First Time-Resolved Diffraction Measurements Made on OMEGA EPSeptember 18, 2023
The first time-resolved diffraction measurements on OMEGA EP were made during the recent TRXRDEP-23A campaign. Principal Investigators D. Polsin, LLE, and L. R. Benedetti, LLNL, added an x-ray framing camera to the powder x-ray diffraction image-plate diagnostic and recorded the body-centered cubic to hexagonal close-packed (bcc-to-hcp) phase transition in shocked iron. The time-resolved x-ray diffraction (XRD) measurements utilizing a 6.7-keV, 1.25-ns x-ray backlighter captured the unshocked (pure bcc), shock transit (mixed bcc and hcp phase), and shock breakout on a shot-by-shot basis.
The figure shows the XRD data captured on the four-strip x-ray framing camera surrounded by image plates. The framing camera strips (each with a temporal resolution of 400 ps) are in the center of each image and spatially aligned with the time-integrated image-plate data. The growth of the high-pressure hcp phase of iron out of the ambient bcc phase can be seen from left to right as the shock enters the iron (left-hand panel) and at shock breakout (right-hand panel). Acquiring high-quality and high-temporal–resolution data required mitigating sources of x-ray fluorescence in the x-ray framing camera and blocking direct lines of sight from the x-ray backlighter to the detector.
In future experiments, Polsin and Benedetti will explore the kinetics of the bcc-to-hcp phase transformation by extending the backlighter duration and further optimizing the signal-to-noise ratio. This campaign represents a significant milestone in the development of an experimental platform to collect time-resolved x-ray diffraction measurements on a single laser shot.