You are right, it's a pulsed system. The operation goes like this: 1. Fill the chamber with D and He3 2. Ionize the fuel and compress the plasma 3. The fusio

You are right, it's a pulsed system. The operation goes like this: 1. Fill the chamber with D and He3 2. Ionize the fuel and compress the plasma 3. The fusion starts and pushes back the magnetic field producing electricity 4. Stop everything 5. Vacuum and start again So before the plasma is polluted with p, T and He4, the pulse has ended. The side reaction D+T does not get the time to happen much. I'm using a different notation than yours: 3He, 3H, 2H, H are He3, T, D, p T is tritium, D is deuterium, and p is protium (a proton)