Göran Ericsson, professor of applied nuclear physics at the Department of Physics and Astronomy

Photo: Mikael Wallerstedt

Research presentation: My research in applied nuclear physics addresses the development of fusion energy. Fusion is the process that releases energy in stars, and if we can create power plants based on this process on earth, it would be a major addition to our energy supply. Today fusion energy is still in the experimental stage, but a worldwide collaborative effort surrounding the so-called ITER experiment has the goal of showing that fusion can be a real complement to the energy supply in the near future. Fusion energy is a form of nuclear power, so measurement methods in nuclear physics are especially useful. In my research I’m especially studying the neutrons that are released in fusion reactors. These neutrons provide information about the conditions in the fusion reactor, making it possible to determine its generation of output, the (very high) temperature and other properties of the fusion fuel that are important for controlling the process. To get the information the neutrons contain, we need to measure their number and their energy. Some of my research is therefore focused on constructing measuring equipment that is especially adapted for fusion neutrons. My group is also exploring new ways to use the data provided by neutron measurements. Here the aim is to help understand the physical processes that occur in today’s fusion experiments, and to devise tools to regulate future fusion reactors.

Kjell Eriksson, professor of theoretical astrophysics at the Department of Physics and Astronomy

Photo: Mikael Wallerstedt

Research presentation: In recent years I’ve devoted more and more of my research time to carbon stars. They are stars that have progressed to late stages in their development. They began their lives billions of years ago and radiated with a constant light intensity most of the time, just as the sun is still doing. When they finally ‘ran out of fuel’, the inner structure of stars changed, becoming denser and hotter at the core while the peripheral parts swelled up and became thinner and cooler – they became bright giant stars, and some of them passed through a carbon star stage for a time.

A carbon star has an incredibly compact core about the size of the earth surrounded by an energy-producing shell that alternately makes helium out of hydrogen or carbon out of helium. The surface of the such stars are as far away from their cores as the earth is from the sun. Between the core and the surface, convection streams transport newly formed elements, including carbon, up to the surface layer of the star, its atmosphere, and from there most carbon stars lose a great deal of their mass to the space between the stars via a stellar wind. The details of this scenario remain unclear, such as what elements are created and in what amounts, how they come up to the surface, the mechanisms behind stellar wind, and the pulsations that stars undergo for about one year. We’re trying to elucidate these details by comparing observations of the spectrums of carbon stars and variations in light with synthetic calculations from models of the stars’ surface layer, using numerical methods based on the laws of physics and computed on ever-faster computers.

Susanne Höfner, professor of dynamic astrophysics at the Department of Physics

Photo: Mikael Wallerstedt

Research presentation: Towards the end of their lives, most stars develop into cool giant stars with a brightness corresponding to from thousands to tens of thousands of suns. This developmental phase is characterized by massive discharges of gas, so-called stellar winds, which transport newly formed elements such as carbon away from the star at an accelerating rate. Specks of dust – tiny solid particles – that are formed in the outer layers of giant stars are the probable driving force behind stellar winds. By capturing some of the star’s radiation, the specks of dust are accelerated away from the star, taking with them the surrounding gas. The goal of my current research project is to understand the processes that transport the new elements formed by nuclear fusion in the core of the stars up to the surface and out into space, where they can become part of new generations of stars and planets. Our research team is developing new numerical models for stellar winds that can be directly compared with observations and yield key data for models of stars and the development of galaxies. Solving the riddles of stellar winds will help us to understand how atoms that now exist in our surroundings and in our own bodies at some time in the past managed to get away from the stars where they were formed.

Olof Karis, professor of physics at the Department of Physics and Astronomy

Photo: Camilla Thulin

Research presentation: In my research I’m interested in interfaces in layered structures of magnetic materials for the digital information age. Trends towards ever higher information density in computer memories present new challenges, as the layer that makes up a magnetic sensor, for instance, has been shrunk to a thickness of just a few dozen atoms. With such thin layers, functionality will be dominated by the interfaces between the layers. This means it will be crucial to understand the properties of the interfaces at the level of the atom. In my research we have devised methods to characterize properties of such interfaces, among other things. This information is obtained by spectroscopically studying how the electron structure of the sample changes when the interfaces involved are altered.

Spectroscopic studies of buried interfaces require special light sources and instruments. Using modern synchrotron light sources, which provide us with extremely intensive x-ray radiation, today we can perform studies of the electron structure at high radiation energies. This enables studies of buried interfaces and properties deriving from the inner parts of the material, rather than its surface, where effects can be identified corresponding to atoms on each side of the interface change places with each other. Such precision is difficult to achieve with other methods. We’re now working with a study of the properties of new material combinations that may come to be used in future magnetic sensors on computer hard drives. These materials have properties that allow the thickness of the magnetic sensor to be shrunk to 50 atom layers with sufficient sensitivity to read the magnetic information. Such small dimensions will be a reality when it is time to increase the density of stored information even further.

Stephan Pomp, professor of applied nuclear physics, specialising in nuclear data at high neutron energies, at the Department of Physics and Astronomy

Photo: Mikael Wallerstedt

Research presentation: What fascinates me about the subject of applied nuclear physics is the interplay between large-scale technological and medical questions and the appurtenant need for basic research in nuclear physics.

A key question of global relevance that my research addresses is tomorrow’s supply of nuclear energy and the need to minimise the problem of nuclear waste. Advanced new reactor systems, the so-called fourth generation, can lead to both better use of resources and a drastic reduction in the necessary final storage period. Also in medical fields, like dosimetry and radiation of cancer patients, we contribute detailed knowledge about nuclear reactions.

Common to all of the above applications is the important and often crucial role of neutrons. Therefore my research in experimental nuclear physics with primarily high-energy neutrons is primarily about careful measurements of nuclear reactions, for example in nuclear fission. The results of the measurements lead to improved theoretical nuclear models and thereby better databases that we can then use in computer simulations to study and optimise large-scale technological systems.

I also appreciate the fact that our type of research is being done in an environment that is strongly characterised by international collaboration, with partners from Finland, France, Japan, and the Netherlands, among others.