Use of coated silicon field emitters as neutralisers for fundamental physics missions in space

Spacecraft neutralisers are required as part of the ion propulsion system for accurate station keeping in fundamental physics missions. A silicon field emitter neutraliser is under development at the Rutherford Appleton Laboratory. Thin layers of insulating materials as coatings for the gated field emitter array structure are described, which are postulated to reduce power consumption and reduce overheating. The power consumption and lifetime of aluminium nitrude and amorphous hydrogen diamond-like carbon coatings were promising, performing better in endurance tests than uncoated samples, but further work is required to characterise the coating's physical properties and its effects on field emission. The thermal conductivity of the coating material appeared to have little effect on the sample lifetimes. Aluminium nitride had reduced power consumption compared to diamond-like carbon coated and uncoated samples. A thin (~5nm)layer was optimal, meeting European Space Agency specifications for the neutraliser engineering model