of Large Helical Device

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1 J. Plasma Fusn Res. SRIS, Vl. 5 (22) 25U254 Stran Mntrng System fr Grygenc Structure f Large Helcal Devce NISHIMURA Arata, TAMURA Htstr, IMAGAWA Shnsaku and SATOW Takash Natnal Insttute fr Fusn Scence, Tk , Japan (Receved: 11 December 21 / Accepted: 3 June 22) Abstract The Large Helcal Devce has the wrld's largest class crygenc structure t supprt huge electrmagnetc frce generated by supercnductng cls. The stran mntrng system was desgned and nstalled n the Large Helcal Devce t evaluate the sundness f the large crygenc structure and the measurement has been dne cntnuusly durng the peratn. Sme expermental results are presented n the paper and the stran behavr s dscussed. N sgnfcant dfference fthe stran has been bserved up t nw. The fact gves a cnclusn that the crygenc structure s wrkng n well wthut any faults. By plng up the data sets, the understandng fr the crygenc structure wll get ahead and the certanty and relablty fr the fault r damage wll be enhanced. Keywrds: Large Helcal Devce, crygenc structure, stran measurement, supercnductng cl, electr-magnetc frce 1. Intrductn A large supercnductng cl system was cnstructed fr the Large Helcal Devce (LHD) t generate a strng magnetc feld f up t 3 T at plasma axs [l]. T supprt the supercnductng cls and the huge electr-magnetc frce, a crygenc structure was desgned and cnstructed I2l. The austentc stanless steel (SUS316) was used as the stmctural materal and the maxmum thckness was 1 mm [3]. The supprt structure s cled dwn t 4 K tgether wth supercnductng cls at each campagn and endures the electr-magnetc frce durng cl exctatn. The plasma experments have been cnducted successfully [4] and the ffth campagn began n September, 21 and s gng n nw. The LHD s the frst machne f whch cls are all supercnductng and wll be perated fr a lng tme. S, a stran measurement and mntrng system was cnsdered and nstalled n the LHD t measure the Crrespndng authr's e-mal: nsh-a@ LHD.nfs.ac.jp stresses and strans and t evaluate the cndtn f the structure under electr-magnetc frce at 4 K. The stran mntrng was carred ut under the same peratn mde and the sundness f the structure was evaluated cmparng wth the data btaned befre. Snce such a stran mntrng system was nt develped befre n the large plasma expermental devces, t s very mprtant t develp the mntrng system and nvestgate the status f the supprt structure frm the pnts f devce engneerng and mantenance engneerng vews fr a fusn machne. In ths paper, an utlne f the stran mntrng system s descrbed and sme data are presented. The data shws that the crygenc supprt structure n the LHD s wrkng n well wthut any prblems. 2. Outlne f Stran Measurement Fr an applcatn t the LHD stran The Japan Scety f Plasma Scence and Nuclear Fusn Research 25

2 Nshmura A. et al., stran Mntrng system fr Crygenc structure f Large Helcal Devce system, a new stran gage was develped t have small apparent stran at 4 K and had plymd cated gage lead wres whch allwed fne-twst f the wres [5,6]. The gage has zr base dameter f 2 mm, a gage length f 5 mm, an electrc resstance f 35 C) and a gage factr f abut 2.. A Wheatstne brdge was frmed near an actve gage usng three dummy gages t reduce the temperature effect n the apparent stran and t cancel the apparent stran nduced by the fluctuatng magnetc feld. The dummy gages were attached n a s-called dummy stage, whch was a 3 mm thck stanless steel plate clad wth cpper, welded near the actve gage. An adhesve f a plyurethane system was used fr the actve gage, because the agent sldfed at rm temperature and t was hard t heat up the supprt structure. Fr the dummy gage, a phenl system was appled and the stage was heat- treated at K t sldfy the agent. A cable cnnectng the Wheatstne brdge t a feed thrugh cnnectr was als newly desgned and fabrcated takng accunt f reductn f the electrc r magnetc nse and heat lad t the HSN3I9 HSN3ll HSN3III (Inner equatr) Center flhd I'u HT3IIT 19 HSN3lIO HSN3III (Inner equatr) IS cl OV cl li]832 (a) Tp vew f Sectr 1. Helcal cl HSN3l12 HSN3l13 HSN3l14 (Outer equdr) HSN3I12 HSN3l13 HSN3l14 (Outer equarr) Crvsenc subdnngpsr (b) Crss sectnal vew f Sectr 1. - TIT3I 19 HT32I9 Fg. 1 Crygenc structure f LHD and lcatn f stran gages. crygenc structure. Tw pars f twsted wres were agan twsted, and the cable was electrcally shelded and fnally cvered wth a flurethylene plymer. One twsted par was used fr a cnstant nput current and the ther was fr an utput vltage. The LHD has a crygenc supprt structure whch sustans ne par f helcal cls and three pars f pldal cls. All cls are supercnductng and cled dwn t 4 K tgether wth the supprt structure. The stnrcture cnssts f ten sectrs and ne sectr cvers 36 degrees at center angle. The tp and the crss sectnal vews f Sectr I are shwn n Fg. 1. On the tp vew, nner vertcal (IV), nner shapng (IS) and uter vertcal (OV) cls are lcated and fxed t the supprt structure (shell structure) wth cl frames. On ths crss sectn, helcal cls are runnng at the tp and the bttm sdes. The helcal cls are set n the cl can and welded t the supprt structure wth tw shell arms. On the assemble prcess, each sectr was welded n upper half and lwer half ndependently and then bth halves were welded at the nner and uter equatrs. Therefre, there are crss jnts f weldng at the crss pnt f the equatrs and trdal crss sectn f the sectr. The stran gages were attached n the crss pnt f the weldng passes [7]. Tr-axal stran gages (three gages were set n ne base) were used, and three tag names were prepared fr ne stran gage base as shwn n Fg. l. HSN319 and 3l12 shw the strans n the trdal drectn, HSN3Illand 3114 ndcate thse n the pldal drectn, and HSN3l1 and 3113 are thse n 45 degree drectn t the trus. HT3I17 and3219 are therm- sensrs (Cernx) lcated under IV-U cl frame and n the uter equatr. In the case f Sectr 2, the secnd number frm left sde n the tag becmes 2. Fr example, HSN3 111 and HSN3 114 change t HSN321 I and HSN32I4 n Sectr 2. Snce the helcal cls are pl blng type supercnductng cls, the cl can s flled wth lqud helum and the temperature s kept at the blng temperature f the helum. The pldal cls are frced flw type supercnductng cls. S, supercrtcal helum s frced t flw nt the cndut f the cl. The nlet temperature s cntrlled at 4.5 K under the gage pressure f.9 MPa. The crygenc supprt structure s cled by tw-phase helum at arund 4.5 K usng 4 parallel clng channels. Dependng n the qualty f the tw-phase helum, the nlet temperature changes slghtly durng the clng. 251

3 Nshmura A. et ai., S1an Mntrng System fr Crygenc Structure f Large Helcal Devce 3. Results and Dscussn The LHD plasma experment prgram has several peratn mdes t create dfferent magnetc surface. In ths paper, the results btaned under #1-d mde wth gamma f wll be presented. Naturally, the stran cndtn f the structure depends n the electrmagnetc frce generated by the supercnductng cls. S, the peratn mde was fxed t cmpare the data sets easly. The helcal cl has 45 turns f supercnductrs whch were dvded nt three parts,.e., nner part, mddle part and uter part desgnated as H-I, H-M and H-O, respectvely. The nner part s the nearest t the plasma. The current f each part can be perated ndependently. Under #1-d mde, a radus f the magnetc axs s 3.6 m and the currents f each part f the helcal cl are 1.749, and ka fr H- I, H-M and H-O respectvely at 2.85 T at the plasma axs. It results n gamma f Ths current dstrbutn gves the current center utward shft n the mner radus drectn. The LHD has n electrcal break n the trus. S, an eddy current runs arund and heats up the structure when the magnetc feld ncreases r decreases s quckly. Ths temperature rse makes the stran measurement dffcult, because the addtnal apparent stran appears. Therefre, the lwer ramp rate f.2 Tl mn was adpted. Fgure 2 shws ne example f the slwer ramp-up and ramp-dwn peratn cnducted n Nvember 29, 21. The peratn mde was #1-d wth 1f as explaned abve. The temperatures near the nner equatr and n the uter equatr vary wthn abut.2 K. The temperature change n the nner equatr becmes larger than that n the uter equatr as reprted befre [5], and ths fluctuatn s cnsdered t be caused by the change f the qualty f the flwng helum. Such slw ramp rate peratns were carred ut three tmes t measure the strans under cl exctatn. The frst was carred ut n Octber 4, 2 at the begnnng f the frth campagn, and the secnd was dne n January 19, 2Ol at the endng f the campagn. The last was perfrmed n Nvember 29, 21 durng the ffth campagn. The examples f the measured strans are shwn n Fg. 3. In the fgure, the results f HSN3 I I I and 3l 14 are descrbed and thse are pltted aganst the square f the magnetc feld at the plasma axs whch s crrespndng t the electr-magnetc frce. Therefre, the relatn becmes straght lne when the structure respnds t the electr-magnetc frce elastcally. The strans n the nner equatr are smaller than thse n the uter equatr, fr the uter vertcal cls generate huge tensle electr-magnetc frce t make an nward shft f the plasma axs. The results f HSN3I I I shws a hysteress curve and ths wuld be caused by the dfferent defrmatn prcess f the helcal supercnductrs n the ramp-up and ramp-dwn prcesses [7]. On the ther hand, HSN presents lnear relatnshp. These tendences are bserved bth n Octber 4,2, January 19, 21 and Nvember 29, 2O1. T nvestgate the dfference and the scatter f these hysteress curves, the measured strans were cmpared at the same magnetc feld. The results are H-I/M/O: 1.749ll 1.628/l L823kA !.l g.5 ; AU F -.5 9: 1: 1 1: 12: 13: 14: Tme (hur:mn.) Fg. 2 Change n temperature and magnetc feld under #1-d mde wth 1f measured n Nvember 29,21. F L6 ' t;- Stran (pe ) 3 Fg. 3 Cmparsn f hysteress curves between square f magnetc feld and measured stran. "'3 t 252

4 Nshmura A. et al., Stran Mntrng System fr Crygenc Structure f Large Helcal Devce shwn n Fg. 4. Fgure 4 (a) ndcates the results f January 19,21 aganst Octber 4,2OO and (b) s the results f Nvember 29,21 aganst Octber 4,2OO. The data acqustn system has an errr f +/- ne dgt fundamentally. S, the errr f +/- tw dgts s nvlved n the results shwn n Fg. 4. In addtn, anther errr f +/- ne dgt wll be generated when the data are cmpared each ther at the same magnetc feld. 25 a t- c.l > 15 ) C) 6 25 I (.r 2 { t rs C) z 1.F! ' #l-d mde B.u* = 2'857 1= ''-.-'-,:., HSN3I s Measured stran n Octber 4, 2 (pe) (a) Cmpars;n f strans measured n Octber 4, 2 and January 19,21. #l -d mde B = Inax ^l '= I3 ; SN 3 '.. I t t Measured stran n Octber 4, 2 (pe) (b) Cmparsn f strans measured n Octber 4, 2 and Nvember 29,21. Fg. 4 Cmparsn f scatter f data set. In bth fgures, the ttal errr wll becme +/- three dgts. Therefre, +/- three dgts bundares, whch crrespnd t abut +l- 7.5 pr, are dsplayed by the dtted lnes. It s very clear that all the expermental pnts fhsn3lll and 3l14 n January 19, 21 and Nvember 29, 2OOl are pltted wthn the +/- three dgts scatter bands. Frm these results, t can be cncluded that the crygenc supprt structue s nt damaged at all after the plasma experments n the frth campagn and the warmng up and clng dwn prcesses befre the ffth campagn. The change n the measured stran n each sectr s summarzed n Fg. 5. The number n the hrzntal axs ndcates the sectr number and measured strans f HSN3XI I and 3X14 are pltted n the crrespndng bx, where X s Sectr number. Rund, trangle and square symbls shw the result f each mntrng n Octber 4, 2, January 19,21 and Nvember 29, 21. Dependng n the sectr, the measured stran changes very much, fr the hrzntal prt shape and dmensns are nt the same. In addtn, the lcatn f the stran gage s nt entrely n the symmetrc pstn. Hwever, when each three data sets are cmpared, the dfference s wthn three dgts, and mstly tw dgts. Takng accunt the errr f tw dgts nt cnsderatn, t s pssble t make a cnclusn that the stran des nt change and that the crygenc structure s nt damaged at all up t nw. These results descrbed abve reveal that the stran measurement system nstalled n the LHD s very effectve t evaluate the status f the crygenc supprt structure durng the cl exctatn. The cntnuus data 1.= r5 e 1 I OOctber4,2 ajanuarylg,2l ::t: r. Nvember 29' 21 Ar, a., rrl ll Il^r^rlI 'rr sta mark: HSN3l 14 OA!. ^. "! al,, Jnn I a_ OA! ntr toa; n ^tr] - I " ; Open mark: HSN3I I Sectr number Fg. 5 Measured strans at 2.85 T under #1-d (^1 = durng the frth and the ffth campagn. l 253

5 Nshmura A. et al., Stran Mntrng System fr Crygenc Structure f Large Helcal Devce acqustn and plng up the data wll enhance the certanty f the mntrng system and the relablty f the evaluatn f the crygenc supprt structure. It s expected that the system wll gve a specal wamng n a certan fault f the structure befre the truble ccurs. 4. Summary The LHD has the large crygenc supprt structure whch sustans ne par f helcal cls and three pars f pldal cls. T measure the stran durng cl exctatn and t evaluate the sundness f the structure, the stran mntrng system has been cnsdered and nstalled n the LHD as part f the fusn devce engneerng. Durng the cnsderatn, new gages and wres were desgned and develped. The stran measurement has been perfrmed cntnuusly and the nvestgatn n the structure has been carred ut under a certan peratn mde specally selected fr ths purpse. In ths paper, the utlne f the stran mntrng system s descrbed and sme results are presented. The man results are summarzed as fllws: (1) The slwer ramp rate peratn cndtn, (#1-d mde, y = 1.258, maxmum magnetc feld; 2.85T) gves a clear data set f the stran mntrng fr the crysenc structure. (2) The hysteress curve between the square f the magnetc feld and the stran des nt change n Octber 4, 2, January 19,2Ol and Nvember 29,21. (3) The ttal stran under the change f the magnetc feld frm zer t 2.85 T shws n sgnfcant dfference amng three mntred data sets. (4) Frm these results, t shuld be cncluded that the crygenc supprt structure n the LHD wrks well wthut any prblems up t nw. (5) The stran mntrng system s wrkng effectvely and expected t gve a warnng befre unexpected truble. (6) The cntnuus data acqustn wll make the certanty and relablty fthe system hgher and the system wrk mre effectvely. References tll M. Fujwara et al., J. Fusn nergy 15, 7 (1996). l2l T. Satw et al.,prc. MT-15, 377 (1998). t3l A. Nshmura er al.,fusn Technl., 873 (1998). t4l M. Fujwara et al.,nu'cl. Fusn 41, 1355 (21). t5l A.Nshmura et al.,prc. MT-15, 1275 (1998). t6l A.Nshmura et al., Adv. n Cry.Bng.45,745 (2). t7l A.Nshmura et al.,2lst SOFT, F-42 (2). 254