Frank Jenko, Director at the Max Planck Institute for Plasma Physics (IPP), is mainly concerned with the theoretical description of fusion plasmas. However, the physicist also heads a working group for plasma astrophysics – a rarity at the IPP. At the beginning of August, he was invited to an important conference in the field. From someone who occasionally reaches for the stars.
“The world is a plasma!” – says Frank Jenko, and this is to be taken quite literally: “The vast majority of visible matter in the universe is in the plasma state,” explains the physicist, who heads a group at the IPP researching cosmic plasmas. “Stars, the environments of black holes, even interplanetary and stellar space itself: All of that is plasma!” Wait, interstellar space too? The cold, empty nothingness? “Many people intuitively associate plasma with very high temperatures, but that’s only half the truth: you can also reach the plasma state if you dilute a gas further and further, as is the case in interstellar space,” explains Jenko.
This is Jenko’s cosmos: a universe made of plasma; and our planet as a glaring exception in the middle. The planet that is home to the IPP, whose task, according to its homepage, is to investigate the “physical foundations for a fusion power plant”. There is no mention of space research and astrophysics in this self-description; fusion power plants are needed here on Earth. So why is tokamak expert Jenko, who otherwise deals with theory and numerical simulations in fusion research, turbulence and magnetic confinement, looking up at the sky?
We meet the physicist during the International Symposium for Space Simulations (ISSS-15) in the foyer of the Arnulf Schlüter lecture hall at IPP. The symposium, which takes place from August 1 to 9, 2024, runs parallel to the International Workshop on the Interrelationship between Plasma Experiments in the Laboratory and in Space (IPELS-16) and is one of the most renowned gatherings of its kind. Leading scientists, as well as doctoral students and postdocs, have come to discuss the big questions in plasma astrophysics in lectures and seminars – and not least during the breaks with coffee and cake – and to make new connections.
This is what Jenko, who is organizing the conference as Chairman of the Scientific Organizing Committee, is all about: To forge links between space research and fusion research. “There are amazing parallels in many areas,” says Jenko, ”and it often happens that someone on one side of the fence knows, can do or has developed something that could also be relevant to the other side.” Examples? There are many, he says. Take turbulence research, for example: “In fusion research, we have accumulated enormous knowledge about turbulence in magnetized plasmas over many years. We were able to greatly simplify the description of plasma turbulence using so-called gyrokinetic equations.” This development can now also be applied to space physics: “The conversion of kinetic energy into heat in the almost shock-free solar wind is much stronger than one would expect if turbulence is not taken into account,” explains Jenko. “But using the equations developed in fusion research, we were able to explain the phenomenon.”
The workshop participants leave the lecture hall; it is getting loud in the anteroom. Brian Reville from the Max Planck Institute for Nuclear Physics in Heidelberg has just given a lecture on the plasma physics of the galaxy’s most extreme particle accelerators; the talk lasted 30 minutes. Judging by the noise level, the lecture was a talking point. “This is indeed a very interesting topic,” says Jenko with a cup of coffee in his hand. “The amazing thing about cosmic radiation is the gigantic energy range it covers: In addition to particles that emanate from the sun and carry comparatively little energy, we also find particles with an energy of up to 10^20 electron volts. That is far more than our best particle accelerators can produce.” The origin of these high-energy particles is one of the big questions in plasma astrophysics. There are many indications that the particles are created at the edge of black holes. “General relativity plays a major role there, and magnetohydrodynamics, which is often used in fusion research, must be extended accordingly and then applied to the acceleration of electrically charged particles,” explains Jenko. “This is an extremely exciting field of research in which there is still a lot to discover.”
Jenko does not see it as a contradiction that the IPP, as a fusion research institute, hosts astrophysical workshops. Even though research in plasma astrophysics at IPP fell somewhat asleep in the 1980s and 1990s, Jenko emphasizes that the topic has been part of IPP’s DNA from the very beginning: “Astrophysics has a certain tradition at IPP,” says Jenko. “The founding directors often came from the field of astrophysics. After all, where would you have gotten plasma physicists in the 1960s if fusion research as such didn’t even exist yet?” Astrophysical research at IPP regained momentum around 20 years ago when Jenko initiated a collaboration between IPP and the Max Planck Institute for Solar System Research. “A few years later, the Max Planck Princeton Center for Plasma Physics (MPPC) was founded on this basis, an initiative of IPP Director Sibylle Günter, in cooperation with Princeton University in the USA,” Jenko recalls. “During this time, astrophysics at IPP became more relevant again, and we realized that many of the findings and tools developed on one side could also be interesting for the other side. After all, the basic plasma physics phenomena are the same.”
The next lecture begins. Jongsoo Yoo from the Princeton Plasma Physics Laboratory talks about the latest observations in a laboratory experiment on magnetic reconnection. The lectures follow one after the other. Many sessions, many seminars, numerous posters with complicated equations and graphics. Don’t you sometimes lose the overview? “…but there are also various social events, which are an important part of such meetings,” Jenko reassures us. “These can also foster connections between participants.” He puts down his cup of coffee. “I have to get going now,” he says, ”otherwise I’ll miss the lecture.”
On Sunday, a day trip to the Herzogstand was on the agenda. The 1700-metre-high mountain is located in the Bavarian Alps near the municipality of Kochel am See, around 80 kilometers south of Munich – Frank Jenko naturally also took part. Whether a mountain tour offers the hoped-for relaxation between sessions remains questionable. What is unquestionable, however, is that the exciting phenomena of plasma astrophysics were also discussed at the summit. Perhaps it helped that they were a little closer to the stars there.
