Fusion Cross-Section & Reactivity
The cross-section measures how likely two nuclei are to fuse at a given energy. D–³He peaks at higher temperature than D–T — shaping the Kronos operating point.
- Cross-section
- Probability of fusion per encounter, vs energy
- Reactivity
- Cross-section averaged over the plasma temperature
- D–T
- Peaks near ~65 keV, easiest to ignite
- D–³He
- Peaks higher — needs hotter plasma
The fusion cross-section quantifies how likely two nuclei are to fuse when they collide at a given energy; averaged over a plasma's thermal distribution it becomes the reactivity, which sets the fusion reaction rate. Both rise steeply with temperature until they peak, so choosing a fuel is largely about where its reactivity peaks and how hot the plasma must run to get there.
Deuterium–tritium has the most accessible peak — one reason it ignites most easily. Deuterium–helium-3 peaks at higher temperature and lower absolute reactivity, which is precisely why Kronos MetroVolt must run hot (central temperatures of 48 keV at the near-thermal Mode-D point) and lean on strong confinement. The reward for that harder plasma problem is a low-neutron, directly-convertible output.