THE DIAGNOSTIC POTENTIALITIES OF ABSORPTION MEASUREMENTS.
Direct measurement of the optical thickness tau can be obtained by attenuating a sufficiently strong beam propagating through the plasma, and tuned around omega-c or its harmonics; the method is well adapted when tau approximately equal 1, i.e., for higher harmonics (n approximately equal 3 -:- 4) and lower harmonics (n <or= 2), when r is in the edge region. Transmission measurements were performed in the Model-C stellarator. The attenuation of the X mode near 2 omega-c was measured and, with the known density, the electron temperature was obtained. More recently transmission measurements of the O mode near omega-c were carried out in the Wendelstein VII-A stellarator, and in the TFR and PLT tokamaks. It was found that, at high plasma density, refraction effects are important. Recently simultaneous emission and transmission measurements were carried out on TFR. Fig. 1 shows the experimental arrangement. In Fig. 2 the transmitted power normalized to the incident power P-t/P-i, the electron temperature TAU, obtained by ECE, the average density n and the plasma current I-p are shown as a function of time. Comparison over the plasma cross-section between the calculated values of tau and those obtained by transmission measurements is shown in Fig. 3. For the importance of wall reflections a transmission experiment was performed in TFR using the O mode at the second harmonic.
Bibliographic Reference: WORKSHOP ON DIAGNOSTICS FOR FUSION REACTOR CONDITIONS, VARENNA, COMO (ITALY), SEPT. 6-17, 1982, PP. 213-217 351 P., 1983, ISBN 0-08-031161-X WRITE TO PERGAMON PRESS LTD., HEADINGTON HILL HALL, OXFORD OX3 OBW (ENGLAND), PRICE: UKL 47, (EUR 8351 EN).
Record Number: 1989123109000 / Last updated on: 1987-01-01
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