Overview of JET results

1
Overview of JET results
New on JET for 2006/2007Divertor for highly
shaped (high d) plasmas, upgraded power and
enhanced diagnostic capability
M. L. Watkins on behalf of JET-EFDA
contributors21st IAEA Fusion Energy Conference,
Chengdu, China 16 October 2006
2
ITER Baseline, Hybrid and ITB scenarios
Schematic of tokamak plasma profiles for various
operating scenarios

• Content of talk
• q profile control of MHD and transport

Pressure, temperature or density

• Core MHD and fast particles
• Density peaking and impurity control
• ELMs and ELM control
• Material erosion, migration and deposition
• Summary and conclusions

Normalised radius r/a
Pa/Ploss n tET f(Zeff) b tE B2
g(Zeff) Performance improvement by MHD,
confinement and impurity control
3
Hybrid modes at low q953 reach bN3
Courtesy of E. Joffrin (2006)
Hybrid and H-mode in ITER-like shape
Characteristics of hybrid discharge at q95 3.2
q953
Hybrid 2006
H89bN/q952
Maintain q0gt1 to avoid sawteeth
q954
Figure of merit
Hybrid 2003
H-mode 2006
Bootstrap current e.bp

• Hybrid performance similar to H-mode at high
  q954
• Improved hybrid performance at low q953,
  slightly better than H-mode with b controlled in
  real time

4
Internal Transport Barriers with q955 and 32MW
X. LITAUDON (EX/P1-12) TUES am
Pulse characteristics
1.9MA/3.1T
Temperature and density profiles
1.9MA/3.1T
During ITB
Before ITB
r/a
Time (s)
2006 ITB discharges extended to lower q955,
higher power (32MW)and high core and edge
densities
5
Control of core MHD (sawteeth) demonstrated
J. ONGENA (EX/P6-9) FRI am
Sawteeth can destabilise Neoclassical Tearing
Modes and degrade performance
Fast particle stabilised sawteeth destabilised
with ICCD
Calculated magnetic shear
Pulse No 58934
t23s
Pulse No 58934
Te0 (keV)
Magnetic shear
PRF (MW)
Time (s)

• Large sawteeth created by ICRF accelerated fast
  particles
• Sawteeth destabilised subsequently, with the
  application of ICCD

F. PORCELLI(EX/7-4RA)FRI am
r/a

• Internal kink mode destabilisation requires
  critical shear of 0.2 for this discharge
• Critical shear exceeded near q1 with -900
  ICCD phasing (counter-current), explaining
  observed sawtooth destabilisation

Criterion for sawtooth crash
Sq1 gt Sq1 critical
Increase shear near q1
dW / (Sq1 tA) lt wI / 2
6
Observation of fast particle losses from core MHD
(sawteeth and tornado modes)
Energy pitch angle of lost fast particles from
scintillator probe

• Spectrograms showing tornado modes

Sawteeth tornado modes appear with q0lt1
67673 1.8MA/2.7T
Interferometer (core channel)
245
240
235
230
225
220
Frequency (kHz)
X-mode refl.
Magnetics
245
240
235
230
225
During sawtooth crash
Between sawteeth

• Multichannel interferometer (and X-mode
  reflectometer) enable mode localisation

220

• Fast particle losses (p, T, D) during tornado
  phase different signature to those during
  sawtooth crash
• Sawteeth losses characteristic of
  ICRH-accelerated ions (p, D)

16.8
17.0
17.2
17.4
Time (s)

• Core interferometer channel shows tornado modes
  before sawtooth crash
• Modes not seen on edge channel, confirming core
  localisation

A. MURARI (IT/P1-23) TUES am
7
Significant density peaking expected on ITER
H. WEISEN (EX/8-4) FRI pm
Merged JET-AUG database on density peaking in
ITER Baseline ELMy H-modes

• Multi-machine data confirm collisionality,
  ?eff, as most relevant parameter for density
  peaking
• Increasing peaking with decreasing ?eff
• Peaking requires anomalous particle pinch, in
  addition to neutral sources

n0/ltngtvol

• Scaling of density peaking to ITER with ?eff
  as regression variable ?
• ne0/ltnegt gt 1.35

?eff

• Favourable for fusion output, bootstrap current
  fraction, density limit

New ITER-like ICRH antenna on JET (installation
April 2007) will allow database to be extended to
higher power, neutral source free RF heated
plasmas
Could impact on impurity accumulation
8
Impurity density peaking less than neoclassical
Measured and predicted density peaking at
r/a0.55
C. GIROUD (EX/8-3) FRI pm

• Neoclassical theory predicts strong impurity
  peaking
• Transient behaviour of injected and laser
  ablated impurities shows impurity peaking less
  than neoclassical

Pulse No66134
Neoclassical
Measurement
-RVz/Dz
GS2 w/o Thermodiffusion
-RVz/Dz
Gz -Dz?nz nzVz ? R/LNzRVz/Dz
GS2

• Impurity transport at ITER-like collisionality
  found to be anomalous
• Turbulence theory predicts saturation in peaking
  as a function of Z at high Z (consistent with
  measurements)
• At low Z prediction of low peaking with
  thermodiffusion, high peaking without

Central peaking (r/a0.15), albeit less than
neoclassical, can still persist
9
Core impurity peaking can be controlled with
electron ICRF heating
Effect of Minority (ion) heating (MH) and Mode
conversion (electron) heating (MC) on Ni
transport in low n ELMy H-modes
Density profiles
Measured convection coefficient
58144
M.E. Puiatti PoP(2006)
58149
Neoclassical x10
V? (m/s)
Normalised Ni profile
C. GIROUD(EX/8-3) FRI pm
r/a
r/a

• Ni accumulation is anomalous, and much lower
  with RF electron heating than with ion heating

• Profile flattening due to outward convection
  with electron heating

Reversal of pinch with e-heating theoretically
ascribed to effect of parallel velocity
fluctuations with R/LTe driven TEM modes
ITER-like ICRH antenna will extend capability
10
Te modulation experiments show ITB as a narrow
layer with reduced heat diffusivity
P. Mantica PRL (2006)

• Modulated RF power deposited either side of ITB
  (at centre and at R3.6m)
• Heat wave propagates towards ITB from both
  sides
• Heat wave amplitude (red) damped strongly when
  wave reaches ITB
• Phase (blue) rises when heat wave approaches
  ITB, showing heat wave slows down

Amplitude and phase of propagating heat wave in
plasma with an ITB

• ITB is a narrow layer with reduced heat
  diffusivity
• Indication of region with turbulence stabilised
  and loss of stiffness

11
ITB forms when qmin exists and approaches (rather
than reaches) an integer value
S.E. SHARAPOV (EX/P6-19) FRI am
Te at various major radii, R, showing formation
of an ITB
ITB formation slightly ahead of Alfvén Cascades
(marking qmin integer)
Pulse No 61347
qmin reaches 2
Start of ITB formation
tAC-tITB (s)
Te (keV)
Case number
Time (s)

• Alfvén cascades seen simultaneously on
  microwave interferometer, O-mode
  interferometer, X-mode reflectometer (not
  shown), and magnetic probe

• ITB formation starts before q2 surface enters
  plasma

12
Measured poloidal velocity in ITB much higher
than neoclassical estimates
T. TALA (EX/P3-16) WED pm
Ion temperature profiles during ITB formation
Poloidal velocity from charge exchange, during
ITB formation
V? (km/s)
Ti (keV)
Rmid (m)
Rmid (m)

• Measured poloidal velocity in ITB layer (60km/s)
  highly anomalous, far higher than neoclassical
  (5-10km/s)

• ITB layer with steep temperature gradient

K. Crombie PRL (2006)

• Er and ExB shear much larger with measured Vq
• Weiland model with measured Vq (rather than
  neoclassical) matches experiment better

13
ELMs can cause damage and must be controlled
R.A. PITTS (EX/3-1) WED pm
Type I ELMs on ITER could expel transiently 3-8
of 350MJ stored energy ?? 0.6-3.4MJm-2
New fast IR camera
Type I ELM energy deposition in the JET MarkII
SRP gas box divertor
Type I ELMs on JET

• ELM energy depositon on inner divertor 2 x
  outer divertor
• Load between ELMs on outer divertor
• May relax outer divertor load on ITER

1MJ ?? 0.2MJm-2 on divertor ?? 25000C

• Filamentary power deposition
• Clear field aligned structures

14
Passive ELM control with high frequency, small
Type I ELMs at low ne (?), high ? and q954-5
Courtesy of A. LOARTE (2006)
High and low d configurations, exploring small
Type I ELMs
A. LOARTE (IT/P1-14) TUES am
?TELM/Tped vs. q95
Height?? (m?)
?
R (m)

• ?TELM/Tped decreases suddenly at q95 4.2 and
  fELM increases
• Small ELMs (DWELM/Wped lt 5) obtained with low
  n at high ?? q95
• Not seen at low d

More highly shaped plasma at higher q95 ?
convective ELMs

• At high ? small, high frequency Type I ELMs
  seen at high q95
• Indication of threshold at q95 4.2

Cost high q95 ? low tE for given B ? Combine
with improved core for improved confinement
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Passive ELM control by plasma shaping, similar to
ASDEX Upgrade with QDN
Courtesy of R.J. Buttery et al (2006)
Previous JET studies gave only transient Type II
behaviour. Refined shape leads to stationary
benign ELM regime with good confinement
Magnetic configurations in new and previous JET
studies
Turbulent magnetic fluctuations coincide with Da
bursts
Blue New 66476
RedPrevious experiment 62430

• ELM behaviour constant over pulse
• Very fine scale activity - distinct ELMs almost
  indistinguishable

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Active ELM control at gt30MW with an ITB and neon
seeding
X. LITAUDON (EX/P1-12) TUES am
D. MOREAU (EX/P1-2) TUES am
JET AT database quasi-stationary (?/?Egt10)
pulses at high ?N and high ?
bN
Target for JET-EP2 AT regimes with 45MW planned
power upgrades

• ELM control with Neon (4-8s) Prad17MW dithering
  H-mode
• B3.1T, I1.9MA, q955 PNBI19.5MW, PICRH8MW,
  PLHCD3.2MW Wdia5.6MJ, bN2

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Material erosion, migration and deposition are
key to fuel retention
A. KIRSCHNER (EX/3-5) WED pm
Location
Behaviour

• Inner divertor
• Outer divertor vertical tiles
• Outer divertor base plate
• Remote areas

• Deposition dominated
• Erosion dominated
• Heavy erosion of W stripe (200mm suggested for
  ITER like wall)
• Deposition dominated
• Material transport sensitive to magnetic
  configuration

• Complex migration pattern

• Fuel retention in divertor (mainly due to
  co-deposition) is 2.7 of input
• (see also T. LOARER (EX/3-6) WED pm)
• Main chamber, tile gaps and SRP contributions
  not included (see also M. RUBEL (EX/P4-24) THU
  am)

• 13CH4 injected in reproducible ELMy H-modes
• Quartz Microbalance measurements
• 3mm thick W stripe on Tiles 1 and 8
• Post mortem analysis of tiles

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Summary and conclusions (1)

• Hybrid performance similar to H-mode at q954
  and slightly better at q953 with bN3 and 75
  Greenwald density

New results on Hybrid

• ITBs extended to lower q95 (5), higher power
  (32MW), high edge and core densities and good
  ELM control with neon injection

New results on ITB

• neff most important parameter for density
  peaking
• Peaking factor gt1.35 expected for ITER
• Impurity transport anomalous, with mild
  accumulation which can be controlled with
  electron heating
• ITER-like ICRH Antenna to extend density peaking
  andimpurity control to higher power / lower
  fuelling

Density peaking and impurity control

• Core MHD (sawteeth and tornado modes) expel fast
  particles
• ITER-like ICRH antenna to extend control
  capability for fast particle MHD and transport
  losses by localised current drive

Core MHD and fast particles
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Summary and conclusions (2)

• Non-stiff profiles with reduced diffusivity in
  ITB layer
• Form slightly ahead of qmin reaching integer
  value
• May be sustained by high ExB shear with
  observed poloidal velocity significantly greater
  than neoclassical
• Potential access to ITER regime with planned
  powerupgrades (Ibootstrap and ntET increasing
  together)

ITB physics

• ELMs must be ameliorated for ITER
• Passive control at high d and q95 (small high
  frequency Type I)
• Passive control with shaping (similar to Type II
  on AUG)
• Active control with Neon injection (ITB with
  Type III?)

New results on passive and active ELM control

• Erosion of outer divertor, strong parallel flow
  in SOL, deposition on inner divertor sensitive
  to magnetic configuration
• Fuel retention at 3 on JET under C-dominated
  conditions

Material erosion, deposition and migration
Need to test ITER wall materials under high
performance conditions, as foreseen in
longer-term JET programme in support of
ITER (Beryllium wall, Tungsten divertor, 45MW
heating power)
20
EFDA-JET contributions to this conference
MONDAY AM M. WATKINS (OV/1-3) TUESDAY AM F
. CRISANTI (EX/P1-1) D. MOREAU (EX/P1-2) R.V.
BUDNY (EX/P1-5) X. LITAUDON (EX/P1-12) C. F.
MAGGI (IT/P1-6) A. LOARTE (IT/P1-14) T.
HENDER (IT/P1-21) A. MURARI (IT/P1-23) WEDNESDA
Y AM H. MAIER (IT/P2-4) WEDNESDAY PM R. A.
PITTS (EX/3-1) A. KIRSCHNER (EX/3-5) T.
LOARER (EX/3-6) D. McDONALD (EX/P3-5) T.
TALA (EX/P3-16) Not referred to in
presentation OV/1-3
THURSDAY AM M. RUBEL (EX/P4-24) THURSDAY PM
H. L. BERK (TH/3-1) FRIDAY AM F.
PORCELLI (EX/7-4RA) J. ONGENA (EX/P6-9) S. E.
SHARAPOV (EX/P6-19) T. A. K. HELLSTEN (EX/P6-21
) V. NAULIN (TH/P6-22) FRIDAY PM C. GIROUD
(EX/8-3) H. WEISEN (EX/8-4) T. C.
HENDER (EX/8-18) V. A. YAVORSKIJ
(TH/P6-7) SATURDAY AM V. PARAIL (TH/P8-5)