Refraction-enhanced x-ray radiography for inertial confinement fusion and laser-produced plasma applications

Abstract

We explore various laser-produced plasma and inertial confinement fusion applications of phase-contrast x-ray radiography, and we show how the main features of these enhancements can be considered from a geometrical optics perspective as refraction enhancements. This perspective simplifies the analysis and often permits simple analytical formulas to be derived that predict the enhancements. We explore a raytrace approach to various material interface applications, and we explore a more general example of refractive bending of x rays by an implosion plasma. We find that refraction-enhanced x-ray radiography of implosions may provide a means to quantify density differences across shock fronts as well as density variations caused by local heating due to high-Z dopants. We also point out that refractive bending by implosions plasmas can blur fine radiograph features and can also provide misleading contrast information on area-backlit pinhole imaging experiments unless its effects are taken into consideration.

Capsule performance optimization in the National Ignition Campaign

“…A further set of in-flight capsule measurements are planned after the first ignition attempts if required to isolate particular capsule physics issues. These include measuring Rayleigh-Taylor growth by x-ray radiography in convergent geometries ͑spherical or cylindrical͒, assessing the in-flight density differential between ablator and fuel ͑and hence the Atwood number and susceptibility to mix͒ using refraction-enhanced x-ray radiography, 29 and measuring the in-flight fuel adiabat ͑essentially 1+ the ratio of T e to the Fermi energy͒ by x-ray spectrally resolved Thomson scattering. 30 For the latter, recent experiments at OMEGA have demonstrated the feasibility of diagnosing imploding capsule conditions using the 9 keV Zn He-alpha resonance line.…”

Development of aerogel-lined targets for inertial confinement fusion experiments

“…The temperature is controlled by the liquid helium, which allows cooling the capsule below the condensation temperature of deuterium [74]. The cryostat has two beryllium windows, which allows the ultra-low density p-DCPD foam inside of the HDC shell to be analyzed with an X-ray imaging system [75,76].…”

Ignition tuning for the National Ignition Campaign

“…In the area of active probes, these include a dual axis VISAR to set the 2 nd -4 th shock pole-to-equator symmetry, 75-100 keV point-projection Compton radiography [15] of the fuel size, shape and r uniformity using 2 quads of NIF, backlit x-ray radiography of ablation front growth of surface divots and bumps to assess Rayleigh-Taylor growth rates, backlit implosion velocity and thickness measurements of the ablator early in the pulse and in cryogenically-layered implosions to check EOS and the presence of a fifth shock, with the added potential to view the low Z fuel interfaces by refraction-enhanced imaging [16]. In the area of passive probes, these include using Au-lined higher albedo U hohlraums to improve hohlraum efficiency [17,18], codoping the CHSi capsules with trace amounts of Ge and Cu for assessing hot spot mix emanating from throughout the inner ablator region as one varies the ablator and fuel thickness and Si dopant level to vary the interface Atwood number, and using I as a radiochemical tracer of mix.…”