A theoretical criterion for the closure of slots filled with low-Z foam

Hydrodynamic motion of radiation-ablated high-Z plasma has a significant influence on the radiation transport in a slot. This work focuses on the closure problem of slots filled with low-Z foam of density varying from 10−2 to 100 g cm−3. A simple one-dimensional model is proposed to study the motion of the ablated high-Z wall plasma in the slot. According to the model, the high-Z plasma first expands to the center of the slot, then reverses because of the competition of the ablation pressure with radiation pressure and the thermal pressure of the low-Z foam. The analytical formulas for the maximum values of reverse time and reverse distance of the high-Z plasma are deduced. Based on the relationship between the expansion-reverse movement of the high-Z plasma and the closing-reopening process of the slot, we obtain a criterion of slot closure by comparing the reverse distance of the high-Z plasma xr and the initial width of the slot w. We predict that the slot finally closes when w/2   xr. Our theory is proved to be valid by the results of simulations using the code MULTI.Hydrodynamic motion of radiation-ablated high-Z plasma has a significant influence on the radiation transport in a slot. This work focuses on the closure problem of slots filled with low-Z foam of density varying from 10−2 to 100 g cm−3. A simple one-dimensional model is proposed to study the motion of the ablated high-Z wall plasma in the slot. According to the model, the high-Z plasma first expands to the center of the slot, then reverses because of the competition of the ablation pressure with radiation pressure and the thermal pressure of the low-Z foam. The analytical formulas for the maximum values of reverse time and reverse distance of the high-Z plasma are deduced. Based on the relationship between the expansion-reverse movement of the high-Z plasma and the closing-reopening process of the slot, we obtain a criterion of slot closure by comparing the reverse distance of the high-Z plasma xr and the initial width of the slot w. We predict that the slot finally closes when w/2 < xr, while it remains...