ITER contributions to closing DEMO physics gaps

Transcription

1 ITER contributions to closing DEMO physics gaps SD Pinches, DJ Campbell, Y Gribov, GTA Huijsmans, S-H Kim, M Lehnen, A Loarte, JA Snipes, G de Temmerman Science & Operations Department, ITER Organization The views and opinions expressed herein do not necessarily reflect those of the ITER Organization Page 1

2 Physics for Fusion Power Plants A fusion power plant requires physics parameters that are simultaneously close to the limits of what might be achievable on the basis of our (experimental and theoretical) understanding Several key issues in (burning) plasma physics for a tokamak power plant must be developed in the current programme and demonstrated (and extended) in ITER: Operating scenario - steady-state High confinement at high density and high radiated power fraction High fusion power high operation robust MHD stability Effective disruption avoidance and control Power (and particle) exhaust with relevant PFCs Tritium efficiency -particle confinement Reactor-relevant auxiliary systems (H&CD, diagnostics, fuelling, control ) Page 2

3 Plasma Stability: MHD & Energetic Particles Magnetic control Radial position control, plasma-wall gap control, reactions to β drop Vertical stability without in-vessel coils Error field measurement and control MHD stability Predict and optimize approach to stability limits in real-time Optimize sawtooth control to maximize performance and avoid NTMs Optimize tearing mode control with ECH/ECCD at multiple q surfaces Optimize resistive wall mode (RWM) control through error field and rotation profile control Energetic particles Runaway electron control to mitigate first wall damage Alfvén eigenmode control to ensure stability of fusion burn and control energetic particle redistribution and losses to plasma facing components Page 3

4 Sufficient Plasma-Wall Gaps to Avoid Melting First Wall Modelling of an H-mode to L-mode Transition at Q=10 with 15 MA Radial inward displacement can be 10cm contact with the inner wall Duration of inner wall contact depends on the central solenoid saturation state Peak engineering heat loads of ~40 MW/m 2 Be tiles would melt in ~ 0.3 s! PCS must maintain large enough gaps or trigger the disruption mitigation system Page 4

5 DEMO-Relevant Integrated Control in ITER Advanced plasma control Actuator sharing management for multiple simultaneous control Event handling for event-driven real-time control changes Faster-than-real-time forecasting to predict approach to operating limits High plasma performance integrated control Simultaneous control of first wall and divertor heat flux, core radiation, MHD stability, and stored energy First demonstrated fusion burn control, D/T fuelling ratio, fusion power, Alfvén eigenmode control Long pulse control Current density, plasma rotation, temperature and pressure profile control Hybrid and steady-state scenario control Requirements for long pulse current drive at high performance Page 5

6 DEMO-Relevant Event Handling Real-time Hot Spot Detection G Arnoux IAEA 2008 #69327, f297 Crucial for machine protection PCS is first line of defense to avoid triggering Central Interlock System To save valuable plasma time e.g., hot spot detection Control scheme changes in real-time Change algorithm to maintain performance or reduce machine damage Automatically switch to alternate segments if initial objective cannot be met Implement real-time forecasts Real-time modeling of performance Predict plasma regime changes Predict and avoid MHD instabilities Predict, avoid, and mitigate disruptions Page 6

7 Burning Plasmas, Q>5 ITER will demonstrate the feasibility of controlled high performance burning plasma operation Covering entry to burn, flat-top burn control and exit from burn Active feedback control on instabilities, performance, parameters and profiles, taking into account the plasma state evolution and engineering/physics limits Optimized feedforward inputs and reference waveforms Identification of necessary diagnostic measurements, actuators, control algorithms and recipes for supervisory system ITER will provide Input for DEMO relevant diagnostics, actuator and control requirements Input for achievable burning plasma confinement and performance in DEMO Operation recipes and ideas for performance control near ignition Input for feasibility of burning plasma operation with a reduced set of controls available in DEMO Page 7

8 ITER Will Enter New Fusion Burn Control Regime Novel aspects of burning plasma physics are key to the ITER Research Programme -particle/energetic particle physics: Energetic particle confinement at low *(= r L /a ~(T ½ /B)/a), influence of self-heating Nonlinearly coupled MHD with Alfvén Eigenmodes (AEs) Enhanced heat loads with high fusion power Burning plasma control scenarios: Burn control through D/T mix profile control Dominant core pellet fuelling is also a new regime Transport barriers and their control (isotope effects in DT?) Nonlinear interactions between and auxiliary heating, plasma pressure, rotation and current density profiles Can Alfvén eigenmode stability be used for burn control? Page 8

9 Steady-State Operation ITER will explore the feasibility of steady-state operation by operating the plasma at a reduced current/density for up to 3000s flat-top ITER will provide input for DEMO-relevant steady-state operation Beyond fully non-inductive operation Zero or negative poloidal flux consumption during the flat-top Study of feasibility of high li (with f NI >1.0) vs. low li (with f NI ~1.0) steady-state operation Internal transport barrier (ITB) control using active profile controls and/or a recipe for stationary ITB formation Requirements for current sources relevant to the steady-state operation and/or active profile control Near on-axis CD (high efficiency) vs. far off-axis CD (for q control) Page 9

10 Steady-State Operation Discovery of internal transport barriers advanced scenarios plasma with reversed central shear + sufficient rotational shear internal transport barrier enhanced confinement reduced current operation + large bootstrap current fraction active MHD control reduced external current drive + current well aligned for MHD stability and confinement enhancement Steady-state operation + High fusion power density But development of an integrated plasma scenario satisfying all reactor-relevant requirements remains challenging Page 10

11 Current drive provides: Current Drive Replacement of the transformer drive towards steady-state plasma Manipulation of the current profile to improve confinement / stability Direct suppression of plasma instabilities Current drive efficiency ( CD = driven current/input power): Typically increases with T e For beams, also increases with E b Favourable for ITER C Gormezano et al, Nucl Fusion 47 S285 (2007) Page 11

12 Heat fluxes in DEMO Heat flux problem becomes even more stringent in a post-iter device P fusion ~ a few GW, but linear dimensions not very far from ITER N. Asakura, 2 nd IAEA-DEMO workshop Very large radiation fractions will be needed Tolerable heat fluxes will be determined by available technology and chosen coolant Probably unreasonable to expect heat extraction capabilities >>10s MW.m -2 for solid plasma-facing components (critical heat flux) 3 rd IAEA DEMO Programme Workshop, ASIPP, Hefei, China, 11th 14 th May 2015 Page 12

13 Helium-induced effects High fluxes of helium ions on divertor surfaces (fusion ash) Low energy (below displacement threshold) High surface temperature (>600K) ~ K ~ K > 2000 K PISCES A: D 2 He plasma PISCES B: pure He plasma M. Miyamoto et al. NF (2009) K, 1000 s, 2.0x10 24 He + /m 2, 55 ev He + M.J. Baldwin et al, NF 48 (2008) K, 4290 s, 2x10 26 He + /m 2, 45 ev He + Pilot PSI: pure He G. De Temmerman et al, JVSTA, submitted 2300 K, 1000 s, 2x10 27 He + /m 2, 50 ev He + Significant morphology changes: continuously evolving material. Observed on many metals: Fe, Al, Mo, etc Not clear yet how problematic this could be (active research) but certainly strongly affects the material thermo-mechanical properties 3 rd IAEA DEMO Programme Workshop, ASIPP, Hefei, China, 11th 14 th May 2015 Page 13

14 Very large fluence effects Besides surface morphology changes, surfaces (esp. in divertor) will be exposed to unprecedented ion doses in ITER (even more in DEMO) Creation of defects in the material way past implantation zone H/He-induced embrittlement, grain boundary weakening, reduced thermal properties E. Bernard, ITPA DivSOL, Nov No understanding of long-term plasma exposure effects on thermo-mechanical properties 3 rd IAEA DEMO Programme Workshop, ASIPP, Hefei, China, 11th 14 th May 2015 Page 14

15 The problem of transients ELM-induced melting significantly affects material structure Tungsten sample exposed to high-energy ELM-like pulses in Pilot-PSI S. Bardin et al, JNM, in press However, significant damage is observed for large(ish) pulse numbers even below melting threshold Cracking due to fatigue Transients need to be mitigated in ITER and most likely completely eliminated in a reactor, at least if solid materials are considered After 100,000 JUDITH pulses at 0.3MJm -2 Th. Loewenhoff et al., PSI rd IAEA DEMO Programme Workshop, ASIPP, Hefei, China, 11th 14 th May 2015 Page 15

16 And what about neutrons? Neutron loading is not a major issue for ITER PFM but will definitely be for any reactor-class device Several effects: microstructure modification, hardening, embrittlement, transmutation, T uptake M. Shimada, et al, Nucl. Fusion 55 (2015) T. Tanno et al, Mat. Trans. 52 (2011) Not yet clear how neutron damage affect materials response to plasma and power exhaust capabilities 3 rd IAEA DEMO Programme Workshop, ASIPP, Hefei, China, 11th 14 th May 2015 Page 16

17 ELMs in ITER Natural ELMs in ITER low collisionality plasma are expected to have ELM energy losses up to 20MJ Divertor lifetime requirements limit acceptable ELMs to 0.7MJ (0.5 MW/m 2 ) In ITER, ELMs need to be stabilised or mitigated by a factor 30 Use in-vessel ELM control coils Pellet pacing of ELMs Use of in-vessel coils for ELM pacing by vertical kicks may be possible up to 10MA Alternative methods, like the QH-mode regime, may be an option ITER will (need to) demonstrate ELM control in the regime of low-collisionality main plasma combined with a high recycling, partially detached divertor Expected to be applicable to DEMO Page 17

18 ITER Pellet Injectors [MaruyamaIAEA2012] Pacing pellets : Geometry: one LFS, two HFS guide tubes Species: D, DT or H Speed: nominal 300m/s (limited by geometry of guide tubes) Size: mm 3 (maximum ablation at top of pedestal) Frequency: nominal 45 Hz, maximum 60 Hz (max 16Hz / injector) Page 18

19 ELM Control Coils Water-cooled picture frame coils mineral (MgO) insulated conductor (CuCrZr/Inconel) Geometry : 9x3 coils (powered independently) toroidal symmetry n=3 or 4 Current: max 90 katurns (6 turns) Page 19

20 ITER ELM control scenario requirements ELM control methods must be compatible with constraints of high Q operation in ITER Low collisionality plasma / high density / semi-detached divertor Reduction in peak heat load (1/30 th, W~0.7MJ) and acceptable wall loads Impurity control Limited confinement penalty Limited fast particle losses Consistent with fuel throughput / pumping capability Consistent with (pellet) fuelling requirements Consistent with low toroidal rotation (low torque input) ELM control close to LH threshold / Influence on LH Threshold ELM control from the first ELM NTM trigger threshold ELM control during current ramp down (q 95 = 3-6) He plasmas In-vessel coil limitations Heating power requirements Controlled erosion and limited dust production Page 20

21 ELMs in DEMO Expected natural ELM size in DEMO(1): up to 100MJ Mitigation by a factor of 8 required (includes broadening of footprint) Wenninger et al., Nucl. Fusion 54 (2014) (8pp) Can small mitigated ELMs be tolerated in long pulse plasmas? DEMO1 at 1GJ Page 21

22 ITER will establish avoidance and mitigation strategies Electro-magnetic and thermal loads, as well as the potential levels of runaway electrons, are far beyond those in present machines Lehnen et al., During most of its operational lifetime, ITER requires highly reliable disruption avoidance and prevention as well as mitigation strategies with high success rate, during DT similar to those in DEMO Page 22

23 Disruption loads and mitigation physics basis The physics basis for disruption loads and disruption mitigation has still significant gaps ITER will expand the physics basis on disruption loads and mitigation towards high current / high energy plasmas Radiation has to be maximised for successful thermal load mitigation ITER ultimately needs more than 90% radiation Lehnen et al., Page 23

24 Avoidance, prevention and prediction in ITER Simulators (IMAS and PCSSP) that can navigate close to stability boundaries for offline pre-pulse validation and real-time control include plasma, actuator, diagnostic, & plant system models Real-time shared actuator management and event/exception handling Predictor to initiate mitigation will be physics-based threshold test complemented by data-driven approaches Tokamak Plant Simulator (IMAS) Actuators Plasma Simulator Event Generator Communication Network Communication Network PCS Simulation Platform Diagnostics Page 24

25 Integrated Modelling Programme Covers all aspects of physics modelling Supports Plasma Operations and Plasma Research Extensive set of Use Cases requiring broad spectrum of codes Engages community in development Close collaboration with ITER Members domestic fusion programmes Particularly for verification and validation (cf. experimental results) Consolidation of physics knowledge into numerical models Standardised interfaces Traceability / provenance Operate and Conduct Experiments Validate and refine models and data Data Model Physics Models IMAS Develop Models Verify Models Prepare Experiments Page 25

26 Summary of ITER contributions Many areas where ITER will help close demo physics gaps Demonstration of controlled high performance burning plasma operation Heating and Current Drive capabilities Fuelling large plasmas PFCs: Material properties and behaviour Robust and reliable ELM stabilisation/mitigation Establishment of physics basis of disruption loads and mitigation Demonstration of reliable operation of Disruption Mitigation System Support to address high priority R&D issues for ITER continues to help close physics gaps for DEMO E.g. Through ITPA Topical Groups Page 26