Re . Sci. Ins um. 89, 10I112 (2018); h ps://doi.o g/10.1063/1.5039311 89, 10I112
A o a y and ecip oca ing scin illa o
based as -ion loss de ec o o he MAST-U
okamak
Ci e as: Re . Sci. Ins um. 89, 10I112 (2018); h ps://doi.o g/10.1063/1.5039311
Submi ed: 07 May 2018 • Accep ed: 11 June 2018 • Published Online: 21 Sep embe 2018
J. F. Ri e o-Rod iguez, M. Ga cia-Munoz, R. Ma in, e al.
COLLECTIONS
Pape published as pa o he special opic on P oceedings o he 22nd Topical Con e ence on High-Tempe a u e
Plasma Diagnos ics
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REVIEW OF SCIENTIFIC INSTRUMENTS 89, 10I112 (2018)
A o a y and ecip oca ing scin illa o based as -ion loss de ec o
o he MAST-U okamak
J. F. Ri e o-Rod iguez,1,2,a) M. Ga cia-Munoz,2,3 R. Ma in,4J. Galdon-Qui oga,2,3
J. Ayllon-Gue ola,1,2 R. J. Ake s,4J. Buchanan,4D. C o ,4D. Ga cia-Vallejo,1
J. Gonzalez-Ma in,1,2 D. Ha ey,4K. G. McClemen s,4M. Rod iguez-Ramos,2,3
and L. Sanchis2,3
1Depa men o Mechanical Enginee ing and Manu ac u ing, Uni e si y o Se ille,
Camino de los Descub imien os s/n, 41092 Se ille, Spain
2Cen o Nacional de Acele ado es (CNA), Uni e sidad de Se illa, CSIC, Jun a de Andalucia, Se ille, Spain
3Depa men o A omic, Molecula and Nuclea Physics, Uni e si y o Se ille, 41012 Se ille, Spain
4CCFE, Culham Science Cen e, Abingdon, Oxon OX14 3DB, Uni ed Kingdom
(P esen ed 16 Ap il 2018; ecei ed 7 May 2018; accep ed 11 June 2018;
published online 21 Sep embe 2018)
The design and unique ea u e o he i s as -ion loss de ec o (FILD) o he Mega Amp Sphe ical
Tokamak - Upg ade (MAST-U) is p esen ed he e. The MAST-U FILD head is moun ed on an axi-
ally and angula ly ac ua ed mechanism ha makes i possible o independen ly adap he o ien a ion
[0◦, 90◦] and adial posi ion [1.40 m, 1.60 m] o he FILD head, i.e., i s collima o , hus maximizing
he de ec o eloci y-space co e age in a b oad ange o plasma scena ios wi h di e en q95. The 3D
geome y o he de ec o has been op imized o de ec as -ion losses om he neu al beam injec o s.
O bi simula ions a e used o calcula e he s ike map and p edic he expec ed signals. The esul s show
a eloci y-space ange o [4 cm, 13 cm] in gy o adius and [30◦, 85◦] in pi ch angle, co e ing he en i e
neu al beam ion ene gy ange. The op ical sys em will p o ide di ec sigh o he scin illa o and simul-
aneous de ec ion wi h wo came as, gi ing high spa ial and empo al esolu ion. The MAST-U FILD
will shed ligh on he dominan as -ion anspo mechanisms in one o he wo ld’s wo la ges sphe ical
okamaks h ough absolu e measu emen s o as -ion losses. h ps://doi.o g/10.1063/1.5039311
I. INTRODUCTION
Fas -ions a e he main sou ce o plasma hea ing in mag-
ne ically con ined usion de ices. Ene ge ic usion-bo n α-
pa icles a e needed o uphold a bu ning s a e. In p esen
de ices, as -ions a e mainly gene a ed by ex e nal hea ing,
such as Neu al Beam Injec ion (NBI) o Ion Cyclo on Res-
onan Hea ing (ICRH). Fas -ions also play a g ea ole in
non-induc i e cu en d i e, so hey can be c ucial in he
ealiza ion o non-pulsed ope a ion. The e o e, good as -ion
con inemen is necessa y o achie e high plasma empe a u es
and non-induc i e cu en d i e. Addi ionally, as -ion losses
may a ec he de ice in eg i y by se e ely damaging plasma
acing componen s.1
The Fas -Ion Loss De ec o (FILD)2,3is a unique diag-
nos ic in he de ec ion o MHD induced as -ion losses.4I
wo ks as a magne ic spec ome e , in e ing he escaping as -
ion eloci y-space by hei s ike poin on a scin illa o pla e, as
illus a ed in Fig. 1. They ha e been used in mos la ge oka-
maks, such as TFTR,2,5ASDEX Upg ade,3,6JET,7NSTX,8
and DIII-D,9among o he s.
In his wo k, he i s FILD o he Mega Amp Sphe -
ical Tokamak - Upg ade (MAST-U) has been designed and
implemen ed, as pa o he majo upg ade ha his sphe ical
No e: Pape published as pa o he P oceedings o he 22nd Topical Con e -
ence on High-Tempe a u e Plasma Diagnos ics, San Diego, Cali o nia, Ap il
2018.
a)Elec onic mail: j i [email p o ec ed]
okamak is cu en ly unde going.10 The MAST-U FILD inco -
po a es he abili y o o a e i s head in a sho - o-sho basis, hus
adap ing i s ape u e o ien a ion o he plasma q95. This is a
unique ea u e o any FILD sys em, and i is especially impo -
an in a sphe ical okamak, whe e he b oade ange o q95 will
make i necessa y o eo ien a e he FILD ape u e in o de o
p ese e accep able eloci y-space co e age.
This pape is s uc u ed as ollows. The FILD wo king
p inciple is p esen ed in Sec. I. The p obe head design using he
FILDSIM code is shown in Sec. II. The dis inc i e ea u es o
he o a y and ecip oca ing sys em a e p esen ed in Sec. III, as
well as a ini e elemen analysis (FEA) o he in- essel sys em.
An ou line o he da a acquisi ion sys em is gi en in Sec. IV.
Sec ion Vsumma ises he cu en s a us and ou look o his
diagnos ic.
II. FILD PROBE DESIGN
The as -ion popula ion ha FILD aims o measu e is ha
p oduced by he NBI hea ing. Two NBIs (on-axis and o -axis)
will injec deu e ium (o hyd ogen) a a maximum ene gy o
75 keV. The hal (37.5 keV) and hi d (25 keV) injec ion ene -
gies should also be conside ed. The local magne ic ield on he
FILD p obe will be in he ange o B= [0.45 T, 0.55 T]. Thus,
he as -ion gy o adius will be in he ange o ρ= [41 mm,
125 mm].
The FILD p obe head is designed making use o he
FILDSIM code.11 FILDSIM akes in o accoun he p obe head
0034-6748/2018/89(10)/10I112/4/$30.00 89, 10I112-1
10I112-2 Ri e o-Rod iguez e al. Re . Sci. Ins um. 89, 10I112 (2018)
FIG. 1. (a) FILD p obe head and escaping as -ion o bi eaching he ape u e.
(b) Scin illa o pla e whe e he collima ed ions a e dispe sed using he okamak
magne ic ield and cha ac e ized by hei gy o adius and pi ch angle.
3D geome y and uses o bi s o wa d acing om he pinhole
o p oduce a syn he ic FILD signal. Wi h his, one can es ima e
he ollowing:
•S ike map
•Collima o ac o
•Veloci y-space co e age
•Signal esolu ion.
Besides, FILDSIM ca ies ou backwa d acing o es ima e
he eloci y-space ange ha would be sel -obs uc ed by he
p obe head ex e nal geome y.
The s ike map o he inal collima o geome y is shown
in Fig. 2(a). Mo eo e , he syn he ic signal o deu e ium
FIG. 2. (a) Syn he ic signal o an a i icial dis ibu ion o deu e ium a he
main (E= 75 keV), hal (E= 37.5 keV), and hi d (E= 25 keV) NBI injec ion
ene gies, co esponding o ρ= 10.1 cm, ρ= 7.2 cm, and ρ= 5.8 cm gy o-
adius alues, espec i ely, o a B= 0.55 T magne ic ield. The dis ibu ion
co e s he en i e pi ch angle ange o he FILD p obe. The o e laid s ike
map shows he ene gy (keV) on he e ical axis and he pi ch angle alues
(◦) on he ho izon al axis, assuming B= 0.55 T and deu e ium as he imping-
ing ion species. (b) Ene gy dispe sion on he scin illa o pla e o se e al
mono-ene ge ic dis ibu ions on he pinhole.
a 75 keV, 37.5 keV, and 25 keV is also shown, showing ha he
collima o geome y deli e s enough ene gy esolu ion o sep-
a a e he h ee NBI ene gy componen s o injec ed deu e ium.
This geome y s ops gy o adii below ρ= 35 mm, hus a oiding
he mal ion de ec ion. I is wo h men ioning ha a la ge La -
mo adius han he maximum shown in he s ike map would
no be obs uc ed by he collima o and hus as -ions a highe
ene gies could in p inciple be measu ed, wi h he ange only
limi ed by he scin illa o pla e size. Backwa d acing shows
ha he ex e nal geome y se e ely obs uc s o bi s below
ρ= 40 mm, hus no a ec ing he FILD signal.
Figu e 2(b) shows how he de ec o esolu ion in gy o a-
dius lessens a la ge gy o adius alues. This is geome ically
caused by he collima o ini e dimensions and is di icul o
a oid.3On he con a y, he esolu ion in pi ch angle emains
almos cons an o he en i e eloci y-space ange,11 being
Λ=±2◦. The o e all de ec ion esolu ion can be enhanced
using omog aphic econs uc ion in he analysis o he FILD
signal, using he FILDSIM code.
III. ROTARY AND RECIPROCATING SYSTEM
In MAST-U, he FILD p obe head is moun ed on an axially
and angula ly ac ua ed mechanism. This means ha he p obe
head posi ion can be modi ied by wo independen se ings on
a sho - o-sho basis, as i is illus a ed in Fig. 3(a). One se ing
makes i possible o modi y he p obe head adial posi ion in
a ange o R= [1.40 m, 1.60 m], adap ing i s dis ance om
he plasma simila o he FILD sys ems in ASDEX Upg ade
and DIII-D. The o he se ing enables changes in he ape u e
o ien a ion in a ange o 90◦. I will make possible o adap
he ape u e o ien a ion o plasma scena ios wi h di e en q95
wi hou losing eloci y-space co e age. This is an especially
ele an ea u e o a sphe ical okamak, whe e he use o lowe
o oidal ields leads o a b oade ange o plasma q95. Thus,
MAST-U FILD has unique e sa ili y in e ms o being capa-
ble o adap ing o di e en plasma scena ios, maximizing he
de ec o eloci y-space co e age.
The mechanical sys em is shown in Fig. 3(b). Since he
MAST-U FILD p obe head only allows o measu emen s
in o wa d ield expe imen s (B clockwise), he de ec o
is loca ed 109 mm abo e he midplane, whe e he as -ion
loss de ec ion will be enhanced by he g ad-B d i , poin ing
upwa d. I s modula elescopic design esul s in a compac sys-
em o an o he wise la ge de ec o . Ligh - igh pa s enable
di ec sigh o he scin illa o pla e, placing he op ical sys-
em ou side he acuum essel. In- essel high ic ion con ac s
ha e been a oided and special ca e has been aken in he ma e-
ial selec ion o con ac bodies o p e en cold welding. The
acuum bounda y consis s o he po pla e and bellow-based
d i es, ensu ing i s in eg i y. The g aphi e cap design has been
e ised o allow ee he mal expansion, and i s empe a u e
will be moni o ed by a he mocouple du ing ope a ion. In sum-
ma y, he mechanical sys em p o ides accu a e posi ioning o
he de ec o head while p io i ising he de ec o in eg i y and
sa e y.
The in- essel assembly is bol ed o a po pla e, o ming
a can ile e o abou 30 kg suppo ed by i . The e o e, good
s uc u al pe o mance o FILD is equi ed o gua an ee he
10I112-3 Ri e o-Rod iguez e al. Re . Sci. Ins um. 89, 10I112 (2018)
FIG. 3. (a) Ro a y ( ed) and ecip oca ing (g een) sys em ha d i es he
FILD p obe head (blue). (b) O e iew o he MAST-U FILD mechanical
sys em.
po pla e in eg i y. In o de o assess his, a ini e elemen anal-
ysis (FEA) o he in- essel s uc u e has been ca ied ou in
ANSYS
®
wo kbench. The analysis mimics a shock caused by
FIG. 4. Equi alen on Mises s ess on he in- essel s uc u al componen s.
S ess concen a ion a eas a e highligh ed.
a dis up ion simula ing a 2 kA cu en going h ough he FILD
s uc u e. Figu e 4shows he esul ing on Mises s ess on he
sys em. The highligh ed s ess concen a ion a eas unde go
s ess magni udes 5 imes below he ma e ial yield s ess.
The o ce eac ions on he o a y bea ings a e 6 imes below
he maximum ecommended by he manu ac u e . The e o e,
he FEA o esees good s uc u al pe o mance o he in- essel
sys em. The FEA also shows ha he guide ails suppo ing he
p obe head [shown in Fig. 3(b)] will be he mos c i ical pa s
o he sys em, so i s pe o mance will be moni o ed du ing he
de ec o ope a ion.
IV. LIGHT ACQUISITION SYSTEM
The scin illa o pla e is isible om a window po a
he ea end o he mechanical sys em. This makes i possi-
ble o place he op ical sys em and da a acquisi ion sys em
ou side he acuum essel, p o iding ull accessibili y du ing
expe imen al campaigns.
The op ical sys em is shown in Fig. 5, and each op ical
elemen is desc ibed in Table I. I is o med exclusi ely by
lenses, le e aging he scin illa o pla e ull esolu ion, in con-
as o sys ems whe e he use o ib e op ics limi s he signal
esolu ion o he size o he ib e bundle. A beam spli e allows
moni o ing o he scin illa o pla e by wo di e en came as
simul aneously. One came a p o ides good spa ial esolu ion
o cap u e sha p pic u es o he scin illa o pla e. Wi h his,
one can esol e he eloci y-space o he impinging ions using
he s ike map desc ibed in Sec. II. The o he came a is an
a alanche pho o-diode (APDCAM 10G)12 came a wi h a sam-
pling a e o 2 MHz. This in combina ion wi h a as scin illa o
ma e ial (P46) makes i possible o de ec as -ion loss luc u-
a ions, which can be co ela ed wi h he MHD ac i i y o he
plasma.
Due o i s high sampling equency, he APD came a has
ela i ely high memo y consump ion, equi ing up o 2.5 GB
pe sho . Fo his eason, a dedica ed pe sonal compu e (PC)
wi h enough memo y is equi ed o acqui e and con ol he
FIG. 5. Op ical sys em and ay acing o he APD came a and he high es-
olu ion came a. The dis ance be ween elemen s (in mm) and he nume a ion
co esponding o Table Ia e also shown.
10I112-4 Ri e o-Rod iguez e al. Re . Sci. Ins um. 89, 10I112 (2018)
TABLE I. Type, ocal leng h, and diame e o each op ical elemen , acco ding
o he nume a ion se in Fig. 5.
Elemen Type Focal leng h (mm) Ø (mm)
1 Ach oma 120 50
2 Plano-con ex 300 31.5
3 Symme ic-conca e

50 22.4
4 Beam spli e
5 Symme ic-con ex 50 31.5
6 Asphe ic 15 18
7 Plano-conca e

30 12.7
8 Plano-con ex 12.5 8
APD da a. Howe e , he high esolu ion came a is no as
demanding, equi ing abou 100 MB pe sho . Thus, a sec-
ond PC will be used o con ol bo h he high esolu ion came a
and he mo o s ha d i e he p obe head linea and o a y
mo ions.
V. SUMMARY
The i s MAST-U FILD, shown in Fig. 6, is now designed
and manu ac u ed. I p o ides enough eloci y-space co e -
age and esolu ion o diagnose he NBI as -ion popula ion in
a b oad ange o plasma scena ios. The mechanical sys em
includes he abili y o adap he FILD ape u e o ien a ion, a
unique ea u e in any FILD de ice. This is combined wi h
a ecip oca ing sys em in a compac mechanism ha p o-
ides he de ec o wi h unp eceden ed adap abili y o plasma
shapes.
FIG. 6. Pic u e o he assembled MAST-U FILD.
The diagnos ic is o be ins alled in MAST-U. Then, he
commissioning will be ca ied ou in pa allel o he commis-
sioning o o he MAST-U sys ems and i s conclusion will
equi e he ope a ion o he NBI hea ing. E en ually, FILD
will be in o se ice om he i s MAST-U campaign, planned
o Janua y 2019. To ha end, as -ion modeling is ongoing o
guide he as -ion expe imen s.
ACKNOWLEDGMENTS
This wo k has been ca ied ou wi hin he amewo k
o he EURO usion Conso ium and has ecei ed unding
om he Eu a om esea ch and aining p og amme 2014-2018
unde G an Ag eemen No. 633053. The iews and opinions
exp essed he ein do no necessa ily e lec hose o he Eu o-
pean Commission. This esea ch ecei ed unding om he
V Plan P opio de In es igacion de la Uni e sidad de Se illa
(PP2016-7145).
The au ho s would like o hank he MAST Upg ade
eam o hei help wi h he echnical aspec s o his
p ojec .
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