File:Million volt x-ray machine Bureau of Standards 1947.jpg

English: A 1.4 million volt x-ray machine at the US National Bureau of Standards (now NIST) in 1947. It was used to conduct basic research such as x-ray crystallography. The two lefthand vertical columns contained a 10 stage voltage multiplier in which 10 capacitors were charged in parallel to a voltage of 140 kV using high voltage kenotron diode vacuum tubes, then discharged in series, creating a high DC voltage on the top terminal. The righthand column is the x-ray tube, which accelerates electrons to 1.4 Mev before they collide with a metal target at bottom. The 9 horizontal conductors linking the corona rings on the separate columns equalize the voltage drops across each insulator, ensuring that the electric field is distributed equally along the columns to prevent arcs. A high value resistor extending down the lefthand column with 10 equal taps divides the voltage equally. The high voltage electrodes have smooth, rounded shapes with no sharp edges to prevent leakage of the charge into the air by corona discharge. Note figure at bottom left for scale.