Joint Conference of17th International Toki Conference and16th International Stellarator/Heliotron Workshop 2007
October 15-19, 2007
Ceratopia Toki, Toki, Gifu, Japan

LHD Project,National Institute for Fusion Science

R. Sakamoto, M. Kobayashi, J. Miyazawa, S. Ohdachi, T. Morisaki, S. Masuzaki,
I. Yamada, M. Goto, K. Ida, S. Morita, S. Sakakibara, K. Tanaka, K. Kawahata,K.Y. Watanabe, Y. Suzuki, H. Funaba, S. Murakami*, N. Ashikawa, Y. Nagayama,
Y. Narushima, B.J. Peterson, M. Shoji, C. Suzuki, M. Tokitani, S. Yoshimura,N. Ohyabu, H. Yamada, A. Komori, O. Motojima and LHD experimental group
National Institute for Fusion Science, Toki Gifu 509-5292, Japan*Kyoto University, Kyoto 606-8501, Japan Motivation
 Experimental setup
 Helical divertor (HD) configuration
 Fueling (particle deposition)
 Magnetic Configuration (position of magnetic axis)
 Change of profile Particle transport Potential model of IDB plasma Sustainability of IDB plasma Core density collapse event in IDB plasma Impurity behavior in IDB plasma

ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

2 /23

 Motivation
 Experimental setup
 Helical divertor (HD) configuration❖ Internal Diffusion Barrier (IDB) Formation in HD
 Fueling (particle deposition)
 Magnetic Configuration (position of magnetic axis)❖ Properties of IDB Plasmas
 Change of profile Particle transport Potential model of IDB plasma Sustainability of IDB plasma Core density collapse event in IDB plasma Impurity behavior in IDB plasma❖ Summary
ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

3 /23 pellet fueled high density discharges
 active pumped local island divertor (LID) configuration
 efficient pumping property due to the localized installation (pump~ 40 %) struggle with high heat flux.
45

LID Headne 1020 (m3)Core Plasma

22TeTe (keV)

m/n=1/1 Islandne33

Wp [MJ]

1.0

4Gas puff
Pellet (IDB)

0.5

11to Pump

0HD
ITC17 / ISHW16HD LCFS

00.5

01.0


R. Sakamoto, National Institute for Fusion Science, LHD

00

Rax= 3.75 m

12

ne 1020 [m-3]

34 /23 heliotron type device with NbTi
super-conducting coils
 high energy NBI heating (~ 12 MW)

NBI#1
screw extruder typerepetitive pellet injector

NBI#2
10 barrel in-situ
pipe-gun injector

 intrinsic divertor configuration inheliotron type device open divertor configuration withforced water cooled carbon targetplate no active pumping capacity
 larger heat receiving area than LID

NBI#3

 10 barrel in-situ pipe-gun injector
 pellet size: 3.4 - 3.8 mm (1.5 2.01021 atoms/pellet)
 pellet velocity: 1,000-1,200 m/s
ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

NBI#4

Divertor leg

Divertor plate(Carbon tile)
5 /23

global confinement

excellent

MHD stability
Characteristics

 outward shift  STABLE inward shift  GOOD
 Rax= 3.6-3.65 m  OPTIMAL

particle orbit

Standard
Configurationpoor

 inward shift  heavy neutrals

3.5

3.6 3.7 3.8 3.9Magnetic axis [m]4.0

concentration in inboard side
Rax= 3.6m

Rax= 3.75m(1019 m-3)
1.2

0.60.03
ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

6 /23❖ Introduction
 Motivation
 Experimental setup
 Helical divertor (HD) configuration
 Fueling (particle deposition)
 Magnetic Configuration (position of magnetic axis)❖ Properties of IDB Plasmas
 Change of profile Particle transport Potential model of IDB plasma Sustainability of IDB plasma Core density collapse event in IDB plasma Impurity behavior in IDB plasma❖ Summary
ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

7 /23

● IDB (Pellet), #68996, 1.466s

Rax=3.75 m, PNBI= 11MW ● Normal (Gas Puff), #63555, 1.236s
120 flux coordinate

real-spacene flat or hollow density profile
due to peripheral fueling

P (kPa)10080
604020 high central pressure(exceeds atmosphericpressure) plasma  become high (> 5%) even at high magnetic
field ( Bt > 2.54 T)
 very large Shafranov shift(/aeff  1/2)

Te

3
210P

1.0

Te (keV) highly peaked density profilene (1020 m-3)

00.5

0-1.0

-0.50
ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

0.51.03.0

3.5

4.0

4.5

R [m]
8 /23

PNBI= 11 MW, BT= 2.54 T central temperature follow quite a similarcourse after pellet injection
 IDB formation and central pressure
rapidly increase at Rax 3.75 m
 Plateau of pressure rise at high density
regime• 2.710 m at R = 3.65 m• 5.010 m at R = 3.75 m• >7.410 m at R = 3.85 m
20-320-320ax

ax

-3ax

 Pressure rise is abruptly terminated by acore density collapse (CDC) event
ITC17 / ISHW16500

ne 1020 [m-3]- IDB formation

1006420Te [keV] attainable central plasma density
becomes higher as the magnetic axis
shifts outward

P [kPa]9 Pellet Injection

Rax= 3.85 m (#69268)
Rax= 3.75 m (#68996)
Rax= 3.65 m (#68956)

210-0.4

R. Sakamoto, National Institute for Fusion Science, LHD

-0.2

0.0

0.2

0.4

0.6

Time [s]9 /23

P [kPa]

PNBI= 11 MW, BT= 2.54 T

 Magnetic configuration (outward shift) is
another factor of the IDB formation inaddition to pellet core fueling.

ne 1020 [m-3]-500432101.0

Te [keV] sharp bend in the density profile around = 0.55
low density mantle and high densitycore Achievement of double density without
fall of temperature

1000.5
Rax= 3.75 m (#68996)
Rax= 3.65 m (#68956)

0-1.0

-0.5

00.5

1.0


ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

10 /23❖ Maximum central density reaches
11021 m-3 at Rax> 3.9 m.

❖ Suppression of pressure rise due toCDC event

ne(0) 1020 [m-3]❖ Central pressure reach its largest value(130 kPa) at Rax= 3.85 m.

3.65m, #68955 @1.20s
3.70m, #68921 @1.26s
8 3.75m, #68995 @1.26s
3.80m, #69261 @1.165s
3.85m, #69268 @1.185s
6 3.90m, #69325 @1.065s
4.00m, #69360 @0.965s

P(0) [kPa]ne 1020 [m-3]

10Maximum ne(0)816Te(0)4ne(0)

2

at maximum P(0)at maximum P(0)

00150

10

42Te(0) [keV]❖ A jump of the central pressure isobserved around Rax= 3.7 m

BT= 2.539 T, PNBI= 11 MW12

100



50

2IDB formation regime0
2.5

3.0

3.5

4.0

4.5

5.00

3.6

3.8

Rax [m]R [m]ITC17 / ISHW16

3.7

R. Sakamoto, National Institute for Fusion Science, LHD

3.9

4.011 /23

❖ Introduction
 Motivation
 Experimental setup
 Helical divertor (HD) configuration❖ Internal Diffusion Barrier (IDB) Formation in HD
 Fueling (particle deposition)
 Magnetic Configuration (position of magnetic axis)
 Change of profile Particle transport Potential model of IDB plasma Sustainability of IDB plasma Core density collapse event in IDB plasma Impurity behavior in IDB plasma❖ Summary
ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

12 /23plateau 1b*10, p*1 at =0.5

 box-profile into linear-profile
 due to lack of particle source inside IDB? or confinement degradation?
ne [1020 m-3]

646

#68996
Bt= 2.539 T
Rax=3.75 m

ne [1020 m-3]

❖242ne(IDB)

0Te [keV]

Te(0)
1.0
0.503210

1.0Te(IDB)

0.50

1.20 s1.36 s1.60 sb*(IDB)Pe [1020 keV/m-3]

Te [keV]0ne(0)

10

1

3.0

3.5

4.0

4.5

0.8

1.0

R [m]
ITC17 / ISHW16

1.2

1.4

1.6

Time [s]R. Sakamoto, National Institute for Fusion Science, LHD

13 /23

❖ Particle transport coefficient of IDB plasma is estimated from time
evolution and gradient of density profile.
where

12
= 0.80 (mantle)
= 0.50 (IDB)
= 0.40 (core)
= 0.20 (core)

10dn/d

864
20
1.2

1.4

1.6

1.8

2.0

Time [s]ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

14 /23 profile change (Box-like into linear profile) is explained by lack of particle
source inside IDB
 not sensitive to collisionality

1.515mantle: = 0.8core: = 0.20

ITC17 / ISHW160123-(dne/d)/ne4m2/s
456.

IDB:
= 0.4

D= 0.042 m2/s

0.510

e/ne

IDB: = 0.5

IDB phasee

D= 0.41 m /s2mantle: = 0.8

Pe/ne [keVm/s]

1.0

IDB phase00

R. Sakamoto, National Institute for Fusion Science, LHD

12-(dTe/d)/a [keV/m]

315 /23

- suppress radiation loss  free-from radiative density limit
secure temperature gradient forhigh density core

coren,Tn(0)mantleIDBT(0)- deep pellet fueling and goodparticle confinement lead tohigh pressure core plasma

ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

rc
minor radius

a16 /23

❖ IDB plasma can be sustained by using repetitive pellet injection
 Demonstrated in low-B, low-power experiment❖ Core fueling is essential to maintain SDC plasma High speed and large pellets are requiredH [a.u.]

ITC17 / ISHW16#59519 200

Wp

150
100
500Iacc,NBI

ne

2.4I acc,NBI (A)

400
300
200
10002015105010864
200.5

IDBMantle

4.0

4.5

2.0

ne 1020 [m 3]

19 -3

ne [10 m ]Wp [kJ]

 High frequency injection is not required

1.6
1.2t= 1.62 s

0.8t= 1.60 s

0.4
1.0

1.5
Times [s]

2.0

2.50

3.0

3.5

R [m]
R. Sakamoto, National Institute for Fusion Science, LHD

17 /23 Core density is abruptly expelled at highpressure regime
 Time scale of CDC is sub-ms Limit central pressure Mechanism of CDC
MHD stability?
Equilibrium limit?
Turbulence?
……

-❖ Potential solution: Suppression ofShafranov shift
 Vertical field control (inward shift) Suppressing P-S currents
Aspect ratio (reduce minor radius)
Ellipticity (vertical elongation)-

ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

18 /23

#69286, Rax=3.85 m, Bt= 2.54 T

 Core density is abruptly expelled at highpressure regime
 Time scale of CDC is sub-ms
 Limit central pressure Mechanism of CDC

Before CDC
t=1.485 s42After CDC

0Te (keV)

0.8❖ Potential solution: Suppression ofShafranov shift
 Vertical field control (inward shift) Suppressing P-S currents
Aspect ratio (reduce minor radius)
Ellipticity (vertical elongation)-6

t=1.500 s

0.6
0.4
0.206

 (%)

-

MHD stability?
Equilibrium limit?
Turbulence?
……

ne (1020 m-3)

84
20-1.0-0.5

0

0.5

1.0


ITC17 / ISHW16

R. Sakamoto, National Institute for Fusion Science, LHD

19 /23

❖ Vertical elongation is effective to suppress the Shafranov shift

 CDC limits central pressure for < 1.2
 CDC disappears when > 1.2
 Higher central beta 6.6 % has been achieved under CDC free condition
related poster at P1-051: Ohdachi and P1-087: Miyazawa
Rax= 3.85 m, Bt= 2.00 T, PNBI 12 MW

4.2

0.30

8

4.1

6

3.8

(0) [%]

R0 [m]

3.9

CDC

0.20

CDC free

(0)

40.15
0.10

20.05

3.7
3.6

Shift [m]eff= 1.01
eff= 1.05
eff= 1.10
eff= 1.14
eff= 1.28
eff= 1.47

4.00.25

Shiftvertical elongation

A= 4.22 m, Rax= 3.85 m
0102030

400
1.0

1.1

1.3

1.4

1.50eff

Pe(0) [keV/m3]
ITC17 / ISHW16

1.2

R. Sakamoto, National Institute for Fusion Science, LHD

20 /23❖ Neoclassical ambipolar diffusion

1.0ne2TiCXS
0.5

1Te000-20-40

Wp (MJ)
Zeff

Er (kVm-1)#73867, t= 0.9±0.04 sTe, Ti (keV)

ne (1020 m-3)

3

neL (1020 m-3) Ti, Te (keV) ne (1020 m-3)

❖ No significant indication ofimpurity accumulation

1.03.0

3.5

4.0

4.5

#70146, Rax= 3.8 m, Bt= 2.0 T
pellet injection

41NBI032Pe(0)0.50ne(0)2nefoot

0
1.5
1.0
0.5
0Te(0)

Tin eL4

 BP

20Zeff2
10
0.6

0.8R (m)
ITC17 / ISHW16

WpPe(0)(1020 keV/m-3)

 ion root (negative radial electricfield)
 impurity accumulation?

R. Sakamoto, National Institute for Fusion Science, LHD

1.0

1.2

1.4

Time (s)21 /23

thermal force

Thermal force dominant

divertorcore
plasmaCarbon density distribution(EMC3-EIRENE)

friction force byplasma flow

[1018 m-3]

nLCFS= 21019 m-3//-B field

1.0 Impurity shielding potential in
ergodic layer
Outward friction force dominate
impurity behavior in high-density
regime-Increase ne❖ EMC3-EIRENE calculation//-impurity velocity

nLCFS= 31019 m-3

0.1

nLCFS= 41019 m-3
0.01

Frictionforce
ITC17 / ISHW16

Friction dominant

Thermal force

related presentation at I-07: Kobayashi
R. Sakamoto, National Institute for Fusion Science, LHD

22 /23

❖ IDB plasma has been reproducibly obtained at the intrinsic helicaldivertor configuration as in LID configuration by optimizing the pellet
fueling and magnetic configuration.
 Core fueling by multi-pellet injection is essential.
 The IDB easily appears in the outward-shifted magnetic configuration.

❖ The central density reaches 11021 m-3 at Rax3.9 m and the centralpressure has reached 1.3 times atmospheric pressure.
❖ Confinement region is separated into low density mantle and highdensity core in IDB plasma. This lead to high pressure core plasma.
 Diffusivity is kept at low level even high density gradient in high density core.
 Low density mantle suppress radiation loss and secure temperature gradient.

❖ CDC event, which arise from very large Shavranov shift, limit operationalregime.
 Suppression of Shafranof shift with ellipticity control can mitigate CDC eventand the central  is increase up to 120 % of standard configuration.

❖ Harmful impurity accumulation has not been observed in IDB plasma.

ITC17 / ISHW16R. Sakamoto, National Institute for Fusion Science, LHD

24 /23