MadSci Network: Physics Query:

### Re: What is the plasma pressure in a Fussion Reaction?

Date: Wed Dec 8 13:01:19 1999
Posted By: Ken Wharton, Post-doc, Laser/Plasma Physics
Area of science: Physics
ID: 943316469.Ph
Message:

The simple answer is that the pressure of a plasma is simply

p = n kT

Where n is the plasma density (charged particles/volume), k is boltzmann's constant, and T is the temperature.

So, once you know the density of your plasma, you're all set. You might be able to figure it out from this graph, which shows fusion yield for a Deuterium-Tritium (DT) plasma as a function of density times the confinement time (at the 10keV (10^8 C) temperature you specified):

If you know your yield and your confinement time, you can calculate n from this graph. Of course you need a yield greater than 1 to get any net fusion energy! Then you can calculate the pressure.

The problem now becomes one of confinement time. The best magnetic confinment devices can keep the plasma confined for about 0.25 seconds. And this is DESPITE the magnetic fields balancing the plasma pressure! This is where the story starts to get more complicated -- just because you have sufficient pressure balance, that doesn't mean that you're not going to lose all your plasma energy through other, more complicated mechanisms. Much of fusion plasma research is just keeping track of all the "instabilities" that dump the plasma energy into the wall. Designing a device with sufficient pressure to theoretically contain the plasma is the easy part -- the hard part is actually keeping it confined.

Anyway, hopefully this is enough information for you to figure out what you need. Here is the Fusion FAQ on the web.

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