Specification of the 1 D – 1 D reaction entails some difficulties, though. To begin with, one must average over the two branches (2i) and (2ii). More difficult is to decide how to treat the 1 T and 2 He products. 1 T burns so well in a deuterium plasma that it is almost impossible to extract from the plasma. The 1 D – 2 He reaction is optimized at a much higher temperature, so the burnup at the optimum 1 D – 1 D temperature may be low. Therefore, it seems reasonable to assume the 1 T but not the 2 He gets burned up and adds its energy to the net reaction, which means the total reaction would be the sum of (2i), (2ii), and (1):