a Pulsed Electron Cyclotron Maser for Plasma Heating.

Available from UMI in association with The British Library. Requires signed TDF. A pulsed electron cyclotron maser (ECM) was designed, built and tested to operate in the Q-band (26.5GHz to 40GHz) range. The operating parameters of current and magnetic field were varied within the range 4 to 1250A and 0.797 to 1.310T respectively; whereas the potential difference across the field emitting, relativistic electron beam (REB) diode was kept constant at 65kV. This potential difference gave the relativistic factor gamma = 1.13. An echellette grating spectrometer was designed, constructed and used for frequency measurements. The grating was blazed at 20^circ and was designed to operate in the 1st order of diffraction. The neighbouring 2nd and 3rd orders of diffraction also proved useful in determining the true ECM emission spectra. Problems arising from partial overlapping of the three orders of diffraction were eliminated using a high pass U-band (f _{rm co} = 31.25GHz) waveguide filter. The emission spectrum of the ECM was measured as the magnetic field and the electron beam current were each systematically varied. Results presented show that at high beam currents (400-1250A), several discrete frequencies were present in the emission spectra which corresponded to multimode excitation. At low electron beam current (4.8A) single frequency emission spectra were observed. Far field radiation patterns were measured using a single calibrated detector which spatially scanned the ECM output. From these patterns the mode of operation was identified. The power of emission and electronic efficiency were also calculated from these patterns. As the magnetic field was systematically increased at low electron beam current, single modes were observed near the fundamental gyroresonance. These were identified as TE_sp{12}{circ} (22.2GHz), TE_sp{02}{ circ} (29.2GHz), TE_sp {61}{circ} (31.2GHz) and TE_sp{13}{circ} (35.5GHz). The ECM when operated at a current of 4.8A in the TE_sp{02}{ circ} mode produced an emission power of 18.5kW with 5.7% electronic efficiency. This mode is widely used in ECMs for plasma heating. The maximum multimode emission power produced was approximately 100kW.