[Triumf-seminars] TRIUMF Special Seminar today at 14:00

[postmaster at admin.triumf.ca]

Date/Time: Tue 2010-05-04 at 14:00

Location:  Auditorium          

Speaker:   Dr. Antoine Cerfon - Hausser Fellowship finalist (MIT)

Title:     Are fusion plasmas compressible? (and why do we care)

Abstract: One of the most promising approaches to controlled nuclear fusion is to use magnetic fields to confine the hot nuclear fuel in the plasma state. This has led to impressive achievements over the past fifty years, but there are technical difficulties that must be resolved for fusion energy to become a practical reality. In particular, it is crucial to find ways to prevent the violent, macroscopic plasma instabilities which can lead to major disruptions and damage the fusion reactor.

The most commonly used model to understand the macroscopic behavior of plasmas is Ideal MagnetoHydroDynamics (Ideal MHD), which describes the plasma as a magnetized, compressible fluid. In this model, plasma compressibility stabilizes some macroscopic modes, and several fusion reactors are designed to rely explicitly on this type of stabilization. The problem is that Ideal MHD assumes the plasma is highly collisional, whereas fusion grade plasmas are at such high temperatures they are essentially collisionless. It is therefore crucial to reevaluate the compressibility stabilization result using more reliable models in the regime of fusion interest.

In this talk, I will introduce three new models for collisionless plasmas: one fluid model and two kinetic models. Using energy variational principles,  I will analyse plasma compressibility in these three models and compare with Ideal MHD. The outcome is surprising: wave-particle resonances, only accounted for in kinetic models, actually cancel the apparent compressibility stabilization. In other words, fusion grade plasmas are inherently incompressible! I conclude by discussing how this new result may affect the design of future fusion reactors.



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