Demonstration of Imprint Mitigation in Planar Geometry by a Combination of X‑Ray–Driven Picket-Pulse Shocks and Directly Driven Targets

A new scheme was tested to mitigate laser imprint in direct-drive inertial confinement fusion. It is based on that the initial shock wave is driven by x rays generated by a short laser pulse followed by a long main laser pulse that directly drives the target. This hybrid scheme uses a target design with 0.5-μm-thick CH membrane coated with 40 nm of Au to generate the initial shock with x rays. The membrane is located several hundred microns away from the imploding shell. Using x rays to drive the first shock promises to significantly eliminate short and medium wavelength modes from laser imprinting. A proof-of-principle experiment was performed in planar geometry showing promising results. We demonstrate x-ray–driven shocks at peak pressures of up to 8 Mbar in quartz and CH layers for different picket energies and distances of the membrane. Face-on x-ray radiography measurements show an imprint reduction in the hybrid target compared to standard plastic foils, most obviously for short wavelengths.