The question was how to increase the electron density without using a magnetic fields or RF my answer is?

My answer is 1) run a dc current thought a quartz tube with  graphite disk having a small hole for the dc current to go through,

2) cause a laser plasma or high brightness ion beam say a hydrogen ion beam focsed to a piont ay the surface where us want the high electron density.

3) CAUSE A HIGH VOLTAGE ARC ( UNI-POLAR ARCS) ON A POINT.

John H Keller