Beam ion losses due to energetic particle geodesic acoustic modes

PAPER Beam ion losses due o ene ge ic pa icle geodesic acous ic modes To ci e his a icle: R.K. Fishe e al 2012 Nucl. Fusion 52 123015 View he a icle online o upda es and enhancemen s. Rela ed con en Con ec i e beam ion losses due o Al én eigenmodes in DIII-D e e sed-shea plasmas - P omp non- esonan neu al beam-ion loss induced by Al én eigenmodes in he DIII-D okamak - Measu emen s o as -ion losses induced by MHD ins abili ies using a scin illa o - based p obe in he HL-2A okamak* - Recen ci a ions Anomalous losses o ene ge ic pa icles in he p esence o an oscilla ing adial elec ic ield in usion plasmas Da id Za zoso and Diego del-Cas illo- Neg e e - Simula ion o ene ge ic pa icle d i en geodesic acous ic modes and he ene gy channeling in he La ge Helical De ice plasmas Hao Wang e al - Chi ping and Sudden Exci a ion o Ene ge ic-Pa icle-D i en Geodesic Acous ic Modes in a La ge Helical De ice Expe imen Hao Wang e al - This con en was downloaded om IP add ess 87.218.223.151 on 17/08/2020 a 20:47 IOP PUBLISHING and INTERNATIONAL ATOMIC ENERGY AGENCY NUCLEAR FUSION Nucl. Fusion 52 (2012) 123015 (5pp) doi:10.1088/0029-5515/52/12/123015 Beam ion losses due o ene ge ic pa icle geodesic acous ic modes R.K. Fishe 1, D.C. Pace1, G.J. K ame 2, M.A. Van Zeeland1, R. Nazikian2, W.W. Heidb ink3and M. Ga c´ ıa-Mu˜ noz4 1Gene al A omics, PO Box 85608, San Diego, CA 92186-9784, USA 2P ince on Plasma Physics Labo a o y, PO Box 451, P ince on, NJ 08543-0451, USA 3Uni e si y o Cali o nia-I ine, I ine, CA 92697, USA 4Max Planck-Ins i u ¨ u Plasmaphysik, Ga ching, Ge many Recei ed 24 May 2012, accep ed o publica ion 31 Oc obe 2012 Published 20 No embe 2012 Online a s acks.iop.o g/NF/52/123015 Abs ac We epo he i s expe imen al obse a ions o as -ion loss in a okamak due o ene ge ic pa icle d i en geodesic acous ic modes (EGAMs). A as -ion loss de ec o ins alled on he DIII-D okamak obse es bu s s o beam ion losses cohe en wi h he EGAM equency. The EGAM ac i i y esul s in a signi ican loss o beam ions, compa able o he i s o bi losses. The pi ch angles and ene gies o he measu ed as -ion losses ag ee wi h p edic ions om a ull o bi simula ion code SPIRAL, which includes sca e ing and slowing-down. (Some igu es may appea in colou only in he online jou nal) 1. In oduc ion Fas ions om neu al beam injec ion, ion cyclo on hea ing, and usion eac ions play a undamen al ole in he hea ing and s abili y o okamak plasmas. La ge as -ion densi ies can d i e collec i e ins abili ies, which in u n deg ade as - ion con inemen and plasma pe o mance. Losses o ene ge ic alpha pa icles om DT usion in ITER will educe he alpha hea ing a ailable o each igni ion, and ha e he po en ial o cause majo damage o he i s wall. Hence he beha iou o as ions and hei in e ac ion wi h plasma ins abili ies in usion plasmas has been ex ensi ely s udied [1,2], mo i a ed by he undamen al impo ance o alpha pa icle hea ing in DT plasmas [3–5]. Ene ge ic pa icle d i en geodesic acous ic modes (EGAMs) occu ea ly in he amp-up o he plasma cu en in he DIII-D okamak du ing coun e neu al beam injec ion [6]. EGAMs a e ene ge ic pa icle modes wi h a mode equency ∼50% below he ideal geodesic acous ic mode (GAM) equency. A luid-kine ic model [7] quali a i ely eplica es he obse ed mode cha ac e is ics, including apid mode bu s ing and equency chi ping, and la ge elec on densi y luc ua ions wi hou de ec able elec on empe a u e luc ua ions. The nonpe u ba i e elec os a ic model shows he ene ge ic pa icle p essu e d i es an n=0 adial elec ic ield and a GAM-like m=1 densi y pe u ba ion. The modes occu in plasmas wi h an ele a ed cen al sa e y ac o (qmin ⩾2)and wi h compa able elec on and ion empe a u es, ele an o p oposed s eady-s a e plasma egimes [2]. Sha p d ops (∼10–15%) in he neu on p oduc ion a e indica i e o s ong beam ion edis ibu ion and/o loss [6]. This pape concen a es on he obse a ion o beam ion losses due o he EGAM mode ac i i y. A scin illa o -based as -ion loss de ec o (FILD) [8] has ecen ly been ins alled on DIII-D ( o oidal magne ic ield =2.1 T, majo adius =1.66 m, and mino adius = 0.67 m) o s udy ene ge ic ion losses induced by Al ´ en eigenmodes (AEs) and o he MHD ins abili ies. Based on he design used on ASDEX Upg ade [9,10], he ligh pa e n esul ing om ions s iking a as ime esponse (decay ime ∼500 ns) scin illa o is imaged by a CCD came a, allowing measu emen s o he pi ch angle and gy o adius o he beam ions eaching he de ec o . Ligh om he scin illa o is also measu ed by a ib e-coupled pho omul iplie o allow iden i ica ion o AE and o he high equency ins abili ies. This pape epo s he i s expe imen al obse a ions o beam ion losses in a okamak due o EGAMs. The measu ed losses a e compa ed o he esul s o a ull o bi simula ion code SPIRAL o be e unde s and he beam ion anspo esul ing om in e ac ions be ween he modes and con ined ions. The EGAM-ion in e ac ion occu s only in ene gy space, compa ed o he AE-ion in e ac ion ha in ol es he ene gy, canonical momen um, and magne ic momen o he ions. The EGAM- ion in e ac ion is p ima ily elec os a ic, wi h he n=0 na u e o he EGAM leading o changes only in he ion ene gy (compa ed o AE-ion in e ac ions ha a ec bo h ion ene gy and canonical momen um), hus p o iding a undamen al es o ou abili y o model he impac o MHD ins abili ies on ene ge ic ions [11]. 0029-5515/12/123015+05$33.00 1© 2012 IAEA, Vienna P in ed in he UK & he USA Nucl. Fusion 52 (2012) 123015 R.K. Fishe e al Time (ms) log( au opowe ) (au) Ip (MA) FILD PMT (V) 210L 210R (a) Sho 142111 (b) (c) 800600400200 F equency (kHz) 0.001 0.200 FILD Au opowe EGAM Al én Eigenmodes 1.2 1.0 0.8 0.6 0.4 0.2 0.0 4 3 2 1 0 120 100 80 60 40 20 0 Figu e 1. Time dependence o (a) neu al beam injec ion om 210R (shown in ed and pulsed) and 210L (shown in blue and on con inuously om 300 ms o 1000 ms) ion sou ces, (b) beam ion loss measu ed by FILD PMT and (c) ime- esol ed powe spec um o he beam ion loss signal showing s ong EGAM ac i i y a ∼15–45 kHz occu ing e y ea ly a e he s a o he beam injec ion. 2. Measu ed EGAM-induced beam ion losses Neu al beam injec ion coun e o he di ec ion o he plasma cu en ea ly in he amp-up o he plasma cu en in DIII-D s ongly exci es EGAMs. Figu e 1is an example o a DIII-D discha ge wi h signi ican AE and EGAM ac i i y. Deu e ium beams (labelled 210L and 210R) injec 75–81 keV neu als in he o oidal di ec ion opposi e he plasma cu en and a e he p ima y beams esponsible o exci ing he EGAMs. The 210L beam is injec ed mo e pe pendicula o he o oidal magne ic ield han he 210R beam [12]. Figu e 1(a) shows ha he 210L beam sou ce is on con inuously om 300 o 1000 ms, while he 210R sou ce is pulsed o 10 ms on and 20 ms o , s a ing a 320 ms. Figu e 1(b) shows he beam ion loss signal measu ed by he FILD scin illa o de ec o , while igu e 1(c) shows he powe spec um o he as -ion losses wi h o oidal Al ´ en eigenmode (TAE), e e se shea Al ´ en eigenmode (RSAE) and EGAM ac i i y. The pulsed losses in phase wi h he 210R beam injec ion include bo h p omp losses and ins abili y-induced losses. O bi modelling shows ha he p omp -loss con ibu ion om he 210R beam eaches he FILD de ec o (loca ed app oxima ely 45◦below he ou e midplane) a lowe alues o he plasma cu en . As he plasma cu en inc eases, he ene ge ic ion banana wid hs dec ease, esul ing in wall s ike posi ions ha a e o he midplane and no longe de ec able by he FILD (a e ∼600 ms). The losses cohe en wi h AE ac i i y in he 50–100 kHz egion [13,14] all as he plasma cu en inc eases since he AE ac i i y becomes mo e co e localized while he as -ion loss bounda ies a e mo ing ou wa d, educing he abili y o he AEs o place beam ions di ec ly on o loss o bi s. This pape concen a es on he EGAM ac i i y be ween 15 and 45 kHz ha domina es he losses e y ea ly ( om 300 o 350 ms) in he discha ge, when he ene ge ic pa icle p essu e is a signi ican ac ion o he o al plasma p essu e. The low plasma cu en a his ime esul s in an ele a ed qmin, allowing he modes o a ise wi hou subs an ial he mal ion Landau damping and leading o a low as -ion be a βh h eshold o he EGAM mode onse [6]. Figu e 2shows an expanded iew o he 300–450 ms ime pe iod when he EGAM ac i i y is la ges . The ime- esol ed equencyanalysiso an ex e nalmagne ic pickup coilisshown in igu e 2(a). Figu e 2(b) shows ha he EGAM ampli ude measu ed by an ex e nal magne ic ield pickup coil (blue ace), and he cohe en componen o he FILD measu ed beam ion loss signal ( ed ace). Bo h signals a e calcula ed based on an ∼2 kHz band cen ed on he ime- a ying EGAM equency. The cohe en beam ion loss peaks sho ly a e beam injec ion s a s a 300 ms, and hen decays apidly, while he mode ampli ude indica ed by he magne ic pickup coil decays mo e slowly. The cohe en componen o he FILD loss signal also clea ly co ela es wi h he pulsed ime beha iou o he 210R beam sou ce. The measu ed cohe en loss shows bo h a ‘ apid’ signal ha occu s in phase wi h he 210R beam injec ion, and a ‘delayed’ componen ha decays o e se e al milliseconds a e he 210R beam u ns o . This decay ime is a longe han he calcula ed <100 µs ansi ime o ions kicked on o a di ec loss o bi , indica ing ha he measu ed EGAM-induced losses a e he esul o esonances ins ead o a simple modula ion o he neu al beam p omp loss. Once he 210R sou ce u ns o , he ene gy o he emaining con ined beam ions decays on he classical slowing-down ime scale. This educes he numbe o beam ions capable o in e ac ing wi h he EGAMs, and is hough o lead o he obse ed decay in he cohe en loss signal a e each 210R beam pulse. On a slowe ime scale, he inc ease in plasma cu en wi h ime mo es he loss bounda y o highe ene gies whe e he e a e ewe beam ions o in e ac wi h he EGAMs. This e ec , combined wi h he mode ampli ude educ ion, is quali a i ely consis en wi h he d op in he obse ed cohe en losses be ween 325 and 425 ms. The bu s ing beha iou cha ac e is ic o EGAMS is clea ly isible when he measu ed as -ion loss signal is iewed on an expanded ime scale, as shown in igu e 3(a). The 2 Nucl. Fusion 52 (2012) 123015 R.K. Fishe e al 300 350 400 Time (ms) 0.0 0.2 0.4 0.6 0.8 1.0 Ampli ude (au) FILD Loss a EGAM dB/d a EGAM 210R Beam Sho 142111 300 350 400 Time (ms) 10 15 20 25 30 35 40 (kHz) -1.4 -1.2 -1.0 -0.8 Log (c oss-powe )1/2 (au) -0.6 -0.4 -0.2 0.0 Magne ics (a) (b) Figu e 2. (a) Time- esol ed powe spec um om an ex e nal magne ic pickup coil showing EGAM mode ac i i y, and (b) ime beha iou o he EGAM ac i i y om he ex e nal magne ic pickup coil (blue ace) and he FILD measu ed beam ion loss ( ed ace). Bo h signals a e he bandwid h il e ed esponse in an ∼2 kHz band cen ed on he ime- a ying EGAM mode equency. Also shown is he pulsed neu al beam injec ion om he 210R ion sou ce (black ace). cohe en oscilla ions a he EGAM mode equency ∼15 kHz a e a signi ican ac ion o he o al loss signal. A 320 ms, he addi ional coun e injec ion due o he 210R beam inc eases he measu ed losses. Figu e 3(b) shows consecu i e ames om he CCD came a imaging he ligh pa e n c ea ed by beam ion losses s iking he FILD scin illa o pla e. A g id indica ing he gy o adius and pi ch angle o he impac ing ions is o e plo ed in whi e. The alse colou images show signi ican losses occu ing in wo egions. The came a was ope a ing a a ame a e o ∼160 ames s−1and an exposu e ime o ∼500 µs pe ame. The ame aken a 325 ms shows a signi ican inc ease in he EGAM-induced losses ( egion ci cled in yellow in igu es 3(b) and (c)) a pi ch angles nea 45◦–50◦. Analysis o he came a da a shows ha he EGAM losses build up du ing a 210R beam pulse and decay a e wa ds, consis en wi h he ime beha iou o he PMT-measu ed cohe en loss signal shown in igu e 2. The o he egion o losses, a pi ch angles nea ∼70◦ ( egion ci cled in ed in igu e 3(b)), does no change signi ican ly be ween ames. Re e se o bi modelling shows ha he losses nea 70◦a e p ima ily due o p omp losses om he 210L beam, which is on con inuously du ing his ime pe iod [14]. P omp losses, o i s o bi losses, esul om ions bo n wi h o bi s ha in e sec he ou e wall. The Figu e 3. (a) Beam loss signal measu ed by FILD shows bu s s o cohe en ( ∼15 kHz) losses cha ac e is ic o EGAMs. The addi ional coun e beam injec ion by he 210R sou ce s a ing a 320 ms inc eases he measu ed loss a e. Consecu i e ames a 319 ms (b) and 326 ms (c) om a CCD came a measu ing he pi ch angle and gy o adius o he losses show ha he cohe en losses appea a pi ch angles nea 45◦–50◦. The losses a pi ch angles nea 70◦ou lined in ed do no change signi ican ly and a e p edomina ely due o p omp losses om he 210L sou ce ha is on con inuously du ing his ime pe iod. The losses nea 45◦–50◦in pi ch angle a e due o EGAM in e ac ions (ci cled in yellow) and 210R p omp losses (ci cled in g een). losses nea 50◦in pi ch angle a e due o bo h i s o bi ( egion ci cled in g een in igu e 3(b)) and EGAM-induced losses, and a e p ima ily due o he 210R neu al beam sou ce. These losses occu o e a ange in gy o adii om ∼2 o 4 cm. The magne ic ield a he de ec o is 1.5 T, so his ange o gy o adii co esponds o deu e ium ion ene gies om ∼25keVup o he maximum injec ed beam ene gy o Eb=81 keV. The 210L and 210R sou ces a e he only neu al beams injec ing coun e o he di ec ion o he plasma cu en in DIII-D (co-cu en beams p o ide ano he ∼2 MW o inpu hea ing in his sho ), so he esul ing beam ions a e bo n on he inne leg o hei banana o bi s and i is no su p ising ha hey domina e he obse ed loss signals. 3 Nucl. Fusion 52 (2012) 123015 R.K. Fishe e al 1.0 28.3 E adial (kV/m) 0.0 E adial 1.0 1.5 R ( m ) Z (m) 2.0 2.5 0.0 –1.0 80 70 60 Pi ch Angle (deg) 50 40 30 4.5 3.5 2.5 1.5 Gy o Radius (cm) 100 0 Coun s 210L hi d 210L hal 210L ull 210R hi d 210R hal EGAM losses Figu e 4. (a) Resul s o a ull pa icle-o bi ollowing code SPIRAL used o simula e he losses due o EGAMs a e consis en wi h measu ed FILD esul s. (b) Calcula ed loss o bi (gold) o a beam ion de ec ed in he EGAM-induced loss egion o he FILD came a da a (E=75 keV, pi ch angle =45◦–50◦). Also shown is he calcula ed adial elec ic ield om he m=0, n=0 elec os a ic po en ial pe u ba ion esul ing om EGAM ac i i y. 3. Modelling and in e ed EGAM loss mechanism SPIRAL is a ull pa icle-o bi ollowing code ha was de eloped o model ene ge ic ion beha iou in okamaks [16,17]. Figu e 4shows he esul s o SPIRAL used o simula e he losses due o EGAMs. In hese SPIRAL code simula ions1, ions wi h he bi h ene gy deposi ion p o ile om NUBEAM [18] a e ollowed as hey slow down and pi ch angle sca e while in e ac ing wi h he m=0, n=0 adial elec ic ield esul ing om he EGAM ac i i y. The adial elec ic ield used in SPIRAL is calcula ed based on a o oidally symme ic elec ic po en ial which is a lux unc ion, and whose magni ude is chosen o ma ch he esul ing densi y 1SPIRAL code was un on 512 AMD op e on p ocesso s using UNIX and ollowed 250000 pa icles (50000 pe beam). pe u ba ion measu ed by a beam emission spec oscopy diagnos ic. The EGAM-induced losses occu be ween 45◦ and 50◦in pi ch angle and o e a b oad ange o gy o adii ( egions ci cled in yellow in igu es 4(a) and 3(b)) as he EGAMs in e ac wi h he slowing-down dis ibu ion o he 210R injec ed ions. Po ions o he egion nea 45◦–50◦ can also include p omp losses om he 210R sou ce. An example is he egion ci cled in g een ha is only p esen du ing 210R injec ion and is consis en wi h p omp losses o he one- hi d and one-hal ene gy componen s o 210R. The SPIRAL esul s in igu e 4a e in good ag eemen wi h he measu ed esul s in igu e 3and he same colou -coding is used o iden i y he di e en loss egions in bo h igu es. Bo h he FILD measu emen s and he SPIRAL code p edic ions show signi ican EGAM-induced losses, compa able in magni ude o he p omp losses o he coun e -injec ed beams. The SPIRAL esul s a e also consis en wi h he measu ed ime beha iou o he losses shown in igu e 2, including he ‘delayed’ cohe en componen a e he 210R beam is u ned o . Re e se o bi ollowing echniques a e used o calcula e he o bi s o he beam ions eaching he FILD de ec o based on hei measu ed pi ch angles and gy o adii. The magne ic ield con igu a ion inside he plasma is de e mined using he plasma equilib ium code EFIT [19], cons ained by cu en p o iles (based on mo ional S a k e ec measu emen s o he magne ic ield pi ch) and he measu ed plasma p essu e. Figu e 4(b) shows he SPIRAL esul o he poloidal p ojec ion o he calcula ed ajec o y (shown in gold) o a 75 keV beam ion a a pi ch angle o 45◦–50◦ eaching he FILD de ec o . The inne po ion o his uncon ined apped pa icle o bi is close o he o bi s o con ined coun e -injec ed beam ions. As he coun e -injec ed beam ions lose ene gy o he wa e, he change in hei pi ch angle pu s hem on an uncon ined apped pa icle o bi , leading o he measu ed FILD loss signal cohe en wi h he EGAM ac i i y. Loss o he beam ions educes he d i e mechanism o he mode, which in u n educes he beam loss a e un il he cycle s a s again. This p eda o –p ey beha iou o he ins abili y leads o he obse ed bu s s in he mode ampli ude and measu ed beam ion loss. 4. Conclusions A new scin illa o -based as -ion loss de ec o on DIII-D has allowed he i s expe imen al obse a ions o as -ion losses due o EGAM ac i i y in a okamak. Neu al beam injec ion coun e o he di ec ion o he plasma cu en s ongly exci es he EGAMs. F om he measu ed pi ch angle and gy o adii o he cohe en beam ion loss signal, e e se o bi ollowing echniques yield a apped ion loss o bi wi h a la ge banana wid h ha eaches well inside he plasma. Th ough he in e ac ion wi h he EGAM, con ined beam ions on coun e - passing o bi s expe ience a change in hei pi ch angle ha places hem on apped pa icle loss o bi s. The measu ed as -ion loss exhibi s he bu s ing beha iou cha ac e is ic o EGAMs, wi h a measu ed g ow h a e consis en wi h he as - ion p essu e d i ing he modes. The measu ed pi ch angles and gy o adii o he measu ed as -ion losses a e consis en wi h he p edic ions o he ull o bi ollowing code SPIRAL used o model he EGAM-induced losses. 4 Nucl. Fusion 52 (2012) 123015 R.K. Fishe e al Acknowledgmen s This wo k was suppo ed in pa by he U.S. Depa men o Ene gy unde DE-FC02-04ER 54698, SC-G903402 and DE- AC02-09CH11466. The assis ance o he DIII-D eam is g a e ully acknowledged. Re e ences [1] Heidb ink W.W. and Sadle G.J. 1994 Nucl. Fusion 34 535 [2] Fasoli A. e al P og ess in he ITER Physics Basis: chap e 5. Physics o ene ge ic ions 2007 Nucl. Fusion 47 S264 [3] Zweben S.J. 2000 Nucl. Fusion 40 91 [4] Heidb ink W.W. 2002 Phys. Plasmas 92113 [5] Keilhacke M. e al 1999 Nucl. Fusion 39 209 [6] Nazikian R. e al 2008 Phys. Re . Le . 101 185001 [7] Fu G.Y. e al 2008 Phys. Re . Le . 101 185002 [8] Fishe R.K. e al 2010 Re . Sci. Ins um. 81 10D307 [9] Ga c´ ıa-Mu˜ noz M. e al 2009 Re . Sci. Ins um. 80 053503 [10] Ga c´ ıa-Mu˜ noz M. e al 2010 Phys. Re . Le . 104 185002 [11] Be k H. e al 2006 Nucl. Fusion 46 S888 [12] Heidb ink W.W. e al 2009 Plasma Phys. Con ol. Fusion 51 125001 [13] Pace D.C. e al 2011 Plasma Phys. Con ol. 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