Take a look at "Report on the Stanford Linear Accelerator Center."
At the bottom of page 5, Loew writes:
"Just to the right-hand side of the console is the domain of the beam operator, sometimes called the beam jockey. Besides numerous telephones and Tektronics (sic) oscilloscopes, the beam operator focuses his attention on beam guidance and the beam spectrum."This greatly predates my own use of the phrase "beam jockey" in the mid-Eighties.