Firstly, you are talking about ionic wind, or electroaerodynamic (EAD) propulsion, and you probably shouldn't use the term "ion drive" or "ion thruster" at all, because that refers to completely different things which are rockets that work in a vacuum and aren't much use in an atmosphere, whereas EAD systems cannot work in a vacuum.
The problem with current designs of EAD aircraft isn't just the ion wind generators themselves... some research suggests "ionic thrusters may be a far more efficient source of propulsion than conventional jet engines. In their experiments, they found that ionic wind produces 110 newtons of thrust per kilowatt, compared with a jet engine’s 2 newtons per kilowatt" (MIT press release, I've not tried to find the actual research paper though), but more the power supply. The power conditioning electronics of the EAD Airframe v2 was the heaviest part of its propulsion system because converting the output of some batteries to tens of kilovolts of DC is hard, and the voltage difference you need to generate increases with the size of the thing you're trying to propel.
- Having more conductive points for air to be charged and used as ion wind.
- Increasing the sharpness of the points to help concentrate electric fields.
One thing you want to avoid with EAD propulsion is arcing, where you get breakdown of the air and sparks jump between the conductors. That will do your power supply no good at all, and the heat of the arcing will probably damage the conductors. Sharp points concentrate the electric field which increases the likelihood of breakdown, which is bad.
Instead, you want as large a propulsion system as possible given the weight and power constraints of the system. Great big long glider wings with long wires string underneath them, sort of thing. There aren't "points" as such... the corona wire is a wire.
- Using magnetic fields to create a Lorentz force that would accelerate the charged ions with a principle similar to a railgun.
I'm not totally certain how useful this would be, but I am not a magnetohydrodynamicist. I don't think you can do much useful acceleration of ions in an atmosphere, to be honest... the electrostatic field that drives ion emission in the correct direction already might actually be as good as it gets.
Remember that most of the thrust is provided by regular air molecules which are colliding with the ions and each other, and the mean free path of ions in air is not very long and the geometry of your accelerating magnets seems likely to increase aerodynamic drag. I'm not going to say you magnetic accelerator is completely pointless, but I'm doubtful.
what could be done to increase the wind speed of an ion thruster?
Get a better power supply. I wonder if you'd be best off with some kind of air-breathing fuel-cell here... certainly, the energy density of batteries is never going to be great, and combustion engine efficiency over rockets and battery powered things is helped by the fact that one part of the energy-providing reaction is literally floating around in the air for the taking (or at least, on Earth it is), which saves carrying it with you
Once you've got a fuel cell with a good enough power-to-weight ratio consuming a suitably energy dense fuel (that's also got a good volumetric energy density... hydrogen fuel tanks are too big and will interfere with your aerodynamics!), you can scale up your thrusters. You'll then need an ultra-lightweight set of materials to build your aircraft from, including electrical conductors and insulators as well as structural materials for spars and lifting surfaces.
Nailing the power requirement is the big one, though.
