Extracting power from a plasma

[rprosser]

I'm exploring an idea for a MHD generator. This may well have been done before but I can't find that much about the subject online so I would appreciate input from PF people.

Assume that a plasma 'ball' is flowing along the axis of a tube, which is surrounded by electromagnet coils. The plasma will of course 'pinch', with the ions and electrons rotating in opposite directions around the axis.

Now if the ball is passed through another coil, the induced EMF from the circulating charges would create a current pulse in the coil, which could then be tapped as an electric generator. An additional EMF in the coil wires will also be created along the axial direction as the plasma pulse passes through; presumably that could also be part of an electric circuit if the conductor was wide enough to permit suitable connections.

I wish to focus on the former case however: how much power could be taken from the plasma in that way? Would the plasma then slow down?

Please note that I know about the various equations involved but I am not that good at maths! I am also well aware that a changing current is required to induce the EMF, hence the 'ball' assumption in the first place.

I would appreciate some typical examples if possible.


Thanks ...

Richard

 

[zhermes]

So we should put copious amounts of power into creating, confining and directing a 'ball' of plasma; then use the motion of that 'ball' to generate current in a coil...
Why don't you just use a generator and cut out the middle man?

The relevant equation you need to look at is:
$$\sum E_\textrm{initial} = \sum E_\textrm{final}$$

 

[rprosser]

Thanks for your response.

Richard

 

[zhermes]

I assume you've been thinking about magnetic confinement plasma systems for Fusion power. In that case, the plasma is just a means for achieving the high energy densities required for sustained fusion reactions. The alternative is "Inertial Confinement," which is far less cool (in my opinion).

The key to plasma fusion is that by pumping tons of energy into the system, you bring it to a level where a whole new reservoir of energy is available---thus making the process worth-while. If you try to use a classical method of extracting power (e.g. induction), you're just going to add tremendous inefficiencies between doing work (converting electricity to heat) and then back again (to electricity).

Hope that more detailed (and less derisive) explanation is helpful.