Pulsed Tokamak Fusion: Net Energy Gain Possibility?

[artis]

Zpinch works by running a strong current through the plasma which sets up a field that tends to confine the plasma, so if the current is switched on rapidly the resulting temperature increase and B field increase tends to compress the plasma channel rapidly, at least this is how I understand the concept in it's basic form.

I tried googling but did not find any related materials, has anyone ever tried to run a tokamak reactor in such a way?
In theory instead of using direct electrodes like in the Z pinch the tokamak creates a plasma current as a secondary from a drive primary transformer, so what would happen if this primary current was a pulsed square wave?
Assuming of course that the plasma stays in the plasma state between pulses.On a more general note, is it possible in theory to have a net energy gain from a pulsed fusion device , even such that the plasma cools off between each pulse?
the confinement time is very small compared to a tokamak burn but on the other hand since confinement is not necessary one could use much higher pressures of DT gas which should result in a higher fusion rate.
I guess the simple requirement is to have enough energy out from each pulse to account for energy spent on each pulse + net energy gain.

 

[dRic2]

From a structural point of view, a tokamak with just a z-pinch mode is very hard to design because of the difference in magnetic pressure from the inner surface to the outer surface. I think other magnetic fields are introduced to balance this "expanding" effect. If I recall correctly a "pure" z-pinch works well in confining a plasma in a cylindrical geometry but as soon as you "bend" the field lines (like in a tokamak) it does not confine the plasma anymore.

From a stability point of view, the z-pinch mode is unstable under small perturbation, so if, due to fluctuations, the magnetic filed changes slightly in a point it could be a very big problem.

Check out the book "Plasma physics for fusion energy", by Jeffrey Freidberg, it a great book and it does not require a very advance knowledge: an undergrad understanding of EM and classical mechanics should be enough.

 

[artis]

right @dRic2 the plasma would push itself outwards , anyway in a standard tokamak they use the toroidal fields to mitigate just this very effect as I believe it is present in every plasma that is toroidal.

but I think there is one thing that is possible only in a toroidal plasma and that is induced current heating as far as I know all cylindrical pinch type have to use some sort of direct current introduction mechanism like electrodes, am I right?

thanks for the book btw I will check it out.

 

[dRic2]

Yes in a tokamak there is a toroidal component of the field and some other external field I think to stabilize even further.

My understand is very limited (I just took a course this year about plasmas), but I am not sure whether the toroidal current is used to heat the plasma or not. I really don't know, but I am a bit skeptical about it. I think some external source is used, like lasers.

 

[artis]

the induced current indeed heats the plasma initially up until some temp, then RF and neutral particle beams pick it up further because the plasma density is low so ohmic heating can only do so much as far as I know.

 

[jartsa]

Zpinch works by running a strong current through the plasma which sets up a field that tends to confine the plasma, so if the current is switched on rapidly the resulting temperature increase and B field increase tends to compress the plasma channel rapidly, at least this is how I understand the concept in it's basic form.

I tried googling but did not find any related materials, has anyone ever tried to run a tokamak reactor in such a way?
In theory instead of using direct electrodes like in the Z pinch the tokamak creates a plasma current as a secondary from a drive primary transformer, so what would happen if this primary current was a pulsed square wave?
Assuming of course that the plasma stays in the plasma state between pulses.On a more general note, is it possible in theory to have a net energy gain from a pulsed fusion device , even such that the plasma cools off between each pulse?
the confinement time is very small compared to a tokamak burn but on the other hand since confinement is not necessary one could use much higher pressures of DT gas which should result in a higher fusion rate.
I guess the simple requirement is to have enough energy out from each pulse to account for energy spent on each pulse + net energy gain.

So this pulsed device might consist of plasma inside a torus shaped tube, which would be surrounded by rings, in which there would a very large alternating current.

If this device is designed so that the plasma moves at very high speed as it is being alternatingly pinched and released, then current in the plasma could stay quite small, which means that the device could actually work, unlike all those devises that dried to induce a large current into the plasma, which then became unstable.

https://en.wikipedia.org/wiki/Z-pinch#History