Sorry to pour cold water on a plasma jet
These are just electric-powered ramjets.
The game has been played at low airspeeds, with a model flown by MIT a few years back, the main difference being that the ionisation and acceleration took place outside the airframe, above the wing. Also, the plane used a DC electrode to ionise the air, not an electron beam.
The Wiki article on ABEP (sic) notes the use of a radio-frequency (RF) magnet to ionise the plasma, just as I did professionally for some years when engineering waferfab stuff (Not that we launched the wafers like UFOs, sadly they lived in tightly-confined chambers).
As any designer of high-altitude ramjets will tell you, you have to get up to hypersonic speeds to achieve sufficient airflow. If you rely on superhigh exhaust velocities, your thermodynamics become inefficient, so you try to shift as much air as possible, as slowly as you can get away with. The trouble is, from a flow-rate perspective there is naff all mass in the air at these near-space altitudes. So you are looking at slightly higher air densities, and hence lower altitudes, in order to maintain efficient thrust.
Also, you have to get up to around Mach 20 before you gain enough centrifugal lift to think of your craft as orbiting rather than flying.
So you end up with a hypersonic ramjet and all the problems of airframe heating that brings. This is the real killer: to get in enough air to generate the required thrust, you have to punch through so much of it that your airframe melts in a few minutes. Your only hope is hypersonic aerodynamics to reduce the thrust required, and new heat-resistant materials and techniques.
Next, we get onto the rate of energy delivery, aka engine power. It is phenomenal. Think of the rocket thrust needed to sustain Mach 20 flight at such altitudes. All that has to come from the electron gun, and any other field-enhancing gadgets you can come up with. You should see the power supplies we built just to sustain a pretty light above a 6" wafer for 30 secs or so. Battery drain would be staggering, recovering ambient energy a drop in the ocean. Increasing the exhaust velocity to allow reduced mass flow would drain the batteries even faster. This is not a satellite but a short-range cruise missile.
The history of electromagnetics has been full of horse shit and snake oil since the days of Nikolai Tesla, and the tradition shows no sign of slowing down.
Biting the hand that feeds IT
