Study of Plasma Fluctuations in the TUMAN-3M Tokamak
during Various Types of Lframe0H Transitions

L. G. Askinazi*, V. V. Bulanin**, V. V. D’yachenko*, S. V. Lebedev*, L. S. Levin*,
V. S. Roitershtein**, and O. N. Shcherbinin*

*Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia

**St. Petersburg State Technical University, Politekhnicheskaya ul. 29, St. Petersburg, 195251 Russia

Received June 14, 2001; in final form, September 18, 2001

Abstract—The reflectometer method is used to comparatively study plasma fluctuations in the edge plasma of
the TUMAN-3M tokamak during L–H transitions initiated by different methods. It is shown that the width of
the spectrum of backscattered microwave radiation is the most representative parameter when comparing the
results obtained in different confinement regimes. The following methods for affecting the edge plasma were
applied: gas puffing, a fast current ramp-up, a rapid increase in the toroidal magnetic field, and ion cyclotron
heating. The studies were performed at different positions of the cutoff of O- and X-mode probing waves. A
similar behavior of the spectral width was observed during transitions triggered by the fast current ramp-up and
the rapid increase in the toroidal field. This provides evidence that the mechanism for transition to the H-mode
is the same in both cases in spite of the different character of the evolution of the current density profiles. The
fastest and strongest narrowing of the spectra was observed during the transition triggered by ion cyclotron
heating. Possible reasons for similarities and differences in the behavior of the spectra during the transitions to
the improved confinement regime are discussed. © 2002 MAIK “Nauka/Interperiodica”.

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