A high voltage controller (32, 32a) that drives a high voltage generator, comprising: a) a voltage select input (126, 322) for setting a desired output voltage, and b) a current select input (128, 320) for setting a desired load current, c) an actual voltage input and d) an actual current input, e) first circuitry configured to generate an alternating current drive signal, f) second circuitry configured to generate a direct current drive signal, and g) closed loop control circuitry configured to adjust the direct current drive signal based on at least one of the voltage select and current select inputs and at least one of the actual voltage and actual current inputs, characterized in that h) the high voltage controller (32, 32a) may operate in one of the following three modes of operation based on the voltage select input (126, 322) and the current select input (128, 320): h1) a voltage controlled mode, h2) a current controlled mode and h3) a combined voltage and current controlled mode; i) in the voltage controlled mode, the current select input (128, 320) is set to the desired load current and the high voltage controller (32, 32a) varies the output voltage of the high voltage generator such that the desired load current is maintained, j) in the current controlled mode, the voltage select input (126, 322) is set to the desired output voltage and the high voltage controller (32, 32a) varies the output voltage of the high voltage generator such that the desired output voltage at the load is maintained, and k) in the combined voltage and current controlled mode, the voltage select input (126, 322) and the current select input (128, 320) are set to the desired values and the high voltage controller (32, 32a) varies the output voltage of the high voltage generator such that at least one of the selected voltage and current set points are maintained at the load. a) a voltage select input (126, 322) for setting a desired output voltage, and b) a current select input (128, 320) for setting a desired load current, c) an actual voltage input and d) an actual current input, e) first circuitry configured to generate an alternating current drive signal, f) second circuitry configured to generate a direct current drive signal, and g) closed loop control circuitry configured to adjust the direct current drive signal based on at least one of the voltage select and current select inputs and at least one of the actual voltage and actual current inputs, characterized in that h) the high voltage controller (32, 32a) may operate in one of the following three modes of operation based on the voltage select input (126, 322) and the current select input (128, 320): h1) a voltage controlled mode, h2) a current controlled mode and h3) a combined voltage and current controlled mode; h1) a voltage controlled mode, h2) a current controlled mode and h3) a combined voltage and current controlled mode; i) in the voltage controlled mode, the current select input (128, 320) is set to the desired load current and the high voltage controller (32, 32a) varies the output voltage of the high voltage generator such that the desired load current is maintained, j) in the current controlled mode, the voltage select input (126, 322) is set to the desired output voltage and the high voltage controller (32, 32a) varies the output voltage of the high voltage generator such that the desired output voltage at the load is maintained, and k) in the combined voltage and current controlled mode, the voltage select input (126, 322) and the current select input (128, 320) are set to the desired values and the high voltage controller (32, 32a) varies the output voltage of the high voltage generator such that at least one of the selected voltage and current set points are maintained at the load.