H. Idei

H. Igami

H. Takahashi

K. Nagasaki

M. Nishiura

M. Osakabe

N.B. Marushchenko

S. Kubo

T. Mutoh

T. Shimozuma

Y. Turkin

Y. Yoshimura

National Institute for Fusion Science (NIFS-Repository)

The 3rd harmonic electron cyclotron heating by theextraordinary mode injection (X3 heating) can enlargea possible heating region up to the higher density re-gion than the 2bd harmonic X mode heating . So farwe successfully performed X3 EC heating experiment at168 GHz, 84 GHz and 77 GHz frequency region 1, 2).The objective of the 3rd harmonic heating experi-ment in this experimental campaign is to obtain a dataset of the target plasma with wide plasma density andelectron temperature ranges, because the absorption ef-ﬁciency of the harmonic heating strongly depends onthem. The X3 heating experiment was conducted us-ing three 77 GHz gyrotrons. The cut-oﬀ density is5 × 1019m−3. We selected the magnetic ﬁeld strengthof 0.95 T so that the position of the magnetic axis coin-cided with ECR, when the Shafranov shift was taken intoaccount. A target plasma was produced by tangentiallyinjected NBI, and it was sustained by perpendicularlyinjected NBI without plasma current. The millimeter-wave power of 77 GHz was injected from 2O-r, 9.5U-inand 5.5U-out antennas. Typically, the absorption ratesand the electron temperature values at the ECH turn-on and -oﬀ timings are plotted for the 5.5U-out antennacase as a function of the line-averaged electron densityin Fig. 1. The maximum absorption rate of about 40%was obtained around the density of 1.5× 1019 m−3 withTe ∼ 1.2 keV at the ECH oﬀ timing. The ray-trace cal-culation (TRAVIS-code) results of the absorption ratefor the same injection conﬁguration in the experimentshow that the density dependence of the absorption rateagrees well with the experimental results shown in Fig. 2.Superposed stepwise injection from three gyrotronswith totally 3 MW increased the central electron tem-perature to about 3.5 times of the initial target plasmatemperature of 0.6 keV, which is shown in Fig. 3. Thisclearly shows that the temperature increase improves theabsorption rate of the subsequent power injection.These results show that the X3 mode ECH can beexpected as methods with suﬃcient absorption, when theEC beam is injected (1) along the ECR over a long dis-tance (U-antenna case) and (2) through the saddle pointof the magnetic ﬁeld strength between two ECR layers(O-antenna case). It is shown also that the high har-monic ECH has a potential to extend the heating regimeof higher density and higher ? fusion-relevant plasmasutilizing optimized injection condition and magnetic con-ﬁgurations with a long-distance resonance.1) T Shimozuma, et al. :, Plasma and Fusion Research,3 (2008) S1080-1 – S1080-5.2) T Shimozuma, et al. :, Plasma and Fusion Research,8 (2013) 2402073-1 – 2402073-5.Fig. 1: Dependence of X3 (U-out antenna) absorption rateestimated at ECH turn-on timing (circles) and -oﬀ timing(squares) on the line-averaged density (bottom). Density de-pendence of electron temperature at the center is also plotted(top).Fig. 2: Calculated absorption rate of X3-mode (U-out an-tenna) is mapped in Te0 - line-averaged ne space. Density andtemperature proﬁles are assumed to be ne(ρ) = ne0(1 − ρ8)and Te(ρ) = Te0(1 − ρ2)3, which approximate the proﬁles inthe experiments. A dashed-line shows a line-averaged cut-oﬀdensity of X3 (=8/9 ne0 cutoff ). Data points of Te0 in Fig. 1(top) are also over-plotted.Fig. 3: The electron temperature proﬁles during X3 ECH.5.6s:just before ECH, 5.7s:1 gyrotron-, 5.8s: 2 gyrotron-, 5.9s:3 gyrotron-injection142§11. Optimization of Third Harmonic ECH Scenario to Extend a Heating Plasma Parameter RangeShimozuma, T., Igami, H., Kubo, S., Yoshimura, Y., Takahashi, H., Osakabe, M., Mutoh, T.,  Nagasaki, K. (Kyoto Univ.),  Nishiura, M. (Univ. Tokyo),  Idei, H. (Kyushu Univ.),  Marushchenko, N.B., Turkin, Y. (IPP Greifswald)

Optimization of Third Harmonic ECH Scenario to Extend a Heating Plasma Parameter Range

Optimization of Third Harmonic ECH Scenario to Extend a Heating Plasma Parameter Range

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