Very interesting, Astro. I wasn't aware of the ion erosion problem.
Ion erosion is a problem is most if not all ion thrusters, whether electrostatic or EM. In magnetoplasmadynamic (MPD), there is the additional problem of cathode spotting - localized accelerated erosion where the arc current is higher.
What is the difference between these engines and the Deep Space 1's engine?
Deep Space 1 is a classic ion thruster, IIRC with a single stage.
whereas, The Dual-Stage 4-Grid ion engine has two stages,
Some new information:
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