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S(tability), D(ivertor, plasma wall interaction) and W(aves and fast particles)

This summary provides an overview of the sessions on stability, divertor physics, plasma-wall interaction, waves, and fast particles at the 21st IAEA Fusion Energy Conference. It highlights the key topics discussed, statistics of papers presented, and the community's assessment of high-priority issues.

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S(tability), D(ivertor, plasma wall interaction) and W(aves and fast particles)

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  1. 21st IAEA Fusion Energy Conference- Summary Session S(tability), D(ivertor, plasma wall interaction) and W(aves and fast particles) Hartmut Zohm MPI für Plasmaphysik, EURATOM Association 21st IAEA Fusion Energy Conference, Chengdu, China, October 21, 2006

  2. Some statistics… • Session D(ivertor, plasma wall interaction and SOL): 39 papers • Retention of H, D, T and gas balance: 10 papers • Bursty SOL transport (including ELMs): 9 papers • Alternative wall materials (W, liquid-Li) + coatings: 6 papers • Wall material erosion, deposition, migration: 4 papers • Divertor physics (detachment): 4 papers • Miscellaneous: 6 papers • Session W(aves and energetic particles): 26 papers • MHD + fast particles (AEs, NTMs) and their effect on H&CD: 10 papers • ‚classical‘ H&CD (ICRH, LHCD) in tokamaks (mostly CD!): 9 papers • new schemes for concepts (EBW, solenoid free start-up in STs): 7 papers

  3. Some statistics… (continued) • Session S(tability): 27 papers • Resistive Wall Modes (including RFPs): 7 papers • NTM / sawtooth control by ECCD (no more NTM physics!): 6 papers • Disruption characteristaion and mitigation: 4 papers • ELMs (partial overlap with bursty transport): 4 papers • Miscellaneous (including dust): 6 papers

  4. Take this as the community‘s assessment of what the high priority issues are: • Session D(ivertor, plasma wall interaction and SOL) • retention of H, D, T may be a showstopper to fusion reactors • bursty SOL transport gives new fundamental insight • Session W(aves and energetic particles) • fast particle physics will be a main theme for ITER • CD is urgently needed for improving tokamak performance • Session S(tability) • NTMs pose the limit to conventional scenarios • RWMs set the ultimate limit to NTM-free scenarii • ELMs could be a serious threat to fusion reactor divertors • Well aligned with ITER high priority research items (!) • Significant contributions also from non-tokamak devices

  5. 21st IAEA Fusion Energy Conference- Summary Session Session D(ivertor physics, Plasma Wall Interactions and SOL Physics)

  6. Session D: Bursty SOL transport MAST ELM MAST L-mode • Overwhelming evidence for bursty structure in SOL during L-mode, • H-mode and ELMs (AUG, C-Mod, DIIID, JET, JT-60U, LHD, MAST….) • first attempts of nonlinear ELM models emerge (filaments connect pedestal • to SOL and are then ejected into SOL)  understanding of ELM size?

  7. Session D: Bursty SOL transport Tore Supra SOL flow experiment • These observations shed new light on the SOL structure • strong poloidal asymmetry in outflow may be due to bursts • bursts could explain observation of far SOL wings

  8. --- Total Injected --- Total exhausted --- Outgased between pulses AUG Low fuelling Session D: Retention of H, D, T and Gas Balance Tore Supra • Significant fuel retention in present day experiments • global gas balance versus post mortem analysis – 10-20% vs. 3-4% • Possible mechanisms that store ‘permanently’ hydrogenic fuel: • bulk diffusion opens ‘infinte’ reservoir • co-deposition with Carbon (chemistry involved  remote areas)

  9. DIII-D Session D: Retention of H, D, T and Gas Balance C-Mod: almost full recovery with disruptions • Solutions are urgently needed and a variety of approaches is being checked • indication that hot C-components store much less hydrogenic fuel • assessment of cleaning techniques (including provoked disruptions ) • move to non-C wall materials…

  10. Session D: Alternative Wall Materials Decrease of plasma C-content with progressive W-coating in AUG Rapid confinement degradation after boronisation (C-Mod) • Tokamaks can be operated at full performance with high-Z wall materials • but may require more frequent wall conditioning than C-wall • problems with ICRH compatibility (high Z influx) and storage of noble gases

  11. Session D: Alternative Wall Materials Operation at n=nG with Li-limiter Li-limiter surface temperature saturates (self-protection?) • Liquid-lithium – first results emerge (FTU, T-11M) • positive impact on discharge – D-pumping, no Li-blooms • but still a long way to go…

  12. Session D: Divertor physics Local island divertor in LHD gives access to very high density (Internal Diffusion Barrier IDB) Empirical rule: whenever a machine obtains good pumping, a new acronym is created (indicative of discovery of a new regime)

  13. 200 150 Frequency (kHz) 100 21st IAEA Fusion Energy Conference- Summary Session 50 4 5 Time (s) 6 7 Session W(aves and fast particles)

  14. Session W: MHD and fast particles Electron driven GAEs in HSX Electron Fishbones in FTU, HL-2A Who said that fast-particle MHD is always driven by ions?

  15. Session W: MHD and fast particles EPMs in CHS RSAEs in JT-60U • Fast particles affected by (fast particle-driven) AEs and low frequency MHD • significant progress in diagnostics (Heidbrink!) allows new insight

  16. Session W: MHD and fast particles ASDEX Upgrade: NTMs or fishbones determine q(r) DIII-D: ‘current deficit’ in the presence of a (3,2) NTM This kind of physics may play an important role in establishing the (self-organised?) improved (hybrid) H-mode (MHD  j(r))

  17. Session W: ‘Conventional’ H&CD in tokamaks Broadening of jNBCD by el.stat. fluctuations? (AUG) Broadening of jNBCD by MHD modes (NSTX) Off-axis NBCD on JT-60U, but shifted? • Conventional schemes not always that well understood (off-axis NBCD) • need to link CD efficiency to MHD/transport properties of the plasma • have to sort this out - vital for future machines (e.g. JT-60SA)!

  18. PNBI (MW) PICRH (MW) PLHCD (MW) ~4.5 sec RC (%) GIM6 13cm -2cm Da Session W: ‘Conventional’ H&CD in tokamaks Long distance (15 cm) LH coupling in JET Advanced Tokamak scenario at high Triangularity using local D2 puff (3 MW for 4.5 sec) • Progress on LH coupling to ELMy H-mode • in need of an efficient CD-scheme, we should investigate all options!

  19. Session W: New schemes for new configurations EBW in MAST EBW in TCV EBW for overdense plasmas (pioneered in stellarator) now in STs, but also in conventional tokamaks

  20. Session W: New schemes for new configurations Plasma startup w/o transformer by Coaxial Helicity Injection In NSTX Plasma startup w/o use of central solenoid by a combination of ECH and vertical field ramp in LATE

  21. Session S(tability)

  22. Session S: Resistive Wall Modes DIII-D JT-60 U • (Positive) surprises as we go to lower net momentum input… • the rotation threshold may be very sensitive to ambient error field! • but physics not yet clear (e.g. role of ni as highlighted by NSTX)

  23. Session S: Resistive Wall Modes RFX EXTRAP2-TR Note: progress in this area also from RFPs (for which it is even more vital)

  24. Session S: Neoclassical Tearing Mode Control NTM stabilisation with ITER relevant broad deposition in ASDEX Upgrade Feedback controlled Deposition in DIII-D Demonstration of individual elements as well as integrated feedback

  25. Session S: Neoclassical Tearing Mode Control most optimistic prediction (La Haye et al.) most pessimistic prediction (Sauter et al.) But extrapolation of ITER requirement on jECCD/jbs still difficult

  26. Session S: Classical Tearing Mode Control Disruption avoidance by ECCD at q=1 and q=3/2 in FTU Study of magnetic island heating by ECCD in TEXTOR Research opportunity for any tokamak with ECRH system!

  27. Session S: Disruption characterisation and Mitigation Reduction of halo currents by noble gas injection (C-Mod) Nimrod modeling of C-Mod • Mitigation by (noble) gas (jet) • makes good progess • (AUG, C-Mod, DIII-D, HL-2A) • jet penetrates the edge only, but MHD takes over!

  28. 2.5 1019m-3 nped also constant <ne> Blue: New #66476 67911 0 1 H98  0.95 Red:Previous experiment #62430 MJ Wtot 0 (a.u.) D 28 29 30 31 32 Time (s) Session S: ELM physics and control Type II ELMs now also on JET Supression of ELMs by helical field on DIII-D • Several routes to mitigate ELMs are pursued in the programme in • may need several options (ITER has unique combination of n* and n/nG)

  29. Summary: Progress in high priority issues and future research directions • Retention of hydrogenic fuel: the problem is clearly defined, we need • detriation techniques and assessment of alternative wall materials. • Bursty SOL transport: good experimental characterisation, need better • link to theoretical predictions/modeling. • Fast particle physics: field is opening up as we develop better diagnostics, • need to measure better the damping rates to assess ITER situation. • CD: electron-based schemes relatively well understood, ion-based • schemes need further investigation. In particular: need to understand • better effect of MHD and fluctuations on CD. • (N)TMs: control by ECCD makes rapid progress, further enlarge • cross-machine scalings to strengthen predictive capability. • RWMs: a positive surprise – but have to understand lower rotation • thresholds before we draw conclusions for ITER. • ELMs: number of control schemes increasing, applicable at quite different • plasma parameters! In lack of a non-linear ELM model, this is reassuring.

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