From Redmond Rocket Scientists Propel Innovation as Space Cluster Grows:

Aerojet Rocketdyne HCT flightweight firing
Aerojet Rocketdyne HCT flightweight firing

BPT-4000 Hall Current Thruster, flying on the first 2 Advanced EHF (extremely high frequency) satellites. The picture was taken in a vacuum chamber during test firing at Aerojet Rocketdyne.