James,
Not a simple 1:1 relationship, ionizing the atom at 10^-5 volts potential might lower the coulomb barrier by a factor as follows…

The mass energy potential of +1 hydrogen ion at ground potential, less the negative potential divided by the total mass energy at ground potential.

So I think the coulomb barrier might be lower by a factor of ((10^9) – (10^5)) / (10^9) = 0.9999

Not much in the scheme of things, but maybe enough to see an improvement in the fusion rate.

Steven