recent progress on pedestal and divertor experiments ... · y. x. wan, et al, nf, 2017 roadmap of...
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Institute of Plasma Physics, Chinese Academy of Sciences
Recent progress on pedestal and divertor experiments towards long-pulse H-mode
operation in EAST
Baonian Wan* for the EAST Team and Collaborators**
*E-mail: [email protected]** See appendix of B. N. Wan et al., Nucl. Fusion 57, 102019 (2017)
2018 BOUT++ WorkshopAugust 14-17, 2018, Livermore, CA USA
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Y. X. Wan, et al, NF, 2017
Roadmap of Fusion Energy Research in China
EAST aims at demonstration of SS high-performance operation under ITER-like condition and address relevant physics basis for
ITER and CFETR
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EAST features strong RF H&CD, ITER-like W upper divertor and Mo first wall, balanced NBIs
Co-NBI
Count-NBI
LHCD-2.45G
LHCD-4.6G
ICRH-1
ICRH-2
ECRH-1,2
W
Mo
C Mo
Mo
Water-cooled first wallTotal injection power ~ 15 MW
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EAST Achieved the Longest Pulse Fully Non-inductive Steady State H-mode Operation with Tungsten Divertor
• Prerequisite: High CD&BS– Efficient non-inductive CD in H-mode/ High fbs
• Prerequisite: Optimized PWI– Low peak heat load/Tolerable transient heat shock/Low
impurity concentration/Efficient recycling control• Integrated operation into long pulse H-mode discharge
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Goal of EAST in the near futurefor the reference of ITER & CFETR SSO
High performance: ~50% bootstrap current fraction
Long pulse: >400s H-mode
Current status: 100s H-mode
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Current status (2018 campaign) towards the goal
p Relevant physics research in support of future long pulse H-mode operation with fBS ~ 50%•Scenarios Development: High beta SSO & Hybrid •H&CD, T&C, pedestal & DSOL physics, dynamic control, EP physics, etc.
p Exploration of high beta regime relevant to ITER baseline with high power injection
Full RF:bP~1.9, bN~1.6
RF + NBI:bP~2.5, bN~2
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Higher βp Scenario Sustained over 20s
Validation of Active Water-cooling Capabilities for W-divertor and LHCD W-guard limiter
❑ 80933, higher βP and βN, RF only− βP~1.9, βN~1.55, q95~6.5, fGr~0.7, Vloop~10mv.
❑ Next goal:− Fully Non-Inductive, vloop~0, for >100s.
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The challenge on edge plasma physics for EAST
• EAST is focusing on the development of truly steady state H-mode scenarios for ITER & CFETR
• For very long pulse plasma operation, the key issue is particle and heat balance.
• Optimizations on edge plasma physics are necessary to achieve the SSO with high bootstrap current fraction scenario:
Ø Pedestal physics: controlling the sourceü Suppression & mitigation of large ELMü Exploration and extension of the small/no ELM scenario
Ø Divertor & SOL physics: reducing the expenditureü Active handling of particle and heat depositions on divertorü Design of the new tungsten lower divertor
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outline
Ø Pedestal physics:ü Suppression & mitigation of large ELM
p Li injection p RMP
ü Exploration and extension of the small/no ELM scenario
Ø Divertor & SOL physics: reducing the expenditureü Active handling of particle and heat depositions on divertorü Design of the new tungsten lower divertor
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EAST has various capabilities for ELM control
• ITER-like full metal wall, low rotation, long pulse
RMP [Sun Y. et al, PRL (2016)]
Low hybrid wave [Liang Y. et al, PRL (2013)] Pellet, SMBI fueling
Li injection [Hu J. et al, PRL (2015)]
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ELM suppression by Li aerosol injection
1 2USN
• Reproducible ELM-free discharges with W divertor
• Same target plasma, fELM~200Hz• #70591, ELM gradually disappears• ELM completely suppressed except NBI
blips• ELM suppressed, before and after Li
injection
Ø Strong reduction in recycling due to Li accumulationand flow rate increase
Ø No impurity accumulations during ELM-free phaseØ Non-inductive à steady-state, essential for long pulse
small/no ELM H-mode
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Full ELM suppression achieved with n=1 and 2 RMP in RF dominant heating plasma in EAST
l A flexible RMP system has been
installed in EAST since 2014
l Full ELM suppression has been
achieved in EAST with RF heating
(ΩΦ~0) using n=1, 2 RMP
l Extended to long pulse (~ 20s)
steady state (Vloop ~ 0.0V)
operation with W divertor
[Sun Y. et al., PRL (2016)]
q95 ~ 5.7, βN ~ 0.8, ν*e,ped ~ 1
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Physical understanding of linear and nonlinear plasma response for ELM suppression
[Sun Y. et al., NF (2017)]
l Linear plasma response by MARS-F
modeling determines the best spectrum
for ELM suppression
l Nonlinear plasma response happens at
the transition from ELM mitigation to
suppression
[Sun Y. et al., PRL (2016)]
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Multimode plasma response directly observed in EAST tokamak
[N.C. Logan et al, NF 58 (2018) ]
l The n=2 plasma response was shown
to be multimodal (clear phase shift)
using two LFS mid-plane magnetic
sensor arrays in EAST.
l GPEC ideal MHD modeling captures
this transition from single-mode to
multimode
l Mode structure change significantly
from LFS kink to dominated edge
resonance, at which phasing
strongest ELM mitigation observed
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Redistribution of divertor particle flux achieved using rotating RMP in EAST
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• 3D pattern of the particle flux during the application of rotating RMP in EAST agrees well with modeling by the TOP2D code
• Plasma response modeled by MARS-F can amplify or shield the RMP, consistent with observed particle flux
Coil current
Particle flux
270o, amplified
90o, shielded
Modeled (MARS-F)Modeled (VAC)
Observed
�������
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Challenges for the active ELM control towards CFETR
• Compatibility of Li injection & FLiLi with reactors
• The nonlinear response of plasma to RMP• Compatibility of RMP with CFETR
• Physics understanding of ELM control by RF• Engineering technology for ELM suppression & pacing by RF
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outline
Ø Pedestal physics:ü Suppression & mitigation of large ELMü Exploration and extension of the small/no ELM scenario
p Grassy ELM
Ø Divertor & SOL physics: reducing the expenditureü Active handling of particle and heat depositions on divertorü Design of the new tungsten lower divertor
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Grassy ELM regime obtained in EAST with metal wall
• Compatible with low rotation• Does not sensitive to Bt direction and LHCD• Typical profiles show wide pedestal and lower
density gradient in the grassy-ELM regime
USN
dRsep ~ 2 cm
Average ELM frequency ≳ 2 kHzVt0 ~ 10 km/sH98,y2 ~ 1.1Loop voltage ≲ 0.005 V with LHCD<ne> ~ 57%nGW
bp ~ 1.8li ~ 1.1q95 ~ 6.8du ~ 0.58, d = (du + dl)/2 ~ 0.46k ~ 1.56#$,&$'∗ ~ 1fBS ~ 31%
( )2p ile b¢D = +
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Type-I ELM ≲ 100 Hz
High q95 high bp
~ 500 HzGrassy-ELM ≳ 2000 Hz
EAST grassy ELM has small peak heat flux and excellent control of W concentration
q95 ~ 4.8, bp ~ 0.85, du ~ 0.5li ~ 1, WMHD ~ 200 kJ
q95 ~ 6.8, bp ~ 1.72, du ~ 0.5li ~ 1.1, WMHD ~ 190 kJ
q95 ~ 6.8, bp ~ 1.78, du ~ 0.57li ~ 1.1, WMHD ~ 190 kJ
GrassyELM
Type-IELM
W droplet decay
• ELM peak heat flux is reduced by more than 10 times
• Low W source due to low transient heat load• Strong W exhaust carried by the grassy ELMs• Strong W neoclassical transport at high q
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The mechanism of EAST grassy ELM has been founddue to less peeling drive compared with type-I ELM
Type-I ELM
Grassy ELM
Grassy ELMs situate near peeling boundary
BOUT++ nonlinear simulation
BOUT++ code successfully reproduce the grassy ELM.
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Fully non-inductive high-performance small-ELM regime are obtained in EAST with W divertor in 2018 campaign
Full RF heating: LHW+ECRHHigh q95 (~ 6.7)High bp (~ 1.9)High density (~0.75 nGW)High fBS (> 45%)Configuration: USNBt direction: favorable
ELMs are more grassy and obtained at lower q95 in 2018 campaign when C impurity concentration is significantly reduced by replacing the LHCD guide limiter from C to W.
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Exploration of small-ELM regime towards lower q95
Towards lower q95 (~5.4):Ø Grassy-like small ELMs can be obtained with unfavourable Bt ;Ø Mixed ELMs appear with favorable Bt.
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Mixed ELMs turn to grassy ELMs by impurity seeding without confinement degradation
Dust
Mixed ELMs
Grassy ELMs
More grassy
Promising to be applied for lower q95 exploration
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Challenge: how to extend the grassy ELM regime to future facility?
Grassy ELM regime prescription:1. High q95
2. High bp + li/23. Wide pedestal4. Strong shaping dIt could be naturally achieved in CFETR.
ELITE
Kink/Peeling Unstable
Stable type-IIne
Further exploring the parameter space of grassy ELM towards CFETR
should concern:
ü High bootstrap current fraction � √ �
ü Compatible with high density � √ �
ü Compatible with radiative divertor� √ �
ü Integrate above in one pulse and long-pulse demonstration (to be
done)
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outline
Ø Pedestal physics:ü Suppression & mitigation of large ELMü Exploration and extension of the small/no ELM scenario
Ø Divertor & SOL physics: ü Active handling of particle and heat depositions on divertor
p Strike point splitting by LHWp Active feed back control p Quasi-Snow Flake in W divertorp W control
ü Design of the new tungsten lower divertor
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LHW-induced strike point splitting shows toroidal asymmetry: 3D divertor footprint features
• 100s H-mode with strike point splitting on W divertor targets
• good handling of heat flux and thus impurity source.
• Both divertor temperature and recycling were well maintained
• Not sensitive to q95, in contrast to fixed RMP coils
• A threshold of PLHW ~ 0.9 MW exists for 3D footprints & ELM mitigation in EAST
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Active feedback control of divertor heat load in H-mode for long pulse operation
l Achievement of feedback ctr. of radiation in EAST [K. Wu, NF (2018)].
l Successful extension of divertorradiation & heat flux ctr. in high βscenario on DIII-D [March 2018].
l Stable feedback ctr. of divertordetachment in EAST [July 2018].
Neon puffing from top divertor
Neon-SMBI from LFS mid-
plane
H-mode
Total radiation power was activelycontrolled by feedback of LFS neon-SMBI seeding.
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QSF compatible with high performance in SSO using W divertor
5 10 15 200
0.25
EAST #71469
5 10 15 20
0
1
5 10 15 200
1
2
3
5 10 15 200
0.5
1
5 10 15 200
1
2
[MW
]
time [s]
IP [MA]Uloop [V]
Te0 [keV]
bP
LHWICRFECRH
ne/nGH98Da
u A steady-state regime with improvedconfinement (H98>1) & high bootstrap current(bP>2) is obtained.
u Outer strike point flux expansion:fm,QSF/fm,SN ~ 3
u Peak heat flux reduced by a factor of 1.5
SNQSF
QSF: Quasi-Snow Flake divertor configuration
Collaborated with ENEA
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Effect of W divertor closure on particle exhaust
l Effective particle exhaust with strike point close to the pumping slot, good forlong pulse operation.
l No significant difference against ion Bx�Bdirections.
1.8
2
2.2
<n
e> (
1019
m-3
)
EAST #67065
2
4
6
SM
BI
(a.u
.)
3.5 4 4.5 5 5.545678
Time (s)
L (
cm)
0481216
Dec
ay t
ime
(s)Strike point sweeping
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Control of W source with various methods
Neon/D2-SMBI assisted impurity injection from LFS mid-plane
à lower Tet, and thus reduced W sputtering significantly.
l LHW, high fELM for relief of W, compatible with RF scenarios in EASTl Reduce divertor heat flux by enhancing DSOL radiation via lithium aerosol
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outline
Ø Pedestal physics:ü Suppression & mitigation of large ELMü Exploration and extension of the small/no ELM scenario
Ø Divertor & SOL physics:ü Active handling of particle and heat depositions on divertorü Design of the new tungsten lower divertor
p Limitations of current C divertorp Design of the new W divertor
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Current PFCs in EAST W-shape graphite lower divertor
W
Mo
CPumping capability of the ITER-like W upper divertor is limited due to very narrow pumping channels through the cassette body.
W
Mo
C Mo
MoMo
Mo
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The current lower divertor cannot fulfill the requirements of the near future goal
Graphite tile
61s long H-mode in 2016
Hot spots on lower graphite divertor
Current limitations:u Hot spots on the lower graphite
divertor is currently the main problem limiting heating power to < 3 MW for ~100 s long-pulse H-mode operations in EAST
u Heavily rely on lithium to reduce H concentration, recycling and impurity
p Steady-state operation of a dissipative divertor with low tungsten sputtering and strong divertor pumping.
p Power and particle exhaust and tungsten impurity control is the key to achieve this global target.
p Tungsten sputtering by light impurities à Tet < 10 eVp Cooling capability of the PFCs à qet < 10 MW/m
Key targets�
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New divertor design for high-power steady-state H-mode operations in EAST
End box:protect against downward strike point excursions
Dome:Improve pumping
Vertical inner target (VIT) Horizontal outer target (HOT)
Baffle: trap neutral,protect the end box
Reflection end box: trap neutral
Water-cooled internal coil ~10 kAt
Cryopump
SMBI
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High neutral pressure near the corner facilitates detachment across the entire outer target
Optimized projection distance~ ln > lq < 1 cm
Pumping slot at high neutral pressure position
Ion flow
reionization
1cm 2cm 3cm
End box nearly parallel to field lines to avoid high heat load on the end box
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Other requirements of the new lower divertor
l Two kinds of water-cooled tungsten PFC tech�• Flat-tile (2mm thickness) PFCs: Dome and baffles
(~5 MW/m2)• ITER-like monoblock PFCs: Divertor targets (~10
MW/m2)l Main engineering constraints for the water-cooled
tungsten PFCs in EAST�• Dome�Curvature radius limit ~9 cm• End box : flat-tile ~5 MW/m2
• Cryopump 75 m3/s on the low field side; 2*106 m3/s at port end ~3m long
l High triangularity should allow access to the small-ELM H-mode regimes & advanced core scenarios
l Compatible with double-null operation
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Schedule
Contents2016 2017 2018 2019
1 2 3 4 5 6 7 8 9 10
11
12 1 2 3 4 5 6 7 8 9 1
011
12 1 2 3 4 5 6 7 8 9 1
011
12 1 2 3 4 5 6 7 8 9 1
011
12
Physics objectivePlasma
configurationPlasma facing
materialCompatibility of
divertor geometry and plasma
configurationDivertor design
and optimizationR&D
Prototype development and
test
Manufacturing
Diagnostic development
Assembly
QA and QC
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Summary: The long-pulse operation of EAST are focusing on the physics design of CFETR
CFETRLong-pulse steady-state
Pedestal physics of EAST:
ELM suppression
ELITE
Kink/Peeling Unstable
Stable type-IIne
Small/no ELMDSOL physics of EAST:
3D footprint
Active feedback control of radiation
Lower W divertor upgradeLithium injection
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EAST near-term planMain targets:Demonstration of long-pulse high-performance H-mode plasma operation in support of ITER and CFETR• 400s high-performance H-mode H98y2>1 with fBS > 50% at q95 = 6-7• Heat & particle exhaust for 100s with 10MW heating power• Robust ELM solutions potentially used in CFETR
Main upgrades:• New W lower divertor (metal wall coverage > 95%)• ECRH injection power 1à2MW (synergy between ECRH and LHCD
is the key for good core confinement, NF 066011 2018)• Diagnostics upgrade (MSE, more divertor diagnostics, etc.)
Main requirements:• Improve ICRF absorption power• NBI long-pulse operation• Advanced magnetic configuration and MIMO control
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Challenges of edge plasma physics from EAST to CFETR
Two main challenges:• Particle balance: only physics solutions• Heat load: physics & engineering solutions
Pedestal physics: control the heat and particle into SOL• Exploration the compatibility of small/no ELM regime• Understanding ELM dynamics: active control of ELM• Particle confinement time• Fueling depth
Divertor physics: particle and heat exhaust• Active control of particle and Heat flux depositions• ITER-like full metal wall & W divertors
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Thank you!
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Advanced geometry and divertor are designed on CFETR
34m
37m
Radial scale of CFETR
L-modeHigh triangularity
L-modeSnowflake
H-modeSnowflake
ITER-like divertor SAS divertor
Advanced divertor