A revised analysis of Lawson criteria and its implications for ICF

Summary form only given. Recently (Panarella, 1994), a re-examination of the breakeven conditions for D-T plasmas were presented. The results show that breakeven might not follow the Lawson nt rule, and in particular the plasma containment time seems to have lost the importance that previously had. Moreover, a minimum particle density of the order of -10/sup 15/ cm/sup 3/ has been found to be required for breakeven (much the same as a temperature of at least -3 keV is required), which indicates that the inertial confinement fusion effort is in the right position to reach the fusion goal. In light of these results, a reassessment of Lawson\´s analysis has been undertaken. Lawson considered the case of a pulsed system that followed this idealized cycle: "....the gas is heated instantaneously to a temperature T, which is maintained for a time t, after which the gas is allowed to cool. Conduction loss is neglected entirely, and the energy used to heat the gas and supply the radiation loss is regained as useful heat." Lawson rightly concludes that, since P/sub R/ and P/sub B/ are both proportional to n/sup 2/, R is a function of T and nt. In order to illustrate how the analysis by Lawson can be improved, the cycle to which the gas is subjected should be divided in three phases: 1st phase: Rapid heating of the gas for a time t/sub 1/ to bring it from the original ambient temperature to the fusion temperature T; 2nd phase: Continuous injection of energy in the plasma for a time t/sub 2/ to maintain the temperature T; 3rd phase: No more injection of energy and cooling of the gas to the ambient temperature.