Tomorrow, the LION exam committee welcomes a new, external member. As of 1 September, at least one of the exam committee’s members has to be from outside Leiden University. The More info
LION committee is very pleased that Dr. Stephan Eijt from TU Delft has accepted their invitation to take a seat as the fifth member. Eijt is already chairman of the exam (sub)committee BSc Applied Physics in Delft, and therefore brings much experience to the table, according to prof. Jan van Ruitenbeek, who chairs the LION exam committee. ‘Plus we have an intensive collaboration with Delft. This exchange helps with that.’
The exam committee is responsible for the overall level of exams, and meets five times a year to discuss individual deviations from the standard curriculum and the implementation of a binding study advice. Students are never excluded through an automated process. If someone fails to meet the requirements for a positive study advice, and thinks this is due to personal circumstances, the committee discusses this and might grant a pardon.
Leiden physicists have discovered that a free, magnetised plasma reconfigures into a stable shape in certain conditions. They demonstrate through computer simulations that initially helical magnetic field lines in a More info
plasma eventually take the form of a donut. Their paper is published today on arXiv.
The Sun holds a great promise for solving the global energy problem. Aside from developing efficient solar panels, scientists are trying hard to fully understand the processes that happen inside our host star. They are eager to learn about one of the sun’s special tricks – nuclear fusion. With a fusion reactor on Earth we would be able to generate nearly unlimited amounts of energy. But to start up an efficient fusion process, we have to peek very carefully, with special emphasis on plasma’s behaviour within the complex magnetic fields inside stars.
Up until now, no description existed of the reconfiguration of helical magnetic field lines within a free plasma. Now scientists at the Leiden Institute of Physics (LION) have created a computer simulation which shows that plasma, starting from different helical configurations, end up in a toroidal shape. They take the parameters from this simulation to formulate a mathematical description of the field lines. The fact that a donut shape is the end product of different initial configurations, shows that this form is a fundamental structure of a free plasma.
Another indication towards that conclusion is that a torus is not just the minimum energy state, into which structures usually degrade, but a delicate balance between the present magnetic forces and the internal pressure within the plasma. Normally it is assumed that a magnetic configuration degrades into a form without forces acting on it, like a weak pudding collapsing without a mould. The Leiden finding contradicts the so-called Taylor’s theorem.
In the peaceful state of equilibrium, magnetic islands appear on the torus’ surface. ‘One of the issues with nuclear fusion is the emergence of small islands in the plasma,’ says lead author Christopher Berg Smiet, PhD student of prof. Dirk Bouwmeester at LION. ‘They fly outwards and damage the reactor wall. In our simulation we see stable islands that don’t do this. We’re talking about a different situation, because our plasma is not captured inside a reactor, but it does give us more insight into plasma’s behaviour.’
This insight is also important for our fundamental understanding of astrophysical processes. Smiet: ‘There are countless of helical magnetic plasma structures in the Sun, which sometimes fly off into space. Now we know that these turn into donuts after a while. This is something we had never expected beforehand.’
‘Self-organizing Knotted Magnetic Structures in Plasma’, C.B. Smiet, S. Candelaresi, A. Thompson, J. Swearngin, J.W. Dalhuisen, D. Bouwmeester. Preprint: arxiv
Start of the simulation, in which the plasma has a begin state with helical magnetic field lines.
End result after the simulation. The field lines have reconfigured to a donut shape.
The 2015 Dissertation Prize of the Global Neutrino Network has been awarded to three former graduate students, amongst others Tri Astraatmadja, who was part of the Leiden/Nikhef ANTARES group during More info
his PhD research. Astraatmadja receives the award for his thesis 'Starlight between the waves: In search of TeV photon emission from Gamma-Ray Bursts with the ANTARES Neutrino Telescope'.
This is the first year that the GNN Dissertation Prize is awarded. It recognises young postdoctoral candidates who have written an outstanding thesis and contributed significantly to the project. Primary criteria of the selection are the scientific quality, the didactics and the form of the thesis.
Astraamadja has focused on the ANTARES telescope, which operated as a gamma-ray telescope. This is possible by searching for down-going muons produced in interactions of gamma-rays in the Earth’s atmosphere. He looked at the short time windows when satellite experiments had announced a Gamma Ray Burst (GRB). The sophisticated tools developed by Astraatmadja will make it possible for the much bigger KM3NeT detector to detect gamma-rays from a GRB with a significance of three standard deviations.
The Netherlands eScience Center has announced to fund a new Path-Finding Project led by Dr. Dorothea Samtleben from the Leiden Institute of Physics (LION). This project aims to make the More info
processing of detection signals more efficient for the KM3NeT neutrino telescope, which is currently under construction in the Mediterranean Sea. High processing efficiency is vital for finding lower-energy neutrinos and the ability to alert other observatories in case of a special astronomical event.
Neutrinos are almost massless particles that have extremely little interaction with anything, so they undisturbedly speed through the Universe, even permeating stars. So when they are produced inside a star, they smoothly travel outwards and eventually reach Earth with all information still intact about their creation. Also, neutrinos have zero charge, so they are not deflected by any magnetic field and point directly to their origin. This makes these tiny particles a valuable source of information for astrophysicists, to study the spectacular events that produce them.
Unfortunately, their properties also make neutrinos incredibly hard to detect. Scientists need large volumes of material to hunt them down, like for example the water of the Mediterranean Sea where the KM3NeT neutrino telescope is under construction. Once in a while, one out of billions of neutrinos interacts with the water in the vicinity of the detector, and produces a light signal, which gets recorded. The trick is to process these signals and deduce the incoming particle’s characteristics as efficient as possible. When this happens fast enough, even real-time observation is possible. In that scenario the computers at KM3NeT can immediately alert their counterparts at optical observatories about a special astronomical event, so they’re able to photograph it. And they can extract online accurate information on the neutrino event candidates, to improve their selection efficiencies also for lower-energy neutrinos.
‘For real-time observation we need professional computing expertise to efficiently address the filtering of our huge data volume,’ says Samtleben. ‘The actual value of this grant is an eScience engineer to work with us for a full year. But mostly we’re establishing this first connection with the eScience center, to build a fruitful collaboration where their expertise and tools will enhance the science potential of the KM3NeT neutrino telescope. And they get a great playground to explore their tools and expertise. This could lead to a long-lasting partnership.’
E. Woldhuis, V. Chikkadi, M.S. van Deen, P. Schall and M. van Hecke (2015) Fluctuations in flows near jamming, Soft Matter, 11, 7024-7031. [DOI][pdf]
Corentin Coulais, Johannes T. B. Overvelde, Luuk A. Lubbers, Katia Bertoldi, and Martin van Hecke (2015) Discontinuous Buckling of Wide Beams and Metabeams, Physical Review Letters, 115, 044301. [DOI][pdf]
8 Sept, 16:15, Academy building, Rapenburg
Thesis Defense Mathias Diez - IL: On electronic signatures of topological
superconductivity Promotor: Prof.dr. C.W.J. Beenakker
18 Sept, 12:14
Van der Waals Colloquium TBA: TBA
23 Sept, 11:15, Academy building, Rapenburg
Theses Defense Andrey Bagrov - IL: The holographic glass bead game: from superconductivity to time machines. Promotores: Prof.dr. J. Zaanen and Prof.dr. K.E. Schalm