1. Scenario development for DT operation at JET
Presented by Luca Garzotti

2. Acknowledgements
L. Garzotti1, C. Challis1, R. Dumont2, D. Frigione3, J. Graves4, E Lerche5, J. Mailloux1, M. Mantsinen6,7, F. Rimini1, F. Casson1, A. Czarnecka8, J. Eriksson9, R. Felton1, L. Frassinetti10, D. Gallart6, J. Garcia2, C. Giroud1, E. Joffrin2, H.-T. Kim11, N. Krawczyk8, M. Lennholm11, P. Lomas1, C. Lowry11, L. Meneses12, I. Nunes12, M. Romanelli1, S. Sharapov1, S. Silburn1, A. Sips11, E. Stefániková9, M. Tsalas13, D. Valcarcel1, M. Valovič1 and JET contributors* 1UKAEA, Culham, UK – 2CEA, Cadarache, France – 3ENEA, Frascati, Italy – 4EPFL, Lausanne, Switzerland – 5ERM, Bruxelles, Belgium – 6BSC, Barcelona, Spain – 7ICREA, Barcelona, Spain – 8IFPILM, Warsaw, Poland – 9Uppsala University, Uppsala, Sweden –10KTH, Stockholm, Sweden - 11JET PMU, Culham, UK – 12IST, Lisbon, Portugal –13DIFFER, Eindhoven, The Netherlands. *See the author list of “X. Litaudon et al Nucl. Fusion
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3. Extension to stationary conditions Conclusions
Outline
Motivation
Scenarios developed
Key results
Extension to stationary conditions
Conclusions
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4. Motivation
The JET exploitation plan foresees D-T operations in 2020 (DTE2).
Focus will be on demonstrating stationary high-performance plasmas lasting for several confinement times and conduct experiments demonstrating unequivocally alpha-particle physics.
Establish a reliable scenario capable of producing 5·1016 neutrons/s for 5 s in D plasmas. (~15 MW of fusion power maintained over 5s in D-T).
Intense activity of scenario development ongoing in D and T.
Combined heating power will be 32 MW NBI and 8 MW ICRH
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5. Scenarios developed Scenarios for performances:
βN~1.8, q95~3. Push the operation towards the high current and field limits with a relaxed current profile. Baseline.
βN~2-3, q95~4. Exploit the advantages of operating at high βN with a shaped current profile and q0>1. Hybrid.
both lines of research aim at achieving a stationary scenario of the duration of 5 s featuring H98>0.9, Wth≈10-12MJ in the domain achievable on JET most relevant to ITER in terms of combined ρ* and ν*
Scenario for alpha-particle physics (ITB scenario):
high plasma performance for 1-2 s to generate a significant population of α-particles.
avoid ICRH in D-T to rule out TAEs destabilized by RF fast particles.
maximize α-particle drive in conditions of elevated q0.
minimize the damping provided by fast beam ions.
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6. Performance so far
Baseline and hybrid plasma reach a maximum yield of ~3·1016 neutrons/s.
Hybrid scenario is more effective in converting stored energy into fusion power. (More peaked density and temperature, higher reactivity for a given stored energy).
Baseline scenario neutrons:
~60% thermonuclear.
Hybrid scenario neutrons:
~30% thermonuclear.
ITB scenario neutrons:
40% thermonuclear.
TRANSP analysis
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7. Baseline and hybrid scenarios
H98~1.1 and a neutron yield of ~ neutrons/s were obtained for >5 energy confinement times (~1.5 s).
Combination of gas and ELM pacing D pellets injection.
H98~1.3, βN~2.5 and a neutron yield of neutrons/s for ~1s.
High βN domain extended to B~2.8T for first time since ILW installed.
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8. Possible explanation for baseline high performance
Pellet & gas fuelled
Fuelled by gas only
Hyun-Tae Kim et al. Nucl. Fusion 2018
Hyun-Tae Kim et al. EX/P1-5
√ψN
√ψN
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9. Proposed explanation for hybrid high performance
Feedback loop between high βp and improved pedestal stability.
Further turbulence stabilisation from high β and fast particles can feed into the loop.
Challis C. et al. Nucl. Fusion 2015
Saarelma S. et al. PPCF 2018
Garcia J. et al. PoP 2018
GENE GK simulations
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10. ITB scenario for alpha particle studies
Concentrated on alpha particle driven TAEs.
After-glow scenario (TFTR).
2.5 MA/3.4 T.
High plasma performance for 1-2 s.
ICRH-induced TAE observed after the NBI switch off, with delay consistent with the beam fast ion slowing-down time.
Dumont R. et al. Nucl. Fusion 2018
Sharapov S. et al. EX/P1-28
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11. ITB formation
q profile exhibits an extended region of low positive shear favourable for the triggering of an internal transport barrier (ITB).
Clear ITBs obtained for the first time since the installation of the ILW in JET. 6 5 4 3 2 1 q
√ψN 1
Mailloux J. et al. EPS conference 2017
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12. DT extrapolation
D-T fusion power calculated assuming D-T, same power for D and T beams.
Best hybrid and baseline pulses extrapolated to high current and additional power.
Self consistent core/pedestal modelling in semi-empirical simulations (Bohm/gyro-Bohm).
Isotope effects taken into account in physics based simulations (TGLF, QuaLiKiZ).
Uncertainty due to different currents and bootstrap current models. 19 15 11 7 3
PFUS (MW)
PIN (MW)
CRONOS-TGFL & JINTRAC-QUALIKIZ: filled symbols
JINTRAC-BGB: open symbols
CRONOS-CDBM: Stars
Hybrid
Baseline
ITB
Garcia J. et al. TH/3-1
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13. Further development
Baseline scenario will be pushed towards higher current and field.
Detailed extrapolation path will depend on many factors, such as:
Optimum βN,
Choice of ICRH heating scheme (H vs 3He minority),
Optimum current and q95.
Hybrid scenario will also be extended to higher field, q95 and βN:
strong emphasis placed on improving the MHD stability of the discharge to extend the MHD free phase to 5 s.
Further challenges common to all scenarios will be addressed.
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14. Disruptions prevention and avoidance
High average disruptivity affects in particular the baseline scenario.
Techniques are being developed for better disruption prediction and avoidance.
Improved termination strategies aiming at controlling impurity accumulation in the current ramp-down phase.
Generative Topographic Mapping clustering of disruptive and non disruptive plasmas
Sozzi C. et al. EX/P1-22
Gerasimov S. et al. EX/P1-24
de la Luna E. et al. EX/2-1
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15. Divertor power load control
Strike-point sweeping.
High power operations (PIN=30 MW for 5 s) are compatible with 3.5 cm sweeping. (Hybrid).
Modelling suggests 40 MW with wider sweeping should be tolerable.
Ne seeding.
Reduces the heating of the divertor tile.
Non-negligible penalty on the fusion yield.
Sweeping favourite option
Silburn S. et al. Phys. Scripta 2018
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16. Impurity accumulation avoidance
On-axis ICRH (fundamental H minority heating) reduces impurity accumulation.
More peaked electron temperature profile → enhanced turbulence drive → flatter density profile → reduced neoclassical impurity convection.
More peaked ion temperature profile (predicted by physics based modelling) → enhanced neoclassical impurity screening.
Other RF schemes foreseen for DT (e.g. 3He minority heating or 3-ion schemes) will be investigated for impurity control.
~Ti
Lerche E. et al. Nucl. Fusion 2016
Casson F. et al. TH/3-2
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17. Real time control improves robustness
JET pulse 92191
Simultaneous real-time control of fELM and βN developed for steady conditions with sweeping.
βN control and q-profile tailoring made possible to maintain βN~2.4 for ~3.5 s at B=2.14T with no detrimental MHD activity (critical for hybrid scenario).
MHD free phase not yet extended to 5 s.
Further optimization needed.
ELM frequency ref. and meas. [Hz]
Total gas injection rate [el/s]
βN ref. and meas.
NBI power [MW]
Lennholm M. et al. ITPA-IOS meeting 2017
Time (s)
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18. Conclusions
Good progress made towards the development of scenarios suitable for JET D-T.
~2.2·1016 D-D neutrons/s over 5 s. Will be improved when 32 MW of NBI at 120 keV and 8 MW of ICRH power will be reliably available.
The scenario developed for the study of α-particle effects, has demonstrated the potential of creating a plasma with α-particle pressure high enough to destabilize TAEs in the afterglow scenario.
All scenarios will be replicated in T to investigate the impact of possible isotope effects.
Real time control schemes to control plasma physics and machine operational parameters such as βN, ELM frequency, plasma isotope composition and divertor temperature will be used to improve the robustness of the scenarios.
The encouraging results obtained so far confirm the prospect of a successful D-T campaign on JET in 2020 with an ITER-like wall and an extended set of diagnostics.
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