QuantumG,

I found a site today that will blow you away. http://www.myelectricengine.com . This fairly new EE set out to build a reasonably priced MPD, and this site documents his theory, math, and hardware in much easier to understand form than anything else I’ve seen so far. I found the cap bank page while doing a string of searches for how to calculate HV buss inductance. The upshot is that the equivalent circuit of his MHD and our DPF is nearly identical. He doesn’t seem to be aware of the DPF.

The biggest difference is his anode is the outer electrode. The electrode geometries are also different. I did a series of sketches integrating professor Lee’s simplified electrical diagram showing the cap bank as 12 parallel branches, the DPF as 2 more, and the MHD as the last 2, for a total of 16 parallel branches. The DPF and MPD inductances are in series with the spark gaps from Krolak’s diagram. I used 4 SCR banks as current gates. The first 2 divide the HV buss into 3 segments- cap bank, DPF, and MPD, the third gates the MPD’s reverse EMF into the inductive energy recovery system that LLP’s patent reserves for the DPF’s reverse EMF. I’m powering the MPD with the DPF’s reverse EMF. The 4th SCR bank connects the energy conversion and recovery circuits (the cap bank recharger and electrical profit), back to the main cap bank.

Noting the spark gap switch challenges of an expensive part, I got rid of the extra parts (hopefully) by letting the cap bank charge to ~90% of trigger voltage pretty much on it’s own, then delivering the last few thousand volts under control of the ignition timing circuit. Not the ideal MPD theory, but it’s fuel and energy are basically free.

So far it looks good as a current diagram. Haven’t done the math yet, so it may or may not work numerically. But it looks like a promising bolt-on to the drift tube to draw the decelerated He4 ions to the MPD cathode. And in space it shouldn’t need the vacuum pumps.