C12A7:e- properties are superior to those of conventional ceramics currently employed in EP neutralizer technology. Apart from less required thermal energy, C12A7:e- lower work function enables devices operating at working temperatures half of the typical operating temperatures of BaO and LaB6 based neutralizers. Additionally, lower heating power is essential to decrease the system power-to-thrust ratio.
Within the NEMESIS project, LaB6 and C12A7:e- comparison has shown an order of magnitude higher emission current density at 900 ºC for a 8 mm diameter disc sample: 0,01 mA vs 0,2 mA.
Thermionic emission from novel electride material C12A7:e- deposited thin films has been documented by the very first time worldwide. C12A7:e- deposited thin film (250 nm) on graphite has shown thermionic emission, thus opening the door to many possible additional applications.
Material synthesis processes have been finetuned, enabling production in Europe of high quality electride from locally abundant unexpensive precursors. Unlike other termionic materials like LaB6 or BaO, both the C12A7:e- electride and its precursors are non toxic. It has also been demonstrated that the material has a long term stability, remaining fully operational after more than two years with just a simple plastic bag storage.
One of the most complex issues to solve was the emission barrier effect and the charge accumulation caused by the thin dielectric layer present at material surface, which is randomly released as sparks, causing instabilities and material damage. Charge coupling technique using a pulsed operation mode was verified as the solution to such sparks and instabilities, which additionally provides twice as much anode current, and a slightly better anode to cathode current ratio. Patent for pulsed operation mode for C12A7:e- based cathodes has been granted to ATD (ES-2897523), and its worldwide extension is in progress
Several engineering model prototypes developed, successfully tested with Xe, Ar, Kr, I, and NH3, coupled with HET thrusters, and reaching high performance figures of merit, reaching performance ratios of up to 10 mA/W, and losses at keeper lower than 5% (Ianode/Icathode > 95%). Some of them operated with powers below 1 W in heater less configurations reaching operating temperatures < 200 ºC and providing anode extracted currents of some tenths of mA.
In only 3 years and with less than 1 M€ budget, a new multi-propellant cathode technology has been matured up to TRL 4 for different designs and propellants in the NEMESIS project and is now ready to take off to higher TRLs to replace of old LaB6 technology and serve the European EP space industry preserving its non-dependance.
