A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 1/25
Physics of ITB’s:
Recent results from experiments
A.C.C. Sips
Max-Planck-Institut für Plasmaphysik, Euratom Assoziation, Boltzmannstrasse 2, Garching.
With contributions from:
Y. Baranov1, C. Challis1, G. Conway, B. Esposito2, T. Fujita3, T. Fukuda3, P. Gohil4, C. Greenfield4,
G.T. Hoang5, G. Huysmans5, R. Jaspers6, E. Joffrin1, N. Kirneva7, X. Litaudon5, D. Mazon5,
A. Peeters, E. Quigley, T. Tala8 and R. Wolf
1: EURATOM/UKAEA Association, Oxon, UK.
2: Associazione Euratom-ENEA sulla Fusione, Frascati, Italy.
3: JAERI, Naka Fusion Research Establishment, Naka, Japan.
4: General Atomics, San Diego, USA.
5: Association EURATOM-CEA Cadarache, France.
6:FOM Instituut voor Plasmafysica Rijnhuizen, The Netherlands.
7: RRC Kurchatov Institute, Moscow, Russia.
8: Association Euratom-Tekes, VTT, Espoo, Finland.
Max Planck-Institutfür Plasmaphysik
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 2/25
ITB formation.
Current Hole.
Electron Barriers.
International database.
Similarity experiments.
Sustainment and control.
ITB`s with quiesent edge (QDB).
Outline
However, we must keep in mind where we need to go !!!
Fukuda – EPS ´02
„Transport Barriers provide great opportunitiesto study the broad dynamics in fusion science“
Schema della proporzioni
Physics
Scenariodevelopment
Reactor application
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 3/25
ITB scenario – Barrier formation
LHCD power level is varied
to change initial q-profile
Challis, Tala – PPCF ´02
Reversed shear, more NBI torque
favours ITB formation. Challis - PPCF ´02
ITB
Strong ITB
Pea
k * T
e =
s/
L Te
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 4/25
ITB scenario – Barrier formation
Esposito – EPS ´02
Strong reversed shear
Weak shear
Turbulence is suppressed when
ExB>m, but well defined region
with s close to 0 is important.
ITB´s startnear s=0
O.II.12, dynamics of e-ITB´s and ion ITB´s
shea
r ITB
shea
r ITB
Time (s)
electrons
ions
Te (
keV
)T
e (
keV
)
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 5/25
ITB formation: synergy between s and ExB shearing rate
Before ITB
After ITB
ExB/ITG
Ma
gn
etic
she
ar
s
Tala – PPCC ´01
In modeling the experimental data:
• Bohm/GyroBohm empirical model, using (–0.14+s-1.47 ExB/m ) (O.II.11)• Simulation of JET data with the Weiland model show that the density
gradient term dominates over the ExB shearing rate (T. Tala, PPCF ´02).
FULL code calculation
0
10
1.00.0 r / a
T i [ k
eV ]
1.4
- 2.0
L [
10
5/ s
]
q
10
2
q
T i
8
6
4
2
1.2
1.0
0.8
0.6
0.4
0.2
0.0
4
5
7
9
3
8
6
Lmodel,
JT-60U 24715, t = 6.0
f (s) = 1
5
4
3
2
1
0
L F
UL
L /
L m
od
el
1.00.50.0-0.5-1.0-1.5-2.0
magnetic shear at L
max
f (s) = 0.42 s +1.37
JT-60U
Comparisons made for the FULL code results after the ITB formation
m f(s), f(s) = 0.42 s + 1.37 for JT-60U
JT-60UFukuda – EPS ´02
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 6/25
Barrier formation: ASDEX Upgade results
ASDEX Upgrade
• Formation of an ITB at low ne, applying the NBI power in one step.
• Good, transient performance: H89L=3.4, N =4.
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 7/25
Barrier position
ASDEX Upgrade (E. Quigley –EPS ´02)
• The foot of the barrier expands to the positive shear region.
• This is important for the alignment of jboot with jtot.
Litaudon – ITPA ´02
weak shearreversed shear
s/LTe 1.4 x 10-2
q=3]
shea
r
Normalised poloidal flux radius
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 8/25
JT-60U: EC preheat is used, to create a reversed shear target and try to expand the ITB radius, Fujita – PRL `01
JET: LHCD is used during the
current ramp phase at low
density, Hawkes – PRL `01
Current Hole, observation and explanation
4
0.0 1.0r / a
[ke
V]
0
25 Ti r6.30 s
6.40 s
6.55 s6.65 s7.18 s
0.0 1.0r / a
0
10
20
0
1
2
0
5
10
0
2
46
3 4 5 6 7 8
0
1
23
010
2030
[ke
V]
[MA
][M
J]
[MW
][1
0 1
6 / s
][ a
rb. ]
E040259
P NB
I P
P EC
Tio
Teo
Time [s]
Wdia
neutron ratem / n = 4 / 1 interchange mode
t = 7.2 s
q min < 2current
hole
q r
40
30
20
10
0 0
j [ M
A / m
2 ]j r
current hole
Te r at 7.2 s
Current Hole
4
0.0 1.0r / a
[ke
V]
0
25 Ti r6.30 s
6.40 s
6.55 s6.65 s7.18 s
0.0 1.0r / a
0
10
20
0
1
2
0
5
10
0
2
46
3 4 5 6 7 8
0
1
23
010
2030
[ke
V]
[MA
][M
J]
[MW
][1
0 1
6 / s
][ a
rb. ]
E040259
P NB
I P
P EC
Tio
Teo
Time [s]
Wdia
neutron ratem / n = 4 / 1 interchange mode
t = 7.2 s
q min < 2current
hole
q r
40
30
20
10
0 0
j [ M
A / m
2 ]j r
current hole
Te r at 7.2 s
Strongly reversed q-profile before NBI
heating starts, which persists during NBI.
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 9/25
Current Hole, explanation for j0=0
JET: Experimental observation: j(0) 0
Hawkes – `02, Huysmans – EPS ´02
J(0)
(A
m-2)
Global max DlnT
• m=1 mode grows exponentially as soon as a q= surface appears.• Re-connection flattens the current density to zero inside the q= surface.• JT-60U: current drive with ECCD inside the current hole: extremely difficult.
Simulation of the current density on axis
with and without the effect of the MHD.
0 2 4 6 8 10 12-0.04
-0.02
0
0.02
0.04
0.06
0.08
J (0)z
time [x10 ]5
A
Huysmans – EPS ´02
J z(0
)
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 10/25
Electron transport barriers
ASDEX UpgradeUsing ECCD:
Counter current drive in the
centre generates a reversed
shear AND a barrier.
However, short duration
MHD unstable
Wolf – IAEA ´00
NEW experiments at ASDEX
in 2001/2002.
Also ECRH: TCV and FTU...
T (
keV
)
T (
keV
)
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 11/25
Electron transport barriers
ASDEX Upgrade new results,Peeters, ´02
More stable regime:
• Higher Ip (600 kA).
• Timing of ECCD.
• Qualitative agreement with
theoretical predictions of the
TEM stabilisation.
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 12/25
Electron transport barriers
Textor
Textor
Jaspers - EPS ´02
Te(r) with 250 kW ECRH alone,
modeled with RTP q-comb
model for e.
ECRH heating a weakly reversed q(r):
• At different deposition radii.
• e-ITB at different rational q´s.e-ITB at q=1 e-ITB at q=2.5
* Results on e-ITB´s from FTU (O.II.10) and TCV (O.II.16) follow after this talk
* e-ITB,s Tore Surpa , Hoang PRL ´00
Te
(keV
) e
(m
2 s-1)
-1.0 0 1.0
2.5
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 13/25
Fluctuation measurements in electron ITB´s
• 2.5 MW LH only , Te > 8keV, ne ~1.5x1019 m-3
• e-ITB forms in negative shear region.
• No rotation shear.
Turbulence reduction coincides with reduced e
Low frequencies reduced not ETG, TEM ?
Conway – PPCF ´02
e (
m2 s
-1)
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 14/25
ITB scenario – International database
Kirneva – 8th TTF ´02
Data from many experiments, however:
• Most of the data are for Ti/Te > 1.
• Best confinement data for ne/nGW < 0.6.
• Confinement increases with ITB radius, favours large radius for qmin. Can these data be used to extrapolate to reactor conditions ?
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 15/25
ITB scenario – International database
Baranov – APS ´01 Sips & Fukuda – ´01
Combination of 1-D data from various Tokamaks show dependences
of access power to ITB: ne (or Ip), and size, weak dependence on Bt.
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 16/25
ITB scenario – International database
Hoang – EPS ´02
ion ITB
electron ITB
At same s , plasmas with stronger reversed shear, require lower input
power to form an ITB.
At low * ITB´s form at lower power when confinement is good, easier to
create rotation shear, and peaked profiles.
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 17/25
ITB scenario – similarity experiments
Similarity experiments on ITB formation: ASDEX Upgrade – JET
• First results from ASDEX Upgrade (to be analysed in detail).
• JET experiments in 2003 to match dimensionless parameters (q,,*,*).
t=0.942t=0.968t=0.994t=1.072
However, this is the collapse of the ITB, due to the ELM´s !!!
ASDEX Upgrade
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 18/25
ITB scenario - duration
Litaudon – PPCF ´02
LHCD to create and sustain q (r).
• 2MA/3.4T, q95 = 5.5.
• H89P = 2.0, p = 1.1,N = 1.7.
• Duration = 36 E (e-ITB).
• Duration = 27 E (i,ne,vtor-ITB).
• Type III ELM`s at the edge due to
high jedge (M. Bécoulet, Y. Sarazin - ´01).
Iboot 1.0 MA
ILHCD 0.5 MA
INBI 0.3 MA
6
5
4
3
2
q-p
rofi
le
1.00.80.60.40.20
normalised radius
#53521 target q-profile from
MSE t=4.3s Polarimetry t=4.5s
6
4
2
0
15
10
5
0
0.8
0.4
0
1412108642Time [s]
3.0
2.0
1.0
015
10
5
0
#53521
PLHCD[MW] Ip[MA]
MW
keV
PNBI PICRH
Tio
neo [1019 m-3]
D [a.u.]
Vs [V]li
Teo
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 19/25
NBI
ITB scenario – duration, but impurity accumulation
MHD collapse, Hender/Hennequin- PPCF
High Z impurities:
- Accumulate (neo-classical
behaviour) (R. Dux – PSI ´02).
- Due to continued density
peaking accumulation of high Z
impurities only becomes worse.
- Cause (radiative) collapse.
s/LTe 1.4 x 10-2
Nickel concentration on axis
ITB reforms, what if PICRH neutron rate, simulating conditions in a reactor ?
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 20/25
ITB scenario – duration and control
(Mazon – PPCF ´02)
Control at “slightly“ lower performance
Pulse 53521 collapses 2x.
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 21/25
QDB combines an ITB with ELM
free steady state H-mode edge,
modulated by MHD activity.
• Counter NBI only.
This also maintains qmin > 1
and reversed q (r).
• Low edge density, due to MHD
and divertor cryo pumping.
Using counter NBI, this ELM free edge
has now been reproduced at ASDEX.
(O.I.01)
ITB scenario - QDB
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 22/25
ITB scenario - QDB
Edge pedestal pressure in QDB Type I ELMy H-mode.
More stable compared to L-mode, No ELMs ITB stays
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 23/25
ITB scenario - QDB
Also in QDB, high Z impurity accumulation is a problem.
Experiments with ECRH in the core in progress (Casper – EPS ´02) 10
15 n
eutr
ons/
s
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 24/25
Some concluding remarks
1.Document differences or similarities on ITB formation:
q-profile is crucial to ITB formation. Reversed shear is favourable for ITB
formation: extreme is a current hole. For ion-ITB ExB shear is required.
Need to improve our models to predict ITB formation in reactor (at least
come to a consensus).
2.Compatibility with ELM´s
We should document ITB collapse with ELM´s.
Type III ELM´s okay, but H factor lower (low edge pedestal pressure).
QDB demonstrates that it is possible to combine an H-mode edge with ITB,
but only with counter NBI, at low density and peaked ne(r).
3.Impurity accumulation: problem in long pulses
In order to avoid this we need a flatter ne(r ), and broader T(r) profiles.
Is this compatible with sustaining an ITB ?
A.C.C. Sips 9th EU-US TTF workshop, Córdoba, 9-12 September 2002 25/25
Finishing with ........Open issues
4. High (edge) density:
Pellet injection (PEP) or operation at high triangulrity.
Why is sustaining an ITB at high density difficult (is it impossible) ?
5. Control in long pulses – good progress has been made:
Still need: duration of ITB >> current diffusion time scale.
Still need: demonstration of control schemes in reactor relevant conditions.
6. Reactor with -heating, Te = Ti and D-T fuel:
Electron heating: ECRH, N-NBI, LHCD and ICRH.
Warning: Even the best results in D-D may be difficult to extrapolate to a
D-T phase (even without -power this was difficult in JET & TFTR !).
After > 7 years of intensive research – still a long way to go
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