Advanced Dispenser Cathodes
Controlled porosity reservoir cathodes offer significantly improved performance over conventional impregnated cathodes. Optimized performance requires additional design to achieve reduced barium deposition on adjacent surfaces, increased lifetime, and high current density emission. This paper describes the achievable performance and the associated design requirements.
The mechanism of sintering of copper
Abstract A study of the sintering of copper has been made using specimens prepared by winding 0.0128 or 0.00526 cm dia. copper wires around copper spools. Changes in the size and shape of the voids between wires were observed as a function of sintering time and temperature. By these means it was possible to investigate both bonding and shrinkage in all stages of sintering. It is concluded that shrinkage in all stages is primarily due to the volume diffusion of atoms from grain boundary sources to the voids. During the initial stages of sintering bonding occurs by the above mechanism and also by volume diffusion between differently curved free surfaces of the voids. These conclusions are consistent with the following results: 1. (1) shrinkage stops when the grain boundaries disappear. 2. (2) shrinkage rates calculated on the basis of the volume diffusion mechanism agree reasonably well with observed rates. 3. (3) the temperature dependence agrees with the volume diffusion mechanism. 4. (4) the sintering scaling law for volume diffusion is found to hold for the wires of different sizes.
Development of backward-wave oscillators for terahertz applications
Calabazas Creek Research, Inc. is funded by the National Aeronautics and Space Administration to develop advanced backward wave oscillators that incorporate energy recovery, air cooling and improved performance. An improved coupler transforms the generated RF power to a high-purity, Gaussian output mode. The construction of a 600-700 GHz BWO is currently underway with higher frequency sources in development. Simulations predict 6-8 mW of RF power over a 100 GHz bandwidth.