The Plasma Physics Aspects of the Tritium Burn Fraction ... Meeting... · The Plasma Physics Aspects of the Tritium Burn Fraction and the prediction for ITER ... Core to edge/divertor

Page 1 A. Loarte – 4th IAEA DEMO Programme Workshop – KIT – 15 – 11 – 2016

The Plasma Physics Aspects of

the Tritium Burn Fraction and

the prediction for ITER

The views and opinions expressed herein do not necessarily reflect those of the ITER Organization

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


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

Outline


Gas Injection System (GIS)

Upper port level GIS : 4 ports

Divertor port level GIS : 6 ports

Fuelling Systems Configuration in ITER - I


Pellet Injection System (PIS)

Two divertor ports

(Two injectors at each port)

Fuelling Systems Configuration in ITER - II

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


Fuelling Capabilities

Parameters Unit

Fuelling gas 4He H2, D2, 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


Basis of ITER burn-up fraction - I

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.50.01

0.1

1

10

100

1000

PSOL

(MW)

20 40 60

divertor

core

puff

Pa

rtic

les (

10

22s

-1)

nsep

(1019

m-3)

~ 100-1000 ratio

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

ITER- SOLPS

A. Kukushkin


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


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


Basis of ITER burn-up fraction - IV

ITER- JINTRAC

F. Köchl

Pplasma (106Pa)

ne (1020m-3)

DDT (m-2s-1)

Inwards anomalous

pinch (GLF23) r/a

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


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/t

throug-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)


Full integrated simulations of ITER scenarios - I

Core to edge/divertor simulations including self-consistent description of

transport in the pedestal and SOL (JINTRAC)

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

ITER- JINTRAC

E. Militello Asp, F. Köchl, V. Parail,

L. Garzotti, M. Romanelli


Pfusion (MW)

<nHe>/<ne> (%)

<nNe>/<ne> (%)

Zeff

Pradcore (MW)

560

500

0.15

4.0

2.0 0.25

1.30

-20.0

-25.0

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

Wplasma (MJ

<ne> (1020m-3)

time(s)

360

350

3.15 3.17

0.615

0.625 0.54

0.64 1.05

1.10

ne-sep (1020m-3)

li

q95

1.15

time(s)


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

r/a r/a

P

ITER - JINTRAC - F. Köchl


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


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

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

ITER – A. Loarte


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


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


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)

LFS = HFS pellets = 33 mm3 = 2.0 1021 particles

Throughput associated with LFS pellet pacing is dominant with these assumptions

ITER- ASTRA

A. Polevoi

QDT = 10 LFS pellets = 33 mm3


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


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

ITER- JINTRAC- M. Romanelli/F. Köchl QDT = 7

r/a


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

AUG – ASTRA - M. Willensdorfer

ne build-up after H-mode transition

nD+ nT(1020m-3)

DD or T (m-2s-1)

VNeoD or T (m-2s-1)

Inwards anomalous pinch

ITER – JINTRAC - F, Köchl


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

Valovic- MAST

ITE

R

ITER-JOREK-Futatani

Use of pellets for fuelling and ELM control should be optimized to reduce throughput

and maximize T-burn fraction

Pellet = 2.0 1021 particles


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)

<Te,div>

Inner

Outer

ITER – JINTRAC – L. Garzotti

Open issues : Transient effects after pellet - II


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*?

Open issues : 3- D field effects on pellet fuelling

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


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>)

Modelling of detached plasmas with 3-D fields for ITER is required for quantitative

evaluation of possible enhancement of gas fuelling level

ITER- ASTRA

A. Polevoi

NSTX-Ahn

ITER-EMC3-Eirene

Schmitz


0.00 0.25 0.50 0.75 1.000

5

10

15

20

De

nsity (

10

19 m

-3)

r/a

ne n

i ECH - Off axis

ne n

i ECH - On axis

ne n

i ICRH - On axis

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

Open issues : core DT transport - I

0.00 0.25 0.50 0.75 1.000.0

0.5

1.0

1.5

2.0

2.5

i &

e (

m2s

-1)

r/a

ITER-ASTRA-Polevoi

Differences in D-T turbulent transport for r/a > 0.2 under study


ITER - NEO - E. Belli

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

inwards n𝑣 (>> NBI) and have opposite directions depletion of T in

r/a <0.2

Open issues : core DT transport - II


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


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

DEMO-ITER differences - I


DEMO-ITER differences - II

ITER – STRAHL+NEOART - Dux

r/a

1.0

0

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 Prad

core


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

nDT

vDTpinch

nAr nNe

vArpinch

vNepinch

ITER – JINTRAC - Parail

Consequences for DEMO fuelling and T-burn ratio with conventional divertor and high

Pradcore should be evaluated

r/a


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 & JT-

60SA can play an important role)


References A.S. Kukushkin, et al., Nucl. Fusion 47 (2007) 698.

M. Valovic, et al., Nucl. Fusion 48 (2008) 075006.

G.W. Pacher, et al., Nucl. Fusion 48 (2008) 105003.

A.S. Kukushkin, et al., Jour. Nuc. Mater. 415 (2011) S497.

H.S. Pacher, et al., Jour. Nuc. Mater. 415 (2011) S492.

M. Willensdorfer, Nucl. Fusion 53 (2013) 093020.

A.S. Kukushkin, et al., Jour. Nuc. Mater. 438 (2013) S203.

A. Loarte, et al., Nucl. Fusion 54 (2014) 033007

R. Dux, et al., Plasma Phys. Control. Fusion 56 (2014) 124003.

J.W. Ahn, et al., Plasma Phys. Control. Fusion 56 (2014) 15005.

A. Loarte, et al., Jour. Nuc. Mater. 463 (2015) 401.

M. Romanelli, et al., Nucl. Fusion 55 (2015) 093008.

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A.S. Kukushkin, et al., Nucl. Fusion 56 (2016) 126012.

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A.R. Polevoi, et al., Nucl. Fusion 57 (2017) 022014.

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Documents

The Plasma Physics Aspects of the Tritium Burn Fraction ... Meeting... · The Plasma Physics Aspects of the Tritium Burn Fraction and the prediction for ITER ... Core to edge/divertor