Max-Planck-Princeton Center for Plasma Physics

Max-Planck-Princeton Center for Plasma Physics

The center fosters collaboration between scientific institutes in both Germany and the USA. By leveraging the skills and expertise of scientists and engineers in both countries, and by promoting collaboration between astrophysicists and fusion scientists generally, the center aims to accelerate discovery in fundamental areas of plasma physics.

A plasma is a gas of charged particles (ions and electrons). Most of the visible matter beyond the Earth is a plasma, including stars, the interstellar medium (matter between the stars) and the intergalactic medium (matter between galaxies). On Earth, plasmas are important for producing energy through fusion reactions, as well as many other technologies.

The goal of the center is to understand several fundamental problems in plasma physics. Solving these problems could lead to new breakthroughs in producing clean and reliable fusion energy, as well as help us to understand the Universe in which we live.

There are four primary research topics under investigation by members of the Center:

  • Magnetic Reconnection
  • Energetic Particles
  • Plasma Turbulence
  • Magneto-Rotational Instability

The MPS is particpating with three working groups.

1) Observations of prominence-cavity systems

Prominences are cool, over dense structures seen suspended in the lower corona above the solar limb. They mainly reside in highly tangled magnetic fields. Coronal cavities, regions of relatively low density, and high temperature, are often seen surrounding the cooler prominence plasma. The cavity structures often contain closed loops which surround the prominence. When the stability of the system is disrupted, the prominence and surrounding cavity material is ejected into interplanetary space as a Coronal Mass Ejection (CME). The aim of our research is to identify conditions leading to instability, by taking full advantage of modern high resolution imaging (e.g. Solar Dynamics Observatory (SDO) and   STEREO) and spectroscopic (IRIS) observations of the Sun. The figure shows two views of a prominence-cavity system just after the prominence plasma was seen to rise up and start rotating, resembling a tornado. In this particular case the tornado-like activity was triggered by flares in the neighbouring active region (identified as AR).

2) Field-aligned flows and currents on the Sun and in the laboratory

The million degrees hot solar corona is built up by coronal loops. In these loops ionized plasma is confined by the magnetic field and by this forms bright arcs that are aligned with the magnetic field. The feeding of mass and energy into these loops is still poorly understood. Usually the buzzword “coronal heating” is identified with the major problem, but the process that provides the mass to form the loops in the first place is closely related to the heating problem. If the heat input into the solar corona is constant in space, heat conduction back to the Sun and evaporation of cooler material would be the main source of plasma in the loops. If the heat is concentrated towards the loop footpoints, as other models suggest, then the mass supply would be through brief injections of cool material that is subsequently heated. We use solar observations, in particular from the IRIS solar space-based observatory, and numerical simulations of the solar corona to investigate field-aligned flows and currents that will be compared to results from the laboratory experiments.

3) Magnetic reconnection at the Sun and in the laboratory

Magnetic reconnection is the fundamental process of magnetic energy release in the Universe. In particular it is important for heating and explosions in the Solar atmosphere.
Due to the heat of the Sun direct, in situ observations of Solar reconnection are impossible. But reconnection can be studied in the laboratory, like in the MRX device of the Princeton University's  PPPL and by the VINETA device in Greifswald (Germany). In the laboratory, however, the solar and astrophysical plasma conditions cannot be reproduced one-to-one.
To bridge the gap between laboratory and astrophysical plasma parameters we in the (former) TSSSP-group of the MPS numerically simulate to understand the basic physics of magnetic reconnection in the outer space. Our results are calibrated on the laboratory experiments and then up-scaled to astrophysical reconnection .

The figure on the left illustrates the evolution of reconnection as the new connection between magnetic fields (black: field lines) through currents sheets (color coded current density) as it evolves with time starting from small natural fluctuations and turbulence and forming in the end macroscopic structures.

The figure below depicts the resulting three-dimensional structure of the magnetic field in reconnection regions. It deeply impacts the dynamical release of magnetic fluxes, generated, e.g., by dynamo processes below the surface of the Sun.

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