Calutron Revisited

In his article “The Uranium Bomb, the Calutron, and the Space-Charge Problem” (Physics Today, May 2005, page 45 ), William Parkins emphasizes the use of electrons generated by ionization of residual gas by a positive ion beam to neutralize space charge in the beam. He says, “We wished to get credit for having discovered and explained the automatic self-neutralization of intense ion beams where there are no applied electric fields. Our manuscript was received [by the Physical Review] on 18 February 1942 and published on 1 December 1947 after declassification.”

It is well known that cathode-ray tubes in the 1920s used “gas focusing.” Positive ions generated by ionization of residual gas by the electron beam were used to neutralize space-charge effects in the beam. ¹

The “discovery” that Parkins refers to is simply an inversion of a well-known principle. It may have been important for the calutron, but I fail to see it as a surprising discovery. It’s like reinventing the wheel.