26aD26P

LHDにおけるHeガス排気実験	 
He gas exhaust experiments in LHD	 

御手洗	  修１），成嶋吉朗 2)，芦川直子 2)，吉沼幹朗 2)，増崎	  貴 2)，後藤基志 2)	 小林政弘 2)	 	 後藤拓也 2)	 	 村上	  泉 2)	 	 相良明男 2)	 O.	 Mitarai1),	 Y.	 Narushima	 2),	 N.	 Ashikawa2),	 M.Yoshinuma2),	 S.	 Masuzaki2),	 et	 al.,	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 東海大1,	  核融合科学研究所2,	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 	 １：Tokai	 Univ.	  	 ２：NIFS	 
1.Introductionin Fig.4. On the	 The ratio of the alpha ash confinement time to thestraight observationline, He ion plumeenergy confinement time (τα*/τE) is one of important
should come in andparameters in designing the FFHR helical reactor. To
out due to the wavy
study the alpha ash confinement time, He exhaustfield line. However
experiments have been performed using the charge
its effect is small
recombination spectroscopy (CXS) system. However,and could be
it was not certain whether we can interpret theneglected in thisexperimental data directly because of complicateddensity regime.
observation geometry in theLHD CXS system and He	 
2.2. 3D geometry
Fig. 3. Signal (two peaks) from He+ ions
ion plume, which is theeffectexcited by NBI and drifted He+ plumetoroidaly drifted to bothIn actual situation, ions.
directions of the NBI
the magnetic field
injection part. Here weline is twisting.
applied the Fonk model toTherefore, 2D
LHD geometry with wavy
geometry ismagnetic field lines [Fig.1]
overestimating theand consider the data
plume effect. We may	 
analysis method. Based	  be able to interpret
Fig.4. Integrated signal with He+
Fig. 1. 2D magnetic fieldon this result we analyze
the data as it is in thisplume along the viewing line forline on the equatorial plane
the past data on He gasdensity regime.
n(0)=1.0x1019 m-3 and Te(0)=1.5 keV.
andtheobservinglinesofexhaust experiments inthe CXS in the LHD.
3. He exhaust
LHD and estimate the Heexperiments in Local Island Divertor (LID)
confinement time.
In the line averaged density regime of 0.7x1019 m-3, He
2. Signal to Noise from the drifted He ion plume
gas puffing into H plasma at 1.5 s with LID
2.1. 2D geometry effectconfiguration has been done using H-NBI modulation.
We assume He++ ion density with the Bi-Fermi
Even when NBI is not applied, He+ line (4686 Å) has
profile which is the double peaks to simulate the skin
been observed from the low temperature plasma edge on
effect of injected He ions as shown in Fig.2. For thethe sight line by He gas puffing. Therefore, NBI
peak electron density of 1x1019 m-3 with profile factor
modulation isαn=0.6, He+ ions created by CX with NBI and thenecessary to obtaintoroidally drifted He+ ion plume distributions is shown inHe++ ion density inFig. 3 usingthe plasma andthe Fonk
NBI injection part.
model [1].
After subtracting
The He+ ion
this base signal,
plume isHe++ ion density
produced bydecay is obtained
electronas shown in Fig. 5.
Fig. 5 He++ decay as a function ofimpact
By using thetime in LID experiment (#73556)
excitation.
particle balance
Here electron	  equation and fitting technique, τHe~ 450ms is obtained
Fig. 2. Assumed He++ ion distribution by
impactwithout source term. As the energy confinement time isgas puffing in LHD.
excitation rateestimated as τE=60~85 ms, τα*/τE=5.3~7.5 has been
is multipliedobtained.
by the factor 5 to take into the -mixing effect based on
the recent ADAS data base. The He ion plume starts[1] R.J.Fonk, D.S.Darrow and K.P.Jaehnig, PhysicalReview A, 29 (1984) 3288
from the NBI injection part. However, it is smaller thanthat in previous studies [1].
Integrated signal profile along the sight line is shown