APPLICATION to access the LULI facilities

2021 –2022

Title of the experiment: Study of metallization in dense and Argon

Principal Investigator (PI): Dr. Valerio Cerantola [to whom all correspondence will be addressed] European X-ray Free Electron Laser facility GmbH Holzkoppel 4 22869 Schenefeld, Germany [Institution status 1]: RES

e-mail: [email protected] phone: +4915771675077 PI status: PDOC 2 citizenship: IT 3 birth date: 23/09/1987 LULI co-PI: Dr. Alessandra Ravasio contacting your co-PI (if any) prior to submission is mandatory; she/he will have to assess the feasibility of your proposal in agreement with the technical staff Summary (less than 350 words - will be published on the LULI web site)

This experiment will study the insulator-to-metal transition in pre-compressed Krypton and Argon using laser-driven shock compression. Pre-compressing the sample to high initial densities in a specially designed diamond anvil cell will allow us to reach ultra-high pressures and temperatures relevant to planetary interiors, and probe previously unexplored regions of the P-T phase diagram. Multiple-shock compression has been the widely used technique to study warm dense matter but has some shortcomings such as the difficulty in direct observation of temperature due to loss of transparency. Using laser-driven shock compression in a pre-compressed sample allows independent measurement of temperature, and more importantly, allows reaching significantly higher densities because shock-induced heating is reduced. Very few studies have used this technique so far and have been constrained to lower pre-compression pressures. Moreover, Krypton and Argon have not been studied using this technique, hence their metallization mechanism remains unexplored at higher densities and temperatures. This experiment will combine high static pre-compression and high energy laser-driven shock compression to give novel insights into the metallization mechanism of Krypton and Argon at extreme conditions.

Number of access weeks requested: 1 on: nano2000 (choose the appropriate facility)

Proposed access route: LASERLAB, STANDARD 4

Do you have received any support for this proposal? no (please select and - if yes - specify)

Keywords (at least 3): pre-compression, shock-compression, metallization, noble gases

Co-investigators (only for those who will physically participate to the experimental campaign at LULI, not including LULI researchers – one line per person) 1. Anand Dwivedi, PHD2, European-XFEL, [email protected], IN 3, 1995 2. Erik Brambrink, EXP2, European-XFEL, [email protected], DE3, 1975 3. Sylvain Petitgirard, EXP2, ETH-Zürich, [email protected],FR3, 1981 4. Thomas Preston, PDOC2, European-XFEL, [email protected], UK3, 1991 5. Karen Appel, EXP2, European-XFEL, [email protected], DE3, 1970 6. Cornelius Strohm, EXP2, DESY, [email protected], DE3, 1973 7. Marius Millot, EXP2, LLNL, [email protected], FR3, 1981 8. Zuzana Konôpková, PDOC2, European-XFEL, [email protected], SK3, 1983 9. Ulf Zastrau, EXP2, European-XFEL, [email protected], DE3, 1980

1 UNI (university), RES (public research organization), SME (small or medium enterprise), PRV (industrial and/or private organization) 2 UND (undergraduate), PHD (student), PDOC (post-doctoral researcher), EXP (experienced researcher), ENG (engineer), TEC (technical) 3 acronym only 4 standard (for all users), LASERLAB (for researchers working in EU member states other than France) or pluri-annual (for French users only) [please see instructions] Study of metallization in dense Krypton and Argon

SCIENTIFIC CASE

Noble gases are important tracers for a variety of planetary processes such as Earth’s accretion and the long-term degassing of the mantle. Recent detections of noble gases and their isotopes in comets [1] and white dwarfs [2] have opened the possibilities of determining the evolution, inner structure, and thermal behavior of extraterrestrial bodies and exoplanets, and the origin of the noble gases themselves. Understanding the behavior of noble gases at extreme conditions of temperature and pressure thus gives a deep insight into planetary and astrophysical evolution. Besides being excellent geochemical markers, noble gases also find use in many industrial applications. The 85Kr isotope of krypton is used in industries for leak testing, while 81Kr can be used to determine the age of ice and groundwater up to 2 million years old. Argon is widely used in the and casting industry, especially in manufacturing . It is also used in the medical field for its narcotic abilities and is being researched for its neuroprotective behavior in models of brain injury.

Having a filled-shell electronic configuration, noble gases are inert at ambient conditions and do not react with other elements. But at high pressure and temperature conditions, noble gases are predicted and shown to form stable compounds. For instance, a compound of argon and nickel, ArNi, is synthesized and shown to be stable at thermodynamic conditions representative of the Earth’s core [3], while DFT calculations predict that a monoxide compound of krypton, KrO, should form spontaneously and remain stable around 300 GPa [4]. Studying noble gases at extreme conditions is therefore of great relevance in the fields of chemistry, physics, Earth, and planetary sciences.

The extreme densities relevant to most exoplanets are not reachable by static compression, i.e. in diamond anvil cell (DAC), or single shock compression techniques. Multiple shocks generated by stacked laser pulses could allow higher densities to be reached, but the thermodynamic state of the system is not easy to access and must be calculated from models. For instance, in the multi-shock compression of Ar [5], it becomes difficult to obtain multi-shock temperatures from the spectral radiance due to the partial transparency loss at the interface and is calculated using a model based on self-consistent fluid variational theory (SFVT). Instead of using the multi-shock compression technique, we can send a laser-induced shock wave through a sample that is pre-compressed at high static pressures inside a DAC. The equation-of-state of the system can then be directly measured through the Rankine-Hugoniot equations from the shock and particle velocities, and temperature can be measured independently with a pyrometric technique. This combination of static and dynamic compression is analogous to multiple-shock compression, allowing us to reach significantly higher densities because shock-induced heating is reduced.

The initial onset pressure of the pre-compressed sample is extremely important because it not only allows the production of off-Hugoniot measurements for shocks incident on samples of various initial densities/pressures, but also because within the same sample, pressure-generated phase transitions could have a huge impact on the compression-density curve, as well as the ultimate pressure achievable, which has not been thoroughly investigated yet.

At extreme conditions, noble gases also undergo an insulator-to-metal transition. The metallization pressures of rare-gas solids are expected to be high given the spherically-symmetric charge distribution due to their completely filled electronic shells. For example, the temperature dependence of the resistivity of Xenon becomes predominantly metallic between 121 and 138 GPa, and shows purely metallic behavior at 155 GPa [6]. While this metallization of Xe occurs near room temperature, Ar requires combined high pressures and temperatures to display conductivity [7][8]. Metallization of Ar is predicted to occur above ~160 GPa and the laser-heated diamond anvil cell data in [7] indicates an enhancement of conduction with temperature. Theoretical calculations of the equation-of-state of solid fcc Kr under high pressures have estimated the metallization pressure to be 316 GPa [10] at room temperature, but has not been verified experimentally. The equation-of-state of dense Kr has been determined up to 155 GPa and 45000 K [9] using multiple-shock reverberation compression experiments, but the conductivity values were obtained only using DFT calculations.

Studying the metallization process in noble gases is also of importance because of the structural transitions associated with it [11]. Total-energy calculations in [11] suggest that the fcc phase of Ar observed at 1-atm should transform to a hcp structure prior to metallization, which in turn should transform to a bcc structure at pressures above metallization. McMahan [11] also suggests that all rare-gas solids may follow a generalized structural sequence of fcc→hcp→bcc, with metallization occurring near, if not within, the hcp interval. Most shock-compression studies of the insulator-to-metal transition of noble gases at extreme conditions have used the flyer-plate based multi-shock technique, which leaves out the region of the pressure-temperature-density phase diagram where these gases might show interesting metallization mechanisms. Very few studies have used the technique of laser-driven shock compression on pre-compressed samples to study metallization in noble gases [12]. The use of this method to study the metallization process in dense Kr and Ar remains largely unexplored so far.

Our experiment aims to study the insulator-to-metal transition in dense Kr and Ar by Figure 1 : Phase diagram of Kr adapted from [9] showing our using high energy laser-driven shock compression simulated Hugoniots of Kr (red, green, and blue curves) on pre-compressed samples in a specially laser-shocked at different initial denities. designed diamond anvil cell. The feasibility of laser-driven shock experiments in pre-compressed samples at LULI is demonstrated in [13], where equation-of-state measurements were made on pre-compressed water samples in a DAC pre-compressed to initial pressures ranging from 1 to 6 kbar. In this proposed experiment, we will use an innovative DAC geometry which owns the promise to reach high pre-compression pressures (greater than 5 GPa) using thin anvils. This design, developed for the European-XFEL facility, is well-suited for low-moderate laser-energy facilities, such as LULI. We will do extensive tests on our pre-compression device in April 2021 and expect to reach pre-compression pressures greater than 5 GPa, higher than the initial pressure reached in any of the previous experiments using this technique. This will enable us to reach greater initial densities of our sample, and upon laser-driven shock compression, will allow us to probe previously unexplored domains of the pressure-temperature-density phase diagram relevant for planetary science and extreme conditions chemistry. In addition, these DACs will have much thinner diamond windows, strongly reducing 2-D effects during shock propagation through the diamond and thus enabling higher shock pressures to be reached. By making optical measurements of reflectivity and temperature, we also aim to study the dependence of the metallization mechanism on the pre-compression density of the sample. Combining our results from this experiment with other experiments such as in-situ x-ray diffraction at the European-XFEL, we also aim to study the dynamics of the structural phase transitions associated with metallization.

References:

[1] M. Rubin et al, “Krypton isotopes and noble gas abundances in the coma of comet 67P/Churyumov-Gerasimenko” Science Advances, vol. 4, no. 7, eaar6297, 2018 [2] K. Werner et al, “First detection of krypton and xenon in a white dwarf” The Astrophysical Journal Lett., 753, L7, 2012 [3] A. A. Adeleke et al, “A High-Pressure Compound of Argon and Nickel: Noble Gas in the Earth’s Core?” ACS Earth Space Chem, 3, 11, 2517-2524, 2019 [4] P. Zaleski-Ejgierd & P. M. Lata, “Krypton oxides under pressure” Sci Rep 6, 18938, 2016 [5] J. Zheng et al, “Multishock Compression Properties of Warm Dense Argon” Sci Rep 5, 16041, 2015 [6] M. I. Eremets et al, “Electrical Conductivity of Xenon at Megabar Pressures” Phys. Rev. Lett. 85, 2797, 2000 [7] R. S. McWilliams et al, “Opacity and conductivity measurements in noble gases at conditions of planetary and stellar interiors” PNAS, 112 (26) 7925-7930, 2015 [8] S. Kuhlbrodt et al, “Electrical Conductivity of Noble Gases at High Pressures” Contrib. Plasma Phys. 45, No. 1, 61-69, 2005 [9] Z. Wang et al, “Equation of state measurements of dense krypton up to the insulator-metal transition regime: Evaluating the exchange-correlation functionals” Phys. Rev. B 103, 014109 (2021) [10] J. Hama & K. Suito, “Equation of state and metallization in compressed solid krypton” Physics Letters A, Volume 140, Issue 3, Pages 117-121, 1989 [11] A. K. McMahan, “Structural transitions and metallization in compressed solid argon” Phys. Rev. B 33, 5344, 1986 [12] Celliers et al, “Insulator-to-Conducting Transition in Dense Fluid ” Phys. Rev. Lett. 104, 184503, 2010 [13] E. Henry et al, “Laser-driven shocks in precompressed water samples” J. Phys. IV France 133, 1093-1095, 2006 SHOT PLAN shots withthe pre and shock for sample quartz and Al simple prepare also will We pre and loaded be will which targets/sDAC, 15 prepare will We multilayer in sample Fig shown allows cell anvil diamond The TARG We will SOP to measure the temperature. nm.532 and running1064 at mode in color two beVISAR should metallization. Thedetect the in breakout shock the measuring is diamondcell which system, VISAR the is experiment this in diagnostic main The this of top The on sits configuration. window diamondanvil anvils thin A sDAC degrees. 40 on ca. of Closeup opening an (Right) has (bottom) (sDAC). anvil perforated Cell Anvil Diamond Shock (Left) 2. Figure diamete Boehler modified a is which anvil, diamond full the at looks and side opposite the x available, When anvil). bottom 2(Figure x to 100 coupled 70, 60, 50, e.g. thicknesses, different of be can o an with anvil, perforated a of use the x larger in environments sample of majority the is sample The plate if necessary. us the in performed be will experiment The SET EXPERIMENTAL e

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The goal of this experimental campaign is to laser-shock pre-compressed Kr and Ar at different pre-compression pressures and using different laser energies. Tests will be performed in April 2021 to determine the achievable pre-compression range of the sDAC. Simulated Hugoniots of Kr laser-shocked at different initial densities are plotted in Fig. 1 and indicate possible different paths on the phase diagram that can be measured by simply modifying the starting pressure.

Pre-compression pressures will be measured beforehand either using the equation-of-state of Kr, with micrometer size X-ray laboratory source, or at synchrotron facilities, or using the standard and calibrated Raman shift of diamond at high pressures.

We aim to prepare 15 targets and we reasonably assume we will be able to perform 5 shots per day for a total of 3 days. We ask for a week of experimental time, which accounts for 2 days of set-up, testing, and calibration, and 3 days of shooting.

EXPERTISE OF THE TEAM

The experimental team has recognized expertise in all techniques covering different aspects of the experiment. This includes static compression, diamond anvil cell preparation and sample loading, shock compression, hydrodynamic simulations, as well as material science at high pressures and temperatures. Moreover, all team members presently work or have worked at large scale facilities such as LULI, ESRF, PETRAIII, and EuXFEL and are very familiar and confident with working at beamlines.

• Anand Dwivedi: experience with DAC preparation, extreme conditions beamline operation, high-pressure/temperature physics. • Valerio Cerantola: expertise in high-pressure static compression experiments, DAC preparation/sample loading, synchrotron/large scale facility instrumentation, high-pressure/temperature physics. • Erik Brambrink: expertise in hydrodynamic simulations, shock wave and laser physics, high-pressure/temperature phenomena, large scale laser installation and instrumentation. • Sylvain Petitgirard: expertise in designing novel DAC designs, developer of miniature diamonds, ultra-high pressure static compression experiments at synchrotron sources. • Thomas Preston: expertise in shock dynamic compression measurements, hydrodynamic simulations/software development, large scale facility instrumentation. • Karen Appel: expertise in beamline development, large scale facility instrumentation/installation, shock compression and high-pressure/temperature physics. • Cornelius Strohm: expertise in large scale facility instrumentation/installation, detector development, high-pressure/temperature physics. • Marius Millot: expertise in dynamic shock compression, warm dense matter physics, optical and transport properties measurements under laser-driven dynamic compression. • Zuzana Konôpková : expertise in large scale facility instrumentaion/installation, dynamic DAC, high-pressure/temperature physics. • Ulf Zastrau : expertise in high energy denity physics, large scale facility instrumentation, installation and development.

PREVIOUS ACCESS

Most members of the experimental team, including the PI, will be first-time users at LULI, while some members have been users at LULI in the past. No previous experiments were conducted at LULI within the last two calendar years.