Experiments and diagnostics of multi-MW, large-orbit, axis-encircling, coaxial gyrotron oscillator

Summary form only given, as follows. Experiments and diagnostics are currently under investigation on large-orbit axis-encircling, coaxial gyrotrons. The electron beam is generated by MELBA (Michigan Electron Long Beam Accelerator) with the following operating parameters: voltage=750-800 kV, diode current=1-10 kA, pulselength =0.5 to 1.0 /spl mu/s. The gyrotron has a coaxial cavity with an inner radius of 3 mm and an outer radius of 3.7 cm. Initial operation of the gyrotron is in the TE11 mode at a frequency of 2.3 GHz. Frequencies of this gyrotron oscillator during operation am measured by Fourier transforming heterodyne mixer data. This high power emission frequency is in agreement with measured cold test resonances and corresponds to calculations for waveguide cutoff of the TE11 mode. Microwave power in excess of 8 MW is measured from the gyrotron oscillator. Microwave power is measured by calibrated crystal detectors. The axis encircling beam is generated by passing the electron beam through a magnetic cusp field. Diagnostic experiments to measure beam alpha (perpendicular velocity/parallel velocity) are conducted using radiation darkened patterns on glass witness plates. Beam alphas of 0.7-1.5 are observed.