H." Funaba

N. "Ohyabu

National Institute for Fusion Science (NIFS-Repository)

o• ••£•• .. •• • .¢ <>• <>+• • >toy.'.: .x x x +••K # * x ..1 2 3 4 5 6 7'power (••)54.0>'(1)..........(J) 2.0I-0.0-1.0 -0.5 0.0 0.5 1.0PFIg.2 Temperature profile in the co-beam heatedDischarge(6MW).• te at 1=3800.• Te at R=4100ux n(dena i ty) to't.-3Co beallt heated4 dischargesTe with input power. This distinct difference is not due toiota change, caused by the beam driven plasma current sincethe electron temperature profile is insensitive to variation inplasma current. The observed burst of the magneticfluctuations, shown in Fig. 4 may be responsible for it. Thefrequency of the modes is around 50 kHz and the modenumbers are m=I,2 and n=I. For high ctr power, amplitudeof magnetic fluctuations and frequency of the burst are high,accompanying drops of the electron temperature. They arealso substantially lower for co-beam heating case.Fig.3 Electron temperatures at R = 3800mm (p=0.5) and atR = 4100mm (p=0.8) are plotted as a function of input powerfor Co beam heated heated discharges (Rax=3.5mconfiguration). Neon doped discharges are indicated by (0 0).128t\l2(a)3....,..__..,-__..,....__.,...__,....In the low density (n <l.5xI019m-3) etr-beam heatedinward shifted (Rax=3.5m) discharges, core flattening of theelectron temperature profile occurs (Fig. 1), deviatingsignificantly from the normal profile in LHD, parabolicprofile. Flattening is localized in the core region within thet/21t = 1/2 surface. With increasing ECH power, a smallbump starts to appear in the center as shown in Fig.I. WithECH power above a threshold, a narrow ITB (with high VTfor p < 0.2) grows rapidly. The power threshold for ITBincreases with n.Core heat transport in the low density co-beam heateddischarges is quite different from that of ctf-beam case. Coreflattening does not occur. With added ECH power, a mildjump in VT appears at p-O. 5. With higher co beam power,core profile flattening occurs (0<p<0.3). But temperature inthe whole region increases and the mild jump disappears(Fig. 2).The present LHD data show that the profile shape(VTIT) in the core region (0< p < 0.4) varies, exhibiting coreflattening and ITB. However, we have not observed anysignificant change in the profile shape in the outer region(0.5 < P < 1), an important region in determining the globalenergy confinement. In Fig. 3, Te(p = 0.5) and Te(p = 0.8)are plotted as a function of input power for co beam heatingdominated discharges. In this scan, the line average densitiesare almost fixed around n-l.Ox I019m·3. The ratios of thesetemperatures are nearly constant (-2), independent of thepower and beam direction. Temperatures increase reasonablywell with input power and are a factor of 1.5-2 times higherthan those in the ctr case, where a fairly severe saturation ofOhyabu, N., Funaba, H.§ 8. Influence of Beam Direction on theElectron Transport in Low Density LHDDischarges-1.Q 0-5- I t o!.-o-o -2-'-:"0"'0-0-4 """""'2L:-O""'Ot (Ill S )Fig. 4 Burst of the magnetic fluctuations which appearduring the etr beam heated discharges.12

Influence of Beam Direction on the Electron Transport in Low Density LHD Discharges

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