Reply To: Focus Fusion Rail Gun

[asymmetric_implosion]

vansig wrote: such current thresholds and field strength thresholds are just constraints to be considered inputs to the design.

OK. The constraint is being able to have a pinch at >100 T next to a superconductor with a peak magnetic field of ~10 T on a really good day. Typically that is accomplished with magnetic shield. Now you have material between the pinch the superconductor which carries the current.

Now the real problem, do you really want a superconductor in your system? Sure, losses transfer is cool and all for DC power transmission but it is a good thing for pulse power. At first, sure it seems like a good idea. Who doesn’t want a more efficient system? Well, the capacitors in the system are resistive so you have some loss there. Probably a fairly large part of the controllable loss. OK, the creative soul is not stopped by this detail. Inductive energy storage is the solution and a superconducting coil is the solution. OK. One problem down. Now, you need to transfer that current in either a switch or cause the plasma focus to breakdown. Either gas conductor is resistive. So you still get some loss, but hey it’s better than before….or is it? A plasma focus is an resistive-inductive-capacitive circuit. You need finite resistance to keep the circuit from going crazy and it is more resistance than the plasma alone can supply. On the forward pulse this seems like a great idea at you get more current but on the reverse pulse you have a great deal of voltage and current to deal with that some components aren’t prepared to deal with. Now the pinch should take a lot of energy which helps but you are relying on the pinch. What if you have a back shot and the pinch fizzles? This will happen and if the pulse power can’t handle the full current in reverse it will be damaged.

Now think about the cost. Copper, tungsten and other metals are pretty good conductors that don’t require much to just work and while the costs vary, you can get the materials relatively easily is the shapes of interest. If you think that tungsten is a problem material, you ain’t seen nothin’. Superconductors typically have to be in a nice crystal structure to work at their best. The plasma erodes the surface on each shot so bye-bye nice crystal structure. Then you need a cooling system with an efficiency typically less than 1% (Thank you, Mr Carot). This means that any heat to take out of the superconductor requires 100X the total system power. Hmmmm. X-rays and UV get absorbed into the anode along with particles. Now you have to remove 100X that heat. The compact, efficient plasma focus just became a tokamek. 🙂