HEATING EXPERIMENTS IN THE FT TOKAMAK IN THE LOWER HYBRID FREQUENCY RANGE
In this work we describe the heating results in the LH frequency range (f = 2.45 GHz, P-RF <= 250 kW, P-S <= 6 kW/cm**2) both in the electron and ion regimes. Efficient electron heating was observed for n <= 5.10**13 cm-3. Increases of the peak electron temperature up to 700 eV were measured. At higher densities the interaction with electrons disappears. In the ion regime fast neutral tails and neutron enhancement were observed. The influence of plasma boundary conditions on the penetration of the wave is demonstrated. The principal physical problems are pointed out and some possible conclusions are given. Two heating modes have been studied: a) electron mode. This occurs for plasma densities n <= 5.10**13 cm-3. Increases of the peak electron temperature up to 700 eV were measured; b) the classical ion heating mode for plasma densities close to those necessary for the occurrence of the Linear Turning Point. Fast neutrals and neutron yield enhancement (in D) are observed while the heating effects are weak. This interaction is present only when parametric instabilities, as recorded by a RF probe in the plasma scrape-off, are absent. In this complex scenario where many different phenomena are interacting some firm points can be extracted: a) both the electron and ion mode results show that the n-2-0 spectrum of the wave inside the plasma must be broader than the one generated by the grill. In a paper of this conference, Barbato and Santini (1983) discuss the focusing properties of the magnetic field helicity. It is demonstrated that there are regions close to the plasma center with very strong electric fields. This can produce non linear wave generation and consequent broadening of the k-20 spectrum. b) the importance of border conditions was demonstrated for densities close to LTP. Cold dense plasma favours the generation of parametric instabilities and dramatically affects the penetration of the wave. It is likely that also in the electron regime border fluctuations (spontaneous or stimulated) can alter the phase fronts of the waves and affect the focusing. This could contribute to the spread of experimental points of Fig. 5. c) There is an upper density limit for the occurrence of the electron wave interaction which appears insensitive to plasma parameters in the power range so far used. d) Electron heating is well localized at the center and highly efficient. Ion heating results are still unclear.
Bibliographic Reference: 11TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS, AACHEN (GERMANY), SEPT. 5-9, 1983 IN ENEA REPORT 83.23/CC, PP. 1-12, 1983 WRITE TO ENEA + CENTRO RICERCHE ENERGIA FRASCATI, SERVIZIO STUDI E DOCUMENTAZIONE, C.P. 65 00044 FRASCATI, ROMA (IT
Record Number: 1989122046900 / Last updated on: 1987-01-01
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