Kein Folientitel

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Development of an ITER Relevant Advanced
Scenario at ASDEX Upgrade the improved H-mode
Otto Gruber A.C. Sips, A. Stäbler, R. Dux, R.
Neu, C. Maggi, Y-S. Na, ASDEX Upgrade Team

• Aim of improved H-mode
• Performance MHD stability
• confinement
• Operational range q95, n, r
• Exhaust relevant high density regime
• Electron heating in core ICRH
• Summary

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• Focus on
• performance-related physics in the ELMy H-mode,
• including ELM mitigation,
• (ii) scenarios and physics of advanced tokamak
  concepts,
• (iii) MHD stability and active stabilisation,
• avoidance and mitigation of disruptions
• (iv) edge and divertor physics aiming at
  optimising
• power exhaust and particle control
• (v) testing of tungsten as alternative first
  wall materials

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- extended pulse length to 10 s flattop ( 10 tR
even at Te(0) 5 keV) - extended PF coil
operational window to run ltdgt 0.55 discharges -
developed ICRH to routinely deliver gt 5 MW in
ELMy H-mode - ELM pacemaking by shallow pellet
injection or vertical wobbling
- increased W coverage of inner wall minimum
erosion low Tritium retention
? ITER - tungsten baffles in the first phase
- full W wall in its reactor like
operation? ? AUG stepwise towards C-free interior
- in 2004 campaign 70 of first wall covered
- W-divertor in upper SN C-divertor in
lower SN ? even improved confinement scenarii
accessible usually W concentration below
10-5 ? machine has been more delicate to run
? central RF heating ELM control by pellets
suppresses impurity accumulation
W

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Characterization of improved H-modes on AUG

• stationary q(r) with low magnetic shear in the
  centre and q0 1
• - early moderate heating
• - increase of heating at start of current
  flattop ? type I ELMy H-mode
• - strong heating up to 20 MW after gttR
• - supported by tailored on- / off-axis NI
  deposition

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Characterization of improved H-modes on AUG

• stationary q(r) with low magnetic shear in the
  centre and q0 1
• - early moderate heating
• - increase of heating at start of current
  flattop ? type I ELMy H-mode
• - strong heating up to 20 MW after tR
• - supported by tailored on- / off-axis NI
  deposition
• - low m,n modes substitute sawteeth

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Characterization of improved H-modes on AUG

• stationary q(r) with low magnetic shear in the
  centre and q0 1
• - early moderate heating
• - increase of heating at start of current
  flattop ? type I ELMy H-mode
• - strong heating up to 20 MW after tR
• - supported by tailored on- / off-axis NI
  deposition
• - low m,n modes substitute sawteeth

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Role of MHD support of stationarity and perf.
limits
? support of stationary q-profile (q0 1) -
fishbones (not always present) - small amplitude
NTMs (5,4) - bootstrap current and NBCD ? ?
benign MHD in high performance phase - no
sawteeth ? no seeding of (3,2) NTMs - low shear
at (3,2) surface and triangularity
? reduced NTM drive - higher m,n tearings
? non-linear coupling further
reduces (3,2) ? broad pressure profiles allow
operation close to no-wall limit up to bN
3.5 at high d
q953.8
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Role of MHD support of stationarity and perf.
limits
? support of stationary q-profile (q0 1) -
fishbones (not always present) - small amplitude
NTMs (5,4) - bootstrap current and NBCD ? ?
benign MHD in high performance phase - no
sawteeth ? no seeding of (3,2) NTMs - low shear
at (3,2) surface and triangularity
? reduced NTM drive - higher m,n tearings
? non-linear coupling further
reduces (3,2) ? broad pressure profiles allow
operation close to no-wall limit up to bN
3.5 at high d ? soft ?-limit due to 3,2 NTMs
(degraded confinement no disruption) ?
disruption due to (2,1) mode ? mode locking
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? transport studies - heat transport still
described by ITG /TEM turb. - threshold in R/LT
? stiff temperature profiles
also in center Ti(r0) ?Ti(r0.4)
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? transport studies - heat transport still
described by ITG /TEM turb. - threshold in R/LT
? stiff temperature profiles
? confinement improvement explained by - more
peaked ne-profiles (correlated with lower
collisionality) ? account to some extend for
higher H-factors - however, for ne0/ne,ped ? 2
H-factors of improved H-modes still higher
- higher pedestal pressure ? indications,
but needs detailed measurements - ITER-H98(y,2)
scaling ? ?N-1 but ?N0 dependence found in
standard H-modes - reduced H-factor for Ti?Te
(ITG / TEM turb.)
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• off-axis NI heating
• peaking of density profile
• due to transport, not core fuelling
• - turbulent D enhanced inward pinch
• (GLF23 model ITG/TEM)
• - reduces to Ware pinch at high densities /
  collisionality

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Impurity Control

• Peaked density profiles, no sawteeth
• ? high central impurity concentration can be
  severe for NBI only heating
• Impurity control by central wave heating
  (divertor configuration)
• low level central ECRH (1-1.5 MW) or central
  ICRH (PICRH ? 0.5 PNI)

core W concentration strongly reduced density
peaking reduced too ? trade-off
minor penalty on H98?N central C
concentration reduced as well
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Improved H-mode compatible with W walls and
targets

• - upper SN configuration with W coated targets
• ? ?N 2.8, H98(y,2) 1
• impurity control by central wave heating
• - feasible at low W concentrations

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Valid scenario for ITER ? ? documentation of
dimensionless parameter range q95 scan / high
denities up to nGW / ? scan 3.2 4.4
0.85?ne/nGW 8 -13 10-3
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q95 scan at fixed Ip, ? 0.2, ne/nGW 0.4,
n/nITER 1.5 - power ramps up to bN-limit of
3.0 (close to no-wall limit) - stationary
discharge at slightly lower b (duration techn.
limited) - H98(y,2) up to 1.4
Parameters scans for improved H-modes q95
scan / high-ne / ? scan 3.25 -
4.4 / 0.85?ne/nGW / 8 - 13E-03
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r scan at fixed q95 5, bN 2.8, ne/nGW 0.5,
H98(y,2) ? 1 - standard H-modes onset of NTMs
scales with r - stationary improved H-mode
discharges by bp feedback - r varied by a
factor of 1.5
ri 0.00646 ?ltTigt /(Bt a)
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Documentation of dimensionless parameter
range q95 scan / high ne/nGW / ?scan
q95 full range 3.2 4.5 accessible at high
performance ? close to ITER value at moderate
ne ?i 4 6 times ?i-ITER ( 2 10-3)
no ?i-dependence of performance ne/nGW high
ne possible ? reactor relevant edge div
conditions
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Fully integrated scenario - ?N 3.5 (at q953.6,
d0.43) - HH98-P 1.15 - particle density close
to Greenwald - up to 40 energy confinement times
type-II ELMs
?N?H98(y,2) / q952 0.31
- combined with type II ELMs close
to double null
- steady target power loads ? in average 2.5
MW power to outer bottom target (10
MW heating) ? 1.3 MW to upper targets
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Data base 2003/04 different time slices, also at
low heating power earlier high-ne
plasmas included Performance vs. measure of
bootstrap fraction ( ?0.5?p)
q95 3 4 H98?N/q952 ? 0.3 ? beyond Q 10
q95 4 5 H98?N/q952 0.2 ? long pulse
lengths at standard ITER performance
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Compatibility w. significant e-heating core ICRH
So far improved H-mode results obtained with
dominant NBI heating ? dominant ion heating
(Ti gtTe) input of particles and
momentum, in contrast to ?-heating in
reactor-type plasma Demonstration of improved
H-mode with PICRH ? PNBI (ICRH dominates core)
Ti Te ?N 2.6 / H98(y,2) 1.2 ? ?N
H98(y,2) / q952 0.24 dominant central
electron heating not yet achieved - ICRH
still heats ions - but inside ? ? 0.3 Pel
enhanced by 2.5
during ICRH central W-concentration strongly
depressed
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demonstrates that advanced requirements for
stability (?N ? 3.5), confinement (H98 gt1) and
exhaust (ne/nGW ? 0.9) can be simultaneously
met stationary (gt10 resistive times) and over
wide range in q95 3.2 4.5 specific
q-profile w. low central shear (q0 close to 1)
avoids sawteeth, allows benign NTMs during high
performance core transport ITG/TEM dominated
- density peaking increases with off-axis heat
dep. and low collisionality - contributes to
H98(y,2) gt1 (trade-off w. impurity
accumulation) - higher pedestal pressure may
contribute widens performance well beyond ITER
baseline scenario q95 lt 4 ?N ? H98(y,2)
/ q952 up to 0.31 q95 4-4.5 ?N ?
H98(y,2) / q952 0.2 with non-inductive CD above
50 dimensionless parameter scans towards
ITER - ? / ?ITER close to 1 at low
densities - no performance dependence on ?i
integration with type II ELMs at high densities
and full performance obtained also with
dominant core RF heating
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• ? strong candidate for ITER beyond baseline
  scenario
• - long pulse hybrid scenario at lower
  current above 1000 s or
• - operation close to ignition at full current
  (Q gt 20)
• Improved H-mode scenario is investigated at other
  devices (DIII-D, JT60-U, JET)
• ? broad extension of ITER relevant database (see
  A.C. Sips, IAEA 2004)