High-brightness, high-spatial-resolution, 6.151keV x-ray imaging of inertial confinement fusion capsule implosion and complex hydrodynamics experiments on Sandia’s Z accelerator (invited)

Abstract

When used for the production of an x-ray imaging backlighter source on Sandia National Laboratories’ 20MA, 100ns rise-time Z accelerator [M. K. Matzen et al., Phys. Plasmas 12, 055503 (2005)], the terawatt-class, multikilojoule, 526.57nm Z-Beamlet laser (ZBL) [P. K. Rambo et al., Appl. Opt. 44, 2421 (2005)], in conjunction with the 6.151keV, Mn–Heα curved-crystal imager [D. B. Sinars et al., Rev. Sci. Instrum. 75, 3672 (2004)], is capable of providing a high quality x radiograph per Z shot for various high-energy-density physics experiments. Enhancements to this imaging system during 2005 have led to the capture of inertial confinement fusion capsule implosion and complex hydrodynamics images of significantly higher quality. The three main improvements, all leading effectively to enhanced image plane brightness, were bringing the source inside the Rowland circle to approximately double the collection solid angle, replacing direct exposure film with Fuji BAS-TR2025 image plate (read with a Fuji BAS-5000 scanner), and generating a 0.3–0.6ns, ∼200J prepulse 2ns before the 1.0ns, ∼1kJ main pulse to more than double the 6.151keV flux produced compared with a single 1kJ pulse. It appears that the 20±5μm imaging resolution is limited by the 25μm scanning resolution of the BAS-5000 unit, and to this end, a higher resolution scanner will replace it. ZBL is presently undergoing modifications to provide two temporally separated images (“two-frame”) per Z shot for this system before the accelerator closes down in summer 2006 for the Z-refurbished (ZR) upgrade. In 2008, after ZR, it is anticipated that the high-energy petawatt (HEPW) addition to ZBL will be completed, possibly allowing high-energy 11.2224 and 15.7751keV Kα1 curved-crystal imaging to be performed. With an ongoing several-year project to develop a highly sensitive multiframe ultrafast digital x-ray camera (MUDXC), it is expected that two-frame HEPW 11 and 16keV imaging and four-frame ZBL 6.151keV curved-crystal imaging will be possible. MUDXC will be based on the technology of highly cooled silicon and germanium photodiode arrays and ultrafast, radiation-hardened integrated circuitry.

Capsule implosion optimization during the indirect-drive National Ignition Campaign

“…In the realm of hydroinstability, the bright spots of CH(Ge) dopant material observed jetting into the symmetry capsule hot spots and recognition of increased sensitivity of CH (vs Be) to surface roughness or isolated defects have spurred designs to measure the ablation front Rayleigh-Taylor growth by in-flight x-ray face-on or sideon radiography. 144 In addition, preliminary designs exist for assessing the in-flight density differential between ablator and fuel (and hence the Atwood number and susceptibility to ablator-fuel high-mode mix) using refractionenhanced x-ray radiography. 145 If a change in ablator material or hohlraum design is deemed necessary to either recover ignition margin from unfavorable physics or to optimize margin, then we would embark on a further capsule tuning campaign after having revalidated adequate hohlraum peak drive.…”

Kα emission and secondary electrons in femtosecond laser target interactions

“…The study and the development of these and similar radiation sources is a present topic of much interest (Reich et al, 2003;Park et al, 2006;Riley et al, 2005;Riley et al, 2006), this stems from the wide range and important applications of these radiation sources. For example, plasma diagnostics by X-ray scattering (Gregori et al, 2006), ultra-fast time resolved diffraction measurements, (Sokolowski-Tinten et al, 2003), flash backlighting of dynamical systems connected to inertial confinement fusion (Bennett et al, 2006), as well as different applications in chemistry and biology (Rischel et al, 1997;Neutze et al, 2000). It is therefore of great importance to know and to be able to predict as best as possible the temporal profile of this radiation source which is most difficult to measure.…”

Stability of fusion target concepts on Z.

“…Example liner targets are shown in Figure 2. On the diagnostic side, monochromatic 6.151 keV backlighting diagnostics [14] had been continuously developed and improved over the preceding several years [15,16,17]. One or two high-resolution (10-15 m) radiographs per experiment could be reliably obtained over a large target field of view (up to 4x20 mm).…”