DerAlbi wrote ...

Sry Uspring, maybe its just me beeing a human showing his most inherent characteristic: i didnt understand it, so i deny it
And honestly i still dont understand it completely (while i am still getting the point). The problem is that B is a function of Space, and current and therefore time and projectile position. I cant break that down to one single line in a heartbeat.

When talking about efficiency i never ever would consider to start out on B. I allways acted upon the allready integrated force on the Projectile. That force is then abstract enough to eliminate enough variables. It just comes down to F=F_0(I_0, x(t))*(I(t)/I_0)^2 with x beeing the projectile position and I0 beeing the constant current with which i determined F_0(x). I then know that P_loss ~ I^2 and then i can calculate, given the right time-function of the current I, the efficiency and with that i can optimize my Current-Waveform, but never B itself.
B(x,y,z,x_projectile, I(t)) could be a viable alternative, but to be honest... i can accept the fact that my last layer of wire should only be half the coil length either on the front or back-side of the coil, but i would not think about changing the coil format extensively. Its a manufacturing-boundary i simply wouldnt cross. But thats me, and me alone having that particular restriction. So... dont bother
Still having written this i think its more beneficial if you try to shape the F_0(I_0, x) - to a waveform thats easily aproximated by a typical inductor current. Of couse this shapes B too.. but the process is more guided if you rely on F instead of B.

No aluminium is hard to get in small quantities. Currently i only know how my models change if i use AL but nothing more and i could live with the predictions. Dont even start to think about Aluminium (which btw most heatsinks are made out of) heat management. If the dissipated energy in a coil is high enough to raise the temperature noticable then you did it wrong The major risk at this point is a thermal runaway of a hotspot.

Concerning the FOM: maybe there is a missunderstanding. I think i get where you are pointing at. Maybe its my fault not to be more precice..... Ekin*Eff^2 is the FOM to which i optimized my switching for the coils <- and only that! The whole conept however is not really influenced by that except the estimation of maximum current through my swithces and the reduced cap-size i need due to the prioritized Efficiency. The cap-size has direct implications on weight and volume of the gun and is to be considered a fact of life in the moment. The same is with the switching-elements since thats a huge price factor. First and foremost i have to make sure that electrically i can reach my goals (like 100J) and then be happy about that its actually quite small too
Its just... when you finally have something working (either in simulation or real life) thats so flexible that you can optimize it at will you need to invent a FOM which repesents your _personal_ goals. It does not mean that until then you have everything built with that FOM in mind. But it might mean that during a redesign you can optimize your gun having the experience in mind which you gained using that FOM.
I found that Ekin*Eff^2 leaves _ME_ with reasonable output power while having a quite small cap bank. I also tried to optimize for otehr FOMs but the predictions werent so nice for my design then. In conrast to that it also means that i acutally need more stages because i push less energy per stage - in the end someone else might have different priorities... but for me adding stages.. no problem.

Yes and No. It depends on what you try to optimize. Changing coil geometry to a complicated shape might yield not much (even if it yields something) compared to the gained complexity. Its what i would call "a bad compromise".
Increasing complexity like switching from SCR to IGBTs is however a worty step. Why? The gained complexity is justified by the gained properties. You dont need to form the B-Field anymore.. you simply form the current waveform yielding the more/same improvement and end up even more flexible.
However this is a completely subjetive thing! So if you have different opinion: totally fine.

I realize that i should not try to stop such research because every gained knowledge is good, however i like to point out that you should expect not much practical use. But who knows. maybe i am completely wrong. That would be awesome!

DerAlbi wrote ...

Soooohh much text agaaaaain

You can concentrate magnetic fields really, really well with the use of a "guide" material, as I learned last night while doing a lot of simulations. [....] The realistic field inside would be 10-12T at peak for what I was simulating

NooooOOOOOoooHHHHhhhh! <- Roasting
Understand the problem with saturations: There is simply no material that is a "guide" at those field strengths. Above 2T every material will just be like "not there" and therefor there is no guidance anymore. This is an important switch that has to click in your head. Just repeat saying it "there is no magnetic guidance above 2T" like Bart Simpson.