1. S(tability), D(ivertor, plasma wall interaction)
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. Session D(ivertor physics, Plasma Wall Interactions
21st IAEA Fusion Energy Conference- Summary Session
Session D(ivertor physics, Plasma Wall Interactions
and SOL Physics)

6. Session D: Bursty SOL transport
MAST L-mode
MAST ELM
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
HFS
BOT
LFS
TOP
Uniform outflux
< 0
 0
> 0
Localized outflux
Measured
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. Session D: Retention of H, D, T and Gas Balance
Low
fuelling
AUG
--- Total Injected
--- Total exhausted
--- Outgased between pulses
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. Session D: Retention of H, D, T and Gas Balance
DIII-D
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. Session W(aves and fast particles)
Time (s)
Frequency (kHz)
100
200 50
150
21st IAEA Fusion Energy Conference- Summary Session
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. Session W: ‘Conventional’ H&CD in tokamaks
PNBI (MW)
PICRH (MW)
PLHCD (MW)
13cm
-2cm Da
GIM6
RC (%)
~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!

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. Session S: ELM physics and control
Time (s) 28 29 30 31 32
(a.u.) MJ
1019m-3 D
<ne>
H98  0.95
Wtot
nped also constant 1
2.5
67911
Blue: New
#66476
Red:Previous experiment
#62430
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.