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

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



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


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


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


Session D(ivertor physics, Plasma Wall Interactions and SOL Physics)



Session D: Bursty SOL transport

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?

MAST L-modeMAST L-mode MAST ELMMAST ELM


Session D: Bursty SOL transport

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

Tore Supra SOL flow experiment

Tore Supra SOL flow experiment

HFS BOT LFS TOP

Uniform outflux < 0 0 > 0 > 0

Localized outflux < 0 < 0 0 > 0

Measured < 0 < 0 0 > 0


Session D: Retention of H, D, T and Gas Balance

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)

--- Total Injected--- Total exhausted--- Outgased between pulses

6

5

4

3

2

1

0

Par

ticl

es (

1023

)

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00

Time (h)

Short pulses

Long discharges

Tore SupraTore SupraLow fuelling

AUG


Session D: Retention of H, D, T and Gas Balance

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…

DIII-DDIII-D

C-Mod: almost full recovery with disruptions

C-Mod: almost full recovery with disruptions


Session D: Alternative Wall Materials

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

Decrease of plasma C-content with progressive W-coating in AUG

Decrease of plasma C-content with progressive W-coating in AUG

Rapid confinement degradation after boronisation (C-Mod)

Rapid confinement degradation after boronisation (C-Mod)


Session D: Alternative Wall Materials

Liquid-lithium – first results emerge (FTU, T-11M)

• positive impact on discharge – D-pumping, no Li-blooms

• but still a long way to go…

Operation at n=nG with Li-limiterOperation at n=nG with Li-limiter

Li-limiter surface temperature saturates(self-protection?)

Li-limiter surface temperature saturates(self-protection?)


Session D: Divertor physics

Empirical rule: whenever a machine obtains good pumping, a new acronym is created (indicative of discovery of a new regime)

Local island divertorin LHD gives accessto very high density(Internal Diffusion Barrier IDB)

Local island divertorin LHD gives accessto very high density(Internal Diffusion Barrier IDB)


100

150

Session W(aves and fast particles)



ElectronFishbones inFTU, HL-2A

ElectronFishbones inFTU, HL-2A

Session W: MHD and fast particles

Who said that fast-particle MHD is always driven by ions?

Electron drivenGAEs in HSX

Electron drivenGAEs in HSX



Fast particles affected by (fast particle-driven) AEs and low frequency MHD

• significant progress in diagnostics (Heidbrink!) allows new insight

RSAEs inJT-60U

RSAEs inJT-60U

EPMs inCHS

EPMs inCHS



This kind of physics may play an important role in establishing the(self-organised?) improved (hybrid) H-mode (MHD j(r))

ASDEX Upgrade: NTMs orfishbones determine q(r)

ASDEX Upgrade: NTMs orfishbones determine q(r)

DIII-D: ‘current deficit’ in thepresence of a (3,2) NTM

DIII-D: ‘current deficit’ in thepresence of a (3,2) NTM


Session W: ‘Conventional’ H&CD in tokamaks

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)!

Off-axis NBCD onJT-60U, but shifted?

Off-axis NBCD onJT-60U, but shifted?

Broadening of jNBCD by MHD modes (NSTX)

Broadening of jNBCD by MHD modes (NSTX)

Broadening of jNBCD by el.stat. fluctuations? (AUG)

Broadening of jNBCD by el.stat. fluctuations? (AUG)


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)

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!

PNBI (MW)

PICRH (MW)

PLHCD (MW)

13cm

-2cm

D

GIM6RC (%)

~4.5 sec


Session W: New schemes for new configurations

EBW for overdense plasmas (pioneered in stellarator) nowin STs, but also in conventional tokamaks

EBW in MASTEBW in MAST

EBW in TCVEBW in TCV


Session W: New schemes for new configurations

Plasma startupw/o transformerby CoaxialHelicity InjectionIn NSTX

Plasma startupw/o transformerby CoaxialHelicity InjectionIn NSTX

Plasma startup w/o use of central solenoidby a combinationof ECH and verticalfield ramp in LATE

Plasma startup w/o use of central solenoidby a combinationof ECH and verticalfield ramp in LATE


Session S(tability)


Session S: Resistive Wall Modes

(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 i as highlighted by NSTX)

JT-60 UJT-60 U

DIII-DDIII-D


Session S: Resistive Wall Modes

Note: progress in this area also from RFPs (for which it is even more vital)

EXTRAP2-TREXTRAP2-TR RFXRFX


Session S: Neoclassical Tearing Mode Control

Demonstration of individual elements as well as integrated feedback

Feedback controlledDeposition in DIII-DFeedback controlledDeposition in DIII-D

NTM stabilisation with ITER relevant broad deposition in ASDEX Upgrade

NTM stabilisation with ITER relevant broad deposition in ASDEX Upgrade


Session S: Neoclassical Tearing Mode Control

But extrapolation of ITER requirement on jECCD/jbs still difficult

most optimistic prediction (La Haye et al.)most pessimistic prediction (Sauter et al.) most optimistic prediction (La Haye et al.)most pessimistic prediction (Sauter et al.)


0

20

40

60

0 5 10 15 20 25

t dis-t

MH

D (m

s)

rdep

(cm)

disruption avoidance

#29979 & #29963#29984

Ip= 500 kABt= 5.3T

<ne>=0.6x1020

m-3

LBO with Mo

Session S: Classical Tearing Mode Control

Research opportunity for any tokamak with ECRH system!

Disruption avoidance by ECCD at q=1 and q=3/2 in FTU

Disruption avoidance by ECCD at q=1 and q=3/2 in FTU

Study of magneticisland heating byECCD in TEXTOR

Study of magneticisland heating byECCD in TEXTOR


Session S: Disruption characterisation and Mitigation

Mitigation by (noble) gas (jet) makes good progess (AUG, C-Mod, DIII-D, HL-2A)

• jet penetrates the edge only, but MHD takes over!

Nimrod modeling of C-ModNimrod modeling of C-Mod

Reduction of halo currentsby noble gas injection (C-Mod)Reduction of halo currentsby noble gas injection (C-Mod)


Session S: ELM physics and control

Several routes to mitigate ELMs are pursued in the programme in

• may need several options (ITER has unique combination of * and n/nG)

Time (s)28 29 30 31 32

(a.u

.)M

J1

019

m-3

D

<ne>

H98 0.95

Wtot

nped also constant

0

10

2.5

67911 Blue: New#66476

Red:Previous experiment #62430

Type II ELMsnow also on JET

Type II ELMsnow also on JET

Supression of ELMs byhelical field on DIII-D

Supression of ELMs byhelical field on DIII-D


Summary: Progress in high priority issuesand future research directions

Retention of hydrogenic fuel: the problem is clearly defined, we needdetriation techniques and assessment of alternative wall materials.

Bursty SOL transport: good experimental characterisation, need betterlink 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-basedschemes 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 enlargecross-machine scalings to strengthen predictive capability.

RWMs: a positive surprise – but have to understand lower rotationthresholds 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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S(tability), D(ivertor, plasma wall interaction) and W(aves and fast particles)

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