Phase contrast imaging to study ablation front stability and shock propagation in the ablator in an indirect drive capsule implosion*

 

An X-ray phase contrast imaging platform using streaked refraction enhanced radiography (RER) [1] was recently developed for capsule implosions at the National Ignition Facility [2]. RER was demonstrated to image in-flight capsule density gradients such as the fuel-ablator interface that is not visible in traditional absorption only radiography [3]. Latest experiments looking at early time of the implosion allowed the precise measurement of the ice-ablator interface trajectory and hence high precision measurement of its velocity[4]. An additional measurement that can be retrieved from the RER is the shock propagation history in the ablator: as the measurement is sensitive to density gradient, it tracks very well the trajectory of the different shocks as well as the rarefaction wave along with an estimation of their density. A careful quantitative analysis of the shock trajectory for two different drive is presented here. It will allow comparison with hydrodynamic simulation predictions and inform on the actual state of the diamond during the early phases of the capsule implosion.

 

[1] A. Pogany, D. Gao, and S.W. Wilkins, Contrast and resolution in imaging with a microfocus x-ray source, Rev. Sci. Instrum. 68, 2774 (1997).

[2] E. Dewald, O. Landen, D. Ho, L. Berzak Hopkins, Y. Ping, L. Masse, D. Thorn, J. Kroll, and A. Nikroo, Direct observation of density gradients in ICF capsule implosions via streaked refraction enhanced radiography (RER), High Energy Density Phys. 36, 100795 (2020).

[3] E. L. Dewald et al., Capsule ablator inflight performance measurements via streaked radiography of ICF implosions on the NIF, J. Phys. 688, 012014 (2016).

[4] Alexandre Do, Christopher R. Weber, Eduard L. Dewald, Daniel T. Casey, Daniel S. Clark, Shahab F. Khan, Otto L. Landen, Andrew G. MacPhee, and Vladimir A. Smalyuk

Phys. Rev. Lett. 129, 215003