4) - Heating and current
- 2 - 3 - 4
5 - 6 - 7 )
|The electron cyclotron wave: a precision tool, putting power where we want it.
c) heating by radio-frequency wave
This time we get to the scale of
about hundred GHz for frequency, corresponding to
millimetre wavelengths. Two modes of propagation are possible for this type of wave
, which propagates perpendicularly to the magnetic surfaces: the O mode, which has an electric field
parallel to the tokamak magnetic field, and the X mode, which has an electric field perpendicular to the tokamak magnetic field.
As in the case of ion cyclotron heating,
the interaction takes place when the electron crosses a resonance layer, determined by the frequency used, and depending on the magnetic field. We may also use harmonic heating. The advantage of this type of heating is to produce very local deposits, and we use it as a precision tool to go and take energy to a well-targeted point of the plasma, which can have a stabilising effect on instabilities. In addition, in contrast to the two others, this mode of heating is less sensitive to edge conditions at the level of the highly simplified antenna, making coupling easier in a wider range of plasma parameters (the wave propagates even in a vacuum!). On the other hand, the power generator used (gyrotron) is more delicate to implement, above all on a long pulse, and Tore Supra is just starting experimentation with a new system adapted to stable operating conditions.
|We see here an FCE heating power generator, under laboratory test..
We can also use this system to generate current, but as the mechanism is indirect, we cannot attain the efficiency attainable with
the hybrid system.