Born in 1955, Mr. Johnson received his Master of Science in Mechanical Engineering at the University of Tennessee in 1983. Until 1993 he worked on the Atomic Vapor Laser Isotope Separation (AVLIS) programme in Oak Ridge and later at Livermore National Laboratory, where he was Mechanical Group Leader for seven years.

Between 1993 and 1999, he was ITER Vacuum Vessel Group Leader at the Garching Joint Work Site. Since 1999 he has been working on the Spallation Neutron Source (SNS) Project at ORNL. Early responsibilities included defining requirements for buildings and oversight of the Architect Engineer and Construction Manager, as well as coordination of mechanical design of the warm linear accelerator, and planning and overseeing all assembly, installationand testing of that system at ORNL. In 2004 he became Experimental Facilities Division Instalation Manager.

He was designated as ITER Deputy Director-General for the Tokamak in July 2006.