Title: Highly radiating type-III ELMy H-mode with low plasma core pollution
1Highly radiating type-III ELMy H-mode with low
plasma core pollution
- J. Rapp, M. de Baar, W. Fundamenski,
- M. Brix, R. Felton, C. Giroud, A. Huber,
- S. Jachmich, E. Joffrin, I. Nunes,
- G.J. van Rooij, M. Stamp, G. Telesca,
- R. Zagorski and JET EFDA contributors
2Motivation
- Proposed solution for acceptable steady-state and
transient heat loads - Strongly radiating Type-III ELMy H-mode by
impurity seeding - Advantage benign scenario for plasma wall
components - Disadvantage confinement reduction with respect
to type-I ELMy H-mode - Compensation could be ITER operation at 17 MA
(q952.6) - Achievements as of 2006
- Radiative power fractions up to 95
- Partial outer divertor detachment
- DWELM in outer divertor down to 0.002 MJ/m2 for
Wdia 3 MJ - Objectives in last JET campaigns
- Improve confinement to high values than
H98(y,2)0.73 - Reduce plasma core pollution to lower Zeff
- Experiments at high current (up to 3 MA), high
density (1.1x1020 m-3), optimized fuelling
3Confinement improvement
- frad0.75
- H98(y,2) was increased to 0.83 by lowering
density (NGW0.85) - bN1.9
- n lowered by factor 2.5
- Confinement is within Q10 ITER operation domain
for 17MA operation
Q10 domain
4Plasma core pollution
- Zeff for nitrogen seeded type-III ELMy H-modes
with frad gt 0.65 - Zeff drops strongly with increasing density, even
more than expected - Check impurity production and Zeff scaling
5Plasma core pollution
- Heating power (bN) scan with fixed radiative
- power fraction and fixed density
- ne 1020 m-3, Prad 10 17 MW, frad 0.7
- Nitrogen flux is increased by factor 4
- Zeff is dominated by nitrogen (background
Zeff0.2-0.3, carbon concentration 1 - Increased nitrogen concentration does not lead to
higher carbon concentration - But physical and chemical sputtering by nitrogen
should increase carbon sources
G s-1 Yphys (10 eV) GC s-1
D 8 x 1022 1.1 x 10-3 8.8 x 1019
N 2.5 x 1022 1.6 x 10-2 4 x 1020
6Carbon sources in divertor
- From CIII (465 nm)
- Strachan et al. Nuclear Fusion 2003
- Divertor carbon fluxes are reduced at lower
powers to the divertor target - High current discharges at high density frad0.7
show only variation of 20
7Carbon sources, outer divertor
- Carbon sources (derived
- from CII, 515 nm)
- Carbon sources from CII are
- about a factor of 2-4 lower
- than derived from CIII
type-I ELMy H-mode
S/XB for CII (514nm) 9-6 S/XB for Da (656nm)
20-15
type-III ELMy H-mode
8Carbon sources, main chamber
- Type-I ELMy H-mode
- factor 10
- Agreement with the fact that
- fuel retention is lower in type-III
- ELMy H-mode Loarer, R3
- Estimation of Zeff from
- carbon sources (divertor)
- fuelling efficiency from nitrogen
- puffing
- Zeff (from carbon) 1.2
9Chemical erosion in outer divertor
- no very clear trend (if at all increase is
observed) - Some increase could be due to higher surface
temperaturre on the target at higher power to the
target
Chemical erosion in divertor 1.5 to fit carbon
sources derived from CII 10 to fit carbon
sources derived from CIII
10Zeff scaling
- Zeff scaling as developed for
- Mk-0, Mk-I, Mk-IIA divertors
- Matthews et al., Nuclear Fusion 1999
- Predictions for ITER (400 MW)
- 15 MA, NGW0.85 Zeff1.7
- 17 MA, NGW1 Zeff1.3
- Good news !
- BUT Zeff scaling does not fit experimental data
in range 1.5 to 2.5 very well
11Zeff scaling
- Zeff scaling has been
- re-evaluated, including
- transport of impurity ions
- ITER prediction more pessimistic
- 17 MA, NGW1 Zeff1.9
12Zeff scaling summary
- Zeff scaling has been improved, however
predictions for ITER seem to be very sensitive on
scalings - Simple scalings do not take into account impurity
profiles (Zeff profile is typically hollow for
JET nitrogen seeded discharges, so that central
Zeff could be 20 lower - Code simulations are necessary to better predict
profile effects in Zeff - Modelling started with COREDIV Zagorski et al.
J. Nucl. Mater.. 2003 - Self consistent radial 1D energy and particle
transport of plasma and impurities (energy
confinement according to H98(y,2) scaling law - coupled to
- 2D multifluid transport in SOL
13Integrated modelling for JET
- Benchmark to JET experiments
- 69354 and 69359 from heating
- power scan
- Plasma profiles (Te, ne) in the
- core have been matched
- Zeff, frad, H98(y,2) have been
- matched too
- Good agreement of modelling and
- experiments !
Erosion by nitrogen not included Carbon erosion
by deuterium and self sputtering Chemical erosion
according to Roth formula No main chamber erosion
14Simulations for ITER, 17MA, high ne
15Simulations for ITER, 15 MA
Demonstrated at JET
- SOBERING Reduction of Q might be inevitable in
15 MA standard scenario for strongly radiating
scenarios
16Summary
- Operational domain of type-III ELMy H-mode has
been increased towards higher current, higher
densities and lower Zeff - Carbon sources are minimized in those high
density discharges, nitrogen is the main impurity - Main chamber erosion is lower in type-III ELMy
H-mode than in type-I ELMy H-mode - Zeff scaling has been re-evaluated, taking into
account transport of impurities, but prediction
for ITER is slightly pessimistic - Type-III ELMy H-mode is compatible with ITER Q10
operation at 17 MA - Q is reduced to 6 in standard 15 MA ITER scenario