A minimum criterion for a fusion reactor is that the thermonuclear power PTh generated in the plasma should replace the power losses PL.
One way of achieving this is to recycle a fraction η of the total power leaving the plasma. This will then be used to reheat the plasma and balance the power losses-
η(PTh+PL)=PL
The
Lawson criterion states this in terms of the product of the plasma
density n and the
energy confinement time τ
E. This criterion is a function of
temperature. At 10
KeV (optimal for the
fusion of
deuterium and
tritium) it is given by-
nτE>1019m-3 s
See also the stricter criterion required for plasma ignition.