Review of measured density fluctuation properties in tokamaks at PPPL and future plans
Abstract
Since the first observation with scattering of electromagnetic waves of a low frequency, small scale turbulence in the ATC tokamak, the same microturbulence was observed in every tokamak where similar measurements were attempted. The observations on plasma microturbulence in tokamaks at the Princeton Plasma Physics Laboratory are summarized. There is at present no conclusive evidence that the observed fluctuations are induced by known plasma instabilities or that they are the cause of anomalous transport. Indeed, it is possible that the observed fluctuations are not the main (or the only) phenomena which affects the plasma confinement in tokamaks. A significant gap exists in the experimental knowledge of long wavelength fluctuations with scale size between those of fluctuations which are detectable with scattering techniques and those visible on soft x ray or interferometric signals. Microwave reflectometry is a technique which offers the possibility of high resolution detection of long wavelength plasma fluctuations. This technique, used on the ATC for the first time in a tokamak, can be considered a special kind of interferometer where the phase of the received wave is determined by both the change of the refractive index along the wave trajectory and by the shift of the reflecting layer. The latter becomes the dominant effect when the scale size of the plasma fluctuation is 3 to 4 times larger than the wavelength of the probing wave. Hence, by using the extraordinary mode of propagation in a TFTR-like tokamak, microwave reflectometry should provide spatially resolved information about plasma fluctuations which presently are not detectable with other diagnostic techniques.
- Publication:
-
Comparison of Theoretical and Experimental Transport in Toroidal Systems
- Pub Date:
- March 1990
- Bibcode:
- 1990ctet.work....6M
- Keywords:
-
- Electromagnetic Radiation;
- Magnetohydrodynamic Stability;
- Microwave Equipment;
- Plasma Control;
- Plasma Physics;
- Plasmas (Physics);
- Refractivity;
- Tokamak Devices;
- Wave Scattering;
- Interferometers;
- Interferometry;
- Low Frequencies;
- Reflection;
- Trajectories;
- Turbulence;
- X Ray Analysis;
- Plasma Physics