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Novel Instrument to probe thermal states of extreme matter on earth

Scientists at Lawrence Livermore National Laboratory (LLNL) have collaborated with Princeton Plasma Physics Laboratory (PPPL) to design a novel X-ray crystal spectrometer.

This spectrometer will provide high-resolution measurements of a challenging feature of high energy density(HED) matter produced by National Ignition Facility (NIF) experiments.

The work is featured in a paper in the Review of Scientific Instruments. The study describes a new crystal shape being fabricated for NIF, the world’s most energetic laser.

High energy density plasmas are found in stars, nuclear explosions, and cores of giant planets. This laser-produced plasma might be the most extreme state of matter created on Earth.

Previous PPPL built spectrometer was quite successful.

The spectrometer, delivered in 2017, provides high-resolution measurements of the temperature and density of NIF extreme plasmas for inertial confinement fusion experiments. The data obtained were presented in invited talks and peer-reviewed publications.

The instruments measure profiles of key parameters such as the ion and electron temperatures in large volumes of hot plasmas that are magnetically confined in doughnut-shaped tokamak fusion devices to facilitate fusion reactions.

NIF laser-produced HED plasmas are tiny, point-like substances that require differently designed spectrometers for high-resolution studies.

Layout of the spectrometer, which will provide high-resolution measurements of a challenging feature of high energy density matter produced by National Ignition Facility experiments. Image by Neil Ose LLNL.
Layout of the spectrometer, which will provide high-resolution measurements of a challenging feature of high energy density matter produced by National Ignition Facility experiments. Image by Neil Ose LLNL.

Marilyn Schneider, leader of the Radiative Properties Group in the Physical and Life Sciences Directorate at LLNL and a paper co-author, said this is the third designed crystal for extended X-ray absorption fine structure (EXAFS) experiments at NIF. These crystals are part of a high-resolution spectrometer named HiRAXS, which is described in another paper in Review of Scientific Instruments. LLNL co-authors include Stanislav Stoupin, Daniel Thorn, Neil Ose, Yuan Ping, Federica Coppari, Bernard Kozioziemski, Andy Krygier, Hong Sio, Jay Ayers, Philip Efthimion, and Schneider. PPPL co-authors include Lan Gao, Ken Hill, Manfred Bitter, and Brian Kraus.

The collaboration will move to NIF in October when the new crystal is scheduled for testing there, with researchers at both laboratories eagerly awaiting the results.

“Experiments at NIF that measure the EXFAS spectrum at high X-ray energies have had low signals,” Schneider said. “The spectrometer design described in the paper concentrates the low signal and increases the signal-to-noise ratio while maintaining the high resolution required for observing EXAFS.”

“Unlike commonly used spherically, cylindrically or toroidally curved crystals, this new shape of crystal follows sinusoidal spirals,” said Yuan Ping, leader of the EXAFS project and the Dynamic Multiscale Material Properties Group. “Such a novel design makes it possible to meet the strict requirements for EXAFS measurements to probe the thermal state of highly compressed higher-Z materials.”

Journal Reference
  1. M. Bitter, A new class of focusing crystal shapes for Bragg spectroscopy of small, point-like, x-ray sources in laser produced plasmas. Review of Scientific Instruments 92, 043531 (2021); DOI: 10.1063/5.0043599
  2. S. Stoupin, The multi-optics high-resolution absorption x-ray spectrometer (HiRAXS) for studies of materials under extreme conditions. Review of Scientific Instruments 92, 053102 (2021); DOI: 10.1063/5.0043685

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