Experimental investigations of the intrinsic profile formation near rational surfaces in tokamaks
This paper presents a high resolution measurement of n(e) and T(e) profiles during the quasi-stationary phase of ohmically heated TEXTOR discharges. The measurements are obtained by a nine-channel HCN laser interferometer and a 40 channel mode analyser. T(e) is derived from the soft X-ray continuum by application of a modified absorber foil method. Procedures are designed to improve the resolving power of the diagnostics. As a result of this signal generation and processing, the sawteeth in TEXTOR are represented by five sets of almost noise-free profiles for the interferometric phase shifts and the emitted soft X-ray intensities which are equidistantly separated in time. From more profiles local values of electron density and emissivity, and their variation during a sawtooth cycle, can be deduced. Inversion procedures to give the shift of the flux surfaces show deviations from symmetry, but on further inversion for the differential emissivity, this disappears, indicating that the sawtooth process takes place on the unperturbed surface structure. Finally by calibration at two radial positions, a T(e) profile of very high spatial resolution is obtained.
Bibliographic Reference: Paper presented: 16th European Conference on Controlled Fusion and Plasma Physics, Venezia (IT), March 13-17, 1989
Availability: Available from (1) as Paper EN 34787 ORA
Record Number: 198910637 / Last updated on: 1994-12-01
Original language: en
Available languages: en