## Dr. Stefan Andreas Weber

Plasma physics is a fundamental subject of relevance to many research areas such as astrophysics, laboratory ionized gases, laser-matter interaction, and controlled thermonuclear fusion. Plasmas are one of the fundamental states of matter and represent most of the non-dark matter in the universe. Plasma physics is the self-consistent description of charged particles and electromagnetic fields.

# Gravitational Waves Generated by Laser-Matter Interactions

The research is performed in the area of gravitational waves generation which connects fundamental gravitational theory with the laser—plasma interaction in the high intensity regime 10PW or higher. This area of research started to be interesting thanks to the remarkable progress in the technology of high power lasers which might enable applications also in the research field of gravitation in the future.

The gravitational wave generation is investigated in the laboratory conditions in various models and the properties of radiation such as metric perturbations and luminosity, spectrum, polarization and the behaviour of test particles are analyzed. The models are based on acceleration of matter to very high velocity by an intense laser pulse. The resulting gravitational waves are in frequency range of GHz to THz. Therefore the currently available detectors, such as resonant detectors and interferometers LIGO or Virgo , are not usefull for their detection and a new technology should be developed to enable experimental research in this area. In the future, such experiments could be possibly performed at our facility ELI Beamlines or other research facilities like PETAL , NIF-ARC or APOLLON.

Current research is even more relevant after the recent detection of gravitational waves in 2016 by LIGO. The detection will definitely open a new era of research in many fields especially in astrophysics.

*The angular distribution of gravitational radiation in the piston model for different intensities (a) non-relativistic I=1020 W/cm ^{2}, (b) weakly relativistic I=10^{22} W/cm2 and (c) relativistic I=10^{24} W/cm2 , the distribution for the light sail model is in image (d) I=10^{24} W/cm2. The angle θ is measured with respect to the direction of laser propagation where θ =0 is on x axes.*

### References:

M. Maggiore, „Gravitational waves: Volume 1: Theory and experiments“, Oxford University Press, New York, 2008.

E. Gelfer, H. Kadlecová, O. Klimo, S. Weber and G. Korn, Gravitational waves generated by laser accelerated relativistic ions, Phys. Plasmas 23, 093107

Hedvika Kadlecová, hedvika [dot] kadlecova [at] eli-beams [dot] eu

Ondřej Klimo, ondrej [dot] klimo [at] eli-beams [dot] eu

Stefan Weber, stefan [dot] weber [at] eli-beams [dot] eu

# High-Energy Density Physics

High-energy density plasmas are generally characterized by pressures above 1 Mbar or energy densities above 1011 J/m3. Lasers are the only way to create such conditions in a controlled way in the laboratory on a small scale (an uncontrolled way would be nuclear explosions).

### Laser-plasma interaction for HEDP conditions:

- Contributes to new schemes for inertial confinement fusion (ICF) such as shock ignition and fast ignition
- Helps to understand strongly correlated systems
- Provides opacity data of compressed materials
- Has many applications for astrophysical phenomena

In contrast to “standard” plasma physics, HEDP-plasmas have often very few particles in the Debye-sphere which makes any numerical or analytical treatment very difficult due to strong correlation effects. Experiments in this field will also help us to refine the theories for HEDP and make prediction models more reliable. HEDP experiments will provide information on the phase transition of insulators to metal-like conductors. In optically thick material radiation is an important player in HEDP as it is altering the structure and dynamics of shocks. Modeling radiative shocks is challenging as it is a multi-scale problem. The physics of pre-pulses in high-intensity laser-matter interaction is a difficult problem of HEDP as up- and down-stream optical depths are very different, affecting the shock-physics. HEDP is strongly linked to laboratory astrophysics (→ html link) and comprises WDM (→ html link). The lasers available in P3 will allow to drive strong shocks and provide sophisticated diagnostic tools for HEDP-research.

**REFERENCES:**

*R.P. Drake, High-Energy-Density-Physics, Springer Verlag 2006**National Research Council, Frontiers in High Energy Density Physics, Natl. Academy Press 2003**S.V. Lebedev, High energy density laboratory astrophysics, Springer Verlag 2009**P.W. Bridgman, The physics of high pressure, Dover 1970**P.O.K. Krehl, History of Shock Waves, Explosions and Impact: A Chronological and Biographical Reference, Springer 2007*

Stefan WEBER, stefan [dot] weber [at] eli-beams [dot] eu

# Laboratory Astrophysics

Laboratory astrophysics is the study of astrophysical and cosmological phenomena on a laboratory scale using high-power lasers.

The notion of laboratory astrophysics goes back to the late 1960s, and the user of lasers in this respect dates back to the 1970s (CO2 lasers). With the advent of new, short-pulse, high-power laser systems this field is taking a step forward. Many astrophysical plasma phenomena can be reproduced on a laboratory scale with intense lasers, such as the following:

- Magnetic reconnection
- Collisionless shocks
- Particle acceleration (cosmic-ray physics)
- Coherent nonlinear structures (e.g., solitons)
- Magnetic field generation
- Jet formation
- Rayleigh-Taylor instability
- Radiation hydrodynamic physics (stellar atmospheres, etc.)
- Radiative shocks.

Modeling astrophysical phenomena in the laboratory is based on the principle of limited similarity. The principle states that exact equivalence of the relevant dimensionless parameters is not required, but that it is enough for these parameters to be large or small with respect to unity, as they are in reality. This assures that the observed physics in the experiment is relevant for the corresponding phenomena on astrophysical scales.

Laboratory astrophysics also has a strong overlap with WDM (→ html link) and High Energy Density Physics (HEDP → html link) as far as calculations such as radiative opacities and the equation of state (EOS) are concerned. It is not possible to imagine plasma astrophysics without magnetic fields. The collisionless interaction of exploding plasmas with magnetized media is fundamental to an understanding of particle acceleration in the universe, Weibel instability, supernova remnants, and gamma-ray bursts, to name just a few.

**REFERENCES**

- S.V. Bulanov et al. On the problems of relativistic laboratory astrophysics and fundamental physics with super powerful lasers, Plasma Phys. Rep. 41, 1 (2015).
- Y.P. Zakharov. Collisionless laboratory astrophysics with lasers, IEEE Plasma Science 31, 1243 (2003).
- P. Chen. Laser cosmology, Eur. Phys. J. ST 223, 1121 (2014).
- D.W. Savin et al. The impact of recent advances in laboratory astrophysics on our understanding of the cosmos, Rep. Prog. Phys. 75, 036901 (2012).
- B. Remington et al. Experimental astrophysics with high power lasers and Z pinches, Rev. Mod. Phys. 78, 755 (2006).
- S.V. Bulanov et al. Relativistic laser-matter interaction and relativistic laboratory astrophysics, Eur. Phys. J. D 55, 483 (2009).
- D.D. Ryutov et al. Scaling astrophysical phenomena to high-energy-density laboratory experiments, Plasma Phys. Control. Fusion 44, B407 (2002).
- S.V. Lebedev. High energy density laboratory astrophysics, Springer Verlag (2007).

Yanjun GU, yanjun [dot] gu [at] eli-beams [dot] eu

Yue LIU, yue [dot] liu [at] eli-beams [dot] eu

Sushil SINGH, sushil [dot] singh [at] eli-beams [dot] eu

Stefan WEBER, stefan [dot] weber [at] eli-beams [dot] eu

# Warm Dense Matter

Warm Dense Matter (WDM) is the study of matter under extreme conditions of pressure. It is a particular sub-field of high-energy density physics.

### This field of research is relevant to an understanding of the following:

- Inertial confinement fusion
- Planetary cores
- The fundamentals of the quantum nature of matter
- The physics of shock waves in dense material
- The non-equilibrium and phase-transition aspects of matter.

The main goal of WDM is to gain an understanding of the equation for determining the states and opacities of compressed matter. Of particular interest are conditions where there is very high-density matter (tens of grams per cubic-centimeter) but moderate and therefore warm temperatures (a few eV to a few tens of eVs). Simulating matter in these conditions is challenging, and effective simulation methods are still under development. The difficulties arise from the fact that matter under these conditions is a system of strongly interacting particles.

The complexity arises from the fact that in this state the potential energy between the interacting electrons and the nuclei is of a similar order to the kinetic energy of the electrons, as opposed to a plasma state where the kinetic energy of the electrons is much greater than the potential energy between the interacting electrons and the nuclei. Well-defined experiments can help to distinguish between conflicting theoretical models. The kilojoule laser, which is available in P3, L4n, will allow important research to be performed in WDM. Having the use of a local betatron as a diagnostic tool for exploiting the highly energetic electrons and the X-rays simultaneously will be a step forward in diagnosing the state of WDM. Even what occurs when hydrogen, the simplest atom, is exposed to extreme pressures is not yet fully understood. Although Wigner suggested in the 1930s that hydrogen has a phase transition to a metallic state, this has still not been fully confirmed.

REFERENCES:

- Y. Ping et al. Warm dense matter created by isochoric laser heating, HEDP 6, 246 (2010).
- S. H. Glenzer et al. X-ray Thomson Scattering in High Energy Density Plasmas, Rev. Mod. Phys. 81, 1625 (2009).
- F.Graziani, M.P. Desjarlais, R. Redmer, S.B. Trickey (Eds.) et al. Frontiers and Challenges in Warm Dense Matter, Springer Verlag, (2014).
- R.W. Lee et al. Warm Dense Matter: an overview, Report UCRL-TR-203844, Lawrence Livermore 2004.

Stefan Weber stefan [dot] weber [at] eli-beams [dot] eu