Self-radiography of imploded shells on OMEGA based on additive-free multi-monochromatic continuum spectral analysis

Abstract

Radiographs of pure-DT cryogenic imploding shells provide critical validation of progress toward ignition-scalable performance of inertial confinement fusion implosions [J. Nuckolls et al., Nature 239, 139 (1972)]. Cryogenic implosions on the OMEGA Laser System [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] can be self-radiographed by their own core spectral emission near ≈2 keV. Utilizing the distinct spectral dependences of continuum emissivity and opacity, the projected optical-thickness distribution of imploded shells, i.e., the shell radiograph, can be distinguished from the structure of the core emission distribution in images. Importantly, this can be done without relying on spectral additives (shell dopants), as in previous applications of implosion self-radiography [V. A. Smalyuk et al., Phys. Rev. Lett. 87, 155002 (2001); L. A. Pickworth et al., ibid. 117, 035001 (2016)]. Demonstrations with simulated data show that this technique is remarkably well-suited to cryogenic implosions and can also be applied to self-radiography of imploded room-temperature CH shells at higher spectral energy (hv ≈ 3–5 keV) based on the very similar continuum spectrum of carbon. Experimental demonstration of additive-free self-radiography with warm CH shell implosions on OMEGA will provide an important proof of principle for future applications to cryogenic DT implosions.