level of energy density, with no regard for the matter that composes it or its properties.

I think this line should be removed due to being inaccurate.

I'm not sure who added it or who would be knowledgable about this sorta thing, so I'll just ping @DontTalkDT @KLOL506

 

[DontTalkDT]

Read the line again. It doesn't say all plasma has that energy density. It says all plasma for which high energy density physics applies does.

 

[Agnaa]

I think that's badly phrased then. Right now it can be read as "High energy density physics applies to plasma, so it has an energy density of at least 10^10 J/m^3". It doesn't help that often parts of sentences that are enclosed by commas can be ignored.

But on a more practical level, I don't really see how a statement like that would be useful. Are there actually verses that say "High energy density physics applies to this plasma"?

If so, I'd suggest a reword to something like "If a plasma is stated to operate under the rules of high energy density physics, it can be assumed to have an energy density of at least 10^10 J/m^3." But if not, I think it's best to delete to avoid confusion (I just had someone post a calc saying that because an energy beam seems to be plasma, they could use that energy density).

 

[DontTalkDT]

The statement is not useful. It's a remnant from a debate where it was debated whether it should apply to all plasma, which was rejected, but people wanted it at least mentioned.
Feel free to reword the sentence as you suggested.

 

[Agnaa]

Yeah okay. Done.

 

[KLOL506]

Plasma-related stuff isn't my cup of tea honestly.