K.Lackner*) Max-Planck Institut für Plasmaphysik, D-85748 Garching

1. Technology and Plasma Physics Developments Needed for DEMO K.Lackner*) Max-Planck Institut für Plasmaphysik, D-85748 Garching *) based largely on work of EFDA and the EU DEMO-Working Group EFDA (D. Campbell, D. Maisonnier, P. Sardain) + M.Q. Tran; G. Janeschitz, K. Lackner, G. Marbach, M. Ravnik, B. Saotic, D. Stork, D. Ward; A.Kallenbach, A. Sips DEMO: implicitely defined by FAST TRACK discussion: single intermediate step between ITER and a (potentially) first of a kind fusion power plant

2. ROOTS: FAST TRACK discussion Power Plant Conceptual Studies

3. a Fast Track version 2002

4. DEMO Working Group following completion of PPCS • identical or scalable with high confidence to a first generation power plant (physics technology AB↔C) • physics and technology demands – except availability – similar to PP • for DEMO (vs. PP): construction costs rather than COE decisive → Pel ≤ 1.0 GW

5. can a DEMO be based on a (largely) demonstrated physics scenario?

6. ITER- baseline ITER-steady 1st generation reactor designs “advanced” reactor designs bn 1.8 3.1 3.5 - 4 > 4 <b> [%] 2.5 2.9 2.2 - 3 3 - 5 5 strong 4 Reversed shear q 3 weak 2 ~ zero shear Standard H-mode 1 0 0 0.5 1 r/a DEMO base-line assumptions 2 basic physics operation modes considered ITER standard operating scenario „internal transport barrier“: ITB -modes „improved H-mode“ a.k.a. „hybrid mode“

7. why “hybride” mode considered • much broader physics base • originally considered for pulsed scenarios

8. considered in the expectation: • could be designed largely on demonstrated physics base • inductive current drive energetically favourable a pulsed DEMO/PP option? • known objections • pulsed loads • need for continuous power output (energy storage requirements) • power supplies for rapid restart • preliminary conclusions (D.Ward et al., based on PROCESS-Code): • same physics basis as pulsed device, allows also (more favourable) DC device

9. why “hybrid mode” considered achieved parameter sets start overlapping with DEMO, PPCS assumptions a 1 GWel DEMO (Process-Code ) • even an established physics scenario needs • extrapolations (to be verified) • development into an integrated scenario

10. PROs and CONs of more “advanced” scenarios

11. what are the “PROs” of ITB scenarios? cause: suppression of turbulence in a layer in core (analogy to H-mode) precondition: weak or reversed shear efficient use of bootstrap current (high fraction & distribution) good confinement (H-factor)

12. AUG DIII-D JT-60U JET 4 unstable 3 bN ? 2 Conventional H-mode 1 2 4 6 Pressure peaking: p0/<p> intrinsic problem of ITB scenarios • pressure and current profiles (li..internal inductance) unfavourable for stability • → only weak barriers, at large radius stable

13. extrapolations: to be verified (or based) on ITER

14. ITER JET AUG at constant n*, for ITER98(y,2) confinement device operating regimes in dimensionless “engineering” variables confirm assumptions for H and “hybrid” H-modes establish a scaling for ITB - modes close to Greenwald dimensionless physics parameters only known after experiment ρ* β ν* • extrapolation to ITER/DEMO • small in β • large in ρ*, and particularly! in ν*

15. figure of merit of efficiency current drive: efficiency and controllability • “hybrid”: • efficiency very important (small fbootstrap) . γ≈ = 0.5-0.6 needed • modest control requirements, central current drive o.k. • “ITB scenarios”: • high control requirements • off-axis c.d. probably needed • controllability : differing • cross-diffusion of fast particles • excitation of AE modes ITER-estimates discrepancy between predicted and observed distribution of NBI driven current on ASDEX Upgrade *) extrapolated to ITER-temperatures – to be demonstrated!

16. (largely) new territory entered with ITER

17. α-particle behaviour (fusion heating) fast particles (due to NBI or ICRH) cause range of resonant interactions, potentially leading to their loss fusion-αs different through isotropy figures of merit: further increase in reactor

18. α-particle behaviour (fusion heating) again more serious issue for ITB-scenarioes thermal ion orbits in an extreme ITB (“current hole”) discharge on JT60U

19. needs of significant quantitative progress (new concepts)

20. ARIES -AT PPCD - D PPCD - A ITER-FEAT, reference achievable β-values: limits depend on discharge duration type of intervention: magnetic feedback + resistiv wall needed for DEMO feedback by localized current drive (ECCD) needed for ITER external current drive wall stabilization most demanding (least demonstrated): control of resistive wall modes NTMs nonstationarity of current (i.e. q) - distribution

21. achievable β-values: resistive wall mode control important for ITB-scenarioes for high li (hybrid H-mode) modest need and gain for low li (“ITB-scenarios”) strong need and significant gain

22. DIII-D achievable β-values: resistive wall mode control method: similar to vertical position control, but on a helical perturbation:

23. integrated physics/engineering issues

24. physics/technology interface: plasma wall interaction tritium retention and material erosion → full high-Z (tungsten) pfc solution: not in ITER starting configuration → to be added – at latest – in phase 2 of operation • divertor load issue more severe on DEMO/PP than ITER • higher power & power density • divertor cooling (He; high duty cycle) not more efficient

25. reduction of divertor load by radiation: • higher fraction of radiative losses than ITER • limits to edge radiation? → higher-Z radiators • less dilution & Zeff • more core losses • effect on H-mode pedestal • benefit from profile stiffness • ITER´s power handling limit, and scaling of problem with size • → no direct test of solution possible • DEMO solution will have to be an extrapolation based on quantitative understanding of carefully chosen experiments on ITER & elsewhere

26. pulsed loads and anomalous events • cyclic pulsed loads (ELMs) • .. DEMO constraints even more severe than ITER (because of duty cycle and availability requirements) • anomalous events: specification 0.1 – 1*) disruption /year • multifaceted nature of disruptions • dedicated campaign phase on ITER to demonstrate achievability (during stage 2 with tungsten)..discharge number rather than time counts • *) depending on mitigation success disruption rate • successive elimination of causes of disruptions: • analogy to radioactive decay characteristics of realistic materials • → when disruption control is improved, previously hidden causes (isotopes) dominate improved control measures

27. Development of Integrated & Controlled Scenario

28. plasma control: a multifacted issue requiring a highly integrated approach example: control of divertor load and tungsten concentration dangers: mitigation (actuators): high heat load to divertors impurity and gas puffing increases radiation losses high radiation losses supress ELMs, absence of ELMs reduces W-impurity screening artificial triggering of ELMs (pacemaking) by pellets screens impurities show on ITER: how does α-particle heating work? peaked density profiles on ITER/DEMO? scaling of needed central heating power? flat heating profile or peaked density causes W-accumulation at center central electron heating by ECRH,ICRH causes impurity pump-out

29. proof of the working of individual actuators effect of a missing pellet on edge impuríty density effect of switching on ECRH on central tungsten concentration

30. example: control of divertor load and tungsten concentration

31. top-level requirements on technology

32. DEMO technology: credible 1st generation PP • from day1 of DT operation: self-sufficiency of tritium • satisfy same high levels of safety and environmental compatibility as demanded in EU PPCS (requiring, among others, use of low activiation materials) • aim at a high availability: • to produce the neutron fluences needed for testing • (during later stage) to extrapolate to an attractive reactor • technology requirements similar to 1st generation PP (also not beyond) • exception: operational experience • in this regard: DEMO an experiment

33. technology develoment needs

34. DEMO technology: progress beyond ITER • use of low activation structural and functional materials (operating temperature window critical) – IFMIF tested including joining (to 80 dpa for first wall/blanket components • RAFM (EUROFER, possibly modified by ODS) • divertor materials t.b.d. (tungsten based) • ITER-like magnet technology – or HTSC? • tritium breeding and handling • as base-line for first stage a blanket validated in modules on ITER phase 1 in thermo-mechanics, thermohydraulics • helium cooled (DC, if SiC-SiC timely available) • full fuel self-sufficiency • tritium accountability O(100) more demanding than in ITER *)classification as established predates Ciacynski-presentation

35. DEMO technology: progress beyond ITER • divertor and first wall • material tested on ITER • divertor cooling concept compatible with blanket (development of He-cooling) • heating and current drive systems • reduce to 2 out of the 4 systems included or options for ITER • raise plug efficiency • possibly push to higher performance (NBI →2MeV ?) • demonstrate the long-pulse, long-term reliability (testing) plug efficiencies expected*) *) conclusions of EFPW 2005

36. Availability: where DEMO is in a different category from ITER • remote maintenance and repair • segmentation driver of effort • compromise between modularity (use testing on ITER) & limited number of elements • design target for availability: • testing of internal components to 50dpa before start of design of FPP -> availability ≥ 33 % • second stage: make credible that if operated in a routine fashion an availability >75% could be achieved T. Ihli et al., this conference

37. Conclusions: how do requirements map to “broader approach”

38. temperature density DEMO requirements consistent with „broader-approach“? ITER + TBM Tokamaks IFMIF Modelling

39. 50 Years of Fusion Power Plant Studies ITER (scaled)