I am currently repeating an experiment performed by Joe Khachan and Matthew Carr in Sydney, Australia.
Their experiment is written up here: “The dependence of the virtual cathode in a PolywellTM on the coil current and background gas pressure” ($1.99 pay wall)
Joe and Matt were able to delivery 2.5kA to the coil:
The coils were driven by a pulsed current power supply that consisted of a 7.5 mF capacitor bank, which could be charged to a maximum voltage of 450 V….A maximum peak current of 2.5 kA was achieved.
We are seeing an effective resistance of ~0.45Ω compared to their 0.18Ω.
We need to lower the resistance and increase the voltage.
I started with raising the voltage. I rewired the coil power supply to use 2 capacitors in series: 0.3mF, 900V
The power supply’s transformer and rectifier only go to 600V (but I pushed them to 800V without issue)
With 800V we get 1300A. More current, but effective resistance increases to 0.61Ω.
OK fine. Lets try lowering the resistance with a dummy coil directly connected to the power supply. 45 turns 6cm diameter. The Polywell coil is same size but 15 more turns.
Here it is connected:
Now we are clearing 2.5kA with 600V! But look at the strange pulse shape. Hmm.
I thought having the coil so close to the power supply might be a confounding factor. I added 1M of 12 gauge stranded wire to distance the coil:
Revealingly, just adding that 1 meter of wire reduced the current by almost half for same 600V:
So clearly delivering current will be a design challenge.
A note on technique. Based on comments I now ensure probes are perpendicular to current: