核融合原型炉における粒子制御の
課題と展望
竹永秀信
原子力機構
第17回 若手科学者によるプラズマ研究会
主題:核融合原型炉に向けたプラズマ制御・炉工学研究の現状と進展
平成26年3月5~7日開催
場所:日本原子力研究開発機構 那珂核融合研究所
核融合炉における粒子制御の役割
○ 自律性の高い燃焼プラズマにおいて、密度は外部からの制御が比較的容易な物理量
であり、粒子制御は燃焼プラズマの制御にとって重要な要素である。
燃焼制御のための燃料密度制御
燃料粒子供給
粒子閉じ込め
粒子輸送
供給方法
粒子排気
ダイバータ排気
第一壁での粒子吸蔵
ダイバータ板損耗抑制のための熱負荷低減
高Z不純物入射による放射損失パワーの
増大
ダイバータ部のみならず、主プラズマ・境
界層でも放射損失増大が必要
過度の不純物蓄積によるプラズマ中心部
での放射損失増大は回避が必要
粒子制御は、粒子・熱のバランスに重要であり、
燃焼プラズマの定常維持にとって本質的役割を
担う。
核融合炉における粒子制御の役割
○ 自律性の高い燃焼プラズマにおいて、密度は外部からの制御が比較的容易な物理量
であり、粒子制御は燃焼プラズマの制御にとって重要な要素である。
燃焼制御のための燃料密度制御
燃料粒子供給
粒子閉じ込め
粒子輸送
供給方法
粒子排気
ダイバータ排気
第一壁での粒子吸蔵
ダイバータ板損耗抑制のための熱負荷低減
高Z不純物入射による放射損失パワーの
増大
ダイバータ部のみならず、主プラズマ・境
界層でも放射損失増大が必要
過度の不純物蓄積によるプラズマ中心部
での放射損失増大は回避が必要
粒子制御は、粒子・熱のバランスに重要であり、
燃焼プラズマの定常維持にとって本質的役割を
担う。
不純物からの放射光
で熱を分散
講演内容
 核融合原型炉での粒子バランスの考察
 炉心プラズマの密度分布と不純物輸送
 ペレット入射装置及びガスジェット装置を用いた場合の閉じ込
めへの影響
 燃焼模擬実験
Fuelling scenario in a fusion reactor
T is fuelled in the main plasma
for minimizing the T fuelling rate.
Fuelling to the main plasma
for sustaining the high tritium and
deuterium densities in the main plasma
Fuelling to the edge plasma
for enhancing the recycling level
Particle balance model
NT = pM (STM - STL) + pESTR
ND = pM (SDM - SDL) + pE (SDE + SDR)
NHe = pMSHeM + pESHeR
(recycling source is treated as a
fuelling in the edge plasma)
the confinement times for the particles
fuelled in the main plasma (pM) and for the
particles fuelled in the edge plasma (pE)
fpumpTdiv = STM – STL and Tdiv = STM – STL + STR
fpumpDdiv = SDM – SDL + SDE and Ddiv = SDM – SDL + SDE + SDR
fpumpHediv = SHeM and Hediv = SHeM + SHeR
SlimCS design parameters
Plasma current
: Ip=16.7 MA
Toroidal magnetic field : BT=6.0 T
Major radius
: Rp=5.5 m
Minor radius
: ap=2.1 m
Fusion output
: Pfus=2.9 GW
STL=SDL=SHeM=1.051021 /s
Vol. averaged density
: <ne>=1.151020 m3
NT=ND=51022
Divertor heat load
: Qdiv=150 MW
(76% radiation)
div~11025 /s for Tdiv=10 eV
3
Niscal=(pM(0)(ne/11019m-3)0.66SM+pE(0)(ne/11019m-3)-0.36SE)
(Ip/1MA)0.2(BT/3.5T)0.3(P/10MW)-1.1
pM(0)=0.38 s
pE(0)=4.7 ms (including divertor/SOL region)
2
1.5
i
N exp [ 1021 ]
2.5
1
H. Takenaga et al., Nucl. Fusion 37 (1997) 1295.
0.5
JT-60U
0
0
0.5
1
1.5
2
N scal [ 10 21 ]
i
2.5
3
fpump=1-4%
H. Takenaga et al., Nucl. Fusion 41 (2001) 1777.
Particle balance indicates that T fuelling is smaller
by a factor of >10 than total D fuelling rate.
JT-60U
pM=2 s, pE=2 ms, fpump=3%, no wall pumping
 NHe= 2.1% of Ne.
 T-recycling is one order of
magnitude smaller than Drecycling, leading the one
order of magnitude smaller
amount of T-cycle system
than that of D-cycle system.
Dependence of fuelling rate on pM&pE and fpump
/s)
23
T
0.1
S
0
1
0
0.3
0.8
pE=1ms
2ms
4ms
0.6
0.4
0.2
M
23
(10 /s)
D
M
23
(10 /s)
D
0.2
(10
M
/s)
23
(10
M
T
S
0.2
0
4
0.2
0.1
0
14
12
E
23
(10 /s)
D
3
2
1
S
 SD strongly depends
on fpump.
E
0.4
S
 The reduction of fpump
does not decrease the
amount of T-cycle and it
increases T-recycling
(disadvantage of T
retention).
0.6
E
23
(10 /s)
D
 On the other hand, SDE
increases with
increasing pM.
0.3
0.8
S
 SDM decreases with
increasing pM and
depends on pE.
1
S
 ST is inversely
proportional to pM and
weakly depends on pE.
pM=2spE=2ms
fpump=3%
M
10
8
6
4
2
0
0
0
1
2
3
M
 (s)
p
4
5
0
2
4
f
pump
6
(%)
8
10
TとD分離しない場合
 TとDを燃料サイクル系で分離しないことも考えられ、その場合トリチウムのダイバータ
への粒子束は約1桁上昇。
 高トリチウム束は、計量管理やトリチウムリンテンションの観点からは好ましくない。
 TとDを分離しない場合、燃料サイクル系の設計が容易となり、上記とのトレードオフ。
 DTペレット生成技術の確立
燃料サイクルでの同位体分離技術を考慮しつつ、核融合原型炉での粒子供給シ
ナリオの策定が重要
ピークした密度分布
Hモードプラズマ
○ トカマクでは、ピークした密度
分布。
○ 内向き対流速度の存在。
高密度化には有利
周辺密度はグリーンワルド密度
限界で制限
不純物の蓄積が課題
密度勾配が大きいと蓄積
最適な密度分布?
Hモードでは軽不純物の蓄積は観測されない
C Angioni, E Fable, M Greenwald, M Maslov, A G Peeters, H Takenaga and H Weisen, Plasma Phys. Control.
Fusion 51 (2009) 124017
DHe is reduced to a NC level, DC and DAr are higher
JT-60U
• (-∇n/n) is smaller than (-∇Ti/Ti) for He, similar for electron and C, and
larger for Ar.
• In the parabolic RS and high bp mode plasmas, both D and ci are at an
anomalous level.
Core radiation loss from Ar can be compensated with
slightly enhanced confinement in a fusion reactor.
A-SSTR2
2
0
-3
Ip=12MA, BT=11T, Rp=6.2m,
a=1.5m, Fusion output
~4GW, Pradmain~400MW,
Aux. heating=60MW
-2
-4
4
35
T (keV)
n (10 m ) 30
e
e
25
20
15
10
5
0
0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1
r/a
r/a
20
5
6
7
8
Zeff
4
3.5
3
2.5
2
1.5
1
0.5
0
nAr(0)/nAr(ITB-foot)~2xne(0)/ne(ITB-foot)
1.6
1.4
1.2
1
0.8
0.6
8
7
6
5
4
3
2
1
2
Neoclassical Ar transport
1.8
HHy2
4
nAr(0)/nAr(ITB-foot)~ne(0)/ne(ITB-foot)
neped/nGW
• Edge density can be reduced by density
peaking.
• HHy2=1.4-1.5 with more peaked nAr(r) by a
factor of 2 than ne(r).
• Zeff=4 for 400MW radiation (0.5% Ar at
edge).
JT-60U
1.6
1.4
1.2
0.5
1
1.5
2
2.5
3
ne(0)/ne(ITB-foot)
3.5
粒子供給装置
 SMBI : density jump was observed and its height decreased with PBK.
 Confinement tended to degrade with relatively larger perturbation induced by
SMBI with higher frequency (~10 Hz) and higher PBK (~6 bar).
Supersonic Molecular Beam
Injection (SMBI)
ne (1019 m-3)
collaboration with CEA-Cadarache
f≤10 Hz, duration~2 ms/pulse,
HFS
~1.2 Pam3/pulse at PBK=6 bar,
~2.2 km/s at Twall=150oC and PBK=5 bar.
Gas-puffing
HFS Pellet
3
Pellet
2
3.2
HFS SMBI
(6 bar)
E048771
2.2
3
HFS SMBI
LFS Pellet
(4 bar)
HFS Pellet
E039645
LFS SMBI
Pellet injector
Size : 2.1 mm cube (2 bar)
Frequency : <10 Hz
Velocity : 100-1000 m/s
Number : 30-40 pellets/shot
2
3
2
E048766
E048770
1s
HFS pellet : H89PL~2 at ne/nGW~0.7.
JT-60U
 SMBI : High confinement tended to be obtained with relatively smaller
perturbation induced by SMBI with lower frequency (~5 Hz) and lower PBK
(~2-4 bar).
 HFS and LFS SMBI has no clear difference in density dependence of
confinement.
 Pped was enhanced in the case with high confinement. Enhanced pedestal
pressure is key to sustain high confinement.
3
H89PL
Central
2.5 fuelling
only
2
SMBI Pellet
HFS
LFS
Pellet
Gas-puffing
SMBI +Pellet
1.5
1
0.4
Gas-puffing
0.5
0.6
ne/nGW
0.7
0.8
ELMy
Central fuelling only
H-mode
HFS pellet
w/o ITB
SMBI
HFS
LFS
gas
HFS pellet + gas
Central Ti decreased even with edge fuelling.
Pellet (E041561)
SMBI 10Hz (E048767)
Ti (keV)
Wdia
(MJ)
2.4
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2
2.3
2.2
2.1
SMBI 5 Hz (E048766)
2.6
2.4
2.2
2
1.8
1.6
2.7
2.6
2.5
2.4
2.3
2.2
2.1
2
2.6
2.4
2.5
2.2
2.4
2
2.3
1.8
2.2
1.6
14
14
14
12
12
12
10
10
10
8
8
8
6
6
6
4
4
4
2
2
2
0
4
4.2
4.4
4.6
TIME (s)
4.8
5
0
4
4.2
4.4
4.6
TIME (s)
4.8
5
0
4
4.2
4.4
4.6
TIME (s)
4.8
5
ne
19
(10 m-3)
• Pellet injection : the Ti decrease was observed in the ITB region. However, it
recovered when pellet was not injected in relatively long period (≥300 ms).
• SMBI with f=10 Hz : transiently decreased central Ti was not recovered.
• SMBI with f=5 Hz : decreased Ti recovered in the latter phase and relatively
good ITB was sustained.
 Optimization of injection frequency and penetration depth (or level of Ti
decrease) is important for sustaining high confinement.
Extended regime to high density
JT-60U
Operation regime has been extended to high density (ne/nGW >
~ 1)
with high confinement (HHy2 >
~ 1) and high radiation loss fraction
(frad>0.9).
HHy2
2
RS
1.5
Key : ITB control
• Fueling (NB, HFS pellet and
gas-puffing)
• Heating
• Impurity seeding
• (Intrinsic impurity)
• Plasma configuration
1
High bp H
0.5
H-mode
frad
1
0.8
Closed : 2003-2004, Open : before
Double lines : w impurity seeding
0.6
0.4
0.6
0.7
0.8
0.9
ne/nGW
1
1.1
1.2
High ne above nGW in RS plasma
JT-60U
5
4
3
2
1
0
20
15
10
5
0
3
nGW
ne
PNB
2
H
Sn
Pradmain
IDa
1
0.5
0
4
4.5
5
5.5
6 6.5
Tim e (s)
t=7.8s
1.5
W
1
IDa (a.u.)
Prad (MW)
PNBabs
PL
2
0
8
6
4
2
0
Ip=1.0 MA, BT=2.5 T,
q95=6.1, d=0.45,
Vp=78 m3
ne/nGW
ne, nGW
(1019 m-3)
- Large Vp with NB and LH heating, and NB fueling only.
• HHy2=1.3, bN=2 and fBS~0.7 at ne/nGW=1.1.
• ne(0)/nGW=1.6 with low needge/nGW (~0.4) by tailoring ne ITB.
• Increase in Pradmain (Pradmain/Pabs~0.65) due to impurity accumulation.
7
7.5
8
0
0.2
0.4
0.6
r/a
0.8
1
Enhanced divertor radiation by Ne seeding
JT-60U
Prad/Pradtot
5
4
3
2
1
0
2.5
2
1.5
1
0.5
0
10
8
6
4
2
0
10
8
6
4
2
0
E043964
nGW
ne
W
D2
0.4
0.2
SOL+DIV
6
6.5
Tim e (s)
7
The same nNe(r) as
ne(r) is assumed.
0.2
0.15
0.1
PradNe
0.05
main
5.5
0.6
0.25
total
5
main
w/o seeding w Ne seeding
Sn
Ne
0.8
0
Prad (MW/m3)
Prad (MW)
Gas
(Pam3/s)
ne, nGW
(1019 m-3)
- Ne puff with D2 gas.
• HHy2=1.1, frad=0.93 at ne/nGW=1.1.
• Divertor radiation ratio increases from ~20% w/o seeding to 40% with
Ne seeding.
1
• Small contribution of Ne to Pradmain.
7.5
0
0
0.2
Measured
0.4
0.6
r/a
0.8
1
High HHy2 and high frad by Ar seeding and HFS pellets
JT-60U
- Ar seeding and HFS pellet with small D2 gas-puffing in small Vp.
• HHy2=0.96 and frad~1 at ne/nGW~0.92 at t=6.95s.
• Peaking of ne(r) and enhanced pedestal pressure.
HFS pellet
Ip=1.0MA, BT=3.6 T,
q95=6.2, d=0.37
Ar
ne, nGW
(1019 m-3)
PNB
(MW)
8
4
0
30
20
10
0
5
nGW
P-NB
N-NB
D2
Wdia
25
Total
0
4
4.5
5
Main
5.5
6
Time (s)
6.5
7
7.5
t=6.95s
6
nGW
4
t=5.0s
2
0
ne
Wdia (MJ)
Gas (Pam3/s) 0 Arx5
Prad
(MW)
E042843
ne (1019 m-3)
8
0
0.2
0.4
0.6
r/a
0.8
1
Central radiation is ascribed to Ar
JT-60U
• nAr(r) evaluated from soft x-ray profile is more peaked by a factor of 2
inside the ITB than ne(r).
• nAr/ne~1% in the center and 0.5% outside the ITB from Bremsstrahlung.
• PradAr~0.4 PradSOL+DIV.
UEDGE
ce=ci=1 m2/s, D=0.25 m2/s,
Dimp=1 m2/s
Prad (MW/m 3)
0.5
0.4
0.3
0.2
0.1
00
0.4 0.6
r/a
0.8
1
Inner divertor
2
rad
0.2
2
outer divertor
1
P
Carbon : sputtering (Haasz rate)
Argon : core-edge density
nAr/ne=0.93%
(MW/m )
3
ncore=1.5x1019 m-3
Pcore=14 MW
PradAr
0
8 10 12 14 16 18 20
channel number
Tungsten is accumulated with peaked density
profile or ctr-rotation.
JT-60U
 The Ferritic Steel Tiles (FSTs) have ingredient of 8%Cr, 2%W and 0.2%V and
cover ~10% of the surface.
 Large tungsten radiation from the core plasma (IW+44) was observed with ctrNB injection even at given orbit loss power, which could be correlated with
tungsten source.
 Heavy impurity accumulation is one of the large concerns with peaked
density profile in ELMy H-mode plasmas.
Large vol. configuration
1
FSTs
ctr
0.6
ctr
0.4
I
W+44
(a.u.)
0.8
bal
bal
co
co
0.2
0
1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9 0
n (r/a=0.2)/<n >
e
e
0.5
1
1.5
PORB (MW)
2
2.5
Burning plasma simulation experiments.
JT-60U
This linkage is experimentally
simulated in JT-60U.
n(r)&T(r)
PEX
Fuelling
• Transport
• MHD …
Pa-simulation
P
j(r), V(t), …
• Burning plasma simulation scheme has been developed using 2 groups of
NB, where one simulates a particle heating and the other simulates external
heating.
• Ti dependence of <v>DT in the range of Ti=10-25 keV is incorporated in the
scheme as Pa~ne2Ti2.
密度制御による燃焼模擬制御
JT-60U
f~Ti2の場合、閉じ込め劣化と圧力分布平坦化によりQsimが減少
f~Ti0の場合、密度上昇によりQsimが上昇
f~Ti2
f~Ti0
f~Ti2の場合
JT-60U
閉じ込め性能が高くなる場合(圧力分布もピーキング)は密度とともにQsim上昇
閉じ込め性能が劣化する場合(圧力分布は平坦化)は密度とともにQsim減少
4.45s
4.05s
f~Ti0の場合
JT-60U
閉じ込め性能に関係なく、密度の上昇に伴いQsim増加
核融合炉の温度領域を10-25keVと考えると、密度だけでなく、閉じ込め性能、
圧力分布等も考慮しつつ燃焼制御する必要がある。
まとめ
JT-60U
• 粒子供給シナリオの策定が急務
• 高密度(ne/nGW >
~ 1)・高閉じ込め(HHy2 >
~ 1)・高放射損失(frad>0.9)の
運転領域は存在。
• 高Z不純物ほど蓄積する傾向にあるが、先進プラズマでもArまで
は許容範囲と考えられる。
• タングステンの蓄積は懸念材料。
• 主プラズマ側での放射割合とダイバータでの放射割合の最適化、
長時間維持のための制御(アタッチ状態への変化を未然に防ぐこ
とは可能か等)は今後の課題。
• 燃焼制御を密度だけで行うのは困難。密度だけでなく、閉じ込め
性能、圧力分布等も考慮しつつ燃焼制御する必要がある。そのた
めの計測装置の開発も重要。
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