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Priority issues in ITER physics R&D

R. A. Pitts, D. J. Campbell on behalf of ITER Organisation, Plasma Operations Directorate. Priority issues in ITER physics R&D. Important to note. Much of the ITER design is now settled, though a number of smaller sub-systems are still to be finalised

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Priority issues in ITER physics R&D

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  1. R. A. Pitts, D. J. Campbell on behalf of ITER Organisation, Plasma Operations Directorate Priority issues in ITER physics R&D

  2. Important to note • Much of the ITER design is now settled, though a number of smaller sub-systems are still to be finalised • Diagnostics, Heating and Current Drive, Plasma Control, Disruption Mitigation - there are ongoing R&D issues related to the design of these subsystems • Major role now for R&D community is to reduce uncertainty in extrapolation to ITER  consolidate aggressive schedule to primary mission goal • As of the end Dec. 2010, the IO and DAs have signed 46 Procurement Arrangements • About 60% of the procurement value for ITER construction

  3. ITER Research Plan - Baseline • Current Integrated Project Schedule: • First Plasma scheduled for November 2019 with minimal in-vessel components • Target of full DT operation in March 2027 • Very aggressive schedule to achieve QDT = 10 demonstration in 2027 • All H&CD systems installed during Phase 2 Assembly (after first plasma) • HNB systems become available for plasma commissioning after ~6 months of plasma operation • Tritium Plant ready for Nuclear Operation at the end of 2024 • Tritium Plant commissioning with tritium starts in mid-2025 at beginning of pre-nuclear shutdown • Trace tritium experiments begin in early 2027 • Full DT operation in 2027 (including short pulse demonstration of Q = 10)

  4. R&D needs • Key elements of ITER’s R&D needs • Emphasis on priority physics areas where input can provide a major contribution in the effort to reach the primary mission goal as rapidly as possible • And on areas (not many) where R&D can still influence the design of sub-systems

  5. R&D needs • The key elements are primarily in the areas of • Improved physics basis for and management of thermal loads – steady state and transient (e.g. detachment control, ELM control, disruption/RE mitigation) • Characterizaton of the plasma-wall interface  erosion, migration, dust production, fuel-retention in the ITER material mix, transient damage, lifetime • Fuel recovery • Integrated operational scenarios (H, He, D, DT), control and diagnostics, especially in an all-metal environment

  6. Thermal loads – steady state Charge Exchange and photonic heat and particle fluxes~0.35 MWm-2 Secondary divertor: up to 20% PSOLq,max ~ 5 MWm-2 • ~900 m2 of water cooled, metal (Be, W) PFCs and high steady heat flux densities with operation close to double null and close fitting wall • Improved physics basis and scaling for parallel heat flux width • Better characterization of secondary divertor and understanding of far SOL heat and particle transport  feeds also into issue of material migration and ICRH coupling • Experimental and code benchmarking of ITER divertor detachment scenarios at high performance Primary divertor:~80% PSOLq,max ~ 40 MWm-2

  7. Thermal loads – transient: disruptions QSPA-T W target • Transient loads due to major disruptions, VDEs and runaway electrons are one of the most serious issues ITER will face • Improvements in experimental database for thermal loads during natural and mitigated disruptions  toroidal and poloidal peaking, footprint broadening • Improved database for thermal loads during current quench phase, including halo current thermal loads • Energy deposition characteristics of unmitigated RE  consequence for ITER Be wall? Plasma flow direction N. Klimov et al., JNM 390-391 (2009) 721 Q > 2.2 MJm-2 ~ energy density expected in a 15 MA ITER L-mode disruption

  8. Thermal loads – transient: disruptions S. Putvinski, IAEA 2010 MGI window • Development and testing of reliable mitigation systems  DMS for ITER is one critical component still to be specified • ITER DMS needs high success rate (0.95), high heat flux mitigation (0.1), sophisticated triggering algorithm • ITER needs low disruptivity (3% major disruption, 1% VDE) • Request being made for multiple injection locations, but experiments required • Experimental testing of RE suppression methods Current quench time (s) Slowing/amplification tCQ,min Nbr. Ne atoms (kPam-3) Common system (MGI)for thermal load and RE suppression appears difficult for ITER  cannot simultaneously satisfy high enough density and long enough tCQ

  9. Thermal loads – transient: ELMs • RMP coils and pellet pacing are the ITER baseline ELM control tools • Physics understanding of ELM suppression criteria – importance or not of resonant effects, role of ergodization? • Physics of particle transport in RMP ELM suppressed regimes  extrapolation to ITER • Effect of 3D RMP field structure on divertor target loads and compatibility with detached divertor? • Interaction between core pellet fuelling and RMP ELM suppression • Many others … A long list of key physics questions also for pellet paced ELMs – no time here to discuss!

  10. Thermal loads – transient: ELMs Thomsen, Eich, et al., IAEA 2010 JET ELM • Understanding ELM physics still high priority, even if emphasis is on learning to control them • Physics of ELM heat flux footprint broadening? • How does it scale with ELM and machine size  impacts the range of Ip over which ITER could operate without or with reduced ELM control • Physics basis for ELM size scaling with pedestal collisionality inter-ELM

  11. Plasma boundary interface • Shaped and conformal beryllium wall with W divertor under long pulse, high performance, high fluence conditions • Previously untested materials combination • How much lower will fuel retention be (in comparison with C and full W)? Low enough? • Erosion yields/rates and migration pathways? • Dust production rates  layer accumulation rate  fuel retention and migration pathway • Material mixing (Be-W alloys) • Radiative divertor operation in Be/W mix at high power (e.g. chemistry with N2) • ITER looks to the JET ILW and supporting programmes for answers

  12. Living with damaged tungsten J. Coenen, TEXTOR • Damage will occur to W monoblocks in the ITER divertors • Energy density transients driving W melting are unavoidable on ITER • Operation on topographically modified W surfaces appears to make matters worse • How might this affect subsequent operation – can we live with it? • What are the consequences on water cooled W material behaviour of long pulse, steady state operation with high frequency, small transients? Procurement of ITER’s 2nd divertor must begin before the 1st is used on plasma. R&D in the next few years will feed into the design

  13. Fuel recovery T removal by 350ºC baking operation 6 mm of deposited Be! J. Roth, IAEA 2010 • A fundamental aspect of ITER nuclear operation • Primary tool will be high temperature divertor bakeout (Be co-deposits) • But main walls identified as possible high risk (low Be erosion yield, shaped surfaces, close wall)  bakeout temperature lower, less frequent • Community needs to continue efforts to help ITER determine the optimum fuel recovery and conditioning strategy • ICWC, ECWC, GDC (HF-GDC), isotope exchange, strike-point sweeping, … ICWC is in the ITER baseline  EU a major player in optimising this method  efforts must continue to establish if use of ITER ICRH antenna hardware is viable and study efficiency of the technique for cleaning and fuel recovery

  14. Plasma scenarios R&D • Physics basis for scenario development (non-exhaustive list!) • Transport during ramp-up and ramp-down phases • Power requirements for H-mode access in all operation phases (e.g. during current ramps, effect of X-ptheight and neutrals, He plasmas etc. • Entry to and exit from H-mode (H98 ~1)  edge/core evolution around L-H/H-L transition and burn simulation experiments to develop control schemes for ITER. • Fuelling of DT plasmas with high neutral SOL opacity  ITER fuel cycle assumptions • Transport in low rotation, majority electron heated plasmas. • Plasma confinement with PNET ~PL-H • H-mode properties of He plasmas  consolidation of ITER non-active operation • Development of hybrid and advanced scenarios for ITER  plan for future H&CD upgrades and continued study of H&CD physics issues

  15. Diagnostics • Many issues associated with diagnostic development  two examples: • Mirrors: about 30 systems on ITER will use first mirrors in view of the plasma  measure ~100 plasma parameters in the nm to mm wavelength range.Material choices (for erosion and deposition dominated conditions)?Cleaning or mitigation of deposition? • Dust and tritium: major area for ITER safety case. Several options for measurement but no selected candidates  long development lead times  high priority About 45 diagnostic systems:Machine protection or basic controlAdvanced performance controlPhysics studiesSeveral systems on the point of procurement agreement signature

  16. Plasma control • Plasma control system is the only main ITER system for which the procurement is under responsibility of IO physics  • Conceptual Design Review planned for 2012 • PCS structure will incorporate axisymmetric magnetic control, kinetic control (e.g. PFC heat loads, radiation, fusion burn, pressure profile, fuelling), non-axisymmetric control (e.g. NTM, ELM, AE, RWM), disruption and event forecasting/handling

  17. Plasma control • Continuous need on current devices for experiments and control models to advance the PCS design or better define diagnostic/actuator/control requirements for ITER • Divertor detachment control at high power in all-metal environment using extrinsic seeding and ITER-relevant sensors • Real time first wall heat load monitoring and control • Control of ICRH coupling • Highest possible disruption prediction success rates • Experiments on core-isotope mix control with dominant core pellet fuelling • Experiments and modeling to study controllability of disturbance transients on ITER • Demonstration of shared actuator control and effective/robust event handling • …..

  18. Summary • Design of most ITER systems now complete and procurement underway • Input from physics R&D still required to complete final design of a few components/systems/diagnostics (e.g. disruption mitigation systems, glow discharge cleaning, dust and tritium diagnostics) • Continuous R&D required to prepare for ITER operations • Consolidation of aggressive plan for start of ITER Operations and efficient path to DT • Development of ITER scenarios compatible with operational restrictions and control capabilities • Optimization of ELM control schemes for maximum ITER performance • Development of disruption avoidance and mitigation strategies • Refinement of material migration, fuel retention, dust extrapolations (including development of measurement techniques and first mirror strategy) • Develop capability for accurate predictive modelling of ITER performance

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