LETTER • OPEN ACCESS
The quasi-con inuous exhaus egime in JET
To ci e his a icle: M. Fai sch
e al
2025
Nucl. Fusion
65 024003
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Nuclea Fusion
Nucl. Fusion 65 (2025) 024003 (9pp) h ps://doi.o g/10.1088/1741-4326/adaa86
Le e
The quasi-con inuous exhaus egime
in JET
M. Fai sch1,∗, M. Dunne1, E. Le che2,3, P. Lomas3, I. Balboa3, P. Bilko a4,
P. Bohm4, A. Kappa ou1, D. Kos3, B. Labi 5, S. Menmui 3, O. Sau e 5,
S. Silbu n3, E.R. Solano7, H.J. Sun3, A. Tookey3, E. Viezze 6,
U. S o h1,8and JET Con ibu o saand he EURO usion Tokamak Exploi a ion Teamb
1Max-Planck-Ins i u e o Plasma Physics, Bol zmanns . 2, D-85748 Ga ching, Ge many
2Labo a o y o Plasma Physics LPP-ERM/KMS, B-1000 B ussels, Belgium
3Uni ed Kingdom A omic Ene gy Au ho i y, Culham Science Cen e, Abingdon, Oxon OX14 3DB,
Uni ed Kingdom o G ea B i ain and No he n I eland
4Ins i u e o Plasma Physics o he CAS, P ague, Czech Republic
5Ecole Poly echnique Fede ale de Lausanne, Swiss Plasma Cen e , CH-1015 Lausanne, Swi ze land
6Depa men o A omic, Molecula and Nuclea Physics, Uni e si y o Se ille, Se ille, Spain
7Labo a o io Nacional de Fusión, CIEMAT, Mad id, Spain
8Physik Depa men E28, Technische Uni e si ä München, 85748 Ga ching, Ge many
E-mail: [email p o ec ed]
Recei ed 25 Sep embe 2024, e ised 12 Decembe 2024
Accep ed o publica ion 15 Janua y 2025
Published 22 Janua y 2025
Abs ac
The quasi-con inuous exhaus (QCE) egime is a egime ha is na u ally ype-I ELM- ee. I
combines he high densi y a he plasma edge needed o powe exhaus wi h he high
no malised ene gy con inemen ypical o H-mode ope a ion. In he QCE egime la ge-scale
ELMs a e a oided and high- equency, low-ampli ude ilamen s a e p esen leading o he
name-gi ing quasi-con inuous edge anspo o pa icles and ene gy. This con ibu ion epo s
ha o he i s ime he QCE egime was success ully achie ed in JET wi h a me al wall.
Mo eo e , i was demons a ed in he ecen JET deu e ium- i ium campaign DTE3 ha he
egime is compa ible wi h D–T ope a ion. Po ing he QCE egime o JET s ongly bene i ed
om he expe imen al and modelling e o s a he medium sized okamaks ASDEX Upg ade
and TCV. Using he physics pic u e de eloped om he ASDEX Upg ade expe imen al esul s,
he ou e o he QCE egime in JET epo ed he e is ollowing closely he app oach ha was
success ul in ASDEX Upg ade. Fi s , s ong plasma shaping—la ge elonga ion and iangula i y
and he highly co ela ed closeness o double null—is de eloped. Second, su icien uelling o
achie e high enough densi y a he pedes al oo , close o he sepa a ix, is applied. In addi ion,
neon seeding p o ed o be e y bene icial o a oid ype-I ELMs when educing he main ion
uelling.
aSee Maggi e al 2024 (h ps://doi.o g/10.1088/1741-4326/ad3e16) o JET Con ibu o s.
bSee Jo in e al 2024 (h ps://doi.o g/10.1088/1741-4326/ad2be4) o he EURO usion Tokamak Exploi a ion Team.
∗Au ho o whom any co espondence should be add essed.
O iginal Con en om his wo k may be used unde he
e ms o he C ea i e Commons A ibu ion 4.0 licence. Any
u he dis ibu ion o his wo k mus main ain a ibu ion o he au ho (s) and
he i le o he wo k, jou nal ci a ion and DOI.
1741-4326/25/024003+9$33.00 P in ed in he UK 1 © 2025 The Au ho (s). Published by IOP Publishing L d on behal o he IAEA
Nucl. Fusion 65 (2025) 024003 M. Fai sch e al
Keywo ds: powe exhaus , ELM- ee, quasi-con inuous exhaus , deu e ium- i ium, plasma edge
(Some igu es may appea in colou only in he online jou nal)
1. In oduc ion
An in eg a ed eac o scena io combines good co e condi-
ions o achie e high usion gain oge he wi h a plasma edge
ha gua an ees a sa e powe exhaus solu ion. Fo many dec-
ades, he high con inemen mode wi h ype-I edge localised
modes ( ype-I ELMy H-mode) was he p e e ed scena io [1].
Howe e , i became e iden ha he ansien i s wall loads
due o ype-I ELMs will be unaccep able o a eac o [2,3].
The ac i e supp ession o ELMs using magne ic pe u ba ion
coils was in es iga ed wi h success as a possible solu ion [4].
Howe e , as di e o de achmen seems di icul o achie e
wi h his me hod, o he solu ions ha e ecen ly been looked
o and he in es iga ion o egimes ha a e na u ally ype-
I ELM- ee came in o ocus. An o e iew o a ious ype-I
ELM- ee egimes is p esen ed in [5,6].
The quasi-con inuous exhaus (QCE) egime is one candid-
a e o an in eg a ed eac o scena io wi hou la ge ansien s
[7]. The egime is also known as he ype-II ELM [8–13] o
a small ELM [14,15] egime and is closely ela ed o he
Enhanced D-Alpha (EDA) H-mode [16]. The QCE egime is
cha ac e ised by modes a he pedes al oo ha p oduce high-
equency and low-ampli ude ilamen s in he sc ape-o laye
[7,17]. The access condi ions a e s ong plasma shaping and
high uelling. In addi ion o he absence o la ge-scale ansi-
en s, he con inemen ime and p essu e a e simila o hose o
he ype-I ELMy H-mode [18].
Signi ican p og ess in he unde s anding o he QCE
egime has been achie ed in ecen yea s. Simula ions wi h he
HELENA s abili y code indica e ha local ballooning modes
become uns able a he pedes al oo . They induce a local
la ening o he p essu e g adien ha s abilises he global
peeling-ballooning modes causing ype-I ELMs [19–21]. A
simila local la ening ollows om he u bulence pa ame e
α , de ined in [22], which is p opo ional o he pedes al oo
collisionali y [18]. This pa ame e is closely linked o esis i e
ballooning modes [23]. Due o s ong gas uelling, he pedes-
al densi y, collisionali y and hus α a e ela i ely high, also
hin ing a he impo ance o esis i e u bulence a he edge o
QCE pulses.
The small ins abili y cha ac e is ic o he QCE egime
is equi alen o ype-II ELMs which we e al eady obse ed
in JET wi h he ca bon wall [9,10]. Howe e , hese p e i-
ous expe imen s showed only ansien phases wi hou ype-I
ELMs while s a iona y phases a e ou inely ob ained in AUG
and TCV. Wi h he newly gained insigh om AUG [7,14,
18–21] and TCV [15,24], a new a emp a ealising s a ion-
a y, ype-I ELM- ee QCE plasmas was s a ed in JET now
equipped wi h ungs en di e o and be yllium i s wall [25].
The key objec i es o hese expe imen s we e (i) o eal-
ise a s a iona y QCE egime, (ii) o dec ease he pedes al op
collisionali y compa ed o he expe imen s in AUG and TCV
whe e ν∗
e,ped is o he o de o 1–10 while in ITER alues in he
o de o 0.1 a e expec ed, and (iii) o p o e ha he egime is
compa ible wi h deu e ium– i ium (D–T) plasma ope a ion.
Achie ing low pedes al op collisionali y is a long- e m
ou s anding challenge o QCE esea ch. As he QCE egime
is na u ally ope a ed a high no malised densi y, only a la ge
de ice wi h high hea ing powe can simul aneously achie e
low pedes al op collisionali y.
The pape is o ganised as ollows: sec ion 2in oduces
he key expe imen al condi ions o each s a iona y QCE
phases wi h app op ia e shaping, uelling and neon seed-
ing. In sec ion 3 he compa ibili y o he QCE egime wi h
a deu e ium- i ium plasma is p esen ed. A discussion on
he achie ed pa ame e anges and conclusions ollow in
sec ions 4and 5, espec i ely.
2. S a iona y QCE egime
2.1. Expe imen al app oach
In JET he QCE egime is achie ed a high plasma shaping as
in AUG and TCV wi h high elonga ion, high iangula i y and,
linked o his, closeness o double null as shown in igu e 1.
A signi ican e o o he shape de elopmen was in es ed.
The shape is based on p e ious a emp s o achie e a ype-
II ELM scena io in JET wi h ca bon wall [9]. The discha ge
wi h he shape in igu e 1, JPN 102902, has Ip=1.5 MA and
|B o |=2.3 T. The magne ic equilib ium is econs uc ed using
he EFIT code wi h p essu e cons ain s [26]. Shown in ed is
he i s wall s uc u e, in black he sepa a ix and in blue he
lux su aces inside he con ined egion as well as in he sc ape-
o laye . The seconda y X-poin is close o he op o he i s
wall s uc u e. The shaping pa ame e s a e
κ=1.83,δlow =0.44,δup =0.47,dR,XP ≈15mm
wi h elonga ion κ, uppe and lowe iangula i y δand dis ance
be ween he p ima y and seconda y sepa a ix a he mid-plane
dR,XP. These alues a e close o he p ojec ed alues o ITER
discha ges wi h κ=1.85 and δ=0.49 [27]. Despi e he p ox-
imi y o double null, no signi ican hea lux o he uppe pa o
he essel was obse ed in he pa ame e ange s udied, how-
e e , isible ligh is emi ed showing ha some ecycling lux
eaches he op o he okamak. The ac i e lowe di e o is in a
e ical inne and ho izon al ou e a ge con igu a ion chosen
o maximise diagnos ics co e age and accommoda e he high
plasma shaping; he ene gy limi o he ungs en ou e di e o
is he main limi ing ac o o he discha ge du a ion [28].
Figu e 2shows he ypical ime aces o he expe imen s.
P esen ed a e an ELMy, JPN 103404, and a QCE, JPN 103451,
discha ge wi h iden ical enginee ing pa ame e s excep o
he uelling a e. Mo e de ails on he uelling dependence a e
2
Nucl. Fusion 65 (2025) 024003 M. Fai sch e al
Figu e 1. Poloidal c oss-sec ion illus a ing he close- o-double-null
shape used in he QCE expe imen s. The seconda y X-poin is close
o he uppe essel s uc u e wi h dR,XP ≈15mm. Shown in
magen a is he line o sigh o he isible spec oscopy used o he
Be-II and W-I line emission.
gi en in sec ion 2.3. The hea ing powe is inc eased s ep-wise
and he H-mode is en e ed wi h he second s ep a ≈11.5 s.
The QCE-compa ible plasma shape (shown in igu e 1) is
eached a ound ≈13.0 s. Abou 0.5 s la e , he o iginally
la ge ype-I ELM oo p in in he di e o (measu ed by in a-
ed came as) is i ually supp essed in he QCE discha ge
(JPN 103451) and he peak di e o empe a u e s ays app ox-
ima ely cons an , indica ing a s ong educ ion in he in a-
ELM hea -loads on he di e o iles. Con e sely, in he ELMy
discha ge (JPN 103404) he ype-I ELMs a e isible in he IR
measu emen s h oughou he discha ge and he peak di e -
o empe a u e inc eases g adually un il he end o he H-
mode phase. The discha ges a e e mina ed by a slow s ep-
wise amp-down o he hea ing powe and shaping om 16.4 s
allowing he densi y o d op be o e exi ing he H-mode phase.
No e ha he ELM oo p in b ie ly e-appea s in he di e o
IR measu emen s in JPN 103451 once he ansi ion ou o he
QCE shape is comple ed ( ≈16.8 s). Bo h discha ges ha e a
mode a e con inemen scaling ac o o H98y2 ≈0.75.
The absence o ype-I ELMs is moni o ed by mul iple dia-
gnos ics ha a e sensi i e o he apid expulsion o pa icles
and hea om he plasma edge ha e en ually each he i s -
wall and di e o s uc u es. Figu e 3(a) shows a ime window
ea ly in he pulse a e he H-mode en y (a ound 11.5 s) using
Figu e 2. Time aces o global plasma pa ame e s o an ELMy
e e ence pulse in ed and a QCE pulse in black. (A) plasma cu en ,
(B) NBI (solid) and ICRF (dashed) hea ing powe , (C) G eenwald
densi y ac ion o he line a e aged densi y, (D) ene gy
con inemen ac o (E) shaping pa ame e as de ined in (1) and (F)
peak su ace empe a u e o he ou e di e o a ge . IR da a is
a ailable only a e 12 s o he pulse in black.
a con en ional s ong shaping o JET (δup =0.40, κ=1.75,
dR,XP ≈20mm). The ypical ELM moni o s, Be-II and W-
I line emission in he ou e di e o , a e shown in (A) and
(B). The ELM equency is ELM ≈110 Hz. The ELMs ha e a
no iceable impac on he pedes al op elec on empe a u e as
measu ed by ECE (using a ixed channel close o ρpol =0.9) in
(C) and in he ou e di e o a ge pla e empe a u e as meas-
u ed by IR he mog aphy [29] in (D).
Figu e 3(b) shows a ime window du ing he inal phase
wi h close- o-double-null shaping (see igu e 1). The Be-II sig-
nal shows clea excu sions bu he pedes al op elec on em-
pe a u e and he a ge empe a u e a e i ually insensi i e
o he plasma edge elaxa ions. We call hese excu sions on
he Be-II emission ilamen s; hey occu wi h a equency o
il ≈300 Hz in his ime window. The ilamen s a e s ill isible
3
Nucl. Fusion 65 (2025) 024003 M. Fai sch e al
Figu e 3. Time aces o ypical ELM indica o s. The pulse has Ip=1.5MA, B o =2.3T, Phea ≈19MW and gas a e
ΓD
el ≈3.0×1022 s−1. (a) ELMy wi h con en ional shape and (b) QCE wi h new shape. The sub-plo s (A) and (B) a e line emissions o
be yllium and ungs en along a line-o -sigh in o he ou e di e o egion. (C) is he elec on empe a u e o an ECE channel close o he
pedes al op (ρpol =0.9) and (D) is he peak su ace empe a u e o he ou e di e o a ge measu ed wi h IR sub ac ing he minimum
empe a u e as indica ed abo e he panel. A unning mean il e o 1.2 ms is applied o all signals o educe he noise le el.
in he W–I line emission as well as in he Langmui p obe ion
sa u a ion cu en (no shown).
We conclude ha hese ilamen s expel plasma om he
con ined egion wi hou a ec ing he pedes al op alues and
wi h only a small amoun o ene gy eaching he di e o .
Howe e , hey s ill cause a measu able ion lux o he di e o
ha may inc ease he spu e ing o ungs en in he condi ions
p esen ed he e wi h a high- ecycling bu a ached di e o .
Fu u e wo k needs o add ess he powe load and spu e ing
ela ed o he ilamen s in la ge okamaks. Fu he mo e, he
compa ibili y o he QCE egime wi h de achmen emains o
be demons a ed also du ing he ilamen s.
2.2. Shape dependence
S ong shaping is c ucial o achie e he QCE egime. Local
ballooning modes become uns able abo e a c i ical p essu e
g adien . This c i ical alue is gi en by Dunne e al [21]:
αc i =0.64κ2.2(1+δ)0.9(1)
Sd=κ2.2(1+δ)0.9,(2)
simila o he c i ical alue p oposed by Be na d e al [30]. A
p oposed window o ELM supp ession opens wi h Sd>3–4
[21].
To demons a e ha a su icien shaping is necessa y, a
slow shaping amp was pe o med a o he wise cons an pa a-
me e s. Figu e 4shows ime aces o JPN 103924, wi h he
shaping a ia ion in (A) and he ou e di e o empe a u e in
(B). The gas uelling a e is cons an a Γel ≈4.8×1022 s−1.
When he shaping alue dec eases below he c i ical alue o
Sd≈5.2, ype-I ELMs e-appea as isible in (B). No e ha
he e occu s al eady a single la ge ype-I ELM jus be o e 15 s
showing ha he uelling le el is al eady ma ginal a sligh ly
highe shaping.
Figu e 4. Time aces o a shaping amp om QCE o ELMy. The
pulse has Ip=2.0MA, B o =2.8T, Phea ≈22MW and
Γel ≈4.8×1022 s−1. The ansi ion occu s a abou 15.5 s as
indica ed by he e ical black line. (A) shaping pa ame e as de ined
in (1) om [21] and (B) peak su ace empe a u e o he ou e
di e o a ge .
2.3. Fuelling dependence
Whils excessi e uelling migh lead o a educed pe o mance
[31] o o an H-L back- ansi ion (and po en ially o a sub-
sequen dis up ion) [32,33], high uelling is bene icial o
powe exhaus as i inc eases he sepa a ix densi y and wi h
his he sc ape-o laye adia ion [34,35]. In addi ion, a lowe
limi o uelling o a oid ype-I ELMs and s aying in QCE is
epo ed in AUG [18]. As men ioned in he in oduc ion, he
uelling dependence can be iewed as a c i ical densi y a he
e y edge o he plasma. Due o he ela i ely ixed sepa a -
ix empe a u e se by pa allel elec on conduc ion, he dens-
i y is he main pa ame e in luencing bo h p essu e and col-
lisionali y. P elimina y analysis indica es ha Te,sep ≈110–
130 eV while ne,sep ≈1.5–3.5×1019 m−3in he JET da a se ,
he de ailed analysis o he sepa a ix pa ame e s is s ill ongo-
ing. We no e ha a a ia ion in empe a u e has a s ong impac
o he collisionali y as shown by [22] and in [18] o QCE in
4
Nucl. Fusion 65 (2025) 024003 M. Fai sch e al
Figu e 5. Time aces o (A) Be-II line emission and (B) peak ou e di e o a ge empe a u e as ypical ELM indica o s. All pulses ha e
Ip=2.0MA, B o =2.8T and Sd≈5.3.
AUG. We ocus he e on he in luence o uelling as ex e nal
con ol pa ame e and show ha indeed also in JET he beha-
iou o he QCE egime is quali a i ely consis en wi h ha in
AUG and TCV. Figu e 5shows he wo p ima y ELM moni -
o s, Be-II line emission and a ge empe a u e, o ou plasma
pulses wi h Ip=2.0 MA and |B o |=2.8 T. The main di e -
ence be ween he wo pulses in (a) and (b) is he uelling a e,
wi h ΓD
el ≈3.6×1022 s−1in pulse JPN 103404 (a) exhibi ing
ELM beha iou and ΓD
el ≈4.9×1022 s−1in JPN 103451 (b)
showing he ilamen a y signa u e ypical o he QCE egime.
Mo e uelling was needed a highe plasma cu en and/o
lowe sa e y ac o in o de o ob ain QCE. This is expec-
ed assuming local ballooning modes a e esponsible o he
absence o he ype-I ELMs due o he dependence on he
sa e y ac o and expec ed s eepe g adien s a highe cu en
[18,21].
2.4. Neon seeding
Neon is a p ima y candida e as a adia ing species in ITER
[36]. In he JET expe imen s epo ed he e, small o mode -
a e amoun s o Ne we e used o p o e he compa ibili y wi h
adia ing plasma condi ions and o educe he di e o hea
lux. Figu e 5(c) shows ELM and ilamen signals o a pulse
wi h a small amoun o neon injec ion (JPN 103407) wi h o h-
e wise he same pa ame e s as pulse JPN 103404, shown in
igu e 5(a). Bo h pulses ha e a deu e ium injec ion o ΓD
el ≈
3.6×1022 s−1while in he neon seeded case a neon in lux o
ΓNe
el ≈0.12 ×1022 s−1is added, leading o a co e neon con-
cen a ion o cNe ≈0.8%. No e ha Ne luxes o de achmen
s udies a e ypically abou one o de o magni ude highe lead-
ing o concen a ions inside he pedes al o he o de o 2.0%
[37,38]. Neon is adia ing p ima ily in he di e o and plasma
edge egions [37,38] wi h a peak in he cooling ac o a ound
30 eV [39].
The ELM/ ilamen beha iou as well as he kine ic p o iles
a e e y simila be ween he neon seeded discha ge and hose
wi h a highe deu e ium gas a e as shown in igu e 5(b). The
amoun o addi ional elec ons in oduced by Ne is oo small
o change he edge densi y su icien ly. We specula e, ha he
inc eased adia ion migh su icien ly lowe he powe lowing
h ough he pedes al in o he sc ape-o laye and hus educe
he empe a u e and inc ease he collisionali y a he pedes al
oo . In addi ion, he colde di e o migh inc ease he e i-
ciency o uelling due o ecycled deu e ium. Bo h ideas a e
suppo ed by IR measu emen s, which indica e educed di e -
o a ge powe loads.
Ope a ing a high gas a e is hampe ed by limi s o he neu -
al p essu e in he NBI duc in JET. Thus, subs i u ing deu-
e ium wi h neon in o de o achie e QCE has a bene icial
consequence o he ope a ion o he NBI sys em. The lowe
neu al p essu e wi hin he NBI duc as well as he lowe coup-
ling esis ance o he ICRF an ennas indica e ha he a -SOL
densi y o he neon seeded case is lowe han wi h he inc eased
deu e ium a e.
While he ion sa u a ion cu en measu ed a he ou e
di e o a ge does no show a clea change, he adi-
a ed powe inc eases signi ican ly om abou P ad ≈5.8 MW
o P ad ≈10.5 MW wi h he addi ion o neon a he same
deu e ium gas a e. The di e o a ge hea lux educes
5
Nucl. Fusion 65 (2025) 024003 M. Fai sch e al
acco dingly. This is in e ed by IR he mog aphy showing an
inc ease o he peak di e o empe a u e o ∆T≈130Ks−1
wi hou neon and ∆T≈40Ks−1wi h neon a e aged o e a
1.5 s long la - op phase wi h cons an s ike line posi ion.
F om his we conclude ha adding neon leads o condi ions
close o powe de achmen , wi hou ob aining a educ ion in
he pa icle lux.
3. QCE ope a ion wi h a deu e ium- i ium mix u e
JET o e s he unique oppo uni y o ope a e in i ium (T)
and in a mix u e o deu e ium and i ium (D–T). Two D–
T expe imen al campaigns we e ecen ly conduc ed, named
DTE2 and DTE3. While DTE2 in 2021 ocused among o he
usion issues on he op imisa ion o usion powe and ene gy
[40], DTE3 in 2023 was mo e ocused on in eg a ed scen-
a ios and powe exhaus in es iga ions [41]. S udies in hese
campaigns showed ha he nea sc ape-o laye powe all-
o leng h does no change ou side o measu emen unce ain-
ies be ween D and T [42] while he densi y may decay mo e
slowly, leading o an inc eased densi y in he a -SOL in T
and D–T [43]. An inc eased plasma p essu e was ou inely
obse ed in D–T and T compa ed o D. The main eason is
an inc eased pedes al op p essu e due o an inc ease in he
densi y a oughly cons an empe a u e, see e.g. [44,45] o
ype-I ELMy H-mode.
The QCE expe imen s we e one o he execu ed ype-I
ELM- ee scena ios in DTE3 [41]. The main objec i e was o
demons a e he QCE egime in a D–T plasma and iden i y
po en ial di e ences wi h D plasmas in e ms o equi ed
gas pu o a oid ype-I ELMs, pedes al p o iles and o e all
con inemen .
As discussed, he main QCE access condi ions a e plasma
shaping and he p o iles a he e y edge o he plasma. We
ix he e he shaping (Sd≈5.3, see c oss-sec ion in igu e 1)
and use a close enginee ing ma ch be ween D and D–T plasma
pulses o show ha we can ans e a D plasma pulse in o a D–
T plasma pulse wi hou losing he QCE access.
Time aces o he D e e ence pulse, JPN 103446, and
a pulse wi h an almos e en mix u e o D–T (wi h he T
a io inc easing o e he pulse om abou 40% o 55%),
JPN 104494, a e shown in igu e 6. They a e ope a ed wi h
Ip=2.0 MA (A) and |B o |=2.8 T (no shown). The hea ing
powe di e s mode a ely due o he a ailable hea ing powe
pe indi idual NBI sou ce, wi h PDD
hea ≈23MW and PDT
hea ≈
25MW wi h D-only NBI, see igu e 6(B). Bo h pulses ha e
neon seeding leading o a e y simila le el and dis ibu ion
o adia ion, he o al adia ed powe is shown in igu e 6(C),
while he co e neon concen a ion is lowe in D–T wi h cDT
Ne ≈
0.6%compa ed o cDD
Ne ≈1.0%.
An inc eased no malised plasma p essu e is obse ed in D–
T compa ed o D, igu e 6(D) as was ou inely obse ed o e a
wide ange o H-mode expe imen s. While o mos scena ios
he inc ease in p essu e was nea ly exclusi ely a ibu ed o an
Figu e 6. Time aces o global plasma pa ame e s o a D
e e ence pulse in blue and a D–T pulse in gold. (A) plasma cu en ,
(B) NBI (solid) and ICRF (dashed) hea ing powe , (C) adia ed
powe , (D) no malised plasma p essu e and (E) shaping pa ame e
as de ined in (1).
inc ease o he pedes al op densi y, we obse e in QCE ha
pa icula ly also he pedes al op elec on and ion empe a -
u es a e ele a ed. Figu e 7shows a compa ison be ween elec-
on and ion empe a u e, elec on densi y and elec on p es-
su e p o iles in he pedes al egion o he wo pulses du ing
he la - op.
Apa om he highe p essu e a simila hea ing powe
le els in D–T compa ed o D, he beha iou was e y sim-
ila , e.g. he same shaping and gas amoun led o he same
ELM/QCE beha iou . Figu e 5(d) shows he ELM signals o
he D–T pulse JPN 104494. The ilamen cha ac e is ics a e
e y simila o he D pulse JPN 103446 (see compa able pulse
JPN 103407 in igu e 5(c)). Indeed, no signi ican change in
beha iou was expec ed as he main heo e ical conside a ions
do no ha e any [21] o only a weak [18] mass dependence. I
has o be no ed ha due o he limi ed amoun o expe imen s
in D–T, small changes ha a e ou side he p obed expe imen al
condi ions migh exis .
Finally, one should be awa e ha he main pu pose o he
D–T uel mix is o achie e usion. The QCE expe imen s we e
no conduc ed o s udy he usion p ocesses, since he QCE
egime is a high densi y egime, which has as a consequence
mode a e cen al empe a u e in JET and wi h his a low usion
c oss-sec ion. The main ocus he e was o demons a e ha a
D–T plasma beha es simila ly o a pu e D plasma in e ms o
access o QCE and absence o ype-I ELMs.
6
Nucl. Fusion 65 (2025) 024003 M. Fai sch e al
Figu e 7. Pedes al kine ic p o iles o a D pulse in blue and a D–T pulse in gold, (A) elec on (do s and i ) and ion (diamonds wi h black
ou line) empe a u e, (B) elec on densi y and (C) elec on p essu e.
Table 1. Pa ame e ange o s eady-s a e (a leas 400 ms) QCE phases.
min max
Ip(MA) 1.5 2.25
B o (T) 2.3 3.3
q95 3.5 6.4
Phea (MW) 11 31
ad 0.2 0.6
¯
ne,co e/nGW 0.68 0.96
ne,ped/nGW 0.5 0.75
ν∗
e,ped 0.9 2.0
βN1.0 2.4
Ze 1.3 3.2
Sd5.1 5.9
cNe (%) <0.1 1.1
4. Achie ed plasma pa ame e s
Wi h he success ul ealisa ion o he QCE egime in JET wi h
me al wall, a da abase wi h a ying enginee ing and plasma
pa ame e s was assembled. This da a se by no means eaches
all he bounda ies, bu a na u al scan in pa ame e s wi hin he
gi en expe imen al ime and machine cons ain s. Some o
he main bounda ies a e speci ic echnical limi a ions o JET,
a he han physics limi s o he QCE egime. Fo example,
he maximum uelling was es ic ed by a limi o he p es-
su e inside he NBI duc . This limi depends on he plasma
shape as well as SOL and a -SOL anspo . We obse ed ha
when he close- o-double-null shape is eached, he duc p es-
su e as well as he ICRF coupling esis ance inc ease, a hin o
an inc eased wid h o he edge densi y p o ile. The limi a ion
on uelling has a di ec consequence on he achie able plasma
cu en , wi h Ip=2.25 MA being he maximum in which QCE
was obse ed in JET.
A summa y o achie ed pa ame e anges is p esen ed in
able 1. The alues a e a e aged o e s a iona y plasma con-
di ions o a leas 400 ms.
4.1. Pedes al op collisionali y
Achie ing lowe pedes al op collisionali y as AUG and TCV
was one o he goals o he JET expe imen s. We use he
de ini ion o [46]
ν∗
e,ped =6.921 ×10−18 Ze lnΛeRgeoq95ne,ped
(ageo/Rgeo)1.5T2
e,ped
(3)
wi h he Coulomb loga i hm lnΛe. A ν∗
e,ped ≈0.9–1.0 was
achie ed in a ious condi ions, i.e. wi h bo h Ip=1.5 MA and
2.0 MA as well as wi h and wi hou neon seeding (a bo h cu -
en s). Fu he educing ν∗
e,ped p o ed di icul because o he
limi ed amoun o hea ing powe (machine speci ic es ic ion)
and he na u ally high pedes al op densi y in he QCE egime.
A de ailed in es iga ion on he pedes al in he QCE egime is
le o u u e s udies.
4.2. Sa e y ac o
The edge sa e y ac o is an impo an pa ame e , bo h o he
achie able usion powe in a u u e eac o as well as o he
unde lying physics o he QCE egime [18,21]. As men ioned
abo e, mo e uelling was needed o achie e QCE a highe
plasma cu en and/o lowe sa e y ac o . The lowes sa e y
ac o q95 =3.5 was achie ed wi h Ip=2.0 MA and |B o |=
2.3 T, hence by educing he o oidal ield s eng h a he han
inc easing he plasma cu en .
7
Nucl. Fusion 65 (2025) 024003 M. Fai sch e al
5. Conclusions
The QCE egime was success ully ealised in JET in D and
in D–T. This p ocess was s ongly assis ed by he expe i-
men al indings and heo e ical unde s anding in AUG and
TCV ha guided he app oach in JET. The necessi y o s ong
plasma shaping oge he wi h su icien uelling was con-
i med in JET, in ag eemen wi h p e ious AUG and TCV es-
ul s and wi h nume ical p edic ions done o JET be o e he
expe imen s [21]. A signi ican a ia ion in he enginee ing
pa ame e s was achie ed wi hin he machine limi s allowing
u he model e i ica ion. This QCE da abase will be u he
analysed in he u u e, wi h special emphasis on he sepa a ix
condi ions, he powe all-o leng h and he impac on o he
main chambe wall, which all whe e shown o be impo an
aspec s o he QCE egime in bo h AUG [7,18,47] and TCV
[15,24].
Acknowledgmen s
This wo k has been ca ied ou wi hin he amewo k o he
EURO usion Conso ium, pa ially unded by he Eu opean
Union ia he Eu a om Resea ch and T aining P og amme
(G an Ag eemen No. 101052200—EURO usion). The Swiss
con ibu ion o his wo k has been unded by he Swiss S a e
Sec e a ia o Educa ion, Resea ch and Inno a ion (SERI).
Views and opinions exp essed a e howe e hose o he
au ho (s) only and do no necessa ily e lec hose o he
Eu opean Union, he Eu opean Commission o SERI. Nei he
he Eu opean Union no he Eu opean Commission no SERI
can be held esponsible o hem. Wo k suppo ed in pa
by a g an PID2021-127727OB-I00 unded by he Spanish
MCIN/AEI/10.13039/501100011033 and by ERDF ‘A way o
making Eu ope’.
ORCID iDs
M. Fai sch h ps://o cid.o g/0000-0002-9809-7490
M. Dunne h ps://o cid.o g/0000-0002-5259-9970
I. Balboa h ps://o cid.o g/0000-0002-5665-2222
P. Bilko a h ps://o cid.o g/0000-0002-6156-9773
P. Bohm h ps://o cid.o g/0000-0003-2590-4420
A. Kappa ou h ps://o cid.o g/0000-0003-3341-1909
D. Kos h ps://o cid.o g/0000-0002-9550-4329
B. Labi h ps://o cid.o g/0000-0002-0751-8182
O. Sau e h ps://o cid.o g/0000-0002-0099-6675
S. Silbu n h ps://o cid.o g/0000-0002-3111-5113
E.R. Solano h ps://o cid.o g/0000-0002-4815-3407
H.J. Sun h ps://o cid.o g/0000-0003-0880-0013
A. Tookey h ps://o cid.o g/0009-0009-6089-7634
E. Viezze h ps://o cid.o g/0000-0001-6419-6848
U. S o h h ps://o cid.o g/0000-0003-1104-2233
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