T. "Yamamoto

T. Seki

T." Watari

"Yamamoto,  T.

Seki,  T.

Watari,  T."

NIFS-Repository (National Institute for Fusion Science)

§33. Effect of Quadra-pole Field Dependence on ICRF Heating Yamamoto, T., Seki, T., Watari, T. Shape of the poloidal cross section of LHD plasma can be changed by the quadra-pole field, BQ. It is interested to study behavior of high-energy ions in different poloidal cross section. Ion cyclotron heating experiments have been done in three different BQ: 67, 100 and 150 %. Figure 1 shows the shape of the poloidal plasma cross section at the vertically elongated toroidal position in LHD. Magnetic surfaces and projection of particle orbit in the ergodic region are plotted. The LHD experiments are usually done in BQ=100%. In this case, toroidally averaged poloidal plasma cross section is circular. The toroidally averaged cross section becomes vertically elongated when the Bq becomes smaller like 67 %. The cross section becomes vertically shortened when the BQ becomes larger such as 150 %. In the experiment, the ICRF power was applied to the NBI-heated plasmas for these three quadra-pole field configurations. Injected ICRF power is 1 - 2 MW. The strength of magnetic field and the position of magnetic axis are 2.75 T and 3.6 m, respectively. The line-averaged electron density is 0.6 - 1.2 x 1019 m-3 and the central electron temperature is 1.8 - 2.2 keV. The energy spectrum of high energy ion was obtained by Natural Diamond Detector1•2> as shown in Fig. 2. Solid circle and solid triangle indicate the case for BQ=100% and 67%, respectively. Unfortunately, signal to noise ratio was bad and the quality of data was not good enough in the case of BQ=150%. Then, the result of BQ=150% is not plotted in this figure. The ion tail is accelerated to higher energy region in the case ofBQ=100%. Effective ion temperature, Teff was calculated using the energy spectrum and Stix formula3): ' ; -... , .' " ~ . ~ 0.5 I o N 0 -o.5 -1 0.5 I o ·· .4 -o.5 -1 I~ / \ I J \ / ·,:.;:,;,;/' Energy [keV] e B =100% Q .A B =67% Q Fig.2. Energy spectrum of high energy ions for BQ=67% and BQ=100%. T z r(l + pabs 'r.s ). eff e 3n HV Hr: 200 The effective ion temperatures derived from the energy spectrum of high energy ion are 14 keV for BQ=67% and 25 keV for BQ=100%. The effective ion temperatures calculated using Stix formula are 13 keV for BQ=67% and 67 keV for BQ=100%. Higher effective ion temperature is obtained for BQ=100%. It is very interesting to compare with the case ofBQ=150%. References 1) Krasilnikov, A. V. et al.: N ucl. Fusion 39( 1999) 1111. 2) Isobe, M. et al.: Rev. Sci. Instr. 72(2001)611. 3) Stix, T.H.: Nucl. Fusion 15(1975)737. 0.5 I o -o.s -1 -1.5 -1.5 -1.5 L......................l~.........J...~.........L....~~ ............. ...L........ ........... 2.5 3.5 4 4.5 5.5 2.5 3.5 4 4.5 5.5 2.5 3.5 4 4.5 5.5 R [m] R [m] R [m] Fig.1. Shape of the poloidal cross section at the vertically elongated toroidal position for three values of the quadra-pole field: B0=67, 100 and 150 %. 38 

Effect of Quadra-pole Field Dependence on ICRF Heating

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