PD/P1-6. Abstract. In order to understand the physics of the ELM trigger and determining the ELM size, fast ELM

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1 PD/P-6 Fast Dynamics of Typ I and Grassy ELMs in JT-6U A. Kojima, N. Oyama, Y. Sakamoto, Y. Kamada, H. Urano, K. Kamiya, T. Fujita, H. Kubo and th JT-6 Tam Japan Atomic Enrgy Agncy, Naka, Ibaraki -9, Japan kojima.atsushi@jaa.go.jp Abstract. In ordr to undrstand th physics of th ELM triggr and dtrmining th ELM siz, fast ELM dynamics of typ I ELMs and grassy ELMs hav bn studid in JT-6U using nw fast diagnostics of a lithium bam prob and charg xchang rcombinat spctroscopy which can masur lctron dnsity and tmpratur with high spatial and tmporal rsoluts. Th volut of th prssur profil is valuatd for th first tim by th dtaild profil masurmnt of th dnsity and tmpratur pdstals. Aftr a typ I ELM crash, th rcovry of pdstal dnsity is fastr than that of lctron and tmpratur. Just bfor typ I ELM crash, th pdstal prssur in co-rotating plasmas is highr than that in countr (ctr)-rotating plasmas. W found that th radial xtnt of th prssur gradint at th pdstal rg in co-rotating plasmas is widr than ctr-rotating plasmas. Th rsult suggsts that th ELM siz is dtrmind by th structur of th plasma prssur in th whol pdstal rg. As for th dynamics of grassy ELMs, th collaps of dnsity pdstal is smallr and narrowr than that of typ I ELMs, as obsrvd in th collaps of tmpratur pdstal. Thus, it is confirmd that both conductiv and convctiv losss du to grassy ELMs ar small.. Introduct For a stady stat oprat of th tokamak fus ractor, H-mod with th dg localizd mod (ELM) is an attractiv scnario in trms of th dnsity and impurity controllabilitis. Although ELMy H-mod has a good compatibility of a high prformanc and stady stat oprat, a damag to a divrtor plat du to a larg ELM hat load is a critical problm for th plasma facing componnts. Thrfor, mitigat of th ELM hat load has bn invstigatd in various tokamaks. In ordr to control th ELM siz and frquncy, ELM mitigat tchniqus and oprats in small ELM rgims hav bn dvlopd and succssfully dmonstratd. In addit, rcnt xprimntal rsults show that th toroidal plasma rotats also affct th ELM siz and frquncy [-]. To improv th ELM controls, th mchanism of ELM triggring and th dtrminat of ELM affctd ara ar ky physics for th ELM control tchniqus, bcaus th ELM triggring and ELM affctd ara dcid th ELM frquncy and siz, rspctivly. In this papr, th ELM dynamics of typ I and grassy ELMs is xprimntally E98 t6.8s n l dg n l cor LiBP CXRS ECE Thomson Figur. Plasma configurat and arrangmnts of th diagnostics (LiBP, CXRS, YAG Thomson scattring, FIR intrfromtrs of dg and cor rgs)

2 PD/P-6 invstigatd to undrstand th ELM triggr and ELM affctd ara. In JT-6U, fast dynamics of typ I ELMs [] and grassy ELMs [5] hav bn studid xtnsivly. Howvr, th tim rsolut of T i masurmnt and th spatial rsolut of n masurmnt wr not high nough to discuss th profil of pdstal prssur. Th xprimntal obsrvat of th prssur profil has bn awaitd in ordr to invstigat th bhavior of th prssur profil as an ELM triggr and th radial xtnt of th ELM affctd ara. To undrstand th dtaild ELM physics, nw diagnostics of a lithium bam prob (LiBP) ( R~cm, t=.5-.5ms) and a charg xchang rcombinat spctroscopy ( R~.6cm, t=.5ms) hav bn dvlopd and installd in JT-6U. Thn, th volut of th prssur D Div a [a.u] n pd [ 9 m - ] n sp [ 9 m - ] T pd [kv] Tim [sc] profil during an ELM cycl can b valuatd for th first tim. This papr is arrangd as follows; Fast dynamics of th dg dnsity profil during typ I ELM is prsntd in Sc.. Th bhaviors of th dnsity and tmpratur profils in cass of co- and countr- rotating plasmas ar shown in Sc.. Comparison btwn low and high Ip plasma with co-rotats is dscribd in Sc.. Th volut of th prssur profil and th gradint is shown in Sc.5. Th ELM affctd aras ar compard btwn grassy and typ I ELM in Sc.6. Conclus is in Sc. 7.. Fast ELM Dynamics of Typ I ELMs Typical volut of on cycl of typ I ELM is invstigatd in ELMy H-mod plasma with co-toroidal rotat. Figur shows th plasma configurat and arrangmnt of th diagnostics. Th dg dnsity profil masurd by LiBP covrs around 8cm from th sparatrix along with a vrtical lin sam as th FIR intrfromtr of cor rg and YAG Thomson scattring. In trms of th dnsity collaps masurd by LiBP, it is notd that th initiat of ELM collaps has th poloidaly asymmtry, and taks plac in th localizd rg nar th midplan at low fild sid. Figur shows a wavform of on ELM cycl of typ I ELM. Th ELM nrgy loss is 89kJ corrsponding to W ELM /W pd of 8%. Frquncy of ELMs f ELM is 7Hz. A drop of th pdstal dnsity n pd at ELM rachs ~% which is largr than th tmpratur drops (typically -%). Just aftr ELM crash (t= s), th incras in th sparatrix dnsity n sp corrsponds to th incras of th dnsity in scrap-off layr (SOL). Ths phnomna indicat th collaps of th dnsity gradint du to ELM crash. 89kJ E98 Co Rotat 86kJ Wdia [MJ] Wdia [MJ] TNELCU-Fring TNELCU-Fring n l cor [ 9 m - ] n l dg [ 9 m - ] Figur. Wavform of typ I ELM in co-rotating plasma. Dashd lins indicat ELM onst. (Ip=.6MA, q95=., δ=., f ELM =7Hz, P B =.7MW, W pd =.8MJ) T pd i [kv]

3 PD/P-6 Th rcovry of th pdstal dnsity is fastr than th tmpratur. Th tim scal (~ms) of th rcovry of th pdstal dnsity aftr ELM is similar to th rduct in lin dnsity n l cor. Figur shows th comparison of th volut of lin dnsity. Th incras and dcras of lin dnsity occur outsid and insid of dnsity pivot as shown in Fig.. n l IN and n l OUT ar lin intgratd valus in th pdstal rg. Th boundary condit of intgrat is pivot point. Th poloidal symmtry is assumd in valuating th lin intgrat along with th vrtical lin. Th ELM collaps inducs th rduct of th n l IN. On th othr hand, th wavform of n l OUT is similar to th lin dnsity n l dg. Thrfor, incras of n l dg indicats th incras of th dnsity around sparatrix. It is notd that incras of n l OUT do not suggst th dnsity xhaust; th tim scal of th dnsity collaps du to ELM is about µs. Incras of n l dg and n l OUT rsult from th incras of th SOL dnsity causd by th nhancd rcycling ffct dut to ELM crash []. In Fig., n l indicats a variat from th pr-elm valu. n l IN and n l OUT ar almost balancd (n l IN +n l OUT ~) during this ELM cycl. Howvr, n l cor along with sam vrtical lin dcrass ms aftr th ELM collaps. Thrfor, th slow rduct of n l cor suggsts th rdistribut of plasma dnsity to compnsat most of th lost pdstal dnsity bcaus n l cor -(n l IN + n l OUT ) mans th chang of th dnsity in th cor rg; n l cor of.x 9 m - nl [ 9 m - ] Dnsity [ 9 m - ].. -. ELM ELM Tim [sc] n l IN t=6.8 t=6.8 t=6.85 Bfor ELM n l OUT pivot R-Rsp [cm] n l IN+OUT n l IN n l OUT n l dg n l cor Figur. Wavforms of n l,, Radial profil of dg dnsity. Dash lins ar fitting curvs using YAG Thomson scattring. SOL rg is assumd to b xponntial dcay. n l I and n l OUT ar spafractd by pivot point. Figur. Wavform of typ I ELM in ctr-rotating plasma. Dashd lins indicat ELM onst. (Ip=.6MA, q95=., δ=., f ELM =5Hz, P B =.9MW)

4 PD/P-6 n [ 9 m - ] Div D α [a.u] E98 t tim rlativ to ELM [ms] 5cm cm cm cm cm Figur 5. Tim volut of dg dnsity. Data ar ovrlappd according to th tim rlativ to ELMs. Dα miss at divrtor rg. corrsponds to % rduct of th dnsity in th cor rg. As for th tmpratur, th lctron and tmpratur monotonically rcovr toward th nxt ELM. Sinc th pdstal profil and th tim scal of th rcovry ar diffrnt btwn th tmpratur and th dnsity, th valuat of prssur profil during ELM is ssntial to th undrstanding of ELM physics.. Typ I ELM Dynamics in Co- and Ctr- Rotating Plasma JT-6U rportd that th normalizd ELM nrgy loss ( W ELM /W pd ) in ctr-rotating plasmas is smallr than that of co-rotating plasmas []. It suggsts that th toroidal rotat can chang th ELM affctd ara. Th ELM affctd aras ar compard btwn coand ctr-rotating plasmas. Typical wavform of ctr-rotating plasma is shown in Fig.. W ELM in th ctr-rotating plasmas is smallr than th co-rotating plasma and th drop of th dnsity and tmpratur ar also small. Figur 5 shows th dg dnsity across an ELM onst. Th ELM frquncy f ELM is 7Hz, and 5 ELMs ar avragd in Fig.. Dnsity pdstal structur is rcovrd ms aftr th ELM collaps. Aftr pdstal format, th dg dnsity is almost stady stat or slightly incrasd. Figur 6 n [ 9 m - ] - n /n Ti [kv] Ti [kv] - T /T i i.6.. E98 t6.5-7 Co 7cm 6cm 5cm cm cm cm - tim rlativ to ELM [ms]. (c)... t= -~ms (Co) t=.5~ms (Co) t= -~ms (Ctr) t=.5~ms (Ctr).6MA Co.6MA Ctr R-Rsp [cm] t= -.5~ms (Co) t= ~5.5ms(Co) t=-.5~ms (Ctr) t= ~5.5ms (Ctr) Co Ctr Ctr Co Figur 6. Comparison btwn co- and ctr-rotating plasma. dnsity profil bfor and aftr ELM, Dnsity loss fract masurd by LiBP(solid lin) and YAG Thomson scattring (dashd lin) R-Rsp [cm] Figur 7. Edg tmpratur at ach posit. Tmpratur profil in pdstal rg in comparison with co- and ctrrotating plasma. (c) Tmpratur loss fract of co- and ctr-rotating plasma.

5 5 PD/P-6 show th dg dnsity profils at t=-~ (bfor ELM),.5~ms (aftr ELM) in comparison with co- and ctrrotating plasmas. Th shouldr of dnsity pdstal is locatd at ~5cm from th sparatrix. In th co- rotating pd plasma, n is highr than th ctr-rotating plasmas. Figur 6 shows th dnsity loss fract du to th ELM crash masurd by LiBP and YAG Thomson scattring. Around th pdstal shouldr, % of dnsity is lost in th co-rotating plasmas. Th dnsity loss fract of th ctr-rotating plasmas is smallr than th co-rotating plasmas. Morovr, ELM affctd ara of th co-rotating plasmas is widr than that of th ctr-rotating plasmas. Figur 7 shows th tmpratur bhavior. Tim volut of th tmpratur as shown in Fig. 7 is Figur 8. Wavform of typ I ELM. Dashd lins indicat ELM onst in co-rotating plasma. (Ip=.MA, q95=., δ=.9, f ELM =75Hz, P B =.9MW) obtaind by sam procss in Fig. 5. Th dg tmpratur is monotonically incrasd aftr th ELM crash. Fig. 7 shows th tmpratur profil in comparison btwn co- and ctrrotating plasmas. Th pdstal shouldrs of dnsity and tmpratur ar locatd almost sam posit in ths cass. Th tmpratur profils in co-and ctr-rotating plasmas bfor th ELM crash ar almost sam; howvr, th loss fract of th co-rotating plasma is largr than th ctr-rotating plasmas as shown in Fig 7(c)..5 n [ 9 m - ].6MA Co.5 MA Co n /n. n pd t= -~ms(ma) t= ~.5ms(MA) MA Co.6MA Co R-Rsp [cm] - (c) Ti [kv]. (d). - Ti/Ti T pd i t= -.5~ms (MA) t= ~5.5ms (MA) t= -.5~ms (.6MA) t= ~5.5ms(.6MA) MA Co.6MA Co R-Rsp [cm] - Figur 9. Comparison of high and low Ip plasma Dnsity profil of MA and.6ma bfor and aftr ELM. Dnsity loss fract (c) Tmpratur profil (d) Tmpratur loss fract.

6 6 PD/P-6 Thrfor, th prviously obtaind small ELM nrgy loss of ctr-rotating plasma rsults from small loss fract and narrow ELM affctd ara for both dnsity and tmpratur.. Typ I ELM Dynamics of High and Low Plasma Currnt ELM dynamics at high and low plasma currnt is invstigatd for th co-rotating plasmas. Figur 8 shows th typical wavform of low Ip plasma. Bcaus of low f ELM, bhavior of th pdstal dnsity is diffrnt from th high Ip cas. Th pdstal dnsity is not saturatd in som ELMs. Figur 9 shows th comparison btwn th low Ip(MA) and high Ip(.6MA) cass. Th pdstal structur is widr in th low Ip plasma as shown in Fig. 9. It suggst th Ip dpndnc of pdstal width, howvr, th pdstal width of th dnsity is also affctd by th pntrat lngth of th nutral particl. Sinc high dnsity pdstal has shortr pntrat lngth of nutrals, th pdstal width may b narrowr. Th dnsity loss fract profils ar obsrvd as shown in Fig. 9, suggsting th convctiv loss (~T n) dos not vary with plasma currnt or dnsity. T i pd is almost sam in both cass as shown in Fig. 9(c). Howvr, tmpratur loss fract profil of th low Ip cas is narrowr than th high Ip cas. Thrfor, th normalizd convctiv and conductiv loss fract has diffrnt dpndnc on plasma currnt. 5. Typ I ELM Dynamics of Ion Prssur In th pling-ballooning modl, th prssur gradint and rsultant dg currnt ar ky paramtr of triggring ELM. As obsrvd in Figs. and, th total and pdstal stord nrgy wr highr in th co-rotating plasma (W pd =.8MJ) than that in th ctr-rotating plasma (W pd =.8MJ), whil th hating powr was similar in both cass (P nt ~MW). Figur shows th rcovry of th prssur profil aftr th ELM crash valuatd by lctron dnsity and prssur assuming spatially uniform Z ff and including dominant impurity of carbon. Th larg W ELM obsrvd in th co-rotating plasma is charactrizd by th larg rduct in th pdstal prssur as obsrvd in Fig. and (c). Evolut of th P [kpa] 6 E98-Co t= -.5~ms t= ~.5ms t=.5~ms (c) P [kpa] 6 E99-Ctr t= -.5~ms t= ~.5ms t=.5~ms - P / r [kpa/m] R-Rsp [cm] (d) - P / r [kpa/m] R-Rsp [cm] Figur. Comparison of co- and ctr-rotating plasma at plasma currnt.6ma. Ion prssur profil in co-rotating plasma. th prssur gradint. (c) Ion prssur profil in co-rotating plasma. (d) th prssur gradint. Grn arrow is sam lngth in.

7 7 PD/P-6 prssur gradint indicats th fastr rcovry of co-rotating plasma as obsrvd in Fig. and (d). Th achivabl prssur gradint of th co-rotating plasma is largr than th ctr-rotating plasma. It suggsts th stability limit can vary with th toroidal rotat. Th rg of strong prssur gradint ovr kpa/m is cm widr in th co-rotating plasma. Sinc th dg currnt dpnds on th prssur gradint, th widr gradint profil rsult in th widr dg currnt profil. Thrfor, th ELM affctd ara of th co-rotating plasma may bcom widr according to th strongr and widr prssur gradint profil than th ctr-rotating plasma. A diffrnt radial profil of th most unstabl mod (pling-ballooning mod) du to th diffrnt prssur profil in th whol pdstal rg is a possibl xplanat of diffrnt ELM siz btwn co- and ctr-rotating plasmas. Tim volut of th prssur gradint is mainly dtrmind by th dnsity profil, which rcovrs quickly (~ ms) as shown in Fig. 5. Tim volut of th maximum prssur gradint toward th nxt ELM is shown in Fig.. In th low Ip co-rotating and high Ip ctr-rotating plasmas, th prssur gradint is not saturatd until th nxt ELM onst; it suggsts that th prssur gradint triggr ELM. On th othr hand, in th high Ip co-rotating plasmas, th saturat of th prssur gradint is unclar; both th prssur gradint and th dg currnt may play a rol for triggring th ELM crash. 6. Fast ELM dynamics of Grassy ELM Th small W ELM in grassy ELMs is charactrizd by th narrow radial affctd ara of th collaps of tmpratur pdstal [5]. Howvr, th loss fract of dnsity pdstal has not n [ 9 m - ] Div D [a.u] α.5 max(- P / r) [kpa/m] tim rlativ to ELM [ms] 8cm 6cm cm.5 cm cm cm tim rlativ to ELM [ms] (c) n [ 9 m - ] (d) - n /n ma Co.6MA Ctr MA Co Figur. Comparison of tim volut of th maximum prssur gradint at ach cas. t= -.5~ms (grassy) t=.5~ms (grassy) t= -~ms (Typ I) t= ~.5ms (Typ I) Grassy (Hz) Grassy (5Hz) Typ I (75Hz) R-Rsp [cm] Figur. Tim volut of dg dnsity at ach posit in grassy ELM phas of mixtur ELM. (Ip=.MA, q95=., δ=.5, f ELM =Hz, P B =9.MW) Dα miss intnsity from divrtor. (c) Comparison of dnsity profil with grassy and Typ I ELMs. (d) Comparison of dnsity loss fract profil with grassy (f ELM ~Hz and 5Hz) and Typ I (f ELM ~75Hz) ELMs.

8 8 PD/P-6 bn masurd. Th fast dynamics of th dnsity pdstal in grassy ELMs is masurd by LiBP for th first tim as shown in Fig.. Th dnsity pdstal structur is sam btwn Typ I and Grassy ELMs in sam plasma currnt. Evn for th low frquncy of Hz (larg amplitud) Grassy ELMs, th % of th pdstal dnsity is lost and its radial xtnt was smallr (5cm) than that in typ I ELMs (~cm), as shown in Fig. (d). Th collaps du to Grassy ELM of 5Hz is comparabl to th nois lvl as shown in Fig.(d). It suggsts th th dnsity loss fract dpnds on th frquncy in cas of Grassy ELM. Sinc th tmpratur loss fract of grassy ELM is smallr than typ I ELM, it is confirmd that both conductiv and convctiv ELM losss du to Grassy ELM ar small. Th collaps of dnsity pdstal is localizd nar th sparatrix, suggsting localizd ign funct at th dg rg. 7. Conclus Fast dynamics of Typ I and grassy ELMs ar invstigatd using nwly dvlopd diagnostics. Th bhavior of pdstal dnsity and tmpratur, thus prssur profil ar obsrvd for th first tim. It is confirmd that th lost pdstal dnsity is compnsatd by cor dnsity aftr ELM crash. In comparison with co- and ctr-rotats, ELM affctd of co-rotating plasmas is largr and widr than ctr-rotating plasmas. Th prssur and th gradint ar highr in co-rotating plasmas. Morovr, th prssur gradint is larg and th radial xtnt of th gradint is widr than ctr-rotating plasmas. It may caus th widr radial ign funct of most unstabl mod, and thn, th ELM affctd ara may bcom larg. In comparison with high and low Ip plasmas, th dnsity loss fract is similar; howvr, th tmpratur loss fract of low Ip plasma is smallr than high Ip plasma. Thrfor, th componnt of convct and conduct in normalizd ELM nrgy loss has diffrnt dpndnc on plasma currnt. Th dynamics of dg dnsity during grassy ELM is obsrvd for th first tim. It is found th dnsity loss fract is lss than % and th radial xtnt is narrowr than Typ I ELM. Thrfor, th convctiv and conductiv loss of grassy ELM is much smallr than Typ I ELM, and th frquncy dpndnc of th dnsity loss fract is suggstd. Acknowldgmnt Th authors ar much indbtd to JT-6 tam for thir support. This rsarch was partly supportd by th Grant-in-Aid for Young Scintists (B) 9766, th Grant-in-Aid for Young Scintists (A) and th Grant-in-Aid for Scintific Rsarch (S) 76 Japan Socity for th Promot of Scinc. Rfrncs [] K. Kamiya, t al., Plasma Phys. Control. Fus 8 5A (6) A [] H. Urano, t al., Plasma Phys. Control. Fus 8 5A (6) A9 [] H. Urano, t al., Nucl. Fus 7 (7) 76. [] N. Oyama, t al., Nucl. Fus () 58. [5] N. Oyama, t al., Nucl. Fus 5 (5) 87.