The aim of this work is to study the heating efficiency of refractory microstructures by excitation of surface plasmon polaritons in the far infrared that can be used for high temperature applications. We have designed metal grating couplers on molybdenum films to maximize the absorption of a 10.6 µm CO2 laser light source. Molybdenum has been chosen since it is an industrial refractory metal combined with the fact that its optical properties in the far infrared are similar to gold but with stable high temperature performance. Linear gratings have been used as plasmonic couplers on large area substrates produced by laser milling. Real time absolute temperature measurements have been performed showing a 42 % increase in the maximum achievable temperature from 702 K to 985 K.
Experiments have been conducted on a dual electric grid thermionic device to investigate an alternative method of space charge mitigation in a thermionic energy convertor (TEC). Two electric grids, the attractor and deflector grids, provide opposing electric fields to overcome space charge while minimizing power losses to the attractor grid. Electron beams are formed in the electrode gap providing a more efficient electron transport from hot cathode to collector. The attractor gird can be run in DC or pulse mode which usefully supports transformer coupling for the energy convertor output. This is a simple low cost inter-electrode space charge solution running at low voltage which has the potential to improve TEC efficiency, increase reliability, and reduce the cost of manufacture.
This paper presents measured optical absorptivity, emissivity and maximum solar-heated temperatures for micro-patterned molybdenum. The molybdenum samples were fabricated using laser micromachining and characterised using an integrating sphere and an infrared microscope. In-air solar simulator-heated temperature results for the molybdenum samples with different microstructures are presented and COMSOL modelling is then used to predict in-vacuum maximum temperatures. A vacuum chamber was developed to reduce the convection heat loss with a mount designed to minimise conduction loss and a maximum measured temperature of 413 ℃ was obtained.
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