Areal Density Measurement of Imploded Cryogenic Target by Energy Peak Shift of DD-Produced Protons

DD-produced protons are used to measure the imploded fuel-shell areal density $\rho \Delta R$. Twelve green beams of the GEKKO XII laser directly imploded a cryogenic foam-shell target containing a liquid or solid ${\mathrm{D}}_2$ fuel. The proton emission is detected through a dipole magnet on a CR-39 plate, whose energy shift from 3.02 MeV yielded the maximum $\rho \Delta R$ of 10 mg/c${\mathrm{m}}^2$ or the density of 6 g/c${\mathrm{m}}^3$, in agreement with that from the secondary neutron method within a factor of 2. The proton energy spread is sensitive to the laser energy imbalance.