Observation of new branch of toroidal Alfven eigenmodes in TFTR Page: 1 of 12
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PPPL-3137 - Preprint Date: November1995, UC-420, 426
RECEIVED
Observation of new branch of
Toroidal Alfven Eigenmodes in TFTR MAR 1 3 1996
E Fredrickson, R Budny, Z Chang, C Z Cheng, G Y Fu, E Mazzucato, 9fafA,
A. Janos, K. M. McGuire, R. Majeski, C. K. Phillips, G. Schilling, G Taylor,
and J. R. Wilson
Princeton Plasma Physics Laboratory, R O. Box 451, Princeton, New Jersey 08540
Experimental observations are presented of a new branch of the toroidal Alfven
eigenmode spectrum during ICRF heating of plasmas on TFTR. The identifi-
cation of the second branch is based largely on direct measurements of the
toroidal mode numbers of the toroidal Alfven Eigenmodes, and by the differ-
ences in the time evolution of the frequency spectrum between the new branch
and the original toroidal Alfven eigenmodes as reported by Taylor et al. Phys.
Fluids B 5 2437 (1993). The new branch has so far only been observed in
relatively low edge q (=4-4.5) plasmas.
Introduction
In this paper are reported observations of a new branch of toroidicity induced Alfven Eigenmode
(TAE) activity observed in ICRF heated plasmas. This new branch appears in higher plasma
current, lower edge q plasmas [q(a)=4-4.5] with H-minority Ion Cyclotron Range of Frequency
(ICRF) heating. The modes are generally at a lower frequency than the global TAE mode
which has previously been discussed [1,2]. This lower frequency branch of the TAE modes,
(labeled LTAE) have multiple peaks in the frequency spectrum corresponding to independent
modes as was seen for the original, higher frequency branch (now labeled HTAE). The modes
in the LTAE branch have a range in the toroidal mode numbers similar to those for the HTAE,
based on direct measurements with a toroidal array of Mirnov coils[3]. Comparison of the
Mimov coil data to the data from the microwave reflectometer show that LTAE modes evolve
from the core localized mode discussed by Nazikian et al [4]. Recently, TAE modes which
are strongly localized within the q=1 surface have been predicted from numerical simula-
tions[5]. The core-localized TAE modes are theoretically predicted to have a higher fre-
quency than the global TAE modes, but the experimentally observed rapid drop in frequency
coupled with the apparent decentralization of the mode have not yet been explained.
Characteristics of the lower TAE mode branch
A typical time evolution of the Mirnov spectrum during high power ICRF H-minority
heating is shown in Fig. 1. The data is displayed as a contour plot of the spectrogram. To aid
in interpretation of the figure, the contour range has been chosen to emphasize the dominant
modes and curves have been added to illustrate the trajectory of the modes in the lower
frequency group. The data is from a 1.7 MA, 3 Tesla plasma heated with 6.6MW of funda-
mental H-minority ion heating power. The RF power, line average density, stored energy in
1
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Fredrickson, E.; Budny, R. & Chang, Z. Observation of new branch of toroidal Alfven eigenmodes in TFTR, report, November 1, 1995; Princeton, New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc669746/m1/1/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.