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-
The Lawson criterion
states this in terms of the product of the plasma density
n and the energy confinement time
. This criterion is a function of temperature
. At 10 KeV
(optimal for the fusion
) it is given by-
See also the stricter criterion required for plasma ignition.