BJ. "Peterson

J.E." Rice

K. Sato

National Institute for Fusion Science (NIFS-Repository)

§ 42. Comparison of Radiation Characteristicsof Wall Limiter and Helical DivertorDischargesPeterson, BJ., Sato, K., Rice, J.E. (PSFC MITUSA) , ,In LHD discharges the plasma facingcomponents are normally the graphite helicaldivertor tiles, however experiments have alsobeen carried out scraping off the plasma on thesteel inboard vacuum wall bychangIng the shape of the magnetic surfacesthrough coil current modification. Bycomparing the radiation profiles from thebolometer diagnostic [1] for these two cases asseen in Fig. 1 the adv.antage of the graphitehelical divertor can be seen in the reduced coreradiation. The source of this core radiation isindicated in the emission spectra from a VUVspectrometer seen in Fig. 2, which showsreduced iron impurities in the case of thegraphite helical divertor. In addition, as seen1000,<{800 to ..;:".,....: .<{·otN "'..;:...... @-q-"::i -.i- ell •...:.::S 600x @ @-u.'8 x =x ><400Ql ><'inc .XCIl20001200 1400 1600 1BOO 2000pixelFig. 2 Emission spectrum from VUV spectrometer forSS wall limiter case (thin line) and graphite helicaldivertor case (thick line) at the times corresponding tothose of Fig. 1.in Fig. 3, using the wall limiter, an oscillationoccurs which has a frequency dependence ondensity which is similar to that of the'Breathing' phenomenon [2] in the low densityregime, but different in the high density regimeindicating a difference in the densitydependence of the impurity transport of theergodic edge layer, which is scraped off in thecase of the wall limiter [3].---en..........i4+#+.,4-4= .,-]X 10£13£99)IE 01Z11Z01i:5..............I..&..I...........&oo1.L.LJ..a."......................o..L.o...........L.L.Ll......Jo 1 234Breathing Density (' 0 19/m 3 )Fig. 3. Density dependence of frequency foroscillations with SS wall limiter and SS helicaldivertor. Dashed line is given by Eq. 1 and solidline is given by Eq. 2.References[1] Peterson, B.l. et aI., Plasm Phys. Contr.Fusion 45 (2003) 1167.[2] Peterson, B.l. et aI., Nuci. Fusion 41(2001) 519.[3] Peterson, BJ. et aI., l. Nuci. Mater. 313-316 (2003) 1178.31.0--.949.· .22. ..---08.t6....... ........16.......0.613.11.0.413.1m"I::::::::::::::0.2(a)(b)0.0LQ)3: 200o0...'D 150.20LJ 1000Ct:5050 f-.-L200o0...Shot # 12112 t = lAOs.350300250] 150f-.-.Q ---- .-g 100 7.RCt:300 -§' 250pFig: 1. ,Radiated power profiles for (a) graphitehehcal dlvertor case and (b) SS wall limiter case (n =2 x 10l9/m3). e0.2 0.4 06 0.8 1.0pShot # 12090 t = 1.60s.35046

Comparison of Radiation Characteristics of Wall Limiter and Helical Divertor Discharges

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