H. Igami

H. Kasahara

H. Takahashi

S. Kubo

T. Mutoh

T. Shimozuma

Y. Suzuki

Y. Tatematsu

Y. Yoshimura

National Institute for Fusion Science (NIFS-Repository)

Third harmonic EC heating experiment by77GHz high power injectionShimozuma, T., Kubo, S., Tatematsu, Y. (FukuiUniv.), Yoshimura, Y., Igami, H., Takahashi, H., ?Kasahara, H., Suzuki, Y., Mutoh, T.The third-harmonic electron cyclotron heating bythe injection of an extraordinary mode (X3 heating) hasa 4/3 higher cut-oﬀ electron density than that of thesecond harmonic (X2) heating when a power source withthe same frequency is used. The X3 heating can en-large a possible heating region up to the higher densityregion. So far, we successfully performed X3 EC heat-ing experiment using 168 GHz 1) and 84 GHz gyrotrons2). The X3 heating experiment using powerful 77 GHzgyrotrons was performed on a relatively high β plasmaaround B � 0.9 T. The cut-oﬀ density is 5 × 1019m−3.We selected the magnetic ﬁeld strength of 0.95 T sothat the position of the magnetic axis coincided with theelectron cyclotron resonance (ECR), when the Shafranovshift was taken into account.A target plasma was produced by co-injected NBIand sustained from t = 0.3 to 2.3 sec. The centralelectron temperature was about 1.2 keV, and the line-averaged density was 0.7 × 1019m−3. The millimeter-wave power of 77 GHz was injected from 5.5U antenna(t =1.31 s - 1.81 s), 9.5U antenna (t =1.51 s - 1.81 s)and 2O antenna (t =1.71 s - 1.81 s). A time evolution ofthe core electron temperature (R =3.76 m) measured byThomson scattering is shown in Fig.1. The core electrontemperature increases with the increase of the injectionpower. Figure 2 shows the electron temperature proﬁlesat t =1.25 s (before ECH) and t = 1.75 s (during ﬁnal77 GHz power injection). The increment of the elec-tron temperature at the center achieved about 0.5 keV.The absorption rate of the ECH power for each antennacan be estimated by the calculation of an increment ofdWp/dt just before and after the turn-on timing of eachECH pulse. A density dependence of the absorption ratewas estimated for each antenna in Fig. 3. The absorp-tion rate generally has a tendency to increase with thedensity. The absorption rates for 5.5U and 9.5U antennainjection were so smaller than the expected values. Be-cause millimer-wave (mmW) beams from the U-port an-tennas were injected almost tangentially to the ECR,more precise optimization of the antenna focal positionwas required. That for 2O antenna was about 20% aswas expected, because the mmW beam could be injectedalmost perpendicularly to the ECR from this antenna.1) T Shimozuma, et al., 27th EPS Conference, Bu-dapest, Hungary, 12-16 June 2000, P4.0192) T Shimozuma, et al., PFR, (2008) Vol.3, S1080-1 –S1080-5.Fig. 1: Injection pattern of ECH and NBI together withthe time evolution of line-averaged electron density , electrontemperature and plasma stored energy.Fig. 2: Electron temperature proﬁles before ECH injec-tion (t = 1.25 s and during the ﬁnal 77 GHz injection pulse(t =1.75 s).Fig. 3: Density dependence of ECH absorption rate for eachantenna injection power87§63. Third H r i  E  Heating Experiment by 77 GHz High Power InjectionShimozuma, T., Kubo, S., Tatematsu, Y. (Fukui Univ.), Yoshimura, Y., Igami, H., Takahashi, H., Kasahara, H., Suzuki, Y., Mutoh, T.

Third Harmonic EC Heating Experiment by 77 GHz High Power Injection

Third Harmonic EC Heating Experiment by 77 GHz High Power Injection

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)