Measurement of areal density modulation of laser-imploded shells through K-edge imaging

A new method for studying the modulations in the rho Delta R of imploded sh ells is introduced: using a recently developed pinhole-array x-ray spectrom eter, core images are obtained at energies below and above the K-edge energ y of a titanium dopant. The ratio of these images reflects the nonuniformit y of the cold shell around the time of peak compression, independently of m odulation in core emission. The two-dimensional images of rho Delta R modul ations are of interest in laser fusion because they show the final result o f unstable implosion evolution. The measured average rho Delta R of the col d shell and the amplitude and spectrum of its modulations are in agreement with the results of two-dimensional code simulations that include imprintin g of laser nonuniformity on the target. (C) 2000 American Institute of Phys ics. [S1070-664X(00)04409-8].