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ASDEX Upgrade
Max-Planck-Institutf
..ur Plasmaphysik
Active in-vessel saddle coils at ASDEX Upgradefor MHD control
Wolfgang SuttropO Gruber, D Hahn, A Herrmann, M Rott, U Seidel, B Streibl, T Vierle, D Yadikin, and
the ASDEX Upgrade Team
Max-Planck-Institut fur Plasmaphysik,
Assoziation IPP-EURATOM, D-85748 Garching, Germany
International Collaboration:B Unterberg, O Neubauer —- TEXTOR (FZ Julich)
P Brunsell —- EXTRAP-T2 (KTH Stockholm)
E Gaio, V Toigo —- RFX (Consorzio RFX Padova)
ITPA Pedestal & Edge Topical Group, San Diego 30 April 2008
The proposal
Install into ASDEX Upgrade
• Active in-vessel saddle coils
• Conducting wall elements
Goals:
1. Edge Localised Modes (ELM)suppression
2. Neoclassical Tearing Mode (NTM)rotation control(locked mode avoidance)
3. Resistive Wall Mode (RWM) stabilisation
Bu
A
Bl
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 2
New possibilities with ASDEX Upgrade saddle coils
In-vessel coils→ fast response (AC operation)→ low coil current needed (≤ 5 kAt)
Three poloidal coil sets→ flexible m spectrumtest importance of resonances for ELM suppression
Eight toroidal coils→ up to n = 4 (avoid core islands)→ quasi-continuous phase variation for n ≤ 3
Goal:Maximum flexibility to assessITER saddle coils and study physics
1.00 2.50-1.59
-1.06
-0.53
0.00
0.53
1.06
1.59
R[m]
z[m]
1.30 1.60 1.90 2.20
PSL
PSL
Avacuumport
upper divertor
lower divertor
Bu
A
Bl protection limitercontour
high fieldside
low fieldside
ASDEX Upgrade
0.70
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 3
Moderate coil current needed for edge ergodisation
Pedestal island “overlap” below 250 At (zero plasma rotation)
n=3, I = 0.24 kA
n=4, I = 0.2 kA, +/-
normalised poloidal flux1.00.8 0.85 0.9 0.95
3
0
1
2
Chi
rikov
par
amet
erσ
|q|=4 |q|=5 |q|=6
max
“Chirikov” parameter[Chirikov 1979]
σ =
ψmax−ψmin
ψqin −ψqout
Radial field lineexcursions:GOURDON code
σ threshold?Poincare plot, Lyapunovexponent: → σcrit = 1at onset of stochasticfield line diffusion
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 4
Core island size reduced with n = 4
n=4, I = 0.2 kA, +/-
normalised poloidal flux1.00.80.7 0.90.6
0.25
0
1
0.75
Fie
ld li
ne e
xcur
sion
[cm
]
|q|=4 |q|=5|q|=3
n=3, I = 0.24 kAmax
0.50.40.30.2
|q|=2
0.5
|q|=5/2
|q|=3/2
|q|=7/3|q|=8/3
|q|=11/4
|q|=5/3
|q|=9/4
Low m components:Parasitic core islands
Unwanted side effects:
• Confinementreduction
• NTM seeding
(Figure:GOURDONfield line tracing,no rotational shielding)
Core island width ( ≈ 2∆R) significantly reduced for high n
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 5
Controlled resonance by coil phasing
For n = 4, four phasings (Bu-A / A-Bl): +/+ +/- -/+ -/-
m spectrum (fixed n = 4) as a function of radius (ψ) [Becoulet et al. 2005, Burrell et al. 2005]
Resonant
n = 4 plus-minus phasing
Not resonant
n = 4, minus-minus phasing
poloidal mode number m
norm
alis
ed p
oloi
dal f
lux
norm
alis
ed p
oloi
dal f
lux
log (Br)log (Br)
+/- phasing -/- phasingn=4
poloidal mode number m
+
+
+
-
-
+
+
+
-
-
n=4
q profile ofAUG 17151t=3.85 s
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 6
Locked mode disruption avoidance
Locked mode disruption:
• Saturated (3/2) NTM
• (2/1) NTM grows(coupled to 3/2) andslows down
• Mode rotation dropsbelow ≈ 1 kHz→ locking, fast growthand disruption
⇒ Rotating error field withf ≥ 1 kHz can avoiddisruption and give controlsystem time to react
0.0
0.5
1.0
1.5
2.0
MA
, a.u
.
3.6 3.7 3.8 3.9
time [s]
0
a.u.
m=2, n=1 m=3 n=2Bθ
4.0 4.1 4.2
D α
Ip
3/2
2/11 kHz
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 7
With conducting wall: RWM stabilisation
Vacuum vessel far from plasma onlow field side
Passive stabilising loop (PSL)reduces vertical growth rate (n = 0)(opposite current direction in upper and
lower branches → radial field)
Extend with conducting wall elementsbetween PSL branches→ allow helical currents
Holes for diagnostics and heating:3D structure
Electromagnetic surface model
˜ 9000 nodes, ˜ 19000 elements
ICRH
ICRH
ICRHICRH
upper PSL
lower PSL
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 8
Physics requirements
Reference point: 10 cm in front of coil (≈ plasma boundary)
Ergodisation by resonant magnetic perturbation: σ = 3 for Bn = 0.6 mTAllow for factor 10 to accommodate shielding by plasma rotation.
RWM control requires bandwidth (thumb rule: f3dB ≥ 40× γ) and phase margin.Field amplitude depends on noise level - RWM signal must exceed background.
Mode rotation ( fmax = 3 kHz) will be done by midplane (A-) coils
Physics parametersQuantity Symbol Value Units Conditions
DC normal field min. Bn 6 mT f = 0, n = 2,3,4AC normal field min. Bn 1 mT f = 500 HzPhase lag of field max. ΦBn−V 0 . . . -150 degrees
→ Verify coil performance in presence of passive conductors (coil housing, PSL)
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 9
Technical requirements
Operational limits (individual coil)Quantity Symbol Value Units Conditions
Number of turns 5Peak coil voltage max. Vcoil 500 V f = 1 kHzDC coil current max. Icoil,DC 1 kA f = 0Operation pulse duration min. tpulse 6 sCool down time max. tpause 15 min.
Isolation voltage min. Vi 3 kV 100% testedHousing temperature max. Th,max 180 0C Icoil = 0Housing temperature max. Th,max 90 0C Icoil 6= 0
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 10
B-coil design - similar to proven W7-X control coils
• 5 turns, copper with cooling channel
• glass fabric wound around coils
• isolation: epoxy cast
• vacuum tight enclosure:1.2 mm Inconel sheet with stiffening ribs
Bu coilupperPSL
A-coil
Conductingwallcontour
Bl-coillowerPSL
outer divertor module
torusaxis
midplane
Mounted on upper and lower PSL
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 11
Electromagnetic model verifies AC capability of coils
“B”-coils : close to PSL, metal casing→ shielding by eddy currents
|Bn| at 10 cm distance to coil (QuickField)
PSL
B-coil
normaldirection
Bn,peak at Icoil,peak = 1 kA
1
10
1 10 100 1000 10000
frequency [Hz]
mag
netic
indu
ctio
n [m
T]
Bu-coilsd=10 mm
Bl-coilsd=30 mm
Phase Bn wrt. Icoil
-45
0
phas
eΦ
Bn-
I[d
egre
es]
1 10 100 1000 10000frequency [Hz]
Bu-coilsd=10 mm
Bl-coilsd=30 mm
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 12
Time schedule
Stage Hardware component Experiments Installation
1 4 upper + 4 lower coils ELM control , n = 2 2009+ 4 upper + 4 lower coils n = 4 2010
2 + 8 midplane coils Four n = 4 2011configurations
3 12 AC power supplies Mode rotation 2012(odd or even n) n = 3 ELM control
4 Conducting wall RWM stabilisation 2012sensors, controller
5 + 12 AC full voltage 2013(option) power supplies max. frequency
simultaneous oddand even n
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 13
Summary: In-vessel coils for MHD control
• A set of 3×8 in-vessel coils is proposed for ASDEX Upgrade
• Most flexible field configuration
⊲ Three coils poloidally to improve m resolution
⊲ n = 4: Core island avoidance
⊲ n = 3: Quasi-continuous phase variation
• ELM suppression experiments
⊲ Investigate physics, in particular resonance condition
⊲ New diagnostics possibilities with rotating error field
⊲ Prepare for ITER, e.g., configuration of ferritic inserts
• Mode rotation control (with AC power supplies)Resistive wall mode feedback stabilisation (with additional conducting shell)
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 14
References
[Chirikov 1979] CHIRIKOV, B. V., Phys. Rep. 52 (1979) 263.
[Becoulet et al. 2005] BECOULET, M. et al., Nucl. Fusion 45 (2005) 1284.
[Burrell et al. 2005] BURRELL, K. H. et al., Plasma Phys. Controlled Fusion 47 (2005) B37.
W Suttrop et al In-vessel saddle coils at ASDEX Upgrade for MHD control 15
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