Upcoming seminars

Seminars at DIFFER cover a wide range of topics and are held on Thursdays at 11.15 AM in the seminar room of the institute (unless otherwise stated). Seminars are open to everybody. If you are interested in visiting a DIFFER seminar or want to subscribe to our mailing list, please follow the instructions for external visitors.

List all past seminars organized at DIFFER

Christopher Smiet
September 6th 2017
11:15 to 12:15
Abstract will follow soon
Gert Jan Kramer
September 7th 2017
11:15 to 12:15
Abstract will follow soon
Hans Goedbloed
September 14th 2017
11:15 to 12:15
The extensive studies of MHD instabilities in thermonuclear magnetic confinement experiments, in particular of the tokamak as the most promising candidate for a future energy producing machine, have led to an ‘intuitive’ description based on the energy principle that is very misleading for most astrophysical plasmas. The ‘intuitive’ picture almost directly singles out the dominant stabilizing field line bending energy of the Alfven waves and, consequently, concentrates on expansion schemes that minimize that contribution. This happens when the wave vector k0 of the perturbations, on average, is perpendicular to the magnetic field B. Hence, all macroscopic instabilities of tokamaks (kinks, interchanges, ballooning modes, ELMs, neoclassical tearing modes, etc.) are characterized by satisfying the condition k0 ⊥ B, or nearly so. In contrast, some of the major macroscopic instabilities of astrophysical plasmas (the Parker instability and the magneto-rotational instability) occur when precisely the opposite condition is satisfied: k0 // B. How do those instabilities escape from the dominance of the stabilizing Alfven wave? The answer to that question involves, foremost, the recognition that MHD spectral theory of waves and instabilities of laboratory plasmas could be developed to such great depth since those plasmas are assumed to be in static equilibrium. This assumption is invalid for astrophysical plasmas where rotational and gravitational accelerations produce equilibria that are at best stationary, and the associated spectral theory is widely, and incorrectly, believed to be non-self adjoint. These complications are addressed, and cured, in the theory of the Spectral Web, recently developed by the author. Using this method, an extensive survey of instabilities of astrophysical plasmas demonstrates how the Alfven wave is pushed into insignificance under these conditions to give rise to a host of instabilities that do not occur in laboratory plasmas.
Wim Zeiler
September 21st 2017
11:15 to 12:15
Abstract will follow soon
Emiel Hensen
September 28th 2017
11:15 to 12:15
abstract will soon follow

Pages