Actually, this was started as a private project. Dr. Chang Díaz has been working on some form of concept/design since his graduate school days at MIT in the late 70s. See the Ad Astra site
"Dr. Chang Díaz invented the VASIMR® concept and has been working on its development since 1979, starting at The Charles Stark Draper Laboratory in Cambridge Massachusetts and continuing at the MIT Plasma Fusion Center before moving the project to the Johnson Space Center in 1994. In the development of the VASIMR® engine, Ad Astra Rocket Company was teamed with NASA JSC, Oak Ridge National Laboratory, University of Texas at Austin, University of Houston and other various government space and research centers, industrial companies and academia including foreign universities."
Ad Astra subsequently went private again on January 14th, 2005.