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FRINATEK-Fri prosj.st. mat.,naturv.,tek

What Makes Magnetic Reconnection Stop?

Alternative title: Hva får magnetisk rekonneksjon til å stoppe?

Awarded: NOK 11.9 mill.

Magnetic fields exist at all scales in the universe, from galaxy clusters and interstellar mediums, and on smaller scales from the solar corona to the magnetosphere and Earth's dipole field. Magnetic fields may pervade the entire universe, and along with gravity, they control and influence structures within it. Across all these vast ranges there is a fundamental process at play in almost all of them: magnetic reconnection. Magnetic reconnection represents the most plausible, if not the only, way of tapping the energy stored in the magnetic field in an explosive manner. How magnetic fields drive these explosions is complex and interesting. At the simplest level, it can be imagined as two oppositely directed sets of magnetic field lines - forming a sheet of electric current - that break and reconnect. The resulting change in magnetic topology releases almost all of the stored energy in the field, which goes to accelerating plasma particles. Solar eruptions, the shape and dynamics of planetary magnetospheres, and major disruptions in astrophysical systems are all enabled, influenced, or controlled by this process. Even in man-made plasmas in the laboratory, reconnection is an important, albeit undesirable, process in fusion machines as it disrupts the plasma kept stationary by magnetic confinement. In Earth's magnetosphere, it facilitates the entry of solar wind magnetic fields and plasma that consequently leads to magnetospheric storms, substorms, aurorae, and deleterious space environment effects known as Space Weather. Past and present research is overwhelmingly focused on the questions of how reconnection operates after it started. The question of how it stops, in contrast, has received very little attention. Only by understanding how and why magnetic reconnection stops can we understand the state of the universe. For instance, what stops the cosmic magnetic field from diffusing away, by continuous reconnection? How would the Sun behave without being able to rapidly expel flux and energy via solar flares? What stops the heliospheric current sheet from experiencing constant magnetic reconnection? Why is Earth?s magnetic field not destroyed by continuous reconnection? The answers to these fundamental questions rely on first understanding what makes reconnection stop and start. The RECSTOP team has a systematic research program that merges new spacecraft observations with state-of-the-art numerical modelling and theoretical understanding in an innovative and comprehensive analysis approach. Observations from the Magnetospheric Multiscale Mission (MMS), which is specifically designed to observe the inner workings of magnetic reconnection, allows us to study 100s of reconnection events. Our state-of-the-art numerical particle models can be tailored to the observations to gain an even greater insight to the mysterious physical processes at play.

Magnetic reconnection is the mechanism behind the often-explosive release of stored magnetic energy into kinetic energy of charged particles. A burst of energy released in the Earth’s space environ-ment is estimated to be as much as 10^16J, and in magnetar flares it can reach up to 1039J. Arguably, this is one of the most important energy conversion and transport processes in astrophysical plasmas, in space plasmas, and in man-made plasmas in the laboratory. Its full understanding, though, remains elusive. We propose a new angle of attack that promises a breakthrough in this scientific challenge. Past and present research is overwhelmingly focused on the questions of how reconnection starts and how it operates after it started. The question of how it stops, in contrast, has received very little attention. This is surprising given the obvious implications hereof for the effectiveness, scale, and impact of the reconnection process on the large-scale system. For example, without knowing when and how reconnection stops, we cannot determine the energy transport into and inside of the Earth space environment, or estimate the size of a solar eruption or a stellar flare. On the most basic level, we will not know when reconnection will occur if we do not know when it cannot occur. We seek to answer this fundamental question regarding magnetic reconnection: what makes it stop? The results will provide key insights that extend far beyond the determination of when and how reconnection ceases in the magnetosphere, in the solar wind, the solar atmosphere and beyond. Many other important applications, for example in relativistic, astrophysical plasmas and fusion plasma research, will benefit from the new knowledge produced here. The goal is to develop a unified understanding of what stops reconnection, which, in turn, implies knowledge of what it needs to work. In this sense, the proposed research will also create fundamental advances in basic reconnection research.

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FRINATEK-Fri prosj.st. mat.,naturv.,tek