As I posted before and as others are now indicating, a safe "shorting stick" is very important to both check that the system is safe (fully discharged) and to enable you to discharge the system in the event of an emergency. That is, a long plastic stick with a metal end (metal screw or pointed rod) with a fairly high current (proper gauge) well insulated (for the voltage) wire connected from that tip to a ground (the same used for the cap bank is fine as long as it has been checked - i.e. is a good ground.) I have one of these for both my fusor and accelerator (its voltage multiplier.) I never touch any part of these systems without first checking them with the ground stick.
Another important safety issue - caps that are rapidly discharged can over heat and explode. Shielding and proper safety eye wear is essential, too.
Those exposed rails on those banks are death traps just waiting to happen and you will very much need some type of stand off shielding for those rails if I am reading your picture correctly.
I see no issues with you getting a plasma in the 20,000 K range at a few hundred amps for a fraction of a second; that said, the ability to accelerate deuterium to any type of significant fusing velocities will not be achieved with such little power and low voltage (building a small accelerator would do far better.) Even a high end neutron detector system would not measure any signal with such a low velocity plasma. However, you are mistaken if you think an atmospheric system will support a plasma that allows increased "mean free path". Sorry, but the only way to change that parameter is to significantly lower the pressure (in the range of 10^-3 torr or more.)
You have some good experience with caps so a voltage multiplier shouldn't be too difficult (getting a 50 kV, high current (for a small fraction of a second) system isn't hard to build (but isn't cheap, however, unless one gets a good deal on the caps but that is another issue.)) The very high vacuum system is another matter and may not interest you for a small accelerator so that might not be for you; however, that, in essence is what you appear (from my read) to be attempting to achieve - accelerate deuterium - with this current system. That will not work at all with such a low voltage much less at atmospheric pressure.