On tokamaks and other toroidal machines, reflectometry is a very rapidly developing technique for density profile measurements, particularly near the edge. Its principle relies on the total reflection of an electromagnetic wave at a cutoff layer, where the critical density is reached and the local refractive index goes to zero. With the new fast frequency synthesizers now available, a method based on pulse compression radar is proposed for plasma reflectometry, overcoming the limitations of the previous reflectometry methods. The measurement can be made on a time-scale which is effectively very short relatively to the plasma fluctuations, and the very high reproducibility and stability of the source allows an absolute calibration of the waveguides to be made, which corrects for the effects of the parasitic reflections. 2 refs., 5 figs.
Costley, A; Prentice, R;  Laviron, C;  Prentice, R 
- Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking
- Compagnie Generale des Matieres Nucleaires (COGEMA), 78 - Velizy-Villacoublay (France)
- Toulouse-3 Univ., 31 (France). Centre d`Etude Spatiale des Rayonnements