The Plasma Physics Aspects of
the Tritium Burn Fraction and
the prediction for ITER
A. Loarte and D. Campbell
Acknowledgements: R. Pitts, A. Polevoi, A. Kukushkin, F. Köchl, V. Parail,
E. Militello Asp, L. Garzotti, D. Harting, G. Huijsmans, S. Futatani
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 1
Outline
 Introduction
 Overview of ITER fuelling systems
 Basis for the estimate of the burn-up fraction in
ITER
 Integrated modelling of ITER plasma scenarios
 Open issues for prediction of burn-up fraction in ITER
 Possible differences between ITER and DEMO
 Conclusions
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Fuelling Systems Configuration in ITER - I
Gas Injection System (GIS)
 Upper port level GIS : 4 ports
 Divertor port level GIS : 6 ports
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Fuelling Systems Configuration in ITER - II
Pellet Injection System (PIS)
 Two divertor ports
(Two injectors at each port)
Pellet injection in ITER leads to
peripheral particle deposition (even
for HFS including drift)
ITER – JINTRAC – HPI-2 – F. Köchl
ne (m-3)
r/a
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Fuelling Capabilities
Parameters
Unit
4He
Fuelling gas
H 2 , D 2 , T2
Bounding average/peak fuelling rate (gas
puffing + pellet injection)
Pa·m3/s
200/400
Average/peak fuelling rate for Tritium for
pellet injection
Pa·m3/s
110/1101)
Average/peak fuelling rate for other
hydrogen species for pellet injection
Pa·m3/s
120/120
Average/peak fuelling rate for 4He
Pa·m3/s
60/120
Duration at peak fuelling rate
s
< 10
GIS response time to 63% at 20 Pa·m3/s
s
<1
1)T
pellets contain ~ 10% D  T fuelling rate ~ 100 Pa·m3/s
200 Pam3s-1 = 1023 DT atoms s-1
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Basis of ITER burn-up fraction - I
 T-burn for Pfusion = 500 MW ~ 2.0 1020 s-1 = 0.35 Pam3s-1
 DT fuelling must provide (besides replenishment of burn-T)
 Core neutral source to maintain plasma particle outflux and provide He exhaust
 Edge neutral source to maintain nsep required for power exhaust
 Main difference between ITER and present experiments is the anticipated
low efficiency of neutral fuelling due to plasma dimensions leading to large
ionization efficiency in divertor/SOL
1000
PSOL (MW)
20
100
22 -1
Particles (10 s )
ITER- SOLPS
A. Kukushkin
40
60
divertor
~ 100-1000 ratio
10
core
puff
1
0.1
0.01
0.5
1.0
1.5
2.0
2.5
19
3.0
3.5
4.0
4.5
-3
nsep (10 m )
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Basis of ITER burn-up fraction - II
 A minimum value of edge plasma density is required for divertor power
exhaust  minimum divertor pressure to get semi-detached plasma
conditions and gas fuelling level (~ 100 Pam-3s-1)
ITER- SOLPS
A. Kukushkin
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Basis of ITER burn-up fraction - III
 A minimum throughput is required to provide He exhaust
- Divertor He enrichment in ITER hHediv > 0.1 and nHecore/ne < 0.05 
DT = a /(hHediv nHecore/ne) > 40 Pam3s-1
- Neutral penetration in the core is typically ~ 10 Pam3s-1  core fuelling
(pellets) is required to provide Helium exhaust
ITER- SOLPS A. Kukushkin
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 8
Basis of ITER burn-up fraction - IV
 Core plasma outflux dominated by particle flux across edge transport barrier
 to sustain time-averaged pressure at MHD stability limit DETB ~ 0.1m2/s
 <Dped> ~ 0.1 m
 nped – nsep ~ 4 1019m-3 (core fusion performance + power load control)
 DTETB ~ 3 1022 s-1 ~ 60 Pam3/s-1
Pplasma (106Pa)
ITER- JINTRAC
F. Köchl
ne (1020m-3)
DDT (m-2s-1)
Inwards anomalous
pinch (GLF23)
r/a
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Basis of ITER burn-up fraction - V
 Simple evaluation of T burn-up fraction in ITER produces very low values
 Maximum DT fuelling 200 Pam-3s-1  Tthroughput-max = 100 Pam-3s-1
 Burn-T Tburn = 0.35 Pam-3s-1
 Tburn/tthroug-max = 0.35 %
 The real T-burn fraction in ITER can be significantly larger than this simple
estimate
 Integrated simulations with stationary pedestal show that required total
fuelling for QDT ~ 10 can be much less that 200 Pam-3s-1 (~ 1/3)
 Low efficiency of recycled neutrals (in principle) allows the use D for
edge fuelling and D+T for core pellet fuelling  Tthroug-max ~ 20 Pam-3s-1
 If this applies in ITER then the T-burn fraction will be much higher than
0.35 % even if the total throughput is as high as 200 Pam-3s-1
 Major open issues :
 Transport in pedestal + SOL
 Throughput required for ELM control
 Level of T retention (not discussed  should be very different in ITER & DEMO)
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Full integrated simulations of ITER scenarios - I
Core to edge/divertor simulations including self-consistent description of
transport in the pedestal and SOL (JINTRAC)
ITER- JINTRAC
E. Militello Asp, F. Köchl, V. Parail,
L. Garzotti, M. Romanelli
 Transport in pedestal and SOL adjusted to maintain grad-P|ped limit
evaluated by edge-MHD stability (EPED) (continuous ELM model)
 Gas + pellet fuelling and impurity seeding
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Full integrated simulations of ITER scenarios - II
 Simulations with GLF23 core transport model + gas fuelling-impurity seeding
to keep qdiv < 10 MWm-2 + pellet fuelling
 Paux = 53 MW and resulting H98 = 0. 92 and QDT = 9.2 with these
assumptions
ITER - JINTRAC - F. Köchl
360
Wplasma (MJ
350
1.10
<ne> (1020m-3)
1.05
0.64
0.54
0.625
0.615
3.17
3.15
ne-sep (1020m-3)
li
q95
time(s)
560
Pfusion (MW)
500
4.0
2.0
0.25
0.15
1.30
1.15
-20.0
<nHe>/<ne> (%)
<nNe>/<ne> (%)
Zeff
Pradcore (MW)
-25.0
time(s)
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Full integrated simulations of ITER scenarios - III
 Simulations include Ne seeding and evaluate He ash exhaust (~ 5% He
concentration in the core and Zeff = 1.4
ITER - JINTRAC - F. Köchl
P
r/a
r/a
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 13
Full integrated simulations of ITER scenarios - IV
 Gas (+ impurity) and pellet fueling adjusted to get <ne> and qdiv < 10 MWm-2
 Simulations done with 50-50 DT fuelling in gas fuelling and pellet fuelling
 Gas fuelling rate 1022s-1 (20 Pam-3s-1) and time-averaged pellet fuelling rate
~ 2 1022 s-1(40 Pam-3s-1)  DT ~ 60 Pam-3s-11
 Effects of ELM control only considered on time-averaged way
ITER - JINTRAC - F. Köchl
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 14
Fuelling requirements associated with ELM control – I
 Transport in ETB is not normally semi-continuous and energy is lost by ELMs in short
bursts  increase of ELM frequency or transport between ELMs is required to
decrease ELM energy loss on divertor and to provide core W impurity exhaust
 For 15 MA operation DWELM < 0.6 MJ is required  fELM ~ 30-60 Hz
 For DWELM = 0.6 MJ  DNELM = 2.5 1020 DT ions  ELM-DT = 15-30 Pam3s-1 
similar flux as in continuous ELM model
ITER – A. Loarte
 ELM control in ITER can be achieved by two approaches both with impact on fuelling:
 Suppression by 3-D fields  increase of edge transport to remove ELMs
 Pellet triggering of ELMs
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 15
Fuelling requirements associated with ELM control – II
 Application of 3-D fields with ELM control coils enhances edge transport and leads to
direct particle losses from the confined plasma to the divertor
 Modelled decrease of core tp ~ 15-35% compared to continuous ELM model 
increase of HFS pellet fuelling by ~ 30 %
 In addition achievement of detached divertor plasmas with non-toroidally symmetric
divertor power loads may affect required edge fuelling
ITER- EM3C-Eirene
O. Schmitz
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Fuelling requirements associated with ELM control – III
 ELMs can be triggered in a controlled way by injection of small pellets
 Estimated LFS pellet size to trigger ELMs in 15 MA corresponds to 2 1021 particles
(possible overestimate by 1.5-1.7 compared to DIII-D experimental results)
 If LFS pellets do not produce significant core fuelling  sizeable throughput
associated with pellet pacing
ITER- JOREK
S. Futatani
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Core/Pedestal + SOL B.C. simulations of ITER scenarios
 Core/Pedestal modelling with boundary conditions from SOLPS and edge
stability limits from EPED (assuming 50-50 DT fuelling in gas and pellets)
 Self-consistent solution including controlled ELM particle losses and pellet injection
for fuelling (HFS) and pacing (LFS)
 Conservative assumptions for pellet pacing : no effective core fuelling by LFS
pellets and pellet size for ELM triggering (2.0 1021 particles for 15 MA plasmas)
ITER- ASTRA
A. Polevoi
QDT = 10 LFS pellets = 33 mm3
LFS = HFS pellets = 33 mm3 = 2.0 1021 particles
Throughput associated with LFS pellet pacing is dominant with these assumptions
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : Pedestal/SOL transport - I
 Integrated modelling done for ITER assumes an edge/SOL transport level
leading l p ~ 3.6 mm  determines nsep and required impurity seeding
 If lp is significantly smaller (Goldston/Eich)  higher nsep is required for
divertor power load control (nsep ~ nped for lowest lp)
 Achievable with gas-DT < 80 Pam3s-1 and impurity seeding but with nsep~ nped
ITER- SOLPS – A. Kukushkin
lp = 3.6 mm, lp = 1.6 mm lp = 1.2 mm
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : Pedestal/SOL transport - II
 High nsep plasmas allow high performance to be achieved (up to Q ~ 7) with
low core fuelling and acceptable power loads (SOLPS+ASTRA, JINTRAC) if
edge transport allows grad-p|ped to build up to MHD limit
 He removal is marginally sufficient (nHe/ne < 0.1) in this case
 Compatibility of large grad-p|ped with low grad-n|ped remains outstanding 
optimization between gas and pellet required to achieve highest QDT and lowest DT
depends on achievable p|ped
QDT = 7
ITER- JINTRAC- M. Romanelli/F. Köchl
r/a
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : Pedestal/SOL transport - III
 All studies performed assuming transport in SOL and pedestal near neoclassical
values  VDTpinch ~ 0 for ITER conditions



Diffusive transport in pedestal (DTpinch < 10 Pam3s-1)
Low neutral source  DTneut ~ 10 Pam-3s-1
Core plasma outflux and grad-n|ped controlled by HFS pellet fuelling
 Experiments are consistent with pedestal VDTpinch ~ 0 but conclusive studies not yet
complete if VDTpinch is large  strong core fuelling of by plasma not neutrals
ITER – JINTRAC - F, Köchl
AUG – ASTRA - M. Willensdorfer
ne build-up after H-mode transition
DD or T (m-2s-1)
Inwards anomalous pinch
VNeoD or T (m-2s-1)
nD+ nT(1020m-3)
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : Transient effects after pellet - I
 ITER simulations assume same edge transport during HFS pellet fuelling and
between pellets  interaction of pellet with edge transport and ELMs can strongly
affect pellet fuelling efficiency as seen in experiment
 Simulations for ITER indicate no significant loss of pellet particles by ELM on MHD
timescales  repetitive ELMs and post-pellet transport determine fuelling efficiency
ITER
Valovic- MAST
ITER-JOREK-Futatani
Pellet = 2.0 1021 particles
 Use of pellets for fuelling and ELM control should be optimized to reduce throughput
and maximize T-burn fraction
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : Transient effects after pellet - II
 Optimization of fuelling by pellets for ITER is not trivial due to large edge
density transients caused by pellet and semi-detached divertor operation
large Tdiv excursions leading to full divertor detachment (+code crash)
ITER – JINTRAC – L. Garzotti
<Te,div>
Inner
Outer
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : 3- D field effects on pellet fuelling
 Application of 3-D fields increases core particle outflux (~ 30% predicted in
ITER modelling)
 Recovery by pellet fuelling with rped > 0.8 ?
 Triggering of multiple ELMs by HFS pellets in suppressed ELM regimes at low n*?
AUG-Valovic
 Density recovery is possible in AUG by adding a pellet flux of 1.5 1021s-1 to compensate
3-D field particle loss (0.5 1021s-1 constant gas fuelling)
 Pellet loss from edge associated with subsequent ELMs
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : 3- D field effects on edge power flows/detachment
 ELM suppression by 3-D fields offers an alternative with possibly less total
throughput than pellet pacing but may require larger gas fuelling due to
effects on power loads (in addition to more core fuelling to recover <ne>)
ITER-EMC3-Eirene
Schmitz
NSTX-Ahn
ITER- ASTRA
A. Polevoi
 Modelling of detached plasmas with 3-D fields for ITER is required for quantitative
evaluation of possible enhancement of gas fuelling level
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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Open issues : core DT transport - I
 Transport in central plasma region is predicted to be close to neoclassical for
ITER with several turbulent transport models
 Neoclassical effects on core D and T transport determine central nDT peaking
and reactivity in r/a < 0.2
ITER-ASTRA-Polevoi
2.5
-3
Density (10 m )
20
1.5
1.0
0.5
0.0
0.00
ni ECH - Off axis
ne
ni ECH - On axis
ne
ni ICRH - On axis
15
19
2 -1
i & e (m s )
2.0
ne
0.25
0.50
r/a
0.75
1.00
10
5
0
0.00
0.25
0.50
0.75
1.00
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 26
r/a
 Differences in D-T turbulent transport for r/a > 0.2 under study
Open issues : core DT transport - II
Neoclassical transport studies carried out to determine physics of core
D and T transport in ITER
 Residual D + T core density peaking due to different ion masses
 Net D & T are determined by balance of outwards 𝐷𝛻𝑛 and
ITER - NEO - E. Belli
inwards n𝑣 (>> NBI) and have opposite directions  depletion of T in
r/a <0.2
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 27
Summary of ITER findings
 Recycling fluxes and gas puffing expected to be very ineffective to fuel the
core plasma  edge and core D/T mixes are decoupled
 Core plasma fuelling requires pellet fuelling  Magnitude of required core
fuelling is relatively low compared to the total throughput ( < 40 Pam-3s-1 out
of 200 Pam-3s-1)
 Core plasma fuelling has to be increased to compensate additional particle
losses from ELM control by 3-D fields (~30% 55 Pam-3s-1 )
 In addition, use of pellet pacing for ELM control itself increases throughput
significantly if pacing pellets do no significantly fuel the plasma
 Decoupling of edge and core D/T fuelling may allow optimization of T-burn
 Tburn = 0.35 Pam-3s-1 + use of D for all fuelling except core T fuelling 
THFS-pellet = 23 Pam-3s-1  T-burn fraction 1.5 %
 Even if T-burn is 1.5% DT fuel reprocessing will remain large if maximum
D+T = 200 Pam-3s-1 is required
 If significant edge pinch  50-50 DT fuelling both in pellet and gas fuelling
required  0.35-0.7% T-burn fraction for D+T = 100-200 Pam-3s-1
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
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DEMO-ITER differences - I
ITER and DEMO plasmas are quantitatively different but qualitatively similar
 Large size and expected ineffective core fuelling by recycling flux
 Similar plasma collisionality, etc.  similar edge and core transport
 H-mode operation and thus need for ELM control
 Self-consistent solution has to include controlled ELM particle losses and
pellet injection for fuelling and pacing (more peripheral pellets ?)
 But much larger Ptot/R  different solutions to edge power load control
 Advanced divertors with very high Praddiv (compared to ITER) and
similar Pradcore to ITER
 Conventional divertor with similar Praddiv to ITER and much higher
Pradcore than ITER  unviable solution in ITER due to H-mode
threshold but possible in DEMO
ITER Q =10 : Pheat = 150 MW, Pcorerad < 50 MW, Psep > 100 MW, PL-H = 70 MW
DEMO1 : Pheat = 460 MW, Pcorerad = 300 MW, Psep = 160 MW, PL-H = 130 MW
 If such level of Pcorerad requires high nZ at plasma edge  DEMO and
ITER fuelling and T-burn fraction may be different
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 29
DEMO-ITER differences - II
 Low grad-n|ped (power load control) and large grad-T|ped in ITER and
DEMO lead to good neoclassical screening of impurities by DT in the
pedestal region an hollow impurity density profiles vZpinch > 0
 Neoclassical force balance leads to vDTpinch < 0  low in ITER Q = 10
due to low nZcore to keep low Pradcore
ITER – STRAHL+NEOART - Dux
0
1.0
r/a
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 30
DEMO-ITER differences - III
 ITER modelling at low Ip/Bt (7.5MA/2.65T) which allows higher Pradcore
in H-mode show that effects of impurities on inwards DT edge pinch
can be significant
vpinchDT ~ -3 to -5 m/s  60 – 120 Pam-3s-1 for 7.5MA/2.65T in ITER
ITER – JINTRAC - Parail
nDT
vDTpinch
nAr
nNe
vArpinch vNepinch
r/a
Consequences for DEMO fuelling and T-burn ratio with conventional divertor and high
Pradcore should be evaluated
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 31
Conclusions
 Evaluation of T-burn and ITER fuelling show that total T and D fuelling
capabilities (and split between pellet and gas) are appropriate for Q = 10
operation taking into account physics uncertainties
 Fuelling and T-burn evaluation requires complex and integrated models due
to strong coupling between fuelling and helium + power exhaust
 Degree of T-burn and throughput minimization depends on :
 Effective level of fuelling by edge neutrals in ITER
 Edge/pedestal transport and degree of separation between core and edge fuelling
(including varying T/D profile across plasma)
 Additional core T fuelling and overall DT throughput required for ELM control
 Additional edge fuelling required for divertor power load control with 3-D fields
and/or lp < 3.6 mm
 Evaluation for DEMO should be carried out along a similar approach to ITER
but final quantitative answer may have to wait to ITER operation
 Experiments on outstanding issues for ITER/DEMO in relevant plasmas
(fuelling with thick-SOLs to neutrals, peripheral pellet deposition, including
ELM control, etc.) and with isotopic mixes (D/H, D/T) are strongly
recommended to improve accuracy of ITER/DEMO evaluations (JET & JT60SA can play an important role)
A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016
Page 32
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