Fusion product losses due to fishbone instabilities in deuterium JET plasmas

LETTER Fusion p oduc losses due o ishbone ins abili ies in deu e ium JET plasmas To ci e his a icle: V.G. Kip ily e al 2018 Nucl. Fusion 58 014003 View he a icle online o upda es and enhancemen s. Rela ed con en MeV- ange as ion losses induced by ishbones on JET C. Pe ez on Thun, A. Pe ona, T. Johnson e al. - Recen p og ess in as ion s udies on JET V.G. Kip ily, C.P. Pe ez on Thun, S.D. Pinches e al. - Ene ge ic pa icle physics in usion esea ch in p epa a ion o bu ning plasma expe imen s N.N. Go elenko , S.D. Pinches and K. Toi - Recen ci a ions Syn he ic diagnos ic o he JET scin illa o p obe los alpha measu emen s J. Va je e al - Full-o bi and d i calcula ions o usion p oduc losses due o explosi e ishbones on JET M. Fi zge ald e al - JET diagnos ic enhancemen s es ing and commissioning in p epa a ion o DT scien i ic campaigns J. Figuei edo e al - This con en was downloaded om IP add ess 87.218.223.151 on 21/07/2020 a 11:43 1 © EURATOM 2017 P in ed in he UK Nuclea Fusion V.G. Kip ily e al P in ed in he UK 014003 NUFUAU © EURATOM 2017 58 Nucl. Fusion NF 10.1088/1741-4326/aa9340 1 Nuclea Fusion Fusion p oduc losses due o ishbone ins abili ies in deu e ium JET plasmas V.G.Kip ily1, M.Fi zge ald1, V.Golobo odko2, S.E.Sha apo 1, C.D.Challis1, D.F igione3, J.G a es4, M.J.Man sinen5,6, P.Beaumon 1, M.Ga cia- Munoz7, C.Pe ez on Thun8,9, J.F.R.Rod iguez7, D.Da ow10,a, D.Keeling1, D.King1, K.G.McClemen s1, E.R.Solano11, S.Schmuck1, G.Sips12, G.Szepesi1 and JET Con ibu o sb 1 Culham Cen e o Fusion Ene gy, UKAEA, Culham Science Cen e, Abingdon, OX14 3DB, Uni ed Kingdom 2 OEAW, Ins i u e o Theo e ical Physics, Uni e si y o Innsb uck, Innsb uck, Aus ia 3 Uni à Tecnica Fusione, ENEA C. R. F asca i, ia E. Fe mi 45, 00044 F asca i (Roma), I aly 4 Ecole Poly echnique Fédé ale de Lausanne, Swiss Plasma Cen e , CH-1015 Lausanne, Swi ze land 5 Ba celona Supe compu ing Cen e , Ba celona, Spain 6 ICREA, Pg. Liuis Companys 23, 08010 Ba celona, Spain 7 Facul y o Physics, FAMN Depa men , Uni e si y o Se ille, 41012 Se ille, Spain 8 EURO usion P og amme Managemen Uni , Culham Science Cen e, Culham, OX14 3DB, Uni ed Kingdom 9 Fo schungszen um Jülich GmbH, Ins i u ü Ene gie-und Klima o schung—Plasmaphysik, 52425 Jülich, Ge many 10 P ince on Plasma Physics Labo a o y, P ince on, NJ 08543, Uni ed S a es o Ame ica 11 Labo a o io Nacional de Fusión, CIEMAT, Mad id, Spain 12 Eu opean Commission, B-1049 B ussels, Belgium E-mail: [email p o ec ed] Recei ed 20 July 2017, e ised 9 Oc obe 2017 Accep ed o publica ion 13 Oc obe 2017 Published 8 No embe 2017 Abs ac Du ing de elopmen o a high-pe o mance hyb id scena io o u u e deu e ium– i ium expe imen s on he Join Eu opean To us, an inc eased le el o as ion losses in he MeV ene gy ange was obse ed du ing he ins abili y o high- equency n = 1 ishbones. The ishbones a e exci ed du ing deu e ium neu al beam injec ion combined wi h ion cyclo on hea ing. The equency ange o he ishbones, 10–25 kHz, indica es ha hey a e d i en by a esonan in e ac ion wi h he NBI-p oduced deu e ium beam ions in he ene gy ange ⩽120 keV. The as pa icle losses in a much highe ene gy ange a e measu ed wi h a as ion loss de ec o , and he da a show an expulsion o deu e ium plasma usion p oduc s, 1 MeV i ons and 3 MeV p o ons, du ing he ishbone bu s s. An MHD mode analysis wi h he MISHKA code combined wi h he nonlinea wa e-pa icle in e ac ion code HAGIS shows ha he loss o o oidal symme y caused by he n = 1 ishbones a ec s s ongly he con inemen o non- esonan high ene gy usion-bo n i ons and p o ons by pe u bing hei o bi s and expelling hem. This modelling is in a good ag eemen wi h he expe imen al da a. Keywo ds: okamak, usion p oduc s, MHD (Some igu esmay appea in colou only in he online jou nal) Le e IOP In e na ional A omic Ene gy Agency a Now deceased. b See he au ho lis o [20]. 2018 1741-4326 1741-4326/18/014003+6$33.00 h ps://doi.o g/10.1088/1741-4326/aa9340 Nucl. Fusion 58 (2018) 014003 (6pp) 2 V.G. Kip ily e al Fusion eac ions as well as addi ional hea ing o usion-g ade okamak plasmas gene a e la ge numbe s o as ions in he plasma co e ha can in e ac wi h he magne o-hyd o-dynamic (MHD) pe u ba ions o he plasma discha ge. The MHD ins abili ies can ejec usion p oduc s (FP), in pa icula alpha- pa icles, which a e he p incipal sou ce o plasma hea ing in bu ning deu e ium– i ium (D–T) plasmas. The in e ac ions be ween MHD pe u ba ions and alpha-pa icles could be esonan i he alpha-pa icles a e in esonance wi h high- equency wa es, e.g. To oidal Al én Eigenmodes (TAE) o non- esonan , when MHD pe u ba ions a e d i en by he - mal plasma o as pa icles o he han he alpha-pa icles. Bo h esonan and non- esonan in e ac ions be ween alpha- pa icles and MHD pe u ba ions could lead o he pa icle edis ibu ion and losses [1] hus a ec ing he usion plasma Q = Pou /Pin and he i s wall. The de elopmen o high usion pe o mance scena ios, bo h ‘baseline’ saw oo hing H-mode wi h sa e y ac o a he magne ic axis q0 ⩽ 1 and he so-called ‘hyb id’ wi h q0 ⩾ 1, o he o hcoming high-powe D–T expe imen s was a main p io i y o ecen deu e ium and hyd ogen expe imen al cam- paigns on he Join Eu opean To us (JET) wi h ITER-like wall. In he hyb id scena io wi h a low magne ic shea in he plasma cen e [2], he saw oo h oscilla ions a e almos always a oided bu a s ong beam ion p essu e d i es ishbones (FB) wi h o oidal mode numbe n = 1, an ins abili y wi h bu s ing ampli ude and sweeping equency in he ange ≈10–25 kHz. The ishbones occu in plasmas wi h high-βpoloidal ( a io o plasma p essu e o poloidal magne ic ield p essu e) and hey a e des abilized by ene ge ic ions p oduced om pe pend- icula and angen ial neu al beam injec ion [3, 4], which in he case o JET expe imen s had p ima y ene gies 90 keV and 110 keV. As i has been shown [5, 6], apped and ci cula - ing beam ions can esona e wi h ishbone pe u ba ion, he co e-localised m = 1/n = 1 mode. In JET and o he oka maks wi h usion eac i i y domina ed by beam-plasma usion eac- ions, neu on a e d ops up o 10% we e obse ed and linked o he esonan in e ac ion be ween he beam ions and ish- bones [7, 8]. In addi ion o he well-unde s ood esonan in e ac ion desc ibed in [5–8], he p esence o ishbones also a ec s sig- ni ican ly he con inemen o non- esonan ions in he MeV ene gy ange. These ions a e p, and 3He p oduced in he deu- e ium plasma due o he ollowing usion eac ions: D + D = p (3 MeV) + (1 MeV) D + D = n (2.5 MeV) + 3He (0.82 MeV). Du ing he ishbone pe iods, a ‘bu n-up’ o i ons and 3He was educed. The educ ion o he bu n-up was measu ed ia 14.1 MeV neu ons p oduced in he D( , n)4He usion eac ion and 14.7 MeV p o ons gene a ed in ano he usion eac ion D(3He, p)4He. The anomalously low bu n-up a e du ing ishbones has been explained by p omp and non- p omp losses o MeV-pa icles [9–11]. Howe e , a pa o he non-p omp losses, e.g. slow i ons, could be due o he eso- nan mechanism o in e ac ion wi h ishbones ( he c oss-sec- ion has a maximum a E ≈ 160 keV), as i was obse ed wi h he esonan beam pa icles. An ea ly s udy o usion p oduc losses ia he 3He bu n-up measu emen s ( he c oss-sec ion has a maximum a E 3 He ≈ 650 keV) was made on okamak PDX [10]. In spi e o he small size o he machine (a low a e o he D(3He, p)4He eac ion), i was possible o iden i y he non- esonan cha ac e o he 3He losses, and d aw a conclu- sion on he possible applicabili y o he loss mechanism o igni ion expe imen s. A non- esonan loss mechanism due o high ampli ude ishbones causing a dis o ion o he o oidal symme y wi h he m = 1/n = 1 pe u ba ion, was p edic ed o non- esonan alphas in bu ning plasmas in [12]. Expe imen ally, such non- esonan losses o as ions in he MeV ene gy ange caused by he ishbones d i en by he beam deu e ons wi h ene gy 80–100 keV we e obse ed in JET discha ges wi h ion cyclo- on ange o equencies (ICRF) hea ing [13]. The high ene gy pa icles ejec ed om he plasma du ing he FB oscilla ions we e iden i ied as H-ions accele a ed du ing ICRH. The losses we e enhanced by abou a ac o o ≈10–20 wi h espec o Figu e 1. Wa e o ms o he deu e ium plasma discha ge #92394 a BT(0) = 2.8 T, IP = 2.2 MA wi h 26 MW deu e ium NBI and 5 MW hyd ogen 1s ha monic ICRH a ICRH = 42.5 MHz. Losses eco ded wi h FILD PMTs co ela e wi h ishbones exci ed du ing pe iod indica ed by shaded a ea. Figu e 2. Fishbones wi h o oidal mode numbe n = 1 de ec ed wi h Mi no coils in he JET discha ge #92394. Nucl. Fusion 58 (2018) 014003 3 V.G. Kip ily e al he MHD-quiescen le els, and he magni ude o he losses was ound o inc ease quad a ically wi h he FB ampli ude. In his Le e , we epo on di ec ly measu ed non- esonan losses o usion p o ons and i ons in high pe o mance expe - imen s wi h hyb id plasmas. The ishbones we e obse ed o igge saw oo h-like econnec ion e en s and neoclassical ea ing modes (NTM), he la e subs an ially educing he plasma pe o mance. JET is equipped well o he s udies o con ined and escaped as ions [14]. The los ion measu emen s a e ca ied ou wi h a scin illa o p obe [15], which is called ‘ as ion loss de ec o ’, o FILD. FILD is loca ed abou 28 cm below he mid-plane o he o us, jus ou side he plasma and p o ides in o ma ion on he los ion pi ch angle, θ = cos−1  /  , wi h 5% esolu ion in he ange 35°–85° and gy o- adius be ween 3 cm and 14 cm wi h 15% esolu ion ( o 12 cm gy o- adius ~2 cm). The ligh emi ed by he scin illa o (decay ime ~0.5 µs) du ing an ion collision, is ans e ed h ough a cohe en ib e bundle o a cha ge-coupled de ice (CCD) came a and a pho omul iplie ube (PMT) 4 × 4 a ay. The 128 × 256 pixel CCD came a can p o ide 20 kHz snapsho s o ligh emission on he pi ch- angle—gy o- adius g id calcula ed wi h he E ipDesign code [16]. The FILD has ecen ly been upg aded, so he as PMT signals a e digi ised by 2 MHz hus allowing a loss spec o- g am o be made wi h he MHz bandwid h. Such loss spec- og ams could be hen compa ed o magne ic spec og ams showing he MHD pe u ba ions. In he hyb id scena io expe imen s, wi h plasma cu en s in he ange IP = 2.0–2.4 MA a cen al o oidal ield BT(0) = 2.8 T, deu e ium neu al beam injec ion (NBI) and H-mino i y hea ing o deu e ium plasmas wi h ICRF a = ω/(2π) ≈ 42.5 MHz o dipole phasing wi h hyd ogen concen a ion nH/ (nH + nD) ≈ 1–3% we e used. Fishbones we e obse ed in discha ges wi h no malized poloidal be a βN > 1.9, how- e e no all o hem led o he FP losses. A ypical example o a discha ge wi h as ion losses du ing pe iod o s ong FB ins abili ies is shown in igu e1. The MHD ins abili y in his discha ge has been iden i ied as n = 1 ishbones by means o a compa ison o he signal phase in o oidally-sepa a ed Mi no coils. The esul o he mode analysis is p esen ed on igu e2. An example o losses measu ed wi h he FILD in discha ge #92394 is shown in he gy o- adius (Rgy ) e sus he pi ch- angle g id in igu e3(a). This is a ypical usion p oduc i s o bi (FO) loss oo p in eco ded wi h CCD came a in he FB- ee pe iod 7.843 s–7.860 s jus be o e a ishbone. I is clea ly seen ha he maxima o losses a e localised along he gy o- adius ( ed dash line), co esponding o he FP bi h ene - gies, 1 MeV o i ons and 3 MeV o p o ons. P omp ICRH losses, H-ions and D-NBI ions accele a ed a ω = ωcH = 2ωcD, would be expec ed o occu along he ed solid line, co e- sponding o he IC esonance laye in he plasma, bu such losses appea o be a he low. The image o losses eco ded du ing he ishbone pe iod 7.860 s–7.877 s is p esen ed in igu e3(b). This image was ob ained by a sub ac ion o he signal eco ded du ing he p e ious no ishbone ime bin shown in igu e3(a). I is impo an o no e ha he loss ion image ob ained by he sub ac ion o he signal eco ded a e he FB pe iod, 7.877 s–7.893 s, is indis inguishable om he one shown in igu e3(b). One can see ha he losses ela ed o he FB ins abili y a e localised along he ed do line, which is a sepa a ix be ween apped and ci cula ing o bi s in he phase space. This indica es ha he ishbone pe u ba ion causes losses by pushing co e-localised usion p oduc s wi h con ined passing o bi s o a phase space a ea co esponding o he uncon ined apped o bi s. The FILD da a analysis shows ha in he FB pe iod he usion i ons and p o on p omp losses a e localised a he pi ch-angle θ ~ 55° and he gy o- adius RG ~ 11 cm ha is ela ed o a maximal signal. The gy o- adius dis ibu ion associa ed wi h he ene gy dis ibu ion has oughly he same Figu e 3. Foo p in s o losses in he discha ge #92394 eco ded wi h CCD came a: (a) in he pe iod 7.843 s–7.860 s be o e a ishbone; ed solid line—a posi ion o he IC esonance on he gy o- adius e sus pi ch-angle g id; ed dash line—gy o- adius ela ed o usion p oduc s: 1 MeV i ons and 3 MeV p o ons; (b) du ing he ishbone pe iod 7.860 s–7.877 s ob ained by sub ac ion o he signal in p e ious ime bin (see (a)); he ed do line ela ed o a sepa a ix be ween apped and ci cula ing o bi s in he phase space; he whi e a eas show ields o iew by PMT #6, #10 and #14. Nucl. Fusion 58 (2018) 014003 4 V.G. Kip ily e al shape as dis ibu ions be o e and a e his pe iod (al hough he o al losses a e highe ); o i ons, he maximum o he losses is a E ~ 1 MeV, o p o ons a Ep ~ 3 MeV. Howe e , he pi ch-angle dis ibu ion o he p omp losses du ing he ishbone is sligh ly shi ed ela i e o he FB- ee dis ibu- ions, om θ ~ 57° o ~55°. Assuming he losses a e o he pa icles wi h apped o bi s, i is impo an o no e ha he majo adius a he bounce e lec ion poin o hese pa icles and he pi ch-angle alue on he scin illa o pla e a e ela ed by R(θ) = RFILD[1 − cos2(θ)], whe e RFILD is adial posi ion o he scin illa o . As can be seen om he di e en ial loss oo p in in igu e3(b), pa icles escaped du ing he FB pe iod a e mos ly coming om he plasma egion nea 55° ela ed o R(55°) = 2.45 m. A back-in- ime FP o bi calcula ion s a - ing om he FILD scin illa o pla e ( igu e 4(a)) shows ha bounce poin s o hese pa icles a e close o he apped/passing Figu e 4. (a) o bi s o i ons/p o ons wi h gy o- adii 8, 10 and 12 cm and pi ch-angle 55° calcula ed back in ime om he FILD scin illa o pla e; hese pa ame e s a e ela ed o he oo p in p esen ed in igu e3(b); black dash line—a posi ion o he IC esonance ω = ωcH; (b) o bi s o H-ions wi h gy o- adii 8, 10 and 12 cm and pi ch-angle 63° (posi ion o he IC esonance on he g id in igu e3) calcula ed back in ime om he FILD scin illa o pla e. Figu e 5. HAGIS calcula ion showing he egion o cons an s-o - mo ion space (Λ, ZR=Rmag , E) in which 3.0 MeV coun e s eaming p o ons unde go o bi opology changes as a esul o hei in e ac ion wi h an ideal MHD n = 1 in e nal kink mode. The ed poin s co espond o los pa icles and he yellow poin s o apped pa icles, which emain con ined. Figu e 6. HAGIS calcula ion o pe u bed p o on o bi s due o he assumed ideal in e nal kink mode. The o bi s a e chosen o co espond o hose ound nea he mode-induced loss egion o phase space gi en in igu e9, wi h he same colou ing classi ica ion. The backg ound shows he s uc u e o he in e nal kink mode elec os a ic po en ial. Nucl. Fusion 58 (2018) 014003 5 V.G. Kip ily e al bounda y in he mid-plane a ~2.45 m. Howe e , he o bi s o H-ions accele a ed by ICRH, calcula ed wi h pi ch-angle θ ~ 63° a e apped and hei u ning poin s a e on he IC eso- nance laye a R ≈ 2.97 m ( igu e 4(b)). These calcula ions gi e us a p oo ha ions escaped om he plasma du ing he ishbone pe iod a e mos ly usion p oduc s. An n = 1 ideal in e nal kink mode was ound wi h he MISHKA-1 code [17] o a JET equilib ium econs uc ion ob ained wi h EFIT [18]. The HAGIS [19] code was used o compu e he usion p oduc d i o bi s assuming he EFIT equilib ium, and he d i o bi changes we e compu ed assuming he MISHKA-1 solu ion ( ull de ails o hese calcul- a ions will be he subjec o a ollowing publica ion). The la ges losses a e p edic ed o pa icles nea he bounda y be ween apped and coun e passing los o bi s. The esul s a e shown in igu e5, whe e Z R=Rmag deno es he Z pa icle loca ion in he uppe midplane whe e i c osses R = Rmag. This is used in place o he canonical momen um Pϕ. The h ee cons an s o mo ion used in he plo s a e Z (canonical momen um), Λ (magne ic momen ) and ene gy E. The plo s a e a ixed E co esponding o he p o on bi h ene gy igno - ing he mal sp ead. One can see ha he lack o pa icles a he pa ame e Λ = 1 (Λ ≡ µmB(Rmag)/E = B(Rmag)[1 − cos2θ]/B) ela ed o on-axis apped o bi s o H- and D-beam ions accel- e a ed by ICRH is consis en wi h he oo p in in igu e3(b). Figu e 6 gi es an illus a ion o he o bi ypes, whe e he g ea es p omp usion p oduc losses a e p edic ed o occu . The coun e a elling usion p oduc o bi s nea he apped/ passing/los iple-poin c oss he in e nal kink mode. So, he ishbone is p oducing a adial con ec ion o hese non- eso- nan usion p o ons in o loss egions. I is impo an o emphasise ha he D–D neu on a e was no a ec ed by he n = 1 MHD ac i i y ela ed o he ish- bones al hough Te(0) d ops ~5%, which looks like saw ee h. Howe e , his Te d op is no so as (~3–5 ms) as in a ypical saw ee h (<1 ms). In igu e7 one can see ha he no malised neu on a e ollows he con inuous losses ela ed o p omp losses o usion p oduc s and he e a e no e iden d ops o he a e du ing he loss spikes. So, despi e he ishbones being d i en by a esonan in e ac ion wi h NBI ions, hey do no appea o a ec signi ican ly he D-beam ion con inemen , since no changes in he neu on a e a e appa en . Also, i is likely some loss o H-mino i y ions ha canno be clea ly iden i ied wi h FILD is esponsible o he ela i ely g adual d op in Te. The FP loss signals ela ed o PMT #6, #10 and #14, whose ields o iew a eas a e shown in igu e3(b) as whi e ec angles a e oughly p opo ional o he FB oscilla ion ampli ude ( igu e 8). Howe e , a compa ison wi h he MeV H-ion loss indings ob ained by au ho s in [13], in pa icula Figu e 7. Fishbones lead o Te d ops in he plasma cen e like saw ee h; neu on a e no malised o FILD losses du ing ishbone- ee pe iod is no a ec ed by ishbones. Figu e 8. The i s ishbone in he discha ge (see igu e7): loss signals eco ded wi h PMT #6, #10 and #14 (see igu e3(b)) d op a he same ime as he ishbone ampli ude. Figu e 9. Fou ie spec og ams o an in- essel magne ic pickup coil wi h bu s ing ishbones and he FILD loss spec og am ha cohe en o he ishbones in PMT #10 (see igu e3(b)). Nucl. Fusion 58 (2018) 014003 6 V.G. Kip ily e al he quad a ic inc ease wi h he FB ampli ude, is no possi- ble in his case; an accu a e dependence o he FP loss e sus he FB ampli ude canno be de e mined because mos o he magne ic signals we e sa u a ed. One can see ha he highes loss signals we e eco ded wi h PMT #10 and #14 and hey a e ele an o he p omp i on/p o ons losses. The measu ed losses a e cohe en o m = 1/n = 1 FB oscilla ions ha can be clea ly seen by compa ing magne ic and FILD-PMT spec o- g ams shown in igu e9. This is ye u he e idence o obse - a ion o usion p oduc s loss induced by ishbones in he JET deu e ium hyb id plasma. The expe imen al obse a ion and modelling o he non- esonan losses o usion p oduc s caused by low- equency ishbones a e con i ming he loss mechanism p oposed in [12]. This e ec could be impo an o usion alpha-pa icles in bu ning plasma scena ios wi h ishbones e.g. hyb ids. 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