Nevertheless, it was still a rocky road to the successful experiment. Pulsed through the magnetic sound barrier When I explained to my colleagues that a thousandth of this amount of chemical energy of the liquid rubidium does not worry me very much, their facial expressions visibly brightened." Thomas Herrmannsdörfer of the HLD: "Our energy supply system for operating the pulse magnets converts 50 megajoules in a fraction of a second - with that, we could theoretically get a commercial airliner to take off in a fraction of a second. The doubts were quickly dispelled, recalls Dr. The team therefore initially had doubts as to whether such a dangerous experiment was advisable at all. The reason for this: the relatively low magnetic field strength of common superconducting coils with constant field of about 20 tesla.īut what about pulsed magnetic fields, such as those that can be generated at the HZDR's Dresden High Magnetic Field Laboratory (HLD) with maximum values of almost 100 tesla? This corresponds to about two million times the strength of the Earth's magnetic field: Would these extremely high fields allow Alfvén waves to break through the sound barrier? By looking at the properties of liquid metals, it was known in advance that the alkali metal rubidium actually reaches this magic point already at 54 tesla.īut rubidium ignites spontaneously in air and reacts violently with water. On the other hand, in all liquid-metal experiments to date, it has been significantly lower. On the one hand, in large plasma experiments the Alfvén speed is typically much higher than the speed of sound. Only the conditions of the magnetic canopy, considered crucial for corona heating, remained inaccessible to experimenters until now. Soon after their prediction in 1942, the Alfvén waves had been detected in first liquid-metal experiments and later studied in detail in elaborate plasma physics facilities.
We wanted to get to exactly this magic point - where the shock-like transformation of the magnetic energy of the plasma into heat begins," says Stefani, outlining his team's goal. Here, sound and Alfvén waves have roughly the same speed and can therefore easily morph into each other. "Just below the Sun's corona lies the so-called magnetic canopy, a layer in which magnetic fields are aligned largely parallel to the solar surface. Just as the pitch of a strummed string increases with its tension, the frequency and propagation speed of the Alfvén wave increases with the strength of the magnetic field. The magnetic fields acting on the ionized particles of the plasma resemble a guitar string, whose playing triggers a wave motion. The new work of the Dresden team focuses on the so-called Alfvén waves that occur below the corona in the hot plasma of the solar atmosphere, which is permeated by magnetic fields. However, it remains controversial whether this effect is mainly due to a sudden change in magnetic field structures in the solar plasma or to the dampening of different types of waves.
That magnetic fields play a dominant role in heating the Sun's corona is now widely accepted in solar physics. For Stefani, the phenomenon of corona heating remains one of the great mysteries of solar physics, one that keeps running through his mind in the form of a very simple question: "Why is the pot warmer than the stove?" His team conducts research at the HZDR Institute of Fluid Dynamics on the physics of celestial bodies - including our central star. "It is all the more astonishing that temperatures of several million degrees suddenly prevail again in the overlying Sun's corona," says Dr. At its surface, it emits its light at a comparatively moderate 6000 degrees Celsius. At 15 million degrees Celsius, the center of our Sun is unimaginably hot.
0 kommentar(er)
