FEATURES OF LOWER HYBRID WAVE TRAJECTORIES IN LOW AND HIGH DENSITY FT DISCHARGES
Ray tracing technique has been used to study propagation and absorption of Lower Hybrid (LH) waves in connection with experiments performed in the Frascati Tokamak (FT). Wave trajectories have been calculated for FT plasma as n-e ranges from 0.5 to 2 times 10**14 cm-3, by using a code where electromagnetic, thermal and toroidal effects are considered. The main interest is devoted to analyze how the rays approach the center at their first pass (no multiple reflections are considered). The typical target plasma, considered in toroidal geometry, is characterized by R = 83 cm, a = 20 cm, T-e about 1.3 keV, I-p about 300 kA, B-o = 60 or 80 kG in H or in D. Profiles of n-e are close to parabolic and those of T-e are close to parabolic square. The typical n //EL spectrum (for the 2-waveguides-grill at S2G = 180 degrees and f = 2.45 GHz) ranges from n-//EL-c to 3. Here the accessibility imposes n-//EL-c = 1.3 at 80 kG and 1.4 at 60 kG in D for n-e about 7 times 10**13 cm-3 (in H, n-//EL = 1.1 a,d 1.3 respectively). The occurrence of ray focusing suggests that the strong central interaction with electrons observed in FT at low density may be connected with the WKB enhancement of the wave field I n-tilde E along the trajectories in the focusing region. The sharp density threshold for this interaction may be connected with this effect even if the ray analysis of Figs 3 and 4 is not to be considered conclusive.
Bibliographic Reference: 11TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS, AACHEN (GERMANY), SEPT. 5-9, 1983 IN ENEA REPORT 83.23/CC, PP. 35-38, 1983 WRITE TO ENEA + CENTRO RICERCHE ENERGIA FRASCATI, SERVIZIO STUDI E DOCUMENTAZIONE, C.P. 65 00044 FRASCATI, ROMA (I
Record Number: 1989122052400 / Last updated on: 1987-01-01
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