I am currently tinkering with a railgun experiment, and I was thinking of using a liquid nitrogen loop to cool the rails down to very low resistance, and inject some nitrogen into the barrel between the rails, to remove some oxygen and prevent corrosion, and excessive arcing. I would run the liquid nitrogen through a hole down the length of the rail, and into the barrel through much smaller holes connecting to the main line in the rail. The nitrogen would go from the tank through a pump, through one rail, into a tubing to the other rail and back to the tank.
Now I know nitrogen is magnetically transparent, and being a mostly inert gas doesn't run the chance of reacting unexpectedly. Some things I am unsure about:
I have looked around but it seems there are not a lot of places that sell tubing and fittings for liquid nitrogen. Is there some place I can browse to look for standard size fittings and tubing, and a small pump to carry liquid nitrogen through my system? The other difficulty is that I need to keep fittings and tubings to magnetically transparent non conductive materials, otherwise the magnetic field while firing (let's say 10 kJ) will mangle them. I am guessing there will be some custom fabrication involved, but still an idea of the basic sizes will help me make some design decisions.
At what pressure is it safe to carry liquid nitrogen through a system like this? Obviously the pressure will not be very high, but since I need to bleed some gas into the barrel, I need to set a target main line pressure to calculate injector channels size.
Is there an inherent danger I am overlooking with running an inert gas through a rail that will conduct a 1 ms pulse of 10 kJ? Obviously it won't ignite or explode, but is there a chance it will ionize at those relatively low energies?
After some more looking, it seems PTFE (Teflon) is the right material for the job, but its stability under a high magnetic field is unclear. Is there a better material for this?
This is a crude cross section of the proposed arrangement. Orange is the copper rails, dark grey is PTFE, light grey is payload.
There has been concern about the heat dissipation in the system, and I should mention that the system is fed power through some large inductors that should dissipate the bulk of the heat. They are in place to stretch out the pulse in the first place. The dissipation in the rails should be very, very low, considering oxygen-less copper at 77K has an abysmally low resistance. The coils will probably also get the nitrogen treatment.