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