Numerical Raytrace Verification of Optical Diagnostics of Ice Surface Roughness for Inertial Confinement Fusion Experiments

Absolute measurement approach for crystal growth height based on a polarization-synchronized phase-shifting interferometer

The quality of the solid deuterium-deuterium (D-D) layer in the inertial confinement fusion (ICF) target plays a vital role in the success of fusion experiments. A good understanding of how the quality is affected by the unstable growth of D-D crystal is required. This article provides an approach of measuring D-D layer absolute height in real time by combining monitoring algorithms and a synchronous phase-shifting interferometer. In the approach taken, a real-time monitoring technology, in which an antivibration algorithm is added, is used to get an absolute height of monitoring zone, overcoming the inability to accurately detect the saltus step in the interferometric measurement. Meanwhile, the polarization-synchronized phase-shifting technology is propitious to retrieve the D-D height distribution in a whole interferogram. Consequently, the categorical altitude of the D-D layer in entire crystalline regions can be obtained. Simulation analysis together with experiments have proved that a non-contact, rapid, and high-precision measurement of the D-D crystal absolute height can be realized by using the interferometer and method proposed.

Simple solution to the Fresnel-Kirchoff diffraction integral for application to refraction-enhanced radiography

We present a simple solution to the Fresnel-Kirchoff diffraction integral that is appropriate for x-ray radiography of strongly absorbing and phase-shifting objects in the geometrical optics regime, where phase contrast enhancements can be considered to be caused by refraction by a semi-opaque object. We demonstrate its accuracy by comparison to brute-force numerical ray trace and diffraction calculations of a representative simulated object, and show excellent agreement for spatial scales corresponding to Fresnel numbers greater than unity. The result represents a significant improvement over approximate formulas typically used in analysis of refraction-enhanced radiographs, particularly for radiography of transient phenomena in objects that strongly refract and show significant absorption.

Refraction-enhanced backlit imaging of axially symmetric inertial confinement fusion plasmas

X-ray backlit radiographs of dense plasma shells can be significantly altered by refraction of x rays that would otherwise travel straight-ray paths, and this effect can be a powerful tool for diagnosing the spatial structure of the plasma being radiographed. We explore the conditions under which refraction effects may be observed, and we use analytical and numerical approaches to quantify these effects for one-dimensional radial opacity and density profiles characteristic of inertial-confinement fusion (ICF) implosions. We also show how analytical and numerical approaches allow approximate radial plasma opacity and density profiles to be inferred from point-projection refraction-enhanced radiography data. This imaging technique can provide unique data on electron density profiles in ICF plasmas that cannot be obtained using other techniques, and the uniform illumination provided by point-like x-ray backlighters eliminates a significant source of uncertainty in inferences of plasma opacity profiles from area-backlit pinhole imaging data when the backlight spatial profile cannot be independently characterized. The technique is particularly suited to in-flight radiography of imploding low-opacity shells surrounding hydrogen ice, because refraction is sensitive to the electron density of the hydrogen plasma even when it is invisible to absorption radiography. It may also provide an alternative approach to timing shockwaves created by the implosion drive, that are currently invisible to absorption radiography.