Michael Bell

EPS Souvenir / MGB / 090727

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A Souvenir of the

36th European Conference on Plasma Physics,

Sofia, Bulgaria, 29 June - 3 July 2009

Michael Bell


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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 sessions1.6 presentations per participant!

Held in the National Palace of Culture in Sofia


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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


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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


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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


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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


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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


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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


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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


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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


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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


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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?


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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!

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Michael Bell