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.