Simple High Voltage Generator
Using a simple 555 timer, one can generate 40-50kV using an automotive ignition coil. The circuit diagram is given below.
The power MOSFET (500V, 15A continuous, 60 A pulse) is available from Digi-Key and others. The output voltage is controlled by the duty-cycle control potentiometer on the right. The frequency of operation is about 100Hz and the duty cycle can be varied from a 2-3% to nearly 95%. In practice, no more than 20-30% duty cycle is necessary. A 500V MOV should be placed across the drain-source pins on the MOSFET (or a fixed spark-gap on the ignition coil secondary which discharges before the primary voltage exceeds 500V) in order to prevent MOSFET failure at high duty cycles.
The diode stack can be any EHT diode which can sustain the required peak reverse voltage on the secondary. Note that the polarity may have to be reversed depending on the type of ignition coil used (a test at “low” voltage is recommended before running at “full speed.”)
Note that this circuit can deliver a nasty, possibly lethal, shock. Do not under any circumstances come within several centimeters with the EHT lines during operation. Contact with conductors under EHT is not needed as arcs of several centimeters are possible! The use of “bleeder” resistors is highly recommended on the EHT capacitor for preventing possible inadvertent electrocution by charge stored in the capacitor. This is not a toy. If you construct this device, you take full responsibility for the consequences of its use (or misuse)!