dc42:
The transistor passes the power (up to 250mA) to the HV multiplier. The op amp cannot supply enough current by itself.The high voltage output is on the right hand side of the schematic. The positive side is marked "+ 0-5 kV", and the negative side is marked Gnd. The negative side is common with Arduino ground. If you wanted negative output instead of positive output, then you would need to use model Q50N and change the arrangement of the voltage divider.
Okay my bad, what i meant was that the lense has to electrode probes that would need the voltage going to. Can this just be divided from the output? I dont understand the 9V at the top section either.