dozens of them arranged on a sample holder – producing a plasma of ionized particles. And, once again, these processes can be investigated in detail at high temporal resolution with the European XFEL’s X-ray flashes. This time, the extreme conditions do not mimic the interior of stars but of exoplanets, for example. In addition to astrophysicists, material researchers are waiting to be able to analyze their samples using this experiment, which will probably be available from 2022. They expect to gain insights into exotic phase transitions or even discover completely novel materials. All those using the high-intensity or high-energy lasers will, however, have to share the valuable beamtimes with other partners in the HIBEF consortium and the international user community. A state-of-the-art diamond anvil cell is already fit for use. It stands in the measurement hut directly next to the vacuum chamber used for the laser experiments. It can be quickly moved on its system of rails into the X-ray beam. Developed under the leadership of the Hamburg research center DESY (German Electron Synchrotron), this experiment also focuses on extreme pressures. However, they are not generated by laser light, but mechanically, by two diamonds. When the diamonds compress the sample, static pressure of up to four million bars is exerted. Moreover, using additional lasers, the sample can be heated up to 10,000 degrees Celsius. Simulating the interior of a super-Earth In this state, the conditions resemble those in the mantle or outer core of our Earth. Geophysicists can thus acquire insights into the state and behavior of liquid rocks and crystals as they are found in the interior of the Earth. New knowledge about geological processes beckons: from the movement of tectonic plates, via earthquakes, through to volcanic activity. Thanks to the extreme static pressures, researchers are confident they will even be able to mimic the interior of super-Earths in their experiments, that is, very large exoplanets, especially as it is thought highly likely that the surface of these planets is very strongly influenced by the dynamics in the planet’s interior. The HIBEF facility is set to be completed by about the end of 2021. Then researchers will not only be able to subject their samples to extreme pressures or intensive laser pulses but also to the extreme cold of minus 269 degrees Celsius and enormous pulsed magnetic fields of up to 60 teslas. This makes the magnetic fields a good 40 times stronger than the strongest permanent neodymium, iron and boron alloy magnet. Produced by electromagnets, however, the extreme magnetic fields last merely a few microseconds. It is only the quick succession of X-ray flashes from the XFEL that generate enough intensity to be able to harvest reliable data in such a short time. Title 27 exact behavior of correlated Cooper electron pairs, which are responsible for zero resistance in superconductors. Materials researchers, above all, can expect to derive new approaches to developing completely novel materials from the measurements. "As part of the High Energy Density station at the European XFEL, HIBEF will generally be open to all researchers worldwide," says Toncian, looking ahead. Today already, many research groups are preparing their experiments with theoretical models and new ideas for samples and measurement conditions, discussing and refining their concepts for extreme tests at numerous workshops. Thus, at HIBEF and HED, uniquely complex measurement technology meets accumulated knowhow from various disciplines. There is, therefore, a good chance that far into the next decade, the measurement station will deliver astounding insights into the stars and new materials. It is very possible that, by then, the cows will have disappeared from the meadows around the lab building and been replaced by thousands of people in a new part of town surrounding the XFEL. Publications: U. Zastrau, K. Appel, C. Baehtz, O. Baehr, L. Batchelor, A. Berghäuser, M. Banjafar, E. Brambrink, V. Cerantola, T.E. Cowan, H. Damker, S. Dietrich, S. Di Dio Cafiso, J. Dreyer, H.-O. Engel, T. Feldmann, S. Findeisen, M. Foese, D. Fulla- Marsa, S. Göde, M. Hassan, J. Hauser, T. Herrmannsdörfer, H. Höppner, J. Kaa, P. Kaever, K. Knöfel, Z. Konôpková, A. Laso García, H.-P. Liermann, J. Mainberger, M. Makita, E.-C. Martens, E.E. McBride, D. Möller, M. Nakatsutsumi, A. Pelka, C. Plueckthun, C. Prescher, T.R. Preston, M. Röper, A. Schmidt, W. Seidel, J.-P. Schwinkendorf, M.O. Schoelmerich, U. Schramm, A. Schropp, C. Strohm, K. Sukharnikov, P. Talkovski, I. Thorpe, M. Toncian, T. Toncian, L. Wollenweber, S. Yamamoto, T. Tschentscher: The High Energy Density scientific instrument at the European XFEL. Journal of Synchrotron Radiation, 2021 (DOI: 10.1107/ S1600577521007335) T. Wang, T. Toncian, M.S. Wei, A.V. Arefiev: Structured targets for detection of Megatesla-level magnetic fields through Faraday rotation of XFEL beams. Physics of Plasmas, 2019 (DOI: 10.1063/1.5066109) T. Kluge, M. Rödel, J. Metzkes-Ng, A. Pelka, A.L. Garcia, I. Prencipe, M. Rehwald, M. Nakatsutsumi, E.E. McBride, T. Schönherr, M. Garten, N.J. Hartley, M. Zacharias, J. Grenzer, A. Erbe, Y.M. Georgiev, E. Galtier, I. Nam, H.J. Lee, S. Glenzer, M. Bussmann, C. Gutt, K. Zeil, C. Rödel, U. Hübner, U. Schramm, T.E. Cowan: Observation of ultrafast solid-density plasma dynamics using femtosecond X-ray pulses from a free- electron laser. Physical Review X, 2018 (DOI: 10.1103/ PhysRevX.8.031068) It will then be possible to measure and understand previously unexplained magnetic effects in solids with crystalline structures. Special materials periodically change their electrical conductivity, for example, when exposed to low temperatures and strong magnetic fields. And under these extreme conditions it would also be possible to analyze the Contact _Institute of Radiation Physics at HZDR Helmholtz International Beamline for Extreme Fields (HIBEF) at the European XFEL Dr. Toma Toncian t.toncian@hzdr.de