Michael Bell

1. A Souvenir of the36th European Conference on Plasma Physics,Sofia, Bulgaria, 29 June - 3 July 2009 Michael Bell EPS Souvenir / MGB / 090727

2. Conference was a bit smaller than usual • 530 participants • 85 invited talks • 15 plenary, 70 in 4 parallel sessions • 72 contributed talks in 4 parallel sessions • 699 contributed posters in 4 afternoon sessions • 1.6 presentations per participant! Held in the National Palace of Culture in Sofia EPS Souvenir / MGB / 090727

3. 1 invited talk and 7 contributed posters from NSTX • "Plasma Response to Lithium-Coated Plasma-Facing Components in NSTX", M. Bell et al. (invited) • "High speed IR camera diagnostic in NSTX", J-W. Ahn et al. • "Multi-energy SXR characterization of stabilized resistive wall modes in NSTX", L. Delgado-Aparicio et al. • "Modeling Fast Ion Transport in TAE Avalanches in NSTX", E. Fredrickson et al. • "Modification of edge plasma profiles in ELM-suppressed discharges with lithium coatings in NSTX", R. Maingi et al. • "Coaxial Helicity Injection Non-inductive Startup on NSTX", B. Nelson et al. • "Fast ion transport by toroidicity induced Alfvén eigenmodes on NSTX", M. Podestà et al. • "High flux expansion divertor studies in NSTX", by V. Soukhanovskii et al. • All had a pretty good reception - good traffic at the posters EPS Souvenir / MGB / 090727

4. JET • Four invited: • Saibene: “Qualification of the ITER baseline operating scenarios in JET” • Beurskens: “Pedestal identity studies in JET, DIII-D and AUG” • Hobirk: “Improved Confinement in JET Hybrid Discharges” • De Vries: “Identity experiments on Internal Transport Barriers in JT-60U & JET” plus many contributed talks and posters • JET confirms ITER design with proviso that H-mode pedestal behaves as expected (Saibene): pedestal height = pmax  wped • pmax set by MHD but how does wped behave? • JET/DIII-D consistent, so far, with wped *0 and excludes wped *1/2 favorable for ITER (Beurskens) • but DIII-D at top and JET at bottom of range: adequate representation? • JET gets ELM size scaling  *0 whereas DIII-D gets  *>0 • Rotation shear does not affect onset of ITG-related turbulence but does reduce rate of rise of thermal flux with gradient above threshold EPS Souvenir / MGB / 090727

5. JET (2) • Toroidal field ripple (varied 0.08 - 1.0 %) affects thermal particle transport below level where it is expected to affect fast-ions • ITER may need to add more ferritic shims to get ripple <0.2% • Success in pacing ELMs with pellets, vertical kicks and n = 1, 2 perturbations • reduces ELM size by 30 - 40% but • also degrades thermal confinement by ~10% – concern for ITER • Have not yet suppressed ELMs with magnetic perturbations • Validate specific operational scenarios for ITER • inductive breakdown with Etor 0.2 V/m • low-internal-inductance x-point discharge by early heating • maintained stable H-mode through current rampdown • Campaign now to develop ELM control further and study occurrence and characteristics of H-mode in helium plasmas • Then install and operate ITER-like wall: beryllium and tungsten EPS Souvenir / MGB / 090727

6. Hobirk: “Hybrid Modes” in JET • Raised many questions and, for me, hackles • JET definition: q0 > 1 or slightly below 1 and a broad region of low magnetic shear with no sawteeth and “mild” NTMs • HH ≈ 1 in JET whereas HH up to 1.5 in DIII-D • Conjectures HH scales with *  not good for ITER • JET uses LH and/or current ramps to set up “hybrid” q-profile • Current ramp-up modified q0 but HH and N limit unchanged • However, current ramp-down increased HH to 1.35 and N limit to 3 %.m.T/MA • Was speaker aware of TFTR results on this? - No! • When plotted against current before rampdown was there a benefit? - Didn’t know • Benefit died out after ~2s ~ current diffusion time • Stability of “AT” regimes in JET also discussed by Buratti O2.007 • Highest N ≈ 4 %.m./MA for qmin ≈ 1; no RWMs in JET EPS Souvenir / MGB / 090727

7. Huysmans “3D non-linear MHD simulations of ELMs • JOREK code encompasses core and open field lines out to conducting boundary • Applied to JET-like equilibrium • Large Jedge due to bootstrap current in edge pressure gradient • Sees growth of pure ballooning mode with dominant n = 9 • For equilibrium from plasma with smaller ELMs, gets n = 18 • Plasma expelled onto open field lines – cools and detaches • Sees fine structure of heat flux to outer divertor target • ELM is not one event but involves discrete bursts over ~200µs • Applied to pellet triggering of ELMs • Model as big local ne perturbation • Pellet triggers low-n, typically n = 2, ballooning-like instability through effect on J(r), p(r), irrespective of pre-existing profiles • Ergodizes edge EPS Souvenir / MGB / 090727

8. ASDEX-Upgrade (AUG) with Tungsten Wall • E. Wolfrum “Investigation of H-mode Pedestal Physics in AUG” • Program R(t) synch’ed to ELM cycle to get high-resolution profiles • Use T(Rsep) defined by 2-point power balance model to locate Rsep • Showed pmax evolving to common limit but well before ELM • So, maybe the pedestal gradient is actually set by transport and • Something else is evolving to trigger ELM: J(r) • Pegourié “Fuelling and plasma control by pellet injection with application to ITER” • ASDEX experience: with HFS pellets, need only get to ~1/2 pedestal height to fuel core • For ITER fueling 5mm pellets on HFS at 10 – 15 Hz probably OK • For ELM triggering, 2.2mm pellets on LFS at 10 – 25 Hz needed • Just within capability of ITER cryo-pumps and tritium plant EPS Souvenir / MGB / 090727

9. ASDEX-Upgrade (AUG) with Tungsten Wall • G. Pautasso “Disruption studies” - massive He,Ne,Ar injection • achieved about 1/4 of density needed in ITER to suppress runaways • V. Rohde “Wall Retention of Deuterium and Gaseous Impurities” • Operated without boronization for many months after W wall installed • Bake only to 150°C • Also eliminated HeGDC • He became buried in W and released later • W-wall recycles deuterium 1 - RD ~ 1.5% • Up to 1/3 of input D held briefly on wall – released over ~10 min • Now puff N2 to maintain edge radiation • Used to be provided by intrinsic C but C lower with all W-wall • Better overall performance than with carbon wall • Related results also in posters (Kallenbach, Herrmann and others) • AUG will return to operation with 2 generators this month EPS Souvenir / MGB / 090727

10. MAST • E. Nardon “ELM control by resonant magnetic perturbations on MAST” • Upper, lower outboard rows of 6 coils each; 6kA-turns • In L-mode get pump-out ne/ne ~ -50% and splitting of outer strike point • Perturbation threshold consistent with ergodization of edge • In DN H-modes, Type III ELMs become dithering with RMP • With Type I ELMs, little effect even with (vacuum) ergodization N > 0.94 • In LSN H-modes, perturbation returns discharge to L-mode • M. Turnyanskiy “Off-axis NBCD experiments on MAST” (contributed) • Displace plasma down - plasma volume does decrease ~10% • Need to move back to midplane to make measurements • TRANSP calculates hollow deposition profile and JNBCD • TRANSP over-predicts Wtot, SDD by 25 - 30 % at 4 MW (better at lower P) • Correlate with fishbone activity • Model with HAGIS code  add anomalous Dfi ~ 0.5 m2s-1 in TRANSP EPS Souvenir / MGB / 090727

11. Tuesday Evening Session on New Facilities • ITER status (A. Loarte, IO) • Mainly discussed Scenario 1 for construction and operation • First plasma with limited capability and diagnostics in late 2018 • Followed by 2+ years of installation, commissioning • Start serious research in H, He plasmas with H&CD in 2021 • Accelerate research and licensing to reach full DT operation in 2027 • JT-60SA (S. Ishida, JAEA) – JA-EU joint project at Naka • “Re-baselined” in 2008 to reduce cost, regain schedule - dumped • TF built in EU, PF in JA, all ferritic steel VV • Reduce B to 2.2T but keep 5.5MA by lower A = 2.5, higher  = 1.9 • NNBI 10MW, PNBI 24MW, ECH 7MW, all for 100s pulse • Full remote handling because of high DD neutron yield 1.5E21 /year • First plasma in 2016, planned to operate for 15 years EPS Souvenir / MGB / 090727

12. Tuesday Evening Session on New Facilities (cont.) • FAST (F. Zonca, ENEA) – “ITER satellite” at Frascati site • Aimed to study fast-ion physics created by ICH instead of fusion • Want to be similar in dimensionless parameters to ITER but have to compromise • * has to go! • Based on cryogenically cooled (20K start) copper TF • R = 1.82m,  = 1.7, BT = 8 (8.5) T, Ip = 6.8 (8.0) MA for 170s (shorter) • Mainly rely on ICH but planning for NNBI and ECH too! • Full tungsten wall • Admits challenge of this with ICH • Question: why is this being built and who will pay for it with ITER demanding more resources? EPS Souvenir / MGB / 090727

13. Other Presentations and Points of Interest (to me) • Angioni (I4.060): Particle transport in tokamaks • Mused on and extolled virtues of density profile peaking for ITER • Paley (I3.045): Plasma control in TCV with ECH • ECH with control of launch angle to broaden J(r) for high- (≈ 2.8) • Implemented real-time analysis of data from 64 channel SXR fan • Allowed control of sawteeth by depositing ECH in-/out- side q = 1 • Control code is adaptive to plasma response • Some hysteresis in response due to cumulative heating • Imbeaux (O2.018): Long-term plasma control in Tore-Supra with LH • Control of LH power by MHD signatures only: OK but not great • Plan to use polarimetry • Van de Sanden (I2.022): Solar cell technology and developments • Ebert (I4.059): Sprite discharges and terrestrial gamma-ray bursts • 50/day, energy > 35MeV: big noisy spectacular stuff! EPS Souvenir / MGB / 090727