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Technical Challenges on the path to DEMO

Technical Challenges on the path to DEMO. Derek Stork Euratom-CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK. This is a personal opinion…………. … intended as a contribution to a debate … How can we gain back time on Fusion’s Development Roadmap?. Outline.

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Technical Challenges on the path to DEMO

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  1. Technical Challenges on the path to DEMO Derek Stork Euratom-CCFE Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK

  2. This is a personal opinion………… … intended as a contribution to a debate … How can we gain back time on Fusion’s Development Roadmap?

  3. Outline • Comments on Fusion Roadmap ‘standard model’ • DEMO mission and critical path • Dividing resources for a “DEMO programme” into: • Baseline • Optimisation programme • Strategic Risk Reduction programme • Categorisation of DEMO Technical Challenges • Baseline, Optimisation or Strategic Risk Reduction? • Characteristic of challenge • Motivate definition of the ‘DEMO Stage’ • Use in refining the Accompanying Programme to ITER (and perhaps ITER “Phase II”?) • Baseline DEMO Technical Challenges & programme elements • ‘DEMO Optimisation’ Technical Challenges & programme elements • ‘DEMO Strategic Risk Reduction’ programme elements Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  4. Fusion Roadmap(still a Fast Track ?) Concept improvements Satellite Tokamak ? JET + Other m/c Power Plants DEMO ITER DEMO IFMIF (Materials testing) ? Need to define the ‘DEMO stage’ mission and facilities Technology Programme Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  5. Roadmap: DEMO’s mission • supply of nett electricity (several 100 MWs) at intermittent times • Demonstration of high levels of reliability and availability at end of programme • allow economic assessment of a fusion power plant Urgent to have early DEMO implementation – ‘existence proof’ important for those outside Fusion! – de-emphasise the economics. EFDA DEMO Ad Hoc Group 2010 Zohm, FST 2010 • The main DEMO reactor is the ‘last research machine’ before the First of a Kind Fusion Power Plant (FPP). • In Europe DEMO’s mission has been quoted as: • completion of nuclear lifetime testing of in-vessel components; • demonstration of tritium self-sufficiency – integration of full breeding blankets into full tritium fuel-cycle plant; • demonstration of efficient and low-turnaround remote maintenance and replacement of the key tokamak systems (divertor and blanket); • demonstration of fusion’s environmental (low activation materials) and safety (safe operation; acceptable licensing/safety case) credits; • supply of nett electricity to the grid; • demonstration of high level of reliability and availability; • supply of economically competitive electricity. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  6. Roadmap: DEMO’s critical items (I) DEMO concept based on PPCS Model C) – KIT, CEA (2007) Load Assembly remains the core of any DEMO machine • System andDetailed design and validation of Load Assembly in-vessel items requires • full nuclear qualification of structural materials. • finalised/qualified Blanket concept • finalised/qualified Divertor concept • Moreover System and Detailed design of Balance-of-Plant and Remote Maintenance requires  finalised/qualified Blanket and Divertor concepts • Clearly these items are the ‘critical three’ for DEMO Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  7. Roadmap:DEMO’s critical items (II) Eurofer embrittlement Creep issues for Eurofer …Use active cooling?…or..… use ODS?…or… Source – 2008 Ann Report of the Association FzK/Euratom – EFDA/06-1454 study E Magnini et al • For the Blanket, the Divertor and the nuclear degradation of their structural and PF materialsEngineers must have validated data and engineering rules for final design against anticipated Load conditions and degradation of properties. • Everything is inter-dependent in a complex way.Detailed examples abound Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  8. Roadmap: DEMO critical paths (I) Requires IFMIF tests ITER schedule gives this as ~2029 • No timetabled path to producing at divertor with ~50 MW.m-2 handling . • Other key items for DEMO detailed design are on critical paths with relatively fixed long lead duration: • nuclear qualification of structural materials to ~ 4-6 MW.a.m-2 14 MeV neutron flux; • output of post-experimentation testing of TBMs from ITER DT operation. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  9. Roadmap: DEMO critical paths (II) IFMIF • No accepted timetable for IFMIF, but we take ‘Critical’ (middle of the road) timescale from EU Road-mapping presentation § • At 20 dpa/fpy 40 dpa is reached in 2030 Conclusion: crucial data from Blankets and Nuclear Materials is not available until ~ 2029-30: marks the point at which ‘system design’ can start § Moslang, Baluc, Diegele, Fischer et al., CCE-Fu Workshop on EU Fusion Roadmap – Garching April 2011 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  10. Dividing the DEMO stage programme areas Resources • All potential programme expenditure (Technology Facilities, Satellite Machines, Development Lines) should fit into one of these programmes. • Use this categorisation to determine where the contributions of eg. ITER can best be utilised, and avoid duplication of effort. • ‘DEMO Baseline programme’ • aim to realise the DEMO machine at the earliest possible time; • Handle the ‘DEMO-phase’ major risks. • ‘DEMO optimisation programme’ • Concentrates on developing technologies/techniques which • make cost-of-electricity more attractive; • Improve reliability of plant • can be ‘feasibly’ incorporated relatively late into DEMO-phase. • ‘DEMO strategic risk management programme’ • handles the ‘long-term’ programme technical risks • develops technologies/systems which will ‘future proof’ a Fusion Economy Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  11. Baselining DEMO choices …carry out preparation/evaluation phase with the basic philosophies of… • Using ‘Systems engineering’ and ‘Systems code’ approach • Not introducing further competing critical paths – Baseline should be conservative. • Aiming for a reliable and available product – maximum use of Industry at this stage in Baseline programme R&D. • Maximising use of synergy/common cause with other technology development fields– Generation IV fission materials, High Temperature superconductors etc.-- both for inclusion and exclusion from the baseline! ….In an EU context – ‘Preparation Phase’ would run to mid-2010s to allow evaluation of the Baseline options, establish Core Design Team(s) and complete BA activities. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  12. ‘Baseline’ will be an evolving entitycan’t fix everything on ‘Day 1’ but all have to be firm in time System Reviews Overall SDR Baseline Programme Optimisation Programme Re-baseline (n – off) Final baseline decision Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  13. Baseline programme should concentrate on: showstoppers to operation – where ‘existence proof is needed’ the novel elements of the DEMO stage – where full-scale integrated tests will occur for the first time the core of the Load Assembly key drivers for Machine Integrity and Availability decisive tests to enable focussing selection from competing solutions to core needs. Baseline Programme Elements: characteristics eg, Divertor eg, Blanket and Ancillary systems eg, Structural Materials, Remote Handling eg, H&CD systems For timely delivery, and technical and political cohesion – Baseline MUST take maximum advantage of ITER and existing facilities – only bring in new facilities where the need is absolute. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  14. Baseline:Structural Materials (I) • DEMO mission + Systems approach with ‘Conservative Baseline’ filter should produce an operating concept to give Baseline structural material. Conservative approach favours existing Reduced Activation Ferritic-Martensitic (RAFM) steels eg. Eurofer. • Improving engineering database for RAFM steels exists • Engineering parameters • Radiation effects • Joining techniques but: • RAFM steels have known narrow temperature operating window • must be ~ > 350ºC to avoid radiation embrittlement • Must be ~ <550ºC to avoid loss of strength/creep rupture issues • and He-induced swelling at high dpa values • If, more developmental HT steels eg. Oxide Dispersion Strengthened (ODS) alloys are to be in the Baseline, they must pass clear, simple criteria for basic properties (eg. ductility at room temperature) by an early date. • Baseline risk-mitigation is needed for known Eurofer shortcomings, eg: • characterise as far as possible ahead of IFMIF tests; • minimise by design choices; • seek common solutions from Fission developments Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  15. Baseline:Structural Materials (II)Eurofer risk-mitigation by design/system choices Design for (examples!): -- high temperature operation (no change in DBTT)or-- high temperature annealing cycles (ductility restored) Gaganidze: J Nucl Matls & IAEA FEC 2008 Baseline slightly higher Cost-of Electricity (CoE) target for the first DEMO – system studies (PROCESS) show decreasing gains above ~ 60 dpa. -- Availability (dependent on Blanket Lifetime) can be sustained by increasing machine size. Ward & Dudarev : IAEA FEC 2008 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  16. Baseline:Structural Materials (III)Risk-mitigation by characterisation of Eurofer ahead of IFMIF Transmutation in pure Fe – realistic reactor FW spectrum simulated – reactor PPCS Model B simulation Lattice helium: He ‘eyes’ – 5.8 103 appm [Gilbert & Sublet: Nucl Fusion 2011] [Materna-Morris et al: IAEA FEC 2008] Surface helium:He2+ beam 103 appm/ ~ 100 dpa Also – ‘early IFMIF’? – based on energy extrapolation of de-rated EVEDA current results ?– solid (phase 1?) C target? Aim for ~3-5 dpa/fpy by early 2020s? ~100M€ ? • Use ‘isotopic tailoring’ to produce He-in lattice • Simulated by (example!) 10 B- doped RAFM steel  He significantly increases brittleness at ~ > 400appm (lattice results) – in conjunction with ~ 17 dpa • Simulate by Ion beam bombardment – He2+ (Caution! – representative of bulk??) • Surface He bombardment shows enhanced embrittlement at ~ 10 – 100 appm/dpa [Jitsukawa et al: IAEA FEC? 2008] Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  17. Baseline:Structural Materials (IV)Eurofer risk-mitigation seeking common solutions with Fission steels ODS-Eurofer ODS Ferritics Eurofer “Future steels development options will be based on evolutionary (ingot metallurgy/classical precipitation) and revolutionary (nanoscale ODS) approaches” – S Zinkle – 23rd SOFT • Generation IV Fission programme needs high-temperature steels • If we aim for ~50 dpa for early DEMO baseline then we overlap requirements of many GenIV concepts (Zinkle, Diegele) • Industry is much more at home with classical metallurgy • Common developments to obtain RA versions of Fission ‘3rd and 4th generation’ FM steels? (research melts have >105 hours at ~ 620ºC) Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  18. Baseline: EU Blankets (I) These Blanket concepts chosen for EU ITER TBM.  EU has a pair for ‘baseline’ concepts – one eventually to ‘optimisation’?. Programmatically, ITER programme pays for this DEMO development EU Power Plant Conceptual Studies (PPCS-2005) featured blanket concepts Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  19. Baseline: EU Blankets (II) Boccacini - Invited Talk; 26th SOFT, Porto, 2010 + 2 Orals; + 14 Posters HCLL HCPB • Concepts differ in Balance of Plant Tritium extraction details • … but at least the Helium balance of plant will have similar issues • Common advantage potential high thermal efficiency from helium cooling. • Common disadvantages: high helium pumping power; lack of developed helium Balance of Plant (compared to PWR ‘off the shelf’ BoP for water-cooled blanket) Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  20. Baseline:EU Blankets (III) • ‘Leading concept’ choice needed eventually to progress DEMO conceptual design of BoP- facility-based R&D to decide this. • ‘Systems Engineering’ based choice - focus on merits & drawbacks: • Corrosion of Eurofer piping by the Lithium-lead coolant - lack of data at blanket flows (few mm/sec to avoid MHD) modelling shows acceptable corrosion rates, ~ 20 mm.yr-1 for the low flow rates; • fabrication of the Li- ceramic pebbles without the cracking currently seen, and also without key impurities which delay hands-on recycling (eg. Pt-193 in the Lithium-ortho-silicate pebbles); • higher radiation damage in the solid breeder - embrittlement of the beryllium pebbles and occurrence of high swelling above 550°C,- compromising high temperature ops; • tritium release from beryllium pebbles poor until temperatures (~750°C) -- too high for known steels ( inadequate tritium recovery and high in-situ tritium inventory);.Alternative beryllide alloys (eg. Be12Ti) with more acceptable tritium release are in development, [Japan-EU BA ] currently no pebble-based solution. • liquid breeder, with low radiation damage issues appears advantageous, but needs more highly enriched fuel (90% 6Li cf. 40% for HCPB) to achieve similar tritium breeding ratios (HCLL TBR, = 1.12; HCPB TBR = 1.15). • HCPB might eventually be regarded as an ‘optimisation programme’ item? Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  21. Baseline: EU Blankets (IV):Determine Remote Handling concept ‘Multi Module Segment’ concept MMS now the favoured EU concept - applies to HCPB and HCLL advantages : - pipe re-welding (He production limit) located in a low neutron flux region - improved manifold design - decreases He pressure drop; - limits EM loads on module attachments in case of disruption Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  22. Baseline: Divertor (I) W • Divertor power loading is a show-stopper issue for a DEMO reactor – ~ 50 MW.m-2 ‘unshielded’ • As a solid, only Tungsten can satisfy criteria of melt-damage resistance, high thermal conductivity and low-erosion under plasma bombardment. • Tungsten validation: • JET ILW should further validate Tungsten as Divertor PFC material (2013-4) • JET DT experiments to validate low-tritium retention in tungsten (seen eg. in D+ plasma streams on Pilot PSI) (2015) • ITER ‘Phase II’ should run a full Tungsten divertor – water-cooled ~ 15 MW.m-2 ITER Divertor monobloc ~ 15 MW.m-2 This programme is important, but not sufficient to test a DEMO concept Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  23. Baseline: Divertor (II) • Divertor baseline will be actively cooled – even if clever concepts can give (see later) order of magnitude relief. • Chosen concept needs a full-power density test: - on a HHF facility but also - in a tokamak environment. • This mission alone is important enough to justify a ‘DEMO stage satellite’ machine – as part of the DEMO Stage baseline programme. • DEMO Divertor satellite would require: • Long pulse (cf. tR) capability for ‘steady-state’ plasmas; • heating, current drive, fuelling, plasma (& ELM??) control systems to enable high radiation fraction plasmas at high b for testing the Divertor. • High pressure, high temperature Helium or water coolant loop (or both!) DEMO Divertor satellite is urgent – could be a conversion/upgrade of existing or planned machine Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  24. Baseline: Divertor (III)Physics Scenarios Availability Physics - high b, high density Thermodynamic efficiency Net electrical power • System studies, eg. PROCESS code in Fusion Power Plan studies show: • CoE depends more heavily on operational and engineering parameters than on physics variables: D J Ward, CCFE EFDA-RP-RE-5.0[2004] • Thus technology development is more important than physics development at the DEMO Stage. • However the physics • determines if the scenario is basically feasible/attractive • scenario interacts with the technology as a key selection criterion (via the Divertor and the H&CD) Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  25. Choosing Baseline Physics Scenarios :- better avoid too much science fiction PPCS plasma cross-sections (& ITER for comparison) High b gives high Bootstrap current reduces external CD • PPCS invoked -- high density operation – significantly above Greenwald and -- enhanced energy confinement to achieve high b and high fusion yield EU PPCS - 2005 D Maisonnier et al. NF47 (2007) 1547 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  26. Choosing Baseline Physics Scenarios (II):– site your machine conservatively.- better find out the scaling laws in DEMO-like plasmas stable ITER Q=10; PPCS Mod A/BPPCS Mod C ‘Advanced’ DEMOs are not sited conservatively eg. - bN • DEMO Plasmas will be in a novel regime. [D J Ward EPS 2010] • Choice between High density and High temperature both with high radiation fraction - impurity-driven radiation for Divertor power reduction and/or - synchrotron radiation • In such plasmas, for a baseline, we need to know asap: - confinement scaling laws? - high-b stability limits? - Confinement of high bFcontent at high bth –relevant populations! • Baseline DEMO programme role for present/approved tokamaks? (JT-60SA/JET) bT,lim =bNx(I/aB) Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  27. Baseline: Divertor (III):High-temperature Helium-cooled divertor? • Conservative baseline for DEMO would favour Helium-cooled divertor, as foreseen in PPCS DEMO Model B‘Only’ ~ 65% radiation required for this design • Tungsten ductile operating window ~ 750°C (set by DBTT) and ~ 1200°C (set by recrystallisation) DEMO He-cooled Tungsten-armoured concept (KIT) W-26%Re W W-La2O3 -Helium-cooled modular divertor (HEMJ) 830ºC 1200ºC Thimbles tested at 12 MW.m-2 ≤ 200 cycles System simplification if Divertor and Blanket coolants are the same. For EU  urgent to evaluate seriously He-cooled divertor development potential Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  28. Baseline H&CD system(s) • Conservative (bN< 3) DEMO Studies call for very high installed Current Drive powers  240 – 270 MW for PPCS Models A/B and AB.. • PPCS assumptions were: • ‘wall plug efficiency’ hwp=0.6 • ‘current drive efficiency’ as 1.5 MeV NNBI gCD=0.45 (1020 A.W-1.m-2) • On today’s H&CD technology/operational achieved status required H&CD grid demand would be much higher • For all real systems: • wall plug efficiency is much less than 0.6 • non-NNBI systems have lower gCD. – but latest ECCD expts? • In all ‘near-term’ designs H&CD systems dominate the power balance (circulating power, nett power to grid) and contribute plant complexity. • A serious and focussed development programme is needed. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  29. Baseline H&CD system(s) (II) • DEMO Baseline should have a minimum number of separate systems. • Each system chosen should have maximal separate task capability (avoid ‘one system per task’ mindset!) • Systems justified on the basis of elaborate feedback loops should be critically examined (are the required diagnostics forming the feedback loop really likely to be on a reactor? • Baseline choice would emphasise those systems which couple easily and flexibly to a range of plasma configurations (NNBI, ECRH) • Initial phase of evaluation should establish for each system: • R&D status – does a source exist? – does a launching system exist? – will the ITER programme, by the end of Phase I, prove the source and launch concept? – what are the R&D needs for developing and optimising the system for DEMO? Can they be handled on ITER? • Physics status – does the database for this system show it can generate relevant high-performance plasmas on its own? – does the database for CD efficiency exist? – will it exist post- ITER Phase I?– what are the urgent needs for demonstration(s) on tokamaks other than ITER? Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  30. Baseline H&CD (III):assumptions vs reality - ITER System efficiencies Auxiliary power (Ion Dump, water cooling pump, Cryo)= 4.4 MW HV and Source power = 58.2 MW Source – courtesy R S Hemsworth - ITER ‘hsource’ ~ 40.8/(58.2+4.4) ~ 0.66 Accelerated beam =40.8 MW NB to plasma = 18.8 MW Neutralised Beam = 23.2 MW hTR ~ 18.8/40.8 ~ 0.46 For NBI hWP ~ 0.66x0.46 ~ 0.30 – half the PPCS assumed value! For ECRH hWP ~ 0.52 – but gCD ~ 0.15 – 1/3 the assumed PPCS value Implies DEMOCD powers of ~ 490 MW – 920MW required! Motivator for a Pulsed DEMO baseline? Do we need steady-state ? Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  31. Reactor Power Flow with ‘realistic’ H&CD (representative - figures in MW) Neutron power Generator h=0.42 Blanket Thermal power Plasma 3600 4140 2346 1351 Electricity Grid 4140 Fusion Power 4500 Bulk Plasma Radiation (R) R 5587 1114 1114-R a- power + Aux power 94 119 Divertor 994 214 ‘Current Drive’ ‘Heating’ 333 Heating and Current Drive Helium coolant pump 285 359 350 644 Recirculating power ~ 1GW circulating power!! Conceptual 4.5GW (fusion); 1.35GW (Electrical) reactor - similar to PPCS Model A – helium cooled – H&CD systems 33% efficient -- Neutron power multiplication in blanket -- divertor takes all charged particle (conducted ) power Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  32. Baseline H&CD (IV): pulsed or steady-state DEMO? • Motivation for a Pulsed DEMO concept depends on Current Drive scenario and technology prospect: • ‘Advanced’ tokamak – hence mainly intrinsic CD? • Can external CD overall efficiency be raised? • Major engineering issue for Pulsed Machine would be fatigue life – for pulse length of 8 hours – then loading of > 30000 cycles during 30 year life. For discussion see David Ward’s talk. • Pulsed DEMO would inevitably be bigger – larger solenoid required for flux swing – predict coe increase by ~ 20% -- but some H&CD power alleviates machine size/ flux needs. Fixed pulse length – 8 hrs D J Ward (CCFE) –PROCESS –EFDA Study 2008 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  33. Baseline: Diagnostics & Control DIIID • Baseline DEMO diagnostics will be limited by: • limited views, blanket module maintenance simplification; • required radiation hardness for systems (especially windows). • systems engineering-based simplification & conservative approach • need to reach high-level of reliability – favours limited, simple systems • Thus number of active feedback control loops will be limited on a reactor. • Multi- diagnostic actuator loops will fall foul of ‘one H&CD system’ philosophy • transfer of some concepts to reactor (eg. in-vessel coils  complex & uncertain Baseline should be framed using ‘sparse control’ concepts as developed in other fields. JT-60SA would be an appropriate machine on which to test baseline strategies Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  34. Baseline for other systems • Pumping • Major issue ITER batch-regeneration cryopumps don’t scale to DEMO • Re-assessment of the existing technological alternatives and choice of most promising continuous regeneration technique (eg. snail cryopumps?)  then vigorous development programme. • Magnet Technology • to enable database gathering from ITER - baseline should be Low Temperature Superconductors (Nb3Sn and NbTi) as in ITER • (HTSC development will be handled by other technology programmes). • Safety and Licensing issues • ITER experience has to be taken for the baseline regulatory rules. • Remote Handling - determined by Blanket and Divertor concepts. • Balance of Plant • Blanket choices drive EU towards Helium circulation systems; • should capitalise on Generation IV fission systems developing these but to minimise risk Helium BoP development be part ofBaseline. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  35. DEMO Optimisation programme • The Optimisation Programme should run concurrently with the Baseline Programme, taking a fraction of the resources and aiming to realise results by the time the critical path detailed design decision is made (2028-2029). • Optimisation Programme content depends on Baseline Choices! • pulsed vs steady-state; • Baseline H&CD ‘set’ (or single system) – for the baseline system, optimisation in Baseline Prog!; • Eurofer alone or +RAFM ODS; • HCPB or HCLL;  etc. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  36. Optimisation of DEMO H&CD: NBI challenges Wall plug efficiency of 50-60% requires simultaneously: • Improvement in neutralization efficiency from 58% (gas) to ~95% • Development of photoneutralizer and/or • Energy recovery of the dumped ion beam • Improvement in transmission from 75% to 95% • Reduction of beam divergence • Removal of halo • Increased current density • Choice of Materials – potential show-stopping issues • In the Drift Duct liner --Copper and CuCrZr eliminated due to irradiation damage  GlidCop is a possible replacement but untested in HHF and HV applications • Beamline structural material within 4m of First-wall has same issues as FW. Achieving reliability requires simultaneously: • Demonstrating HV holding of >1MV at 10-50A current • Present status: 750keV/221mA & 500keV/20A (few seconds) at JAEA • Breakdown follows clump theory but degraded for large grids • Replacement or control of caesium • Alternative proving elusive; understanding role for improved management Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  37. EU Roadmap to DEMO NB DEMO design process define type of DEMO Power/ voltage define NB role integration geometry injector design efficiency EFDA work programme neutralisation transmission source energy recovery high voltage materials ops exp MITICA ops exp ITER ITER programme ops exp SPIDER maintainability operational requirements reliability E Surrey – EFDA PPP&T meeting – Garching – March 2011 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  38. Optimisation of DEMO H&CD: ICRF • Technical status of ICRF sources/transmission at ITER frequencies shows advantages: • commercial (tetrode) sources/generators 60-70% efficient; • transmission line relatively standard – developed for ITER ~95% efficient • launcher (ITER development) ~ 95% efficient Experimental current drive efficiency in agreement with theory • However: • maximum RF power coupled into H-mode is still ≤12MW (and data is from 1989-1990!) • RF coupling to shaped plasmas with H-mode/ ELMy edge is problematical and not proven by large experimental database. • FW current drive efficiency is low (scales to ~0.15 at Te(0) ~ 20 keV) needs experimental proof • If ICRF is to be retained in the baseline, high power (>20MW) systems need to prove generation and sustainment (CD) of high performance plasmas. ITER Physics Basis [NF 39(1999)2512 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  39. Optimising ICRF: High frequency FW? Ntor=90 Ntor=30 Develop HF system for FWCD off-axis? DEMO simulation at 250 MHz • Promising in theory but: - ITER will not test the system (needs modified launcher for high k⁄⁄ - new source development)- what would then be the purpose of ITER ICRF? [Van Eester & Lerche EFDA CCIC-08 ] Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  40. Near-Term EU FWCD Assessment Confirm , k// Options Assess g Assess Coupling Assume ITER SOL Comments: -community should then review ITER ICRF - please include strong large Tokamak- based programme! DEMO ICD Requirement Systems Design Option Assessment: Impact on DEMO; RAMI analysis; cost; R&D requirements. • Performance estimate. • SWOT Analysis • Sensitivity studies. • Strawman design(s) • R&D programme • Cost, manpower, timescale Option Recommendation Arcing inside in-tokamak structure? Materials and dielectrics to withstand FW 14MeV flux? R Koch – EFDA PPP&T Meeting – Garching March 2011 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  41. Optimisation of ECRH systems ECRH NNBI • ECRH has great advantages over NBI of small ‘nuclear island’ extension (capital cost reduction) • ECRH has few coupling problems, but still not employed as the dominant heating system in a high performance plasma context. • Key experiment for development would be 100% ECR-heated plasmas with high performance (20+ MW on JET or raise ECRH power on JT-60SA?) • Also for ECRH, experimental investigation of current driveefficiency merits special programme. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  42. Optimisation of ECRH systems(II) • Investigate reduction in complexity of in-tokamak launch by developing frequency tuneable EC H&CD - allows for antennas with fixed launching angle and removal of the remote/front steering mirror concepts  fundamentally different development branches of EC H&CD components. • Develop the broadband synthetic diamond window options and improve diamond window reliability? • Gyrotron efficiency (ITER prototype at JAEA) is now ~55% and transmission is ~95%. Improvements in gyrotron efficiency could come by improving the electron gun performance and making use of multi-stage depressed collectors the gyrotron  55% to > 70% possible? • RAMI analysis especially Materials assessment of radiation hardness of in-port launcher system – identification of issues. M Thumm – EFDA PPP&T meeting – Garching – March 2011 Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  43. DEMO Divertor Optimisation :‘advanced divertors’ – magnetic shaping, not technology Super-X divertor concept • ‘Super-X’ is one concept where magnetic geometry could handle extremely high Divertor loads • SOL taken to large major radius – natural flux expension; • SOL passes through low PF region - connection length is increased – further spread of power – - volume to enable power radiation before striking target. • Concept to be tested on MAST-Upgrade. If successful could be incorporated into Divertor satellite and DEMO • Issues – in-vessel coil shieldingEFDA evaluation beginning Kotschenreuther, Valanju, U Texas Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  44. Other DEMO Optimisation programme elements? • Other likely programme lines: • Development of high purity versions of Eurofer, and low activation versions of conventional high temperature FM steels. • Development of ODS Ferritic steels (if not in baseline!). • Resolution of issues relating to ‘second string’ Helium-cooled blanket concept. • Other solutions to Divertor problem by magnetic concept (‘snowflake’?) rather than engineering. • Possible programme lines: • Divertor technology back-ups (water-cooled as back –up form helium or vice-versa!); Liquid lithium divertor? • (If baseline is pulsed) Fusion-relevant energy storage systems. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  45. DEMO Strategic Risk Reduction • An assessment of strategic risks to a DEMO programme is urgent (elements of this are proposed in the EFDA 2012 PPP&T programme) • Two elements stand out for this presenter: • Component Test Facility • High Temperature superconductors, as a guard against future Helium shortages[associated to this – helium leak reduction programme.] Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  46. DEMO Strategic risk reduction (I):A Component Testing programme? • Critical paths mean DEMO is unlikely to be ready for commissioning before the late 2030s. • Consequently it is high priority to ensure an efficient DEMO programme – high availability for Blanket Testing. • Should get to ‘plateau’ region of radiation embrittlement (~> 6 MW.a.m-2 or 60 dpa) as soon as possible. This is 3 full power years. At 30% availability takes 10 years. • DEMO requires to breed tritium, relying for high availability operation on some of the components under test; • DEMO is a large and complex machine. Mean-Time-To-Replace (MTTR) test components will thus be large – leading to possible significant delays in a test programme. • IFMIF does not test components. • As a strategic risk reduction exercise, the goals of a Components testing programme and the feasibility of a pre-DEMO Components Test Facility (CTF) should be examined.[EU Fusion Facilities Review -2008; UK 20 year Fusion Review 2009] Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  47. CTF • To be useful a CTF must: • produce long periods of steady-state plasma burn to achieve the required integrated neutron yield – • with a fusion spectrum; • in a tokamak environment with accompanying stress fields; • be compact and tritium efficient enough not to depend on tritium breeding; • accommodate fully functional test components on the scale of ~ 1 m2 (relevant scale for component issues); • deploy significant area, over 10 m2, to test several scaled components in parallel(e.g. blanket modules); • be able to test prototype components up to some level before the serious start of a DEMO programme. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  48. Compact CTF design – testing capability • Testing to 20 dpa (2 MW.a.m-2) at 1MW.m-2 and 33% availability takes ~ 6 years. • Does CTF have a consistent DEMO-stage mission?? ST-CTF (Culham, EU) MAST-Upgrade will test ST physics Compact Spherical Tokamak Fusion power ~ 36 MW Neutron wall- load ~ 1.0 MW.m-2 PDIV ~ 30 MW.m-2 2009 version has Super-X concept Tritium consumption ~ 1.8 kg/fpy Tritium bred ~ 47% of usage Tritium would be available from Candu programme for both ITER and a CTF. Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  49. A tentative time-lineCTF looks late unless we move fast Pre-concept + Baseline select Baseline Concept + R&DConcept DR (Baseline Blanket ) Baseline Scheme+R&DIFMIF ITER TBM data Detailed DEMO Design Construct DEMO DEMO Divertor Satellite Site Commission Design + Constuct 20 dpa CTF ? Design Construct Operate 60 dpa Irrad Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

  50. DEMO Strategic Risk reduction (II):High-Temperature superconducting magnets • High-temperature superconductors as a replacement for ~ 4K technology lead to: • Very modest power savings ( ~ 20 MW out of 570 MW BoP power for ‘Model B HCLL reactor goes to cryoplant); • simplification of cryogenic plant & shields etc. very much ‘Generation II’ issues – other industries will develop HTSC and we cannot match their huge research budgets. • …but strategically, high-T superconductors are needed in Fusion Technology because of the Helium resource problem. • Terrestrial Helium presently comes from Natural Gas exploration – finite resources (~100 years) • Huge reserves in atmosphere ~ 4 109 tonnes – enough for ~ 107ITER cryosystems • ….. air separation of helium will be expensive to develop (can we afford it in our baseline???)…… Problem will hit ‘roll-out’ of Fusion Economy (CCFE/Cambridge/Linde modelling). • Long-term Fusion should unlink itself from Helium where possible, (and strategically needs to develop leak-tight He systems!) Technical Challenges on the path to DEMO - D Stork invited talk PPPL MFE Roadmapping meeting

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