High Emissivity Arcjet Anode

Improved cooling of the anode can increase the efficiency and lifetime of arcjet thrusters. Smooth tungsten anodes have low emissivity ~0.3 that severely limits radiative cooling heat transfer can be increased 300% by improvements in emissivity, and thereby significantly increase arcjet power. Prior attempts to increase tungsten emissivity have problems: ceramic coatings tend to flake off under high temperature cyclic arcjet operation and surface roughening by arc and sputter texturing does not succeed on tungsten. This project will investigate a novel processing technique for texturing surfaces with small diameter fibers. The process involves the application of short fiber flock and a chemical vapor deposition coating to obtain high density, well oriented, large aspect-ratio microcavities on substrate materials such as tungsten, carbon and refractory ceramics. In Phase I, a series of carbon fiber flocked samples will be prepared and characterized to aid modeling of the infrared optical properties of flocked surfaces and to guide design. Sample tungsten surfaces will then be prepared and characterized at high temperature to assess the feasibility of the approach for arcjet anodes. Other anode materials will be surveyed and the potential benefits for arcjet propulsion will be assessed. Other potential optical and thermal applications will be surveyed. In Phase II, the process would be developed and prototype anodes would be fabricated for testing under arcjet relevant conditions.