I've gone through the calculation of fusion cross-section before, to show you how you need, on average, millions of passes for a fusion event, even at the supposedly enormous pressures that will be found in a Polywell, let alone at the micron range of fusors.
That is a pretty good proof that fusors have never generated a single neutron ever. None of them gets millions of passes.
Not at all. It just shows that you are out into the multiple-sigma end of the distribution when generating neutrons, hence why it'll never get to break even.
Look at it this way - to get break even with a, say, 2.5MeV neutron energy capture from a cadre of 100keV deuterons, you'd need at least 1 in 25 to fuse to get Q=1.
The mean free path to a fusion event of a 100keV deuteron in 1 micron is 1/(1E19.1E-29)=1E10m. So if you need at least 1 in 25, so that they each
then need to cover 1E10m/25=400,000km so that the total 'mileage' they've covered is the 1E10m total.
OK, now let's think of statistics and the distribution: If a fusor is sized to be 1m total flight per pass, we need 1E10 particles to set off to get the 1E10m total flight required, for a fusion event, in the first pass. In the meantime, the mfp for those deuterons to hit a background is around 1/(1E19.1E-20), or 10m. So we can estimate that this first 1m generates one single fusion event and knocks out 10% of the deuterons. 1E9 deuterons @ 100keV = 1E14eV. The fusion event liberates 2.5E6eV. So the efficiency would be (2.5E6/1E14)=2.5E-8.
Now.... let me guess.... what'd'ya think the efficiency of a fusor is????....