Experimental demonstrations that internal discharges through the dielectric of a capacitor (but without arcs or ions), cause a net force on the capacitor, towards the anode. Here the capacitors are symmetric unlike the alleged Biefeld Brown effect.
The effect is proportional to the mass of accelerated electrons (at about 1019 m/s², which is a big acceleration but not extraordinary for electrons in an electric field).
"The observations suggest that a wave field around the capacitor is the cause of the thrust and that this field is correlated to accelerated electrons. This also may suggest that this phenomenon could be a quantum mechanical effect."
https://arxiv.org/abs/1810.04368
Only 0.4 N/KW: low but nothing is optimized. As the EMDrive, this would be revolutionary for space propulsion.
Two thoughts about this subject.
With forces on capacitors, I always fear experimental biases because when the forces are low, then they can be explained by electrostatic forces between the plates and the environment like the ground, due to potential differences.
I also wonder if a reciprocal effect exists. It's always easier to detect an electric signal caused by a mechanical force than to generate a mechanical force from electricity. But here I wouldn't know how to do it.