1) I am not really implying that the cross section is wrong. It's more like a basic case. Let me give an analogy. A person falling towards a massive body falls based on the equation d=vt+.5gt^2. d=distance, v=initial velocity, g=acceleration due to gravity. This equation is absolutely correct...until the man falls into a black hole. At that point, relativity must be accounted for.
I believe there is a similar effect hiding in the cross section. The cross section is measured based on firing neutrons at a target, then extrapolating based on the density of the target and the neutron flux.
2) Heating of the grids: I'll let everybody jump on me when I get this wrong...The heating of the grid has six sources: a) collisions from ions accelerated inward, b) electron beams ejected from the core of the fusor, c) migration of electrons to or from the grid, d) collision of neutral particles, e) collision of energetic neutrons form heating, f) radiative heating (absorption of photons).
Some of these heat sources are more significant than others. For example, I would expect heating from neutrons to be rather insignificant.
Created on Monday, December 11, 2000 8:30 PM EDT by Clay G Codner