particle control study towards burning plasma control in jt-60u
DESCRIPTION
I-16. Particle control study towards burning plasma control in JT-60U. H. Takenaga 1) and the JT-60 Team 1) Japan Atomic Energy Agency 18th International Conference on Plasma Surface Interactions Toledo, Spain May 26-30, 2008. JT-60U. - PowerPoint PPT PresentationTRANSCRIPT
Particle control study towards burning plasma control in JT-60U
I-16
H. Takenaga1) and the JT-60 Team
1)Japan Atomic Energy Agency
18th International Conference onPlasma Surface Interactions
Toledo, Spain May 26-30, 2008
Introduction
JT-60UParticle control plays a key role in burning plasmas.
particle/impurity transport, fuelling, pumping, etc..
It is important to establish effective particle control for both increase and decrease in QDT towards first burning plasma experiments in ITER.
n(r)&T(r)
•Transport•MHD …
PEX
Fuellingj(r), V(t), …
P
Wall pumping
Divertor pumping
0
0.2
0.4
0.6
0.8
1
1.2
0 0.2 0.4 0.6 0.8 1r/a
p(r)/p(0)
0
5
10
15
20
25
0.8 0.9 1 1.1 1.2<ne>/nGW
Ti(0)=10-25 keV
Ti(0)=10 keV
HH98(y,2)=0.8
T i(0)=15 keV
T i(0)=20 keV
HH98(y,2)=1.0HH 98(y,2)=
1.2
PEX=40 MW
T i(0)=
25 keV
ITER : Ip=15 MA, BT=5.3 T, R=6.2 m, a=2 m, Fixed n&T profiles
(a)
HH 98(y,2)=1.0 (a)
(b)
(b)
Outline
JT-60U
Controllability of density profiles and effects of density profiles on impurity transport.
Controllability of confinement and pedestal using edge fuelling.
Controllability of edge density using divertor pumping.
Burning plasma simulation experiments.
Controllability of density profiles and effects of density profiles on impurity transport.
JT-60U
ITG/TEM turbulence theory has predicted peaked density profile formed by anomalous inward pinch and it also indicated that density peaking decreases with increasing effective collisionality (eff=ei/De).
De is the curvature drift frequency, which provides an estimate of the growth rate
of the most unstable mode for ITG and TEM. It is important for establishment of an effective particle control scenario to
understand mechanisms for regulating the density profile.
Peaked density profileHigh fusion output with low
edge density High impurity accumulation
level ?
Flat density profile High edge density for high f
usion outputLow impurity accumulation
level ?
Density profiles have large impacts on fusion output and impurity accumu
lation.
Collisionality dependence of density peaking is consistent with ITG/TEM turbulence theory.
JT-60U
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1r/a
The density profile is more peaked in low density plasmas than in high density plasmas.
The density peaking factor decreases with increasing effective collisionality.
Ip=1.0 MA, BT=2-2.1T, PNB=8-10 MW
ELMy H-mode plasmasELMy H-mode plasmas
<ne>=3.4x1019 m-3
<ne>=1.5x1019 m-3
Note that density peaking factor used here is not affected by the edge boundary condition when particle source is zero ( n/n=v/D).
@ r/a=0.5
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
0.1 1eff
ITE
R
Density peaking factor increases with ctr-rotation.
JT-60U
1.5
1.6
1.7
1.8
1.9
-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5
VT (105 m/s)
0
1
2
3
4
-2
-1.5
-1
-0.5
0
0.5
0 0.2 0.4 0.6 0.8 1r/a
ctr
co
ctr
co
ctr
bal
co
JT-60T-NBIP-NBIP-NBIT-NBIP-NBIP-NBIP-NBINNBI (#15,16)CO dir.CTR dir.#2#3, 4#6#7, 8#9, 10#12#13, 14Ip
P-NB perp.: 7 units co: 2 units
ctr: 2 units
Perp. NB power scan with co-, bal- and ctr-injection. E// is larger in the ctr-case than in the co-case. However, Ware pinch velocit
y (~0.02 m/s@r/a=0.3) is one order of magnitude lower than particle source induced flux velocity (/n).
Small Ware pinch contribution to determination of density profile.
Large vol. configuration
@ r/a=0.2
0
0.5
1
1.5
2
2.5
0 0.2 0.4 0.6 0.8 1r/a
Carbon density is relatively flat in all cases.
JT-60U
0.4
0.6
0.8
1
1.2
0.1 1eff
-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5
VT (10
5 m/s)
Carbon density measured using CXRS has a flat or slightly hollow profile, although neoclassical transport theory predicts inward pinch velocity.
No clear dependence of carbon density profiles on effective collisionality and toroidal rotation.
No concern of light impurity accumulation even with peaked density profile in ELMy H-mode plasmas.
ELMy H-mode plasmas
ctr bal co
eff=1.8
eff=0.24
@ r/a=0.2@ r/a=0.5
Tungsten is accumulated with peaked density profile.
JT-60U
FSTs
0 0.5 1 1.5 2 2.5
PORB
(MW)
0
0.2
0.4
0.6
0.8
1
1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9n
e(r/a=0.2)/<n
e>
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) is observed with ctr-NB 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.
ctr
balco
ctr
bal
co
Large vol. configuration
Controllability of confinement and pedestal using edge fuelling.
JT-60U HFS shallow pellet injections can sustain high confinement at high density, w
hile gas-puffing reduces confinement.
Possibility of flexible control using combined fuelling. However, plasma responses to gas-puffing could be slower and huge amount
of gas-puffing is necessary. In order to improve controllability, supersonic molecular beam injection (SMB
I) has been installed in collaboration with CEA-Cadarache.
Frequency : <10 Hz, Duration : ~2 ms /pulse, Gas flow : ~1.2 Pam3/pulse at PBK=6 bar (measured),
Speed : 2.2 km/s at T=150oC and PBK=5 bar (calculation)
Quick decrease in ion temperature is observed at r/a~0.8 by SMBI.
JT-60U
0.290.35
0.18
0.21
0.90
012345678
4.35 4.4 4.45 4.5
Ti
(keV
)
Time (s)
2.1
2.3
2.5
0.410.560.720.81
r/a
dt=0.167ms
dt=1ms
Density jump can be seen after SMBI pulse as similar as pellet injection.
SMBI could directly affect the plasma parameters at r/a~0.8, although light from SMBI mainly emitted out
side the separatrix. The SMBI speed estimated from the fast TV camera is slower than the cal
culation. Ionization front could move slowly towards plasma boundary.
HFSLFS
Divertor
Confinement degrades at high density with constant pedestal pressure in the case of SMBI.
JT-60U
Confinement degrades with SMBI, while it is kept constant with HFS shallow pellets, indicating flexible control using combined fuelling.
The penetration position of the pellet was estimated to be r/a=0.77-0.84, which is inside the pedestal top.
Pedestal pressure is almost constant in the case of SMBI, which is similar as in the case of gas-puffing. Pedestal pressure is enhanced in the case of pellet injection.
1
1.5
2
2.5
3
0.4 0.5 0.6 0.7 0.8ne/nGW
Central fuelling only
HFS Pellet
Gas-puffing
SMBI
Controllability of edge density using divertor pumping.
JT-60U
Wall saturation and even outgas from the wall have been observed in the long pulse discharges in JT-60U.
Behavior of wall retention can not be understood using simple static model.
Outgas from the wall increases just after divertor pump on.
4
01
01
-1
2010
0
0
15 20 25 30Time (s)
PN
B
(MW
)
n e(1
019 m
-3)
I D
(102
3 s
-1)
(1
022 s
-1)
Divertor pumpoff on
MARFE
Div
Wall
E045331 Dynamic plasma-wall interaction
Increase in degree of self-regulation
Slower response
Dynamic model is required in addition to static model.
Simulations using the UEDGE code.
JT-60U
Recycling coefficient
Static wall retention
Rst=0.995
Dynamic wall retention
Rdy=CQ(Q/Q0-1)+C(0/-1)
Divertor pump
Rpump=-0.02(1-exp(-t/0.25))
Total
Rtot=Rst+Rdy+Rpump
Rdy is assumed to increase with increasing heat flux and decreasing particle flux.
QBC=6.5 MWBC=7.5x1020 /si=e=1.0 m2/sD=0.25 m2/s
R is determined by the balance among reflection, trapping (potential and chemical), thermal desorption, and sputtering (physical and chemical).
Dynamic plasma-wall interaction slows plasma responses to the divertor pumping.
JT-60U
CQ=C=0 CQ=0.1, C=0.4CQ
CQ=0.08exp(-t/1.0)+0.02exp(-t/100),
C=0.4CQ
Total pumping
Wall pumping
Divertor pumping
Time dependent CQ and C are required for reproducing the experiment. This result indicates that wall retention depends on wall condition, i.e. amo
unt of wall retention.
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
0
2
4
6
8
10
0 1 2 3 4 5Time (s)
0 1 2 3 4 5Time (s)
0 1 2 3 4 5Time (s)
Rdy=CQ(Q/Q0-1)+C(0/-1)
Burning plasma simulation experiments.
JT-60U
External heating simulation : PEX
ne & Ti
particle heating simulation :
P~ne2Ti
2
• Burning plasma simulation scheme has been developed using 2 groups of NB, where one simulates 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 P~ne
2Ti2.
Real time measurement
NB system
Group A
Group B
SMBI
n(r)&T(r)
•Transport•MHD …
PEX
Fuellingj(r), V(t), …
P
This linkage is experimentally simulated in JT-60U.
P-simulation
Wdia
SMBI decreases simulated fusion gain due to confinement degradation and flattening of pressure profile.
JT-60U
02468
101214
02468
101214
0
2
4
6
8
00.5
11.5
22.5
3 4 5 6 7 8
TIME (s)
BPS
Wdia FB
E048281
0
1
2
3
BPS
Wdia FB
SMBI ~7Pam3/s4atm, 10Hz, LFS
E048352
3 4 5 6 7 8
TIME (s)
Qsim=5xP/PEX 3.7(4.1s) 40(~5.8s) 5.1(4.1s) 24(4.4s) 5.1(6.2s)
HH98(y,2) 0.87 0.83 0.79 0.89 0.72
p(0.2)/p(0.8) 8.5 9.8 8.6 9.1 7.9
Summary
JT-60U
Particle control study has been conducted to expand understanding of burning plasma controllability.
Peakedness of density profiles increases with decreasing collisionality, which is consistent with ITG/TEM turbulence theory. Other control parameters, such as toroidal rotation, exist.
Metal impurity accumulation is observed with peaked density profile, while light impurity accumulation is not.
Confinement degrades with SMBI, while it is kept constant with HFS shallow pellets, indicating flexible control using combined fuelling.
The UEDGE simulation suggests that dynamic plasma-wall interaction slows plasma responses to divertor pumping.
Using the burning plasma simulation scheme, it is demonstrated to reduce the simulated fusion gain with SMBI due to confinement degradation and flattening of pressure profile.