The magnetically insulated transmission line oscillator (MILO) is a gigawat
t-class cross-field microwave tube that requires no external magnetic field
due to inherent self-magnetic insulation. The tube operates with a 500 kV,
60 kA electron beam which, along with high rf fields, poses quite a challe
nge for diagnosing the device. We report on the comprehensive set of experi
mental diagnostics (both beam and microwave) employed in the MILO experimen
t, and show how these diagnostics, teamed with particle-in-cell computer si
mulations, have been instrumental in discovering problems with the tube. [S
0034-6748(00)01903-1].