Research On High-Efficiency Coaxial Relativistic Backward-Wave Oscillator

Coaxial relativistic backward-wave oscillator (CRBWO) is considered to be the effective technical approach to achieve the high output efficiency of the high power microwave (HPM). This dissertation studies CRBWO through the theoretical and technical research and experiment, which prove the advantage of CRBWO in the high efficiency and its feasibility.The theoretical study shows that the interaction range over the longitudinal wavenumber of CRBWO is wider than that of the hollow RBWO and the device starts oscillation fast owing to the excellent harmony of the coaxial slow wave structure (SWS). The startup of the oscillation suffers from the mode competition severely. The starting current increases with the electron kinetic energy over the range from 400 keV to 800 keV. The distribution of the field in CRBWO benefits the wave-beam interaction compared with that of the hollow RBWO so that the output efficiency reaches up to 40% by optimization of the reflection at both of the ends.The structural parameters and the reflection at both of the ends are designed and optimized carefully through the theoretical prediction and the numerical method. The simulation results indicate that CRBWO operates in the forward-wave region of the quasi-TEM mode. The output frequency 7.33 GHz is close to theπmode. The output power 754 MW and the efficiency 37% are obtained under the diode voltage 508 kV and the beam current 3.97 kA. It is found that the maximum of the electric field in the device, about 1.4 MV/cm under the output power of the GW level, is prone to induce the secondary emission and breakdown. In order to enhance the power capacity the components of CRBWO are processed by the series of the surface treatments. And the vacuum system adopts the oil-less pump. The delicate annular supporter is invented to improve the coaxiality of the inner and outer conductors. The further study convinces the new type of the reflector appropriate for the narrow-aperture anode of CRBWO and the output efficiency is promoted up to 43%.The electric probe and the calorimeter are employed to measure and diagnose the output of HPM. The coupling degree of the electric probe designed for CRBWO is almost constant during 7.40±0.10 GHz. And the energy absorbing efficiency of the calorimeter, which is hardly affected by the frequency, is higher than 98%. The regularity of the effect of the structural parameters on the output drawn from the experiment is similar as that obtained from the numerical simulation. Employing the electron beam of 498 kV, 4.28 kA and 28 ns, CRBWO generates the microwave pulse of the power 733 MW, frequency 7.40 GHz, efficiency 34.4% and the pulse width 20 ns, which is close to the theoretical and numerical prediction. The enhancement of the pulse amplitude and the prolonging of the pulse width in the experiment affirm the validity of the surface treatments. It can be concluded that for the titanium nitride coated device, the field emission is likely to occur when the field on the surface is higher than 1.2 MV/cm.