平成24年度ダイバータおよびPWI合同研究会

LHDのダイバータ及びRMPコイル実験の概要
増崎 貴
LHD実験グループ

23 July 2012, S. Masuzaki

OUTLINE
 Introduction
 Divertor experiments
 Divertor particle control experiments−Towards a closed and pumped divertor
 Divertor heat control experiments−Application of RMP−Impurities seeding Summary
23 July 2012, S. Masuzaki

Introduction
Helical devices are free fromplasma current, and thusfrom disruption. This is a big
advantage for fusion reactor
design.
Plasma performance of LHD
has been developed largelyin this decade.
Understandings of core andedge plasma properties havebeen accumulated.
Large Helical Device
R=3.9m First wall : SS316
a=0.65m Div. plates : gaphite
25 May 2012, S. Masuzaki

Introduction

To realize a heliotron-type reactor, further divertor heat and particle
control experiments have to be conducted in LHD to gain
understanding of their physics which can be extrapolated to ahelical reactor.
25 May 2012, S. Masuzaki

Helical divertor

 Helical divertor is an intrinsic magnetic structure in a heliotrontype magnetic configuration.
 It looks like double null divertor in tokamaks.
 Poloidal field component is dominant in the divertor region.
 A few meter from X-point to divertor plates.
25 May 2012, S. Masuzaki

heat and particle depositions on
the helical divertor are non-uniform0

Rax=3.6m

150

Poloidal angle, θ。( )

510

15

100

50

50

00-50-50

-100

-100

-150

-150

0

20

40

60

25

outboard

Rax=3.75m

150

100

20

topinboard
bottomoutboard020

4060

Toroidal angle,φ (°)

25 May 2012, S. Masuzaki

heat and particle depositions on
the helical divertor are non-uniform
0Lc (m)

310210101002010152025outboard

Rax=3.75m

150

1063

Rax=3.6m

150

440 60 80 100 120
position (mm) The profiles are roughly
determined by the magnetic
field structure connecting to thedivertor plates like the “lobe”structure.
 Long field lines coming fromnear LCFS, are the main channelof particle and heat flux.

Poloidal angle, θ。( )Γdiv (1022/m2s)

5100

100

50

50

00-50

-50

-100

-100

-150

-150

02040

60

topinboard
bottomoutboard
0204060

Toroidal angle,φ (°)Γdiv (1022/m2s)

Lc (m)

4106
310
30402101016080100position (mm)12025 May 2012, S. Masuzaki

OUTLINE
 Introduction
 Divertor experiments
 Divertor particle control experiments−Towards a closed and pumped divertor
 Divertor heat control experiments−Application of RMP−Impurities seeding Summary
23 July 2012, S. Masuzaki

heat and particle depositions on
the helical divertor are non-uniform
0Lc (m)

3102

10

10

10020

10152025

outboard

Rax=3.75m

150

106

3

Rax=3.6m

150440 60 80 100 120position (mm) The profiles are roughly
determined by the magnetic
field structure connecting to thedivertor plates like the “lobe”structure.
 Long field lines coming fromnear LCFS, are the main channelof particle and heat flux.

Poloidal angle, θ。( )Γdiv (1022/m2s)

5100

100

50

50

00-50

-50

-100

-100

-150

-150

0204060

top
inboardbottomoutboard020

4060

Toroidal angle,φ (°)Γdiv (1022/m2s)

Lc (m)

410

6
3

10
3040

2

10

101
60

80
100
position (mm)120

23 July 2012, S. Masuzaki

Design of CHD was carried out by using
EIRENE code with full 3-D meshPresent divertor

closed helical divertor(CHD)

25 May 2012, S. Masuzaki

Design of CHD was carried out by using
EIRENE code with full 3-D mesh

Present divertor

closed helical divertor(CHD)

The 3-D simulation using EIRENE code predicted about 10
times higher neutral pressure in CHD than that in thepresent divertor.
25 May 2012, S. MasuzakiTest baffle components without in-vessel pump wereinstalled in two out of ten toroidal sections to examine
the neutral particle compression in 2010.
23 July 2012, S. MasuzakiMuch higher pressure was observed inCHD as predicted by the 3-D simulation
100
CHD
10-1
10-250

open

10-3

10-4
1234

567

8

P0_CHD/P0_opne

neutral pressure (Pa)100

09ne,bar (1019m-3)

 Though divertor particle
fluxes in CHD and theopen divertor were almost
same, more than 10 times
higher neutral pressure in
CHD was observed.
 Neutral pressure ratio
between in CHD and in the
open divertor has density
dependence.
 The ratio increase withdecreasing density

Line averaged density dependence of the neutralpressure in divertor.
23 July 2012, S. MasuzakiHα emission in the ergodic is significantly
reduced in the CHD configuration
CHD

Hα emission distribution

Hα Filtered CCD camera image of CHD
and the open divertor werereproduced by using EIRENE code
Filteredcamerasimulation
23 July 2012, S. Masuzaki

ダイバータ閉構造化計画

23 July 2012, S. MasuzakiA helical shaped cryo-pump with ~7m3/s ofpumping speed has been installed

23 July 2012, S. MasuzakiSummary ofparticle control experiment Divertor modification from “open” to “closed” has been
conducted at torus-inboard side.
 Test baffle components were installed partially (20%)
in 2010, and examined neutral compression in CHD.
 Neutral compression predicted by 3-D neutraltransport code, EIRENE, was confirmed in experiment.
 Higher neutral particle confinement in the test baffle
divertor than that in the present open divertor wasalso observed by filtered CCD camera.
 Divertor in 50% of toroidal section is closed andequip with an in-vessel pump in a toroidal
section in 2012.
23 July 2012, S. Masuzaki

OUTLINE
 Introduction
 Divertor experiments
 Divertor particle control experiments−Towards a closed and pumped divertor
 Divertor heat control experiments−Application of RMP−Impurities seeding Summary
23 July 2012, S. MasuzakiIt is a crucial issue how to achieve
stable radiation enhancement
 To reduce divertor heat flux, radiation enhancement isnecessary.
 But, Prad/PNBI is less than 0.2 in LHD usually, and discharge
becomes unstable in the region of Prad/PNBI~0.3.
Prad (MW)Prad/PNBI
12

0.8
0.6
10.4
0.2
0234

5ne,bar (1019m-3)

607
Peterson et al., PFR 1 (2006) 045.

23 July 2012, S. MasuzakiTwo scenarios to achieve stableenhanced radiation were investigatedIntensefuel gas
puffing

Density increment
Temp. reduction

Radiative
collapse

Application of RMP for
generation of n/m=1/1
island in the ergodic layer

Impurity
seeding

StableEnhancedradiation

Radiative
collapse
23 July 2012, S. Masuzaki

3-D plasma simulation with EMC3-EIRENE code predeictradiation enhancement with n/m=1/1 island
Intenseradiation at
O-point

Intenseradiation at
X-point

With RMP
simulation

Simulation results
23 July 2012, S. Masuzaki

n/m=1/1 island in the ergodic layer
generated by RMP field enhances radiation
Prad (MW)321
radiative collapse

0
radiative collapse

Isat (A)1 Operation parameters
 PNBI ~ 8MW
 Magnetic axis R=3.9m
 IRMP=3.4kA
 Divertor particle flux decreased
 RMP did not change density limit

00246810ne,bar (1019m-3)
Experiment
23 July 2012, S. Masuzaki

Expansion of low temperature region in
the edge cases the radiation enhancement

w/o RMP Te at peripheral and in the ergodiclayer reduced with the island
generation.
 While Te and ne in the center was
not affected.
 The island structure extend low
temperature region in which impurity(mainly carbon) radiate intensely.
 Carbon radiation increases withTe reduction in the range of
10eV<Te<100eV

w/ RMP

Radial profiles of ne and Te
23 July 2012, S. Masuzaki

3-D effect on divertor particle loadIsland expansion
6-O
1-O
ダイバータ干渉計(3-O)

電子密度の電子密度の緩やかな上急激な減少
昇イオン飽和 イオン飽和
電流の急速な減少
な増大

静電プローブ
電流の急速(10.5U)

摂動磁場による周辺磁場構造の違いに応じて、ダイバータプラズマ
挙動にトロイダル異方性が観測されている。
トータルで熱負荷は軽減されているが、局所的な熱粒子負荷変化を明らかにする必要がある。
23 July 2012, S. MasuzakiTwo scenarios to achieve stableenhanced radiation were investigatedIntensefuel gas
puffing

Density increment
Temp. reduction

Radiative
collapse

Application of RMP forgeneration of n/m=1/1
island in the ergodic layer

StableEnhancedradiation

Impurity
seeding

Radiative
collapse
Gas puffing from a bottom port
23 July 2012, S. Masuzaki

ne,bar (1019m-3) Stored energy (MJ)

Stable enhanced radiation (Prad/PNBI~0.3)
was achieved by Ne sdding
10.8
0.6
0.4
0.206

 Plasma heating power ~ 14-15 MW Gas flow rate
 H2: ~ 7x1021 /s
 Ne: ~ 4x1020 /s (120 ms from t=4s)
 Prad~0.15PNBI (w/o Ne)
 Prad~0.3PNBI (w/ Ne)

Ne puffing

42

Prad (MW)04

w/ Ne2

 Prad reached its maximum after 100 ms fromthe seeding termination. And the high Pradstate was sustained for several hundered ms
without additional seeding.

ne, div (1019m-3)

00.6
0.3

Te, div (eV)

020
100
3.4

3.6

3.844.2time (s)

4.4

4.6

23 July 2012, S. Masuzaki

0.1

1
0.8
0.6
0.4
0.2
06

Isat (A)ne,bar (1019m-3) Stored energy (MJ)

Drastic reduction of divertor particle flux was
observed only at the peaks of its profile
Ne puffing

right top

w/o New/ Ne

0-120-100 -80 -60 -40 -20
position (mm)
0.2

42

020

right equator

Isat (A)Prad (MW)04w/ Ne

2

0.3

0.2

0w/o Ne

0.1
w/ Ne
0-120 -100 -80 -60 -40 -20
position (mm)

103.6

3.8

4
4.2
time (s)4.420

right bottom

0.3
Isat (A)ne, div (1019m-3)

0.6

020

Te, div (eV)w/o New/ Ne
0-120-100 -80 -60 -40 -20
position (mm)
0.4

00
3.4

0.1

0

4.6

23 July 2012, S. Masuzaki

Radiation limit is Prad/PNBI=0.3-0.6,
and depends on density
1.2

3600
103846

0.6

3000

0.8

2400

0.6

1800

4s

0.4

1200

4.3s

0.2
00.4

600

4000

4200
4400
R (mm)

4600

0 In the low density region, Ne
puffing effect penetrates
inside LCFS The higher ratio is
possibly attributed bycore radiation.

0.3

1.2

Prad,max

0.2

P

rad123

4

before Ne puffing

567ne,bar before Ne puffing (1019m-3)

13000

0.8

2400

0.61800Te (eV)

0.1
03600
103833

Te normalized by T e@4s

Prad/PNBI

0.5

1Te (eV)Te normalized by T e@4s

0.74s
0.4

1200
4.2s

0.20600

4000

4200

4400
R (mm)

4600

0Operation space of Ne seeding discharge
23 July 2012, S. Masuzaki

Effects of Ar, N2 seeding on the plasma properties
are similar to them with Ne seeding
Ar seeding It should be noted that in N2 seeding case, radiation power
reduced promptly after terminating seeding.
 Difference of recycling between N2 and Ne, Ar.
23 July 2012, S. Masuzaki

Reconstructed radiation distributions measured by AXUVD
array shows the penetration of Ne and Ar into the core

In the case of N2 seeding, the shallower penetration was observed.

23 July 2012, S. MasuzakiSummary Particle control experiment using closed helical divertor has
been started.
 Partially installed test baffle components proved highneutral compression in CHD as predicted by simulation.
 Experiment campaign in 2012 will be conducted withCHD installed into 70% of toroidal section.
 Two control knobs, application of RMP and impurity
seeding, for divertor heat control have been investigated.
 30-60% of heating power can be radiated stably.
 Further investigation is necessary to understand theirphysics and achieve higher radiation power.
23 July 2012, S. Masuzaki