R. Kumazawa

S. Masuzaki

T. Watanabe

National Institute for Fusion Science (NIFS-Repository)

102 468Inboard section..........ai100Q)L:lEc:Q)13:eeua..References[1] Masuzaki, S., et. aI., Nuclear Fusion, 42(2002)740.[2] Watanabe, T., in Japanese, J. Plasma Fusion Res., 34(1998) 267.[3] Kubota, Y., private communication.150 ..-..,........,r--...,..._-............-Fig.2 Counts number of high-energy ions hittingcfi.vertor plates calculating an orbit of ions startedfrom the cyclotron resonance layer near the lastclosed magnetic surface.ICRF heating power radiated from the lower antenna is threetimes larger than that from the upper one, the temperatureincrease could have been interpreted It is not known thatthere is a cfi.sagreement between the experimental dlte on#36194 and the calculated high-energy ion loss. However themitigation of the cfi.vertor heat load will be tried by changingthe location of the ion cyclotron layer, because the highenergy-ions started from the inboard layer calculated toequally scattered on the divertor plates.It is not assure what is the cause of the Ha signalincrease and the uncontrollable electron oonsity increase,which was OOscribed in the previous section. However thelocal temperature increase in the 2-1 and 3-1 cfi.vertor plates isconsioored to be a feasible cancfi.dlte of the uncontrollableoonsity increase. We are installing a graphite sheet having agood heat conductance between the cfi. vertor plates and theheat sink made of copper [3].500 r---.....,r---.......ooQ) 400+-"eua.o300tQ)200"'C-oci 100E0O-.--"'"---..a.---.......------...4 6 10Inboard sectionFig.l Toroidtl cfi.stribution of the graphite temperatureof the inboard side divertor plates.Kumazawa, R., Watanabe, T., Masuzaki, S.§ 49. Assessment of Heat Load on DivertorPlatesIn the previous section it was found that the localtemperature increase in the inboard-sioo cfi.vertor platesalmost up to 400°C was experimentally observed Thethermo-couple is installed to 90 plates among 1,700 cfi.vertorplates aligned along the helical cfi.vertor traces. The measuredpoint is 10mm beneath the suIface of the cfi.vertor plate [1].The large temperature increase is observed at the inboarddvertor plates in both the heating methods, i.e., the neutralbeam (NBI) heating and the ICRF heating. An asymmetry ofthe temperature increase in the cfi.vertor plates is observed inthe toroidtl cfi.rection as shown in Fig. I. In this figure thetemperature cfi.stribution of another long pulse plasmacfi.scharge (the duration time of 127s, #26195, the ICRFheating power, the electron oonsityIle"'8xI018m-3) is also plotted with that in this 150s longpulse cfi.scharge (#36194, the electron OOnsityIle=5-6xl018m-3). In both plasma cfi.scharges theuncontrollable oonsity increase prevented the cfi.scharge fromcontinuing the steady state cfi.scharge. It is found that thetemperature increase is remarkable in 2-1 and 31 dvertorplates; here it should be noted that the ICRF heating antennais located at the vacuum ports of 3.5U&L.The long pulse plasma cfi.scharge was carried out in thebest heating more of the ICRF heating: This is the case ofRax=3.6m, B=2.75T. The cyclotron resonance layers areseparately located on the sadie points in the mod B suIface.In this magnetic configuration the behavior of high-energyions started at the cyclotron resonance layer is examinedusing the full orbit calculation [2]. Two thousand; high-energy ions with its energy of l00keV are started from theupper and the lower ion cyclotron resonance layers justinsioo of the last closed magnetic suIface, respectively. Thestarting position ranges from R=4.14m (p=I.05) to ofR=4.17m (p=I. 1) with their pitch angles from 45° to 135 0.Many the high energy-ions hit the dvertor plates withinseveral circulations along the toroidtl cfi.rection. Thenumbers of high-energy ions hitting at each ten cfi.vertorplates of the inboard sioo are plotted in Fig.2 to compare themeasured temperature increase as shown in Fig. I. It is foundthat the loss ions flow cbminantly to 2-1 and 3-1 as shownin Fig.2. Here loss particle numbers are counted separatelyLe., for started from the upper ion cyclotron layer (opencircles) and the lower ion cyclotron layer (open squares).There is a cfi.fference in the numbers of loss ion between theupper and the lower ion cyclotron resonances. Thetemperature increase in 2-1 will be larger in using the upperICRF heating antenna The total count is largest in 2-1using both antennas. When comparing these dlla with theexperimentally measured temperature increase and thistenooncy agree with dlta of #26195, in which the plasmawas sustained only by the upper ICRF heating antennaHowever in 36194 the maximum temperature was observedin 3-1, which cfi.sagrees with the calculation result. If the53

Assessment of Heat Load on Divertor Plates

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)