ECRH EXPERIMENTS IN W VII-A USING DIFFERENT MODES
In the W VII-A stellarator ECRH of OH-currentfree plasmas at 28 GHz, 200 kW, 40 ms (B-res = 1 T, n-e,crit = 1x10**19 m**-3) was investigated using the TE-O2, TE-01, TE-11 and HE-11 modes as well as different wave launching systems. Discharges at optimum confinement conditions (t = 0.46, 0.64) are compared. The angular spread of the incident beams varies resulting in different power deposition profiles. An increase of the central electron temperature from 0.6 keV (TE-02) to 0.9 keV (TE-01) and finally to 1.2 keV (HE-11) is due to the narrowing of the power deposition profile. The heating efficiency (determined by pulse modulation techniques) can be explained by O-mode single pass absorption only. The X-mode fraction does not contribute significantly may be due to disturbance of the UH layer leading to wave absorption. For the TE-11 (HE-11)- case parametric decay of the X-mode pump wave near the UH resonance layer occurs. Both decay wave spectra were measured and show a rapid drop near the lower hybrid frequency. A high energetic ion tail is observed to be strongly correlated with the wave decay. Experiments with the ECR-layer off axis were performed. With resonance layer shifted by 5 cm outward, the absorbed RF power has same energy content as compared to central resonance.
Bibliographic Reference: 5TH INTERNATIONAL WORKSHOP ON STELLARATORS, SCHLOSS RINGBERG, BAVARIA (GERMANY), SEPT. 24-28, 1984 VOL. I, PP. 191-201, EUR 9618 EN (1985) FS, VOL. I AND VOL. II, 787 P., BFR 3500 (BOTH VOLUMES), EUROFFICE, LUXEMBOURG, POB 1003
Record Number: 1989124118900 / Last updated on: 1987-01-01
Available languages: en