Measurement of density fluctuations in the JIPP T-IIU tokamak
Abstract
Low frequency density fluctuations caused by the microstabilities which universally exist in tokamak plasmas were considered to enhance particle and energy losses of the confined plasma across the magnetic field. For the study of the microinstabilities, it is necessary to know their characteristics; frequency and wave number spectra, spatial distribution, and absolute level of density fluctuations. The collective scattering method with submillimeter waves is an ideal means for the study of microinstabilities in a tokamak plasma. In the JIPP T-IIU tokamak, a HCN laser scattering system with a heterodyne detection was developed. The main radiation source is a 5 m long HCN laser which delivers a linearly polarized beam of 0.5 W with a wave length lambda(sub i) = 337 microns. For the heterodyne detection another HCN laser is operated as a local oscillator at the beat frequency of 2 MHz. In low density ohmically heated (OH) plasma, the density fluctuations mainly propagate in the direction of the electron diamagnetic drift, and the peak in the power spectra shows a linear dispersion relation for various wavenumber. In high density OH plasmas, it was found that the energy confinement time deviates from the Alcator scaling and at the same time the ion mode which propagates in the ion diamagnetic drift direction is excited in addition to the electron mode. The value of eta(sub i) = (dlT(sub i)/dlnn(sub i)) evaluated experimentally is about 1.0 to 1.2 when the ion mode is excited. Effects of an ice pellet injection on the instabilities and electron density profiles will be also discussed.
- Publication:
-
Comparison of Theoretical and Experimental Transport in Toroidal Systems
- Pub Date:
- March 1990
- Bibcode:
- 1990ctet.work....8K
- Keywords:
-
- Density Measurement;
- Energy Dissipation;
- Magnetohydrodynamic Stability;
- Particle Energy;
- Plasma Control;
- Plasma Density;
- Plasmas (Physics);
- Tokamak Devices;
- Wave Dispersion;
- Beat Frequencies;
- Diamagnetism;
- Electron Density Profiles;
- Hcn Lasers;
- Laser Outputs;
- Magnetic Fields;
- Power Spectra;
- Scattering;
- Spatial Distribution;
- Submillimeter Waves;
- Plasma Physics