CONDITIONS FOR THE IGNITION OF IMPLODING SPHERICAL-SHELL TARGETS

An analytical model for the study of the conditions for central igniti on of imploding shell targets is presented. The model is based on a de scription of the stagnation phase in which the shell is considered to stagnate isentropically except in a central region of the fuel where t he ignition profiles are determined by the competition of the energy l osses due to thermal conduction and radiation with the heating due to compressional work and alpha particle deposition of energy. As a resul t, the temperature and the confinement parameter of the central spark are found to be dependent on the implosion velocity v(0) and the ignit ion conditions are obtained consistently with the implosion dynamics. In addition, the minimum energy of the beam Epsilon(B)(ign) required f or ignition is calculated and the scaling Epsilon(B)(ign) alpha v(0)(- 5) is found, which is in good agreement with previously reported simul ations.