Magnetized plasma Acceleration Processes in Cosmos: The Legacy of Hannes Alfvén
Tid: On 2019-09-18 kl 14.15 - 15.00
Föreläsare: Rickard Lundin, Professor Emeritus, IRF
Plats: Lecture hall - FD5 AlbaNova, Roslagstullsbacken 21
Abstract. Sixty years of in-situ space explorations have offered a wealth of scientific data in space plasma physics, specifically on the solar wind interaction with planets and other celestial objects in the solar system. In-situ space data opened a new window to cosmos, changing the concept of vacuum space to plasma space. This lead to a better understanding of episodic and long-term (solar cycle) phenomena induced by the Sun. The hot expanding solar corona plasma, omnipresent in the solar realm out to the galactic wind, dominates plasma physics phenomena (e.g. aurora) in the near space environment of planets. Similar phenomena are expected to apply for planets orbiting other stars in our galaxy as well as in other galaxies in Universe. To quote Alfvén: ”The plasma Universe”.
Solar system plasma acceleration process serves as a road map for plasma acceleration processes in other stellar plasma systems, not accessible by in-situ measurements. Bright cosmic phenomena (such as aurora) characterized by filament structures is a signature of plasma controlled by magnetic fields. Extended bright beams are characteristic of magnetized plasma acceleration. Based on that, a number of astrophysical objects complies with magnetized plasma acceleration processes. Hannes Alfvén was first to point out the importance of the magnetic field to understand and order cosmic phenomena. He stated already 1930 that strong magnetic fields are involved in the acceleration of high energy cosmic ray particles. This was one year before Fermi, a more reputable physicist of that time.
The acceleration of plasma boils down to electric fields, waves and magnetic fields. Ponderomotive forcing is a useful concept to describe wave forcing and plasma acceleration. A particularly efficient force that applies to the proposals by Alfvén and Fermi in the 30’s, is the Magnetic Gradient Wave force (MGW). In short, this force scales with the wave power and the divergence of the magnetic induction. MGW-forcing, leading to outgoing field-aligned ion beams from the Earths polar region, is applicable to a number of other cosmical phenomena, such as solar streamers, pulsars, and HerbigHaro objects. Such forcing can be scaled “down to Earth”. The strong divergence of a dipole magnetic field enables MGW-acceleration up to MeV energies over relatively short distances.
The lecture is part of a series of annual Alfvén Lectures, in memory of KTH-professor Hannes Alfvén, who received the Nobel Prize in Physics, 1970. The lecture is supported economically by the Royal Swedish Academy of Sciences, through its Nobel committeé for physics.
Note: The event is open to everyone so no notification is needed!