Just some thoughts....
Originally posted by: dlane
Generally the dielectric strength of air is taken to be 3kV/mm. There are plenty of texts out there on physics or insulation engineering to support that such as;
i.e. flat or lightly curved surfaces with no sharp points that unnecessarily amplify the local voltage gradients will help.
The dielectric strength will vary dependent upon the humidity and pressure of the air.
This is the way most electrical engineers are taught to model the electrical properties of air. It is great when you are not interested in modelling what is happening close to or at breakdown initiation - engineers generally want to avoid that.
In regards to standard texbooks - what happens using 50/60 Hz voltages is not necessarily the same as what happens in high frequency breakdown initiation in air.
If you don't have the option of re-engineering the system to avoid breakdown, then you can also consider and model air as analogous to a weak ionic liquid conductor, rather than considering it analogous to a solid insulator. (i.e. a ionic solvent that conducts electricity via the motion of ions. This may be a better way of thinking about things anyway given your ion accelerator application).
Obviously as the discharge itself is initiated this simplistic model becomes invalid, as a cascade of ionisation leads to a hot ion channel plasma being formed. The maximum discharge current will presumably depend on the capacitance and inductance of the chamber, the current supply capability of the voltage source. the impedance of the rest of the circuit and the voltage frequency being used...etc
Ion mobility, in air, decreases as the size and mass of the ion increases. (Fast acceleration of smaller ions may be more important to the breakdown cascades the acceleration of the larger ions, I don't know)
If you add strong alpha or beta emitting sources into the air space the air conductivity will increase, because of the massive increase in the number of positive and negative ion pairs available due to ionisation; you could certainly check the effect of adding lots of small ions with low levels of dust and other pollution in the air this way.
If the discharges in the chamber are initiated like lightning, by up (ion channel) leaders meeting down leaders, then putting PTFE cladding may give an opportunity to reduce the maximum discharge current.
It might be possible to measure the discharge current load on the power supply by adding a secondary earth plane skin to the insulator, and attaching this to the main earth via a calibrated impedance.