WAS THE ROVER PROGRAM DEVELOPING A PLASMA CORE ENGINE?

When the NERVA program was cancelled in 1973 America had just begun to publicize development of vapor core reactors known as the Nuclear Furnace. After the NERVA program was canceled the reactor vessels were "cannibalized" to make way for experiments on nuclear pumped lasers using plasma core engines. The ROVER/NERVA program supposedly employed solid core reactors. Solid core reactors would be very limited in terms of what they could do in terms of their ISP. Vapor cores or even liquid core reactors have much higher potential ISP. I suspect that upper stages of Apollo utilized nuclear engines. The Phoebus NTR produced exactly the same amount of thrust as the J-2 rocket engine. So, I don't think that this was any accident. The NERVA engines could be "cannibalized" for this purpose because it was a plasma core rocket all along.