0

1

2

3

4

0

10

20

30

40

1

10

1 10

χi/χ

iNC

-P NBonly

-P NB+EC

Effects of low central fuelling on density and ion temperature profiles in reversed shear plasmas on JT-60U

H. Takenaga, S. Ide, Y. Sakamoto, T. Fujita Japan Atomic Energy Agency, Naka Ibaraki 311-0193, Japan

11th IAEA Technical Meeting on H-mode Physics and Transport Barriers" 26 - 28, September, 2007Tsukuba International Congress Center "EPOCHAL Tsukuba", Tsukuba, Japan

0

0.5

1

1.5

2

3456789

10

01234567

0 0.2 0.4 0.6 0.8 1r/a

0

1

2

3

4

5

0 0.2 0.4 0.6 0.8 1r/a

-1.4-1.2

-1-0.8-0.6-0.4-0.2

0

0 0.2 0.4 0.6 0.8 1r/a

CH

12

03

0

3

2

1

04

3

2

1

03 4 5 6 7 3 4 5 6 7

Time (s)Time (s)

Ti (keV)

ne (1019 m-3)

Ip (MA)x10Pinj (MW)

ne (1019 m-3)Qgas (10 Pam3/s)

EC N-NB P-NB

Qgas

ne

IpE046144 E046146

02468

101214

(a) E046209 (b) E046220

EC N-NB

P-NB

0

0.5

1

1.5

2

0

2

4

6

8

10

0

1

2

3

4

3 3.5 4 4.5 5 5.5 6Time (s)

3 3.5 4 4.5 5 5.5 6Time (s)

ECP-NB

r/a=0.4 r/a=0.4

r/a=0.6 r/a=0.6

r/a=0.4

r/a=0.6r/a=0.4

r/a=0.6

r/a=0.4

r/a=0.6

r/a=0.4

r/a=0.6

0

0.5

1

1.5

0

5

10

15

02468

10

3 3.5 4 4.5 5 5.5 6 6.5 7Time (s)

PNB

PEC

Ti(0)

Te(0)

E041738, BT=3.7T

€

Γ=−Deff∇ne

0.001

0.01

0.1

1

0.1 1 10χi (m

2/ )s

- P NBonly

- +P NB EC

Strong ITB

Weak ITB

ITB formation with low central fuelling and dominant electron heating at Ip=1 MA and BT=3.7 T.

During Ip ramp-up,

Low central fuelling case

EC+N-NB+P-NB (1u perp.+0.5u ctr.)

High central fuelling case

P-NB (4u perp.+0.5u ctr.)

Reversed shear plasmas in JT-60UP-NBI central fuelling & ion dominant heatingN-NBI & ECH low/no central fuelling & electron dominant heating (reactor relevant condition)

Peaked density profile It is possible to achieve high fusion output with relatively

low edge density (<nGW). Suppression effects on ITG instability Impurity accumulation is one of the largest concerns.

but, when impurity accumulation level is smaler than neoclassical prediction, peaked density profile is acceptable.

1.2

1.4

1.6

1.8

2

0.6

0.8

1

1.2

1.4

1.6

0.5 1 1.5 2 2.5 3 3.5ne(0)/ne(ITB-foot)

nAr(0)/nAr(ITB-foot)~ne(0)/ne(ITB-foot)

nAr(0)/nAr(ITB-foot)~2xne(0)/ne(ITB-foot)

Neoclassical Ar transport

Experiment : Impurity accumulation is smaller than neoclassical prediction.

high p H-mode plasma (weak shear)

nAr(0)/nAr(ITB-foot)~2xne(0)/ne(ITB-foot)

RS plasma

High confinement is demonstrated with high radiation loss in the main plasma. (Prad

main/Pnet~0.8).

Calculation :ASSTR-2 : Ip=12MA, BT=11T,

Rp=6.2m, a=1.5m, Impurity=Ar Fusion output ~4GW, Prad

main~400MW, Aux. heating=60MW

E = W / (Paux. + P - Prad(r/a<0.9))

ASSTR-2

OUTLINE Introduction

Summary

Introduction

NBI and ECH system in JT-60U

Effects of low central fuelling after strong ITB formation

Effects of low central fuelling during ITB formation

Relation between density ITB and ion temperature ITB

Summary

Effects of low central fuelling on density and ion temperature profiles have been investigated using N-NBI and ECH in reversed shear plasmas of JT-60U.

Strong density and ion temperature ITBs were maintained when central fuelling was decreased after the strong ITB formation.

Similar density and ion temperature ITBs were formed both in low and high central fuelling cases.

Strong correlation between density gradient and ion temperature gradient was observed.

Particle transport and ion heat transport are strongly coupled or density gradient assists the ion temperature ITB formation through ITG mode suppression.

These results indicated that effects of low central fuelling on density and ion temperature profiles are not strong. Thus, it is possible to obtain density ITB in a fusion reactor.

• The electron heating power is higher by a factor of 1.6 than the ion heating power at t = 6.5 s.

• HHy2~2 is achieved with Te(0) > Ti(0).

• Strong ne and Ti ITBs were maintained with low central fuelling under dominant electron heating.

024681012

00.20.40.60.81Te,i (keV)

r/a

TeTi

(a)

0123456

00.20.40.60.81ne (1019 m-3)

r/a

(b)

• Time evolutions of ne and Ti in the low central fuelling case are similar to those in the high central fuelling case, although time evolution of Te is quite different for two cases.

• Gas-puffing rate necessary for ne feedback control is slightly higher in the low central fuelling case than in the high central fuelling case.

• The ne and Ti ITBs are formed in the region of r/a = 0.4-0.6 even in the low central fuelling case, which are similar to those in the high central fuelling case.

In the low central fuelling case, wide current hole (CH) was produced due to higher Te, thus, Ti profile in the central region is flat in the low central fuelling case.

Te profile is different for two cases.

ne gradient near the qmin location was attempted to increase by gas-puffing stop/decrease and to decrease by LH transition.

ne raise by gas-puffing

similar effect to central fuelling

Particle flux in the core

Gas-puffing stop/decrease

E046144:

After gas-puffing was stopped at t = 4.4 s,

The edge ne decreased just after gas-puffing was stopped, while the central ne continued to increase, resulting formation of ITB like structure in the ne profile.

At the same time, the central Ti largely increased.

ne and Ti ITBs were formed simultaneously.

E046146:

After the LH transition at t ~ 5.0 s, The edge ne increased and the ne gradient decreased.

Increase in the central Ti seems to be prevented.

Decrease in gas-puffing rate The central Ti restarted to increase together with increase in the

ne gradient.

NBI and ECH in JT-60U

#1#2#31MW, 110GHz Gyrotrons#4JT-60UVacuum Vessel

Antenna for EC#4Antenna for EC#1-3

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

ECHGyrotron

4 units110GHz≤1MW/unit

Transmission line~60m70-80% transmitted

AntennaA : fixed for co-ECCDB : steerable for co-/ctr-ECCD or ECH

P-NB : 80-85 keV, 2-2.5 MW/unitperp. 7 units (1 unit for CXRS)co 2 unitsctr 2 units (1 or 0.5 unit for MSE)

N-NB : 350-380 keV, 2-3.5 MW/unitco 2 units

Effects of low central fuelling after strong ITB formation

Effects of low central fuelling during ITB Relation between density ITB and ion temperature formation

It is important to characterize density and ion temperature ITBs under condition of low central fuelling.

• The central ECH was applied from t = 5.6 s after the strong ITB was formed using P-NB and the P-NB heating power was reduced at t = 5.8 s.

• Deff is smaller in the low central fuelling case.

• DHe/DHeNC in the low central fuelling case i

s similar to or even larger than that in the high central fuelling case at the same χi/χi

NC.

DHe : He gas-puffing modulation exp.

W

neQgasD2

QgasHe

02468

10

Low central fuelling High central fuelling

Profiles in the low & high central fuelling cases

AB

32

10

IDouter divertor

(1019 ph/m2 sr s)

Increase in ne gradient

LH transition

Increase in edge density

Decrease in density gradient in the core

The ne and Ti gradients are strongly linked. Particle transport and ion heat tran

sport simultaneously decrease ? ne ITB assists formation of Ti ITB ?

Time delay of the increase in Ti gradient from the increase in ne gradient was not obvious.

The fast CXRS system is being developed in JT-60U.

0

1

2

3

4

5

0 0.5 1 1.5 2 2.5 3 3.5 4

E046144E046146

-(dne/dr)/ne (/m) at r/a~0.5

E046146

E046144E046146