Reply To: Where are Japan and China in funding Focus?

[jamesr]

While it is always good to test ideas with a simple model like the ideal gas law, to get rough ballpark figures. You should also be aware of under what conditions they are a good approximation and when they will break-down, (and they do break down at any fusion capable densities/temperature/timescales) .

In plasma physics it is common to order each term in the equations in a characteristic time and length scale (or characteristic speed). So for example the conservation of energy gives you the rate of change of pressure, which in turn gives you the characteristic speed(s) of a pressure fluctuation, which for a normal gas is just the speed of sound. In a plasma however there is not just one solution to the equation, there are many.

If the local fluid velocities are small in comparison to the speed of sound then the adiabatic term is the only one you need. However, as the temperature & pressure gradients increase the velocities of the individual ions/electrons become further from Maxwellian and you need to take into account the other terms such as the heat flux.

At that point, if you want to stay with the fluid model, you can either just keep adding on the extra equations of the higher order moments of the velocity distribution function with a closure at a higher order. Or move to a full kinetic model and use a PIC (particle in cell) approach.

If you’re interested in looking at the maths the full fluid equations are described here http://farside.ph.utexas.edu/teaching/plasma/lectures/node32.html