Something I’ve crafted for the new X-ray experiments: a half wave, eight stage Cockroft Walton multiplier (or a Villard cascade, whichever name you like), submerged in oil, providing a theoretical maximum output voltage in excess of 220 kV with a maximum supply voltage of 10 kV AC, with headroom.
Sixteen 2.2nF and sixteen 30mA rectifiers, all rated 30 kilovolts, form the 8-stage half wave multiplier. Capacitors need to be rated for the peak voltage + reserve, diodes 2 times the peak voltage + reserve. In my case, as mentioned above, a theoretical maximum of 10 kV AC root-mean-square can be supplied (10*2*1.41, with a 2 kilovolt headroom). The circuit is quite evident from the wiring below:
Theoretical output voltage (that means, when unloaded, input is a sine wave, frequency is sufficiently high and excluding voltage drops on parts) is then calculated with a simple equation:
Uout = 2 * Uin * sqrt(2) * stages
where 1 stage equals to a pair of 2 diodes and 2 capacitors.
Of course, the whole setup needs to be submerged in oil, to prevent arc over and corona losses. I have used transformer oil to be on the safe side. Although clean and de-humidified vegetable or mineral oil will suffice.
If you have taken a look at the wiring above, you can say that the output kilovoltage is positive with respect to ground.
However adding a capacitor extra on the “unused end” allows you to change this polarity, if connected in reverse. In my “lunch box design” such an approach is not possible, because that’d need good insulation; to prevent pairs of terminals from arcing between each other.
If your approach leaks, seal them properly, and not with e.g. hot glue, as certain oils (if not all) dissolve it.
The photo above shows the multiplier, fed with a limited square-wave AC input out of this small driver. At load, the supply voltage of such a purposely-low-powered driver drops to approximately three kilovolts AC, estimated by spark ignition distance. Which is good, as this setup was not made with arcs in mind (30 mA rated rectifiers).
This multiplier is used in the (upcoming X-ray setup), coupled with this ZVS driver and a Soviet 8kV AC flyback.
… and again