Session T3: AETD: Radiography and Tomography 2

New proton radiography diagnostics.

Implosion experiments at the Los Alamos proton radiography facility are planned to provide very high pressure equation of state data. 800-MeV proton radiography does not have sufficient transmission and statistics to infer areal density to sufficient precision. Thus, new diagnostics have been developed in order to obtain areal density data with on the order of several 0.1{\%} precision. Initial tests have shown this precision can be provided by using a Cherenkov converter, a vacuum photodiode and a high bandwidth (50-GHz) oscilloscope to record individual 100 ps long proton pulses from the LANSCE 800 MeV accelerator. This detector measures proton time-of-flight to better than 2-ps precision in order to provide both transmission and energy loss information. These results will be presented.   

Feasibility Studies of the Use of Inelastic X-ray scattering as a Temperature Diagnostic of Transiently Compressed Matter

Recent experiments at LCLS have demonstrated the feasibility of using femtosecond x-ray pulses to inelastically scatter from phonons in a solid.[1] In principle, measuring the relative intensities of the Stokes and anti-Stokes peaks could provide a direct measure of the temperature without recourse to needing to know the Debye temperature. However, the number of inelastically scattered photons is low, and thus absolute temperature measurements on laser-compressed samples will need to accumulate data over many shots. We present here simple calculations of the cross section, compare them with the data provided in [1], and comment on the long-term feasibility of using this technique at the European XFEL. We further consider the degree of elastic scattering with which the inelastic signal will need to compete owing to intrinsic and shock-induced defects in samples of interest. Synthetic phonon spectra and scattering signals are calculated in various materials under dynamic compression using large-scale molecular dynamics simulations.\\ (1) E.E. McBride {\it et al.}, Rev. Sci. Instrum. {\bf 89}, 10F104 (2018)   

X-ray diffraction of dynamically compressed matter on the Z-accelerator

Experiments on the Sandia Z-accelerator have demonstrated the ability to produce dynamically compressed states of matter with unprecedented uniformity, duration, and size, which are ideal for investigations of fundamental material properties. X-ray diffraction (XRD) is a key material science measurement since it provides direct observation of the compression and strain of the crystal lattice, and is used to detect and identify phase transitions. Because of the low signal levels of XRD and due to the destructive nature of Z-Dynamic Materials Properties (DMP) experiments, it is very challenging to detect the XRD pattern close to the Z-DMP load and recover the data. Instead, a new Spherical Crystal Diffraction Imager (SCDI) diagnostic has been developed to relay the diffracted x-rays away from the load debris field. The SCDI diagnostic utilizes the Z-Beamlet laser to generate 6.2-keV Mn He$\alpha $ x-rays to probe a shock-compressed sample on the Z-DMP load. A spherically bent crystal composed of highly oriented pyrolytic graphite (HOPG) is used to collect and focus the diffracted x-rays into a 1-inch thick tungsten housing, where an image plate is used to record the data.   

Demonstration of Multi-GeV Electron Radiography

Charged particle radiography with 800 MeV protons has been used for decades at LANL and developed around the world to study dynamic material properties. Recently, charged particle radiography has been demonstrated with the use of high-energy electrons. Because of the difference in the mass of the electron compared to the mass of the proton the radiographic processes are substantially different and well suited to the study of fast dynamic processes in relatively thin systems. This presentation will show the layout required for such measurements along with data collected from this recent demonstration performed with 14 GeV electrons generated at the SLAC National Accelerator Laboratory. The radiographic performance for flash measurements will be presented along with the limitations of this measurement technique.