23P089-P
Measurement of High-Frequency Density-Fluctuations with Microwave
Reflectometer in GAMMA 10
GAMMA 10におけるマイクロ波反射計を用いた高周波密度揺動の測定
T.Sato, R.Ikezoe, M.Ichimura, M.Hirata, T.Yokoyama, T.Iwai, Y.Ugagin, T.Iimura, Y.Saito,
T.Iimura, M.Yoshikawa, J.Kohagura, Y.Shima and T.Ima
佐藤達典、池添竜也、市村真、平田真史、横山拓郎、岩井透、宇賀神ゆめと、斎藤裕希、飯村拓真、吉川正志、小波蔵純子、嶋頼子、今井剛
Univ. Tsukuba PRC
1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
筑波大プラズマ研究センター 〒305-8577 茨城県つくば市天王台1-1-1
We have studied the excitation mechanism of the Alfvén Ion Cyclotron (AIC) waves in GAMMA10. AIC
waves are excited owing to temperature anisotropy of the plasma. Up to now, magnetic probes have beenused for the measurement of AIC waves in the peripheral region. In this study, we used reflectometer tomeasure the density fluctuations due to AIC waves in the core region. We constructed microwave
reflectometer system. Ordinary mode (O-mode) horn antenna was newly installed on GAMMA10. We
measured radial profile of the density fluctuations and also the z-profile of the density fluctuations by using
an axial array of horn antennas.

1. Introduction
We have conducted the experiments for forminga high-temperature and high-density plasma in
GAMMA10. Magnetically confined plasma isheated perpendicularly by a strong ion cyclotron
range of frequency (ICRF) wave. Plasmas withstrong temperature anisotropy are produced by
ICRF heating. Alfvén ion cyclotron（AIC）waves areexcited spontaneously in such plasmas. The
magnetic probes installed in the peripheral region
have been mainly used for measurement of the AICwaves. The frequency spectrum of the magnetic
probe signal installed is shown in Fig.1. A peak of
6.36 MHz is the frequency of heating ICRF wave
and discrete peaks on the left side are those of theAIC waves. AIC wave causes pitch angle scatteringof ions to the magnetic field line, and has big
influence on the ions in GAMMA 10. The
excitation mechanism of AIC wave is not clear until
now.
In this research, the excitation mechanism fromdetailed spatial and time behavior of the AIC wave
in the inside of plasma, measurement using amicrowave reflectometer was performed. Four hornantennas were installed in the vacuum vessel of theGAMMA 10 central cell. We measure the spatial
profiles of density fluctuations in the direction of
the magnetic field line and radial directions. The
correlation between the magnetic probe and thereflectometer signals is observed.

Fig.1. Power spectrum of AIC waves (t=79ms). The
waves measured by a magnetic probe. The left
peaks are AIC waves and right peak is ICRF.

2. Principle of homodyne reflectometer
Outline of homodyne reflectometer is shown inFig.2.The flow of signal processing is as follows.
The wave from electronic oscillator is divided intoa reference wave and the incidence wave in a
directional coupler. The incidence wave enters into
plasma with a horn antenna through a circulator.
When incident electromagnetic waves reach cutoff
layer, a refractive index will be set to 0. The wave isreflected and returns to horn antenna again.

Theoretical cutoff frequencies of each polarization(O-mode and X-mode) are shown in Fig.3. In thisfigure, thick line and thin line indicate in the eachcase of the central density of 2.0×1018m-3 and1.5×1018m-3 respectively. The experiment wasconducted with the Frequency oscillator indicatedby double-headed arrow in Fig.3. The reflected
waves from plasma are injected to mixer throughcirculator from the horn antenna. Incident wave andreflected wave are detected by square-law, andtransmitted to an oscilloscope. This signal isFourier-transformed and the density fluctuation inplasmas is detected.

Directional
coupler～

Circulator

Referencewave

Hornantenna

fluctuations in the peripheral region.

PlasmaReflected
wave

Degitizer

Fig.4. Coherence between signals of reflectometer andmagnetic probe. (a)row signals of the reflectometersystem and magnetic probe, (b)frequency spectra ofthose signals, (c)coherence between both signals.

Fig.2. Outline of homodyne reflectmetory

20X-mode(R)

4. Summary
Reflectometer system has been constructed andused in GAMMA10 for the measurement of thedensity fluctuation due to ALC waves. Four hornantennas have been installed parallel to themagnetic fieldline. We observe the same
frequency of AIC waves in radial direction andcoherence between the density fluctuation in thecore region and magnetic fluctuations in theperipheral region.

Fr e qu e n c y(GHz)15O-mode
105X-mode(L)

00

0.03

0.06

0.09

0.12

0.15

0.18

Radiu s(m )Fig.3. Theoretical cut off layer of each polarization.

3. Experimental result
Figure4 shows the temporal evolution of the raw
signals of the reflectometer system and magnetic
probe (a), the frequency spectra of those signals (b)and the coherence between both signals (c).The
period where correlation is strong, and the placewith no correlation exist. It seems there aredifferent characteristics between the density
fluctuations in the core region and magnetic

Acknowledgments
The authors would like to thank members of ICRF
group of the University of Tsukuba.
This work was supported in part by a Grant-in-Aidfor Scientific Research from the Ministry ofEducation, Culture, Sports, Science and Technologyof Japan (No. 21540506) and in part by the NIFS
Collaborative Research Program(NIFS09KUGM040).