You will have some possible field emission from the right angle edges of your grid wires, but this should not impact the overall operation.
The power supply currents, if a continuous DC type supply is used, will be on the order of 10-50ma. Voltages for demo devices can be as low as 3kv or go up into the 30kv range.
A bell jar is a dangerous item if voltages in excess of 4kv are used and current of over 15ma are run, as electron beam impacts can stress the glass and super heat it in micro spots to the point of perhaps creating an implosion. Use only a borosilicae glass bell jar and am inmplosion shield to be on the safe side.
Older posts on the old message board covered this in some detail.
Richard Hull
Created on Tuesday, January 16, 2001 5:39 PM EDT by Richard Hull