An imaging heavy ion beam probe diagnostic for the ASDEX Upgrade tokamak

An imaging hea y ion beam p obe diagnos ic o he ASDEX Upg ade okamak J.Galdon-Qui oga1, G.Bi kenmeie 1,2, V.Ole skaia1,2, M.Socho 1, G.Anda3, K.Bald1, M.Dunne1, M.Ga cia-Munoz4, A.He mann1, K.Kaune 1, D.Nagy3, J.F.Ri e o-Rod iguez4, M.Rod iguez-Ramos 4, V.Rohde1, E.S umbe ge 1, J.J. Toledo 4, E.Viezze 4, E.Wol um1, S.Zole nik3, U.S o h1,2and he ASDEX Upg ade4Team 1Max Planck Ins i u e o Plasma Physics, Ga ching, Ge many 2Physics Depa men E28, Technical Uni e si y o Munich, Ga ching, Ge many 3Wigne RCP, EURATOM Associa ion HAS, Budapes , Hunga y 4Cen o Nacional de Acele ado es (CNA), Uni e si y o Se ille, Spain In oduc ion A new diagnos ic - he imaging hea y ion beam p obe (i-HIBP) [1, 2] - o he simul aneous measu emen o plasma po en ial, magne ic ield and densi y luc ua ions is being de eloped a he ASDEX Upg ade (AUG) okamak. The diagnos ic uses an ion beam in o de o ex ac in o ma ion o he plasma as in classical hea y ion beam p obes (HIBP) [3], bu uses an injec o echnology simila o hose o beam emission spec oscopy (BES) diagnos ics and a scin illa o pla e as pa icle de ec o like in as -ion loss de ec o s (FILD) [4]. The measu emen p inci- ple is illus a ed in Fig.1 o e e ence [1]. A neu al beam o hea y a oms (Cs in his case) is launched in o he plasma wi h an ene gy o 70 keV. As his neu al p ima y beam pene a es he plasma, i is ionized leading o he gene a ion o a an o cha ged seconda y beams which a e de lec ed by he okamak magne ic ield. The an o seconda y beams is collec ed by a scin il- la o pla e placed behind he limi e shadow o he machine. The selec ed scin illa o ma e ial is he so called TG-G een (S Ga2S4:Eu2+), widely used in o he diagnos ics such as FILDs. The ligh pa e n emi ed by he scin illa o , which is imaged by a as came a, con ains adially esol ed in o ma ion abou he densi y, po en ial and magne ic ield in he edge and sc ape-o laye egions o he plasma. The use o a neu al p ima y beam allows o educe he p obing beam ene gy compa ed o s anda d HIBPs, while he use o an in- essel scin illa o as de ec ion sys em makes he sys em mo e compac and imp o es he adial esolu ion o he sys em. The plasma densi y can be eco e ed om he in ensi y measu emen , while displacemen s o he ligh pa e n - in he ollowing s ike-pa e n - p o ide in o ma ion abou plasma po en- ial and magne ic ield luc ua ions. Magne ic ield luc ua ions, such as hose expec ed due o changes in he cu en densi y p o ile, lead o a shi o he whole s ike-pa e n, while luc u- a ions o he plasma po en ial lead o local shi s o he s ike-pa e n. This way he displace- 46 h EPS Con e ence on Plasma Physics P1.1017 men s due o magne ic ield and po en ial pe u ba ions can be disc imina ed. The di e ence in he ime-scales o he phenomena o be in es iga ed can also be used o disc imina ion. Beam modelling The ajec o ies o he seconda y beams ha e been calcula ed wi h he ull-o bi ollowing code FIOS [1], which can handle 3D elec ic and magne ic ields. I was ound ha he o oidal ield ipple should be included in he simula ions since i can lead o a shi o he s ike-pa e n o up o ∼3.5 cm, i an unapp op ia e o oidal injec ion posi ion ela i e o he o oidal ield coils is selec ed. In o de o calcula e he signal in ensi y a he scin illa o pla e, a model o he beam a enua ion has been implemen ed which akes in o accoun elec on impac ioniza ion and cha ge exchange eac ions. The model is desc ibed in e e ences [1] and [2]. I is ound ha he seconda y ion cu en densi y eaching he scin illa o s ongly depends on he plasma densi y p o ile. Fo a scena io wi h a co e line a e aged densi y o ¯ne=2.6·1019 m−3, a cu en densi y o he o de o ∼mA/m2is expec ed a he scin illa o pla e, while o a scena io wi h ¯ne=7.8·1019 m−3, he cu en densi y expec ed a he scin illa o pla e is educed o ∼nA/m2. A numbe o simula ions ha e been ca ied ou o ob ain he op imal pa ame e s o he beam injec ion and de ec ion geome y. The op imiza ion p ocess aimed a achie ing maximum signal le el a he scin illa o pla e as well as maximum s ike-pa e n displacemen s due o magne ic ield and po en ial pe u ba ions. A he same ime, he op imiza ion p ocess was cons ained by space limi a ions, po a ailabili y and compa ibili y wi h cu en ly exis ing diagnos ics in he same sec o . The inal injec ion pa ame e s a e o a baseline scena io wi h a plasma cu en Ip and magne ic ield B o I p/B =0.8MA/2.5Ta e: o oidal injec ion angle θ o =5o; poloidal injec ion angle θpol =0o, injec ion ene gy E0=70 keV. The adial co e age o he diagnos ic is expec ed o be om ρpol >0.85. The expec ed ange o ope a ion o he diagnos ic is expec ed o be wide enough o co e all he possible scena ios in o wa d ield con igu a ion. This is illus a ed in Fig.1. In o de o es ima e his ope a ional ange, we assume ha he injec ion ene gy o he beam should be changed o di e en B in o de o keep he same e ec i e La mo adius o he seconda y beams. The e o e, he injec ion ene gy has o be scaled as Eb= ( B B0)2·E0, whe e he subindex 0 e e s o he baseline se up. On he o he hand, we assume ha a ia ions o he plasma cu en lead o a global displacemen o he s ike-line o 1 cm / 100 kA, as in e ed om he simu- la ions discussed abo e. The alidi y o his es ima ion has been assessed by he s ike-pa e n calcula ion a speci ic scena ios, indica ed by he colo ed diamonds in Fig.1, spanning di e en B and Ip alues. The beam ene gy was scaled acco dingly as desc ibed p e iously. In all cases he s ike-pa e n was ound o lay wi hin he scin illa o limi s. 46 h EPS Con e ence on Plasma Physics P1.1017 Figu e 1: Es ima ed op- e a ional ange o he i- HIBP diagnos ic a AUG. The con ou lines indica e he injec ion ene gy o he beam. The shaded egion indica es he ope a ional space accesible o he di- agnos ic, wi hou aking in o accoun he beam de- lec ion pla es. A sensi i i y s udy has been ca ied ou o de e mine which physics phenomena can be in es iga ed wi h he i-HIBP a AUG [5]. To his end, he displacemen o he s ike-pa e n on he scin- illa o pla e due o magne ic ield and plasma po en ial luc ua ions has been e alua ed o di e en phenomena such as: cu en den- si y e olu ion du ing an edge localized mode (ELM) cycle, applica- ion o ex e nally applied magne ic pe u ba ions (MP) o geodesic acous ic modes (GAMs) among o he s. The expec ed s ike-pa e n displacemen s and sensi i i y a e in ag eemen wi h hose desc ibed in [1], anging om ∼0.2mm local shi s due o po en ial pe u ba- ions up o ∼3mm global shi s due o magne ic ield pe u ba ions. Ha dwa e a angemen : ou essel The main ou - essel componen o he diagnos ic is he beam injec o . The injec o will be placed in sec o 13 o AUG, whe e he injec ion is done h ough a po loca ed sligh ly abo e he mid- plane. The injec o is o ien ed 5o o oidally owa ds sec o 14, ac- co dingly o he baseline injec ion pa ame e s ound in he p e i- ous sec ion. The injec o is based on he design desc ibed in [6] and has been p o ided by he Wigne Ins i u e. The main elemen s a e: a high- ol age cage ha con ains he ion sou ce, he emi e (∼70kV) and ex ac o (∼60kV ) elec odes; an elec on supp es- sion ing (∼ −0.5kV ); a pai o de lec ion pla es o beam poloidal and o oidal s ee ing (±0.5kV ), as well as o as beam chopping (up o 250 kHz); a neu alize chambe ; and a diagnos ic chambe , which con ains a Fa aday cup and 2 came as o beam moni o ing, and which has been e- designed o include a se o collima o s o educe he size o he beam. An addi ional Fa aday cup can be placed be ween he de lec ion pla es and he neu alize , and a mi o can be placed be ween he HV box and he de lec ion pla es o obse a ion o he ion sou ce. Ha dwa e a angemen : in essel The main in- essel componen s o he diagnos ic a e an op ical head and an image guide. The op ical head, shown in Fig.2 con ains he scin illa o pla e (16.9 cm heigh x 6 cm wid h) o he measu emen o he seconda y beams, a he mocouple o moni o he empe a u e o he pla e, a cu en measu emen and a lamp. The op ical head is p o ec ed by a ile on he plasma acing side, which is 2.5 cm behind he shadow o he limi e su ace. The op ical head has an 46 h EPS Con e ence on Plasma Physics P1.1017 Figu e 2: (a) Op ical head o he i-HIBP diagnos ic. (b) Pic u e o he scin illa o powde de- posi ed on he s ainless s eel pla e. opening o app oxima ely ∼5x15 cm in he op side, in o de o allow he seconda y beam ajec o ies in o he scin illa o . A shu e ha closes his opening is also ins alled o a oid he coa ing o he scin illa o du ing bo oniza ions. The ligh emi ed by he scin illa o is imaged by an objec i e consis ing o 6 lenses which p ojec s he image o he scin illa o on o a 1.8 m long SCHOTT image guide, consis ing o 1700x700 glass ibe s, which is hen imaged om ou side he acuum window wi h a high speed came a. Summa y An imaging hea y ion beam p obe has been designed and will be ins alled in he AUG oka- mak. Modelling o he beam ajec o ies has been ca ied ou wi h a ull o bi ollowing code which can handle 3D magne ic and elec ic ields, while he a enua ion o he beam is calcu- la ed aking in o accoun elec on impac ioniza ion and cha ge exchange eac ions. Based on hese simula ions, he injec ion and de ec ion geome ies ha e been op imized while espec ing he spa ial es ic ions, and he in- and ou - essel componen s ha e been designed acco dingly. Labo a o y expe imen s a e cu en ly ongoing o cha ac e ize he beam and he scin illa o e- sponse o Cs i adia ion, while he manu ac u ing o all componen s o he diagnos ic is being inalized. The i-HIBP a AUG is o eseen o go in ope a ion by he end o 2019. Re e ences [1] J.Galdon-Qui oga, Jou nal o Ins . 12, C08023 (2017) [2] G.Bi kenmeie e al, Jou nal o Ins . (submi ed) [3] A.V. Melniko e al, Nucl. Fusion 57, 072004 (2017) [4] M.Ga cia-Munoz e al, Re . Sci. Ins um. 80, 053503 (2009) [5] V.Ole skaia e al, DPG Con e ence (2019) [6] G.Anda e al, Re . Sci. Ins um. 89, 013503 (2018) 46 h EPS Con e ence on Plasma Physics P1.1017