Thermionic cathodes

Thermionic cathodes (e.g. Thales-Thompson M44)

These have

Excellent space heritage (20+ years)

excellent demonstrated lifetime (20000+ hours continuous)

cathode requires heating

some degradation above 10^-7 mbar due to O_2

a) configuration of M44 Thales-Thompson Thermionic cathod (courtesy of ARCS) b) the thermionic cathode c) in-FEEP thruster with thermionic cathode