The way the magrid of a polywell is usually depicted in Bussard’s descriptions has the coil containers as the “accelerating anode”. Ideally the coils and their power supply would all float at full electron drive positive potential.

For small electron drive voltage (not many kV) this could be done by having insulation between the coils and the magrid coil casings (which are not attached, here). That way the coils could actually be at any convenient voltage, whilst contained in well insulated containers at anode potential.

This trick becomes difficult for full scale, as you run out of space for the insulation at full voltage within the coil containers. Any insulation failure there blows up the machine, as the electron short circuits to the coil supply. Easier in this case to just float the whole coil current supply at full potential, and then you needn’t worry about much insulation between the coils and the containers.

For this rig, I’d try putting a loose “anode grid cage” about each of the coils – could just be a loose winding about each toroid, and have this used as the accelerating anode as one connected piece. For decent vacuum and relatively short distance, it should hold off a fairly large voltage – these could be looped about the outside of the teflon coil formers, and won’t need much support.

Firing the coil supply shouldn’t induce much current in the anode – and it wouldn’t matter much if it did – each winding need not actually form a circuit – it’s only job is to act as a cage that can have positive voltage connected to it, without shorting to the magrid coils themselves.

Of course, rather than having a large positive voltage on the guts of the thing, and the container + guns grounded, one could instead have the guts at ground, and have a large negative voltage on the container + guns. This does tend to mean a lot of arcing from the vacuum chamber and pump to everything nearby, and so I don’t think it’s a particularly good idea – much better to have to deal with a HV+ cage with a coil supply in it (or a very well insulated transformer to drive the coil supply, or even a long insulated rod with a motor at one end and a generator at another…) than have the whole apparatus at deadly voltage. Either way there will be a need for high voltage standoffs through the vacuum chamber, and the effective electric field within the device itself is identical (as it has to be).

Still, As is this work so far is still pretty damn exciting.

Especially that last one. I wonder if perhaps you had an arc?

Maybe it would be worth adding a photodetector inside the vacuum chamber to look for flashes of light coincident with arcing… BW always said there was maximum signal from the photodiode just as the PW went into WB mode….

Maybe leaving the 60 Hz in there was a stroke of serendipity! You would have been scanning through different electron beam energies and currents as you were also scanning through different magnetic field strengths…

Sometimes with experimental work, running with something you *know* is “slightly broken” turns out not to be so broken after all…

I’d consider trying to synchronize your cap bank discharge with the 60 Hz mains as Wayne Farmer suggests, prior to trying to suppress all the AC on the heater. Use a diac+triac with an adjustable phase delay – look up “dimmer switch” circuits. You can probably just use a little transformer to couple the triac’s pulse out to trip your bank. That circuit will let you adjust the “phase” relatively easily as well.

Another thing you could do is, after changing the filament over to DC heating, split the accelerator anode so you have a “gate” ring closer to the cathode. You could then use this with a relatively small potential to control the electron beam current – with the accelerator potential to control the electron beam energy.

But before you change anything, just repeat – do another run with the same settings, and get some more traces recorded, maybe that last shot will just happen every now and then?

Might be worth automating the cap discharge, so you can just leave it running overnight – don’t bother synchronizing it, just let it slowly perform the parametric sweeps for you. :) Good way to collect a lot of data to look at later.

Fantastic!