Theoretical and practical considerations in forming solid fuel layers inside vacuum insulated inertial confinement fusion targets

Vacuum layer ICF targets can be manufactured in such a way that a uniform cryogenic solid layer may be formed within the fuel container. By using either condensable gases or a mixture of He and a condensable gas as the exchange gas, the final mass density within the vacuum layer may be specified by the designer. To evaluate the potential uniformity of a solid cryogenic fuel layer within a specific design the time to condense and freeze the fuel must be calculated. A general model is offered to calculate this information and it is shown that for the case of He and H2 exchange gases in the continuum regime of cooling the fuel layer uniformity should be as good as current experimental results with simple targets. Further extension of this model to include other exchange gases and encompass the transition and free molecule regimes of cooling will allow evaluation of a broader range of these vacuum layer targets