Advanced Member level 5
The ionization is caused by field ionization. For a sharp tip (pointed), the radius of curvature is very small and the electric field (V/r) is very high. In post #32, there is a reference to a video (that I looked up; it is clear and concise) that uses a carbon fiber bundle as the electrode. Being very fine, they will be very effective at 5kV. Perhaps in a dark room you should be able to see the corona discharge (not to be confused with the recent pandemic)- but I am not very sure. Some idea may be gained from https://en.wikipedia.org/wiki/Corona_dischargeAlso how many pins should be used (any reference will be helpful)
Let me try to elaborate. Once you have done some significant amount of ionization, the negatively charged gas will look for a short path towards the positive electrode. Else, this charged gas shall form a capacitor with the earth and can cause a discharge to the ground (if there are no other path)....and size of plate affect this current.
With sufficient charge present in the air, inside of the room will appear to be a rather field free space.
So the ground electrode may be placed around 1-2 ft away and file off sharp edges (sharp edges can also act as corona points (emit positively charged molecules).