Hello, I am curious about fusion reaction cross sections, and fusion power in general, and have been trying to self-teach myself in this area. I saw some emprical data for cross section curves in a paper that I read recently, and thought I understood enough of what made the curve (cross section vs rel particle energy) look that way to model it with a classical point charge model. I derived an expression for the radius of an approach envelope for particle A to get within some radius ri of particle B (presumably where the strong nuclear force takes over and reactions start happening). The curve only has one unknown fudge factor (the radius ri), and so only one degree of freedom. Other than that, on first inspection, the curve I derived seemed correct - the behavior as vA -> infinity was for ra->ri, and there was some vmin where ra->0 (where there isn't enough energy to overcome coulomb repulsion even with a dead-on trajectory). ra = sqrt(ri^2 - 2*ri*C*q1*q2/((ma*mb)/(ma+mb)*vab^2))))) When I plugged the numbers into the equation though, I couldn't get the curve to converge to emprical data on the D-D fusion cross section. When I chose ri such that the cutoff was similar, the cross section was 4 orders of magnitude too high (and it was a very large ri from the standpoint of atomic diameters). When I chose ri small enough such that the cross sections were in the right order of magnitude, the relative particle energy required was orders of magnitude too high. The problem could be either in my derivation or in the model. If it's in my derivation, a numerical model I'm turning the crank on should let me know (good old forward Euler method - what would I do without it). If it is my model though, I wonder if you guys could help point out what is wrong. I realize that at low enough particle energies, some sort of quantum mechanical effects take over, spreading the cross section out due to particle-position diffraction. That's why neutron cross sections look like they do - the spatial extent of the neutron spreads faster as the energy approaches 0. I was banking that that wouldn't be important enough in the model to cause such gross inaccuracies, which takes place with particles massed 1+ proton mass in the 10-100keV range, but I may be wrong. Other things that may be wrong with my model - the strong nuclear force extends some distance from the nucleus and causes some attenuation of the coulomb repulsion at distances greater than the reaction distance. Even when the particle hits the reaction distance, there is only a 1/10000 chance that it will react for some reason. Do any of you have experience with this? What do you think?