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In severe thunderstorms electric fields can become so high, that high energy radiation – such as X-rays and gamma rays - can be generated. Even antimatter can be formed. The highly complex interactions between high electric fields and particles in thunderstorms were not well modelled yet. Christoph Köhn, PhD student from research centre Centrum Wiskunde & Informatica (CWI) in Amsterdam, modelled and simulated these processes in a new way. On Tuesday, 28 October 2014 he defended his PhD thesis 'High-energy phenomena in laboratory and thunderstorm discharges' at Eindhoven University of Technology. In his research he simulated for the first time how thunderstorms create positrons - antimatter - and other particles such as neutrons and protons.
Natural particle accelerator
In 2011 a satellite detected by accident antimatter that was created by strong thunderstorms. This antimatter consisted of positrons – the antiparticles of electrons. Previously X-rays and gamma rays (radiation with the highest energy on Earth, which is otherwise mainly generated in radioactive decay) were measured by satellites and aircrafts. "For several reasons it isn’t good to fly above thunderstorms, and radiation is one of them," the researcher says. "We are presently learning that lightning should be considered as a natural particle accelerator. Yet people don’t have to worry much about this radiation. When a violent lightning stroke is heading for you, there are definitely other problems to care about. "
During his research the PhD researcher computed for the first time quantitatively how lightning produces a multitude of particles: electrons, photons, positrons, protons and neutrons. His models and simulations agree well with experiments.
"Our simulations are better than those of the competitors," Köhn says. "We have modelled the production and movement of these particles with a technique that is able to monitor individual particles. We used specific mathematical methods and added new factors to the calculations. The special feature of our method is that it not only describes the electron motion for very high or very low energies but also for the intermediate region. The latter is really new. We have thus shown that, for example, quite a lot of positrons with energies of a few MeV are produced, which can be measured up till a few kilometers above their source. So the next time you see lightning, you’ll know that antimatter is created there."
Köhn did his research in the CWI Multiscale Dynamics research group, headed by 'lightning professor' Ute Ebert. The research was co-funded by STW.
Picture: Creation of highly energetic electrons by lightning. In colour the electron density distribution in a plane; in black the leader. Source: Christoph Köhn.