28 Nov 2001

"HF" stands for "High Frequency", in this case High Frequency radio wave, "Langmuir turbulence" stands for a plasma turbulence involving Langmuir modes (and what is a Langmuir mode? Correct, a certain wave mode in a plasma.).
If we send an electromagnetic wave into a plasma, it can start processes that increase the fraction of its energy that is absorbed in the plasma, so that this fraction increases with the intensity of the electromagnetic wave. Many of these processes have the character of a parametric instability. It is the saturated stage of one such process that is referred to above as "Langmuir turbulence". The plasma of the ionosphere ~200km above us has turned out to be a well suited  laboratory for the study of this process, with the driving "HF" radio wave transmitted by an antenna system (the "Heating" facility) at Ramfjordmoen 25km outside Tromsø, and with the EISCAT radars as diagnostics.
In 1972, V. E. Zakharov published a model for Langmuir turbulence which we today call "the Zakharov model". An outcome of that model is "collapse" - that a finite amount of energy contracts to a point in finite time. One issue I shall discuss, is whether manifestations of such phenomena will be/has been observable by the experimental set-up described above.
I thought to use two seminars for this. It will be about physics, maybe with a minor attention to numerical methods and some to the modelling. I intend to keep everything at a simple qualitative/untechnical level, including a five minutes' crash course in plasma physics.