Relativistic magnetron operation with explosive emission and ferroelectric plasma source cathodes

Abstract

In this report we present results of comparison of experimental research of the relativistic magnetron operation with commonly used explosive emission plasma cathode and novel ferroelectric plasma source (FPS) cathode. The experiments were carried with relativistic S-band magnetron powered by Linear Induction Accelerator (LIA) (∼350kV, 4kA, 200ns). Using time- and space-resolved electrical, optical and spectroscopic diagnostics plasma parameters (density, temperature and expansion velocity) were studied during the accelerating pulse. In the case of explosive emission plasma it was found that the plasma is not uniform and consists of separate plasma spots whose number increases during the accelerating pulse. It was shown that the microwave generation is accompanied by a significant increase in plasma density and ion temperature, up to ∼5·1016 cm−3 and ∼8 eV, respectively. The plasma electron temperature was found to be ∼8 eV. It was shown that the plasma expansion velocity in the axial direction reaches ∼107 cm/s and ≤2·105 cm/s in the radial direction. Investigation of the plasma parameters during the magnetron operation with FPS cathode showed also increase of the plasma density up to ∼7·1014 cm−3 electron and ion temperature up to ∼7 eV and ∼4 eV respectively. It was shown that the application of the ferroelectric plasma cathode allows one to avoid a time delay in the appearance of the electron emission, to achieve better matching between the magnetron and LIA impedances, and to increase significantly (∼30%) the duration of the microwave pulse with a ∼10% increase in the microwave power. The latter results in generation of microwave radiation to be 30% more efficient than with the use of explosive emission cathode where the efficiency ≤20 %.