The tritium burn-fraction in DT fusion

Abstract

The fraction of the tritium that is burned during one pass through a DT fusion system, $f_{tb}$, is a central issue for success of fusion energy. Reducing the tritium fraction, $f_t$, in a $DT$ burning plasma below a half increases the burn fraction, $f_{tb}\propto 1/f_t$ but also the required confinement to achieve a burn $nT{\tau }_E\propto 1/f_t(1-f_t)$. A doubling of the fractional burn entails only a 4/3 enhancement of the required $nT{\tau }_E$. The energy confinement time ${\tau }_E$ in tokamaks and stellarators is empirically gyro-Bohm with an approximate factor of two between the best and worse results used to construct scaling laws. Gyro-Bohm is also the approximate level of transport needed in a power plant. What has received little study are ${\tau }_t/{\tau }_E$, the ratio of the tritium to the energy confinement time, and ${\tau }_{\alpha }/{\tau }_E$, the ratio of the alpha particle to the energy confinement time. The tritium burn fraction is proportional to ${\tau }_t/{\tau }_E$, so the larger the better. The contamination of the plasma by helium ash is proportional to ${\tau }_{\alpha }/{\tau }_E$, so the smaller the better.

This is a short note on a critical issue in DT fusion energy, the tritium burn-fraction

Cited by in corpus (1)

• Stellarators as a Fast Path to Fusion