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ASIPP/ EAST
High Confinement Steady-state Operation with
Quasi-snowflake Magnetic Configuration on EAST
B.J. Xiao1,2, Z.P. Luo1, J.G. Li1,2, Q.P. Yuan1, K. Wu1, Y. Guo, Y.H. Wang, Y. Huang1 X.Z. Gong1, L. Wang1, G.
Calabrò3, R. Albanese4, R. Ambrosino4, G. De Tommasi4, F. Crisanti3 & EAST Team 1Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, 230031, China
2School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230031, China 3ENEA Unità Tecnica Fusione, C.R. Frascati, Via E. Fermi 45, 00044 Frascati, Roma, Italy
4 CREATE, Universittà di Napoli Federico II, Universittà di Cassino and Universittà di Napoli Parthenope, Via Claudio
19, 80125, Napoli, Italy
bjxiao@ipp.ac.cn
1
2nd IAEA technical meeting on divertor concepts,
13-16, Nov., 2017, Suzhou, China,
ASIPP/ EAST
Contents
• Motivation
• EAST QSF RZIP & ISOFLUX-SISO control
• QSF results: non-inductive ELMY free high confinement long
pulse discharge
• Summary
2
ASIPP/ EAST 3
Motivation: potential of X-d (QSF), Super X, or Snowflake
for heat load reduction
15
Figure 7: (left) A standard divertor has a single, main x-point (shown in blue).
(center) An X-Divertor introduces a secondary x-point (shown in green)
in the downstream SOL to increase poloidal flux expansion at the
targets. (right) A Super X-Divertor draws the divertor leg out to a larger
major radius to increase toroidal flux expansion, as well as poloidal flux
expansion.
It is also hypothesized that the XD and SXD may create beneficial conditions for
stable detachment, the third goal of advanced divertors highlighted at the beginning of
this section. This possibility is discussed in great detail in Section 6.4.
The other category of advanced divertor is the Snowflake Divertor (SF), first
published by Ryutov et al. at Lawrence Livermore National Laboratory (LLNL) in 2007
[7]. Unlike the XD or SXD, the Snowflake utilizes a second x-point in or very near the
private region, often almost so as to be coincident with the main x-point. The resulting
six-lobed magnetic geometry gives the SF its apt name (Fig. 8). By doing this, a large
region is created where not only BP is very small, but its gradient as well, leading to very
large flux expansion in the immediate vicinity of the main x-point.
Standard Divertor X-divertor Super X-divertor
• M. Kotschenreuther, IAEA FEC, (2004) • M. Kotschenreuther, POP 14, (2007) • P.M. Valanju, POF 16, (2009) • D.D. Ryutov, POP 14, (2007)
• D.D. Ryutov, POP 15, (2008)
• D.D. Ryutov, Phys. Scr. 89, 88002 (2014)
ASIPP/ EAST 4
EAST is not feasible for SF
12 PFs : 14 kA/ 12 PSs，
DN/SN
Far from plasma in comparison to
normal tokamaks
EAST PFs：
Higher Ip requires coil
currents exceed limit
Solution?
Quasi-Snowflake
Ip=250 kA
ASIPP/ EAST
Modeling shows achievable high flux expansion at higher Ip
5
Black: SN: Connection Length: L=95m & Flux Expansion: fm=2.1
ASIPP/ EAST 6
LQSF achieved in 2014 compared with LSN
Schematic 2D view of EAST with SN #47038 at t=4.5s (black solid line) and QSF (red solid line) at t=4.5s plasma boundaries.
R [m]0.5 1 1.5 2 2.5 3
Z [m
]
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
PF1
PF2
PF3
PF4
PF5
PF6
PF7
PF8
PF9
PF10
PF11
PF12
PF13
PF14
IC1
IC2
4703848971
D=79cm
Main magnetic geometry for QSF and SN
QSF
48971@4.5s
SN
47038@4.5s
SOL Volume [m3] 0.389 0.260
Connection Length [m] 189.91 144.38
Magnetic flux
expansion at outer SP
fm,out 8.22 2.01
Magnetic field angle at outer SP αout [deg] 0.33 1.22
Magnetic flux
expansion at inner SP
fm,in 4.71 2.34
Magnetic field angle at inner SP αin [deg] 0.90 1.29
Peak heat flux
[MW/m2] 0.10 0.21
ASIPP/ EAST
Heat load is reduced under QSF
7
Time evolution of main plasma quantities
for SN (#47038) and QSF discharge (#48971)
Spatio-temporal profiles of ion saturation
current density jSAT for SN (#47038) and
QSF discharge (#48971). Once QSF
configuration becomes stable, the peak
of jSAT is observed to drastically drop
indicating a possible heat flux reduction.
ASIPP/ EAST
Heat flux: QSF vs SN (2014, shot 48971)
8
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
-0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25
Distance along target [m]
MW
/m2
SN
QSF
SNexp
QSFexp
Infrared camera measured (SNexp & QSFexp)
and simulated power density (SN & QSF) at the lower outer target.
#48971@4.5s
q”max：
SN/QSF
~ 4(simulation）
> 2(Exp.）
ASIPP/ EAST
EAST QSF by ISOFLUX control
Schematic diagram for
ISOFLUX control segments
✦ QSF shapes were controlled in feed-
forward, with a feed-back component added for shape & position control.
✦ QSF target configuration was designed
by EFIT/F2EQ code, with pre-calculated coil currents as feed-forward.
✦ QSF discharge was switched to ISOFLUX
from 2.7s to 2.8s, with SISO/MIMO algorithm.
✦ LSN-based & USN-based QSF was
carefully designed to fit the divertor geometry.
PF6
PF12
PF5 PF11
9
ASIPP/ EAST 10
H-mode: QSF vs LSN
1
0
✤Flux expansion of
QSF at out strike
point is factor ~3
than LSN
ASIPP/ EAST 11
ELMY behavior LQSF(70391) LSN(70398)
ASIPP/ EAST 12
Peak Heat flux @H-mode: LQSF vs LSN
1
2
✦ IR measurements point out a peak heat load reduction for
QSF of a factor ~1.5 with respect the LSN
ASIPP/ EAST 13
High confinement ELMY free under UQSF UQSF(71464)
vs USN(71562)
1
3
✤Flux expansion of
QSF at out strike
point is factor ~3
than LSN
UQSF USN
ASIPP/ EAST 14
UQSF High confinement behavior (Shot 71464)
ASIPP/ EAST
All the UQSF H-mode shots are ELMy- free
Shot number 𝑯𝟗𝟖 𝜷𝑷 𝒏 𝒆 [𝟏𝟎𝟏𝟗𝐦−𝟑]
Heating[MW]
LHW ICRF ECRH NBI
71307 1.21 2.3 2.3 2.0 0.7
0.3
2.6 71308 1.22 2.4 2.4 2.0 1.0 71309 1.30 2.6 2.7 2.3 1.0 71372 1.14 1.9 2.9 2.0 0.8
0 71375 1.12 1.9 2.7 2.3 0.8 71379 1.28 2.1 2.7 2.3 1.0 71380 1.18 2.3 2.9 2.3 1.0
2.5 71381 1.09 2.1 3.2 2.0 0.7 71382 1.30 2.6 3.1 2.3 1.0 71464 1.15 2.0 2.7 2.4 1.6
0.4 0 71467 1.14 2.0 2.7 2.4 1.5 71474 1.15 2.2 2.7 2.6 2.0 71475 1.21 2.3 2.7 2.6 2.5
ASIPP/ EAST
Long Pulse Non-inductive QSF Discharge
H98~ 1.1
ne~2.8*1019/m3
βp~ 2.1
Ip~ 250 kA
Steady state
Non-inductive
16
ASIPP/ EAST
Radiation Feedback Control Loop (P-22)
Latency： Gas Puff > 100 ms, SMBI ~ 1-2 ms
17
SMBI
UD-GP
ASIPP/ EAST
Radiation Feedback Control
18
ASIPP/ EAST
Summary
• By RZIP and ISOFLUX shape feedback control, QSF discharge has
achieved reliable performance;
• QSF discharge has been demonstrated the potential for heat load
reduction to the divertor target;
• ELMY free, w/o impurity accumulation and high confinement mode has
been found with upper QSF under various heating and plasma
conditions; non-inductive steady state long pulse operation has been
demonstrated;
• More efforts to improve QSF shape will be continuing, for more flexible
shape and robust control, higher Ip and extension of the operation
window for long pulse… radiation control or divertor heat flux control
will be integrated.
19
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