Advanced design of a low energy electron source
A multiphysics-based modeling design of a low energy electron source using a thermionic cathode is described in this paper. The proposed device produces a narrow beam employable in delicate applications where dimensions are critical. The effects of multiple physics influencing factors due to the cathode heating over the beam dynamics have been predicted through a multiphysics design approach. This paper would provide the needed knowledge for virtual prototyping of such devices. For this aim, several strategies have been adopted to obtain a simple model, which shows clearly the investigated mechanisms. According to this study, the appropriate materials and shapes can be chosen.
Present status of thermionic RF-gun for terahertz source project at Tohoku university
A thermionic RF gun for an accelerator-based terahertz source has been commissioned at Electron Light Science Centre, Tohoku University. Recently we constructed the measurement system to obtain the momentum distribution of the extracted beam from the RF gun. The system consists of the analyser magnet, tungsten beam slit followed by a Faraday cup and a Hall probe for the realtime magnetic field measurement. The momentum resolution of the spectrometer is estimated to be about 0.15 %, which will be sufficient to analyse the detailed distribution of highest energy part for the extracted electrons from the gun. The preliminary results of measured momentum spectrum and the current status of the terahertz source project are presented.
EVOLUTION OF O STARS. I. HYDROGEN-BURNING
The evolution of an O-type star of 30 M sub solar is considered from its initial main-sequence state to the point where the hydrogen content of the core has decreased from 70 per cent to 7 per cent by weight. The O stars are characterized by convective instability in the envelope and the full CNOcycle of energy generation. Radiation pressure is important throughout the star, and electron scattering dominates the opacity. The inhomogeneous models consist of four zones: (I) a radiative envelope retaining the initial composition, (II) an outer semiconvective zone with a continuously varying composition that has a discontinuity at the interface with (III) an inner radiative zone also with a continuously varying composition, and (IV) a homogeneous convective core. Due to increasing radiation pressure, the semiconvective zone grows more rapidly outward than inward, but produces little effect on the important stellar quantities. The mass fraction of the core decreases from 0.69 to 0.34 and the mean hydrogen content of the star gets 40 per cent depleted. The age, 4.7 million years, is shorter than that for other sequences computed for stars of mass approximately 30 M sub solar because of a higher luminosity. This is mainly the resultmore » of choosing a higher mean molecular weight and CNO content. (auth)« less