PRINCETON PLASMA PHYSICS LABORATORY

PPPL

Study of Integrated High-Performance Regimeswith Impurity Injection in JT-60U Discharges

K. W. Hill,1 W. Dorland,2 D. R. Ernst,3 D. Mikkelsen,1 G. Rewoldt,1

S. Higashijima,4 N. Asakura,4 H. Shirai,4 T. Takizuka,4

S. Konoshima,4 Y. Kamada,4 H. Kubo, 4 and Y. Miura4

1Princeton Plasma Physics Laboratory, Princeton, NJ, USA2Institute for Plasma Research, Univ. of Maryland, College Park, MD, USA3Plasma Science and Fusion Center, MIT,Cambridge, MA, USA4Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki, Japan

Presented at the 19th IAEA Fusion Energy ConferenceOctober 14-19, 2002 • Lyon France

PRINCETON PLASMA PHYSICS LABORATORY

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MOTIVATION

• Achieve good confinement at high density in ELMy H-modedischarges

• Reduce steady-state and ELM-induced heat loads to divertor.

OUTLINE• Reactor requirements almost simultaneously achieved in

JT-60U with Ar seeding

• Experimental results from JT-60U with Ar seeding

• Linear microinstability analysis with GS2 and FULL codes

• Predictive modeling with “stiff” models for Ar seeding cases• Summary and future work

PRINCETON PLASMA PHYSICS LABORATORY

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Summary – Argon seeded discharges

Part I

• Near reactor requirements of high confinement, density, radiatedpower fraction, and fuel purity achieved simultaneously in JT-60U.

• Transient ELM heat load reduced by factor ~1/5 – 1/3 in dome-topconfiguration

• Particle confinement increased.

Part II

• Confinement enhancement with argon seeding is consistent withgyrokinetic microstability calculations.

• Reduced ITG growth rate in outer region is largely a Ti-profileeffect; dilution causes a smaller effect.

• Effect of rotation is small.

PRINCETON PLASMA PHYSICS LABORATORY

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JT-60U has achieved near ITER performancerequirements simultaneously with argon seeding

Parameter JT-60U(no Ar)

JT-60U (Ar) ITER

HH98(y,2) 0.65 1 1

ne/nGW 0.67 0.8 0.85

Prad/Pheat 0.6 0.8 0.7

ELM-inducedheat spikes

large x 1/3-1/5reduction

small

Fuel Puritynd/ne

0.8 0.7 0.8

Two plasma configurations have been explored for high ne.

•Standard (S)d = 0.36, q95 = 3.4

Ip=1.2MA, Bt=2.5T•Dome-top (D)d = 0.37, q95 = 4.1E39530, 9.4s

2 3 4R (m)

-1

0

1

Z (m

)

E36916, 9.1s

2 3 4R (m)

-1

0

1

Z (m

)

D2

Ar

pumping slots

to pump

Motivation Dome top (outer strike point on divertor dome top); efficient fueling of D and Ar due to recycling near X-point

HH~1, Prad>0.8Pnet at ne~0.8nGWin dome-top configuration with Ar injection.

D

Reference(S, no Ar)

S

0.4

0.6

0.8

1

1.2

0.4 0.5 0.6 0.7 0.8 0.9

HH 9

8(y,

2)

ne /nGW

0.2

0.4

0.6

0.8

1

0.4 0.5 0.6 0.7 0.8 0.9

Pra

d / P

net

ne /nGW

By Ar injection, the confinement is improved by ~50% at 0.65 nGW. Standard; HH98(y,2) decreases rapidly around 0.7 nGW. Dome-top; HH98(y,2) ~1 even at 0.8 nGW.

The radiation-loss-power fraction reaches 80% at high density.

Improved H-factor with Ar is correlated with increase in Ti ped.

With Ar injection, the pedestal ion temperature remains high at high density. Standard; Ti

ped decreases rapidly around 0.7 nGW. Dome top; Ti

ped remains high even at ne ~ 0.8 nGW. (efficient fueling of D and Ar due to recycling near X-point?)HH increases with the pedestal ion temperature.T(r) is stiff inside the pedestal.ne(r) is slightly peaked with Ar injection. -> Ar modifies pedestal physics • Dilution • Reduces drive for ITG/TEM

0.4

0.6

0.8

1

1.2

0.5 1 1.5 2

HH 9

8(y,

2)

Tiped (keV)

D

Reference(S, no Ar)

S

0.5

1

1.5

2

0.4 0.5 0.6 0.7 0.8 0.9

T ipe

d (ke

V)

ne /nGW

In dome-top case, nD/ne ~ 0.7 at 0.8 nGW: ITER nD/ne ~ 0.8.

At 0.65 nGW, Ar injection increases nDxtE by ~25% despite a reduction in nD/ne from ~80% to ~65%, because of a significant confinement improvement.

At 0.8 nGW, nD reductions due to intrinsic impurity (~ C) and Ar are 15% each.Ar density optimization and carbon density reduction are required for high purity.

0

0.2

0.4

0.6

0.8

1

0.4 0.5 0.6 0.7 0.8 0.9

n D /

n e

ne /nGW

Intrinsic impurity(~ Carbon)

A

r

Reference(S, no Ar)

Ar injection (S, D)

PRINCETON PLASMA PHYSICS LABORATORY

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Core microstability analysis of argon-seededdischarge

• Linear stability analyses with FULL and GS2 codes indicate:

• ITG maximum growth rate significantly lower in outer region ofAr-seeded discharge, relative to reference discharge.

• ETG maximum growth lower across entire profile.

• Rotation effect very small.

• Effect of adding argon to reference discharge or removingargon from Ar-seeded discharge (change in dilution) relativelysmall.

Dome Top (Ar)

20

468

10

Reference (no Ar)

T i (k

eV)

0 0.2 0.4 0.6 0.8 1.0

2

4

6

8

0

T e (k

eV)

012345

n e ( 10

19 m

- 3)0.40

12345

0.0 0.2 0.6 0.8 1.0Z e

ff

r/a

• Te, Ti, Zeff higher with argon• ne more centrally peaked

Plasma profiles with and without argon seeding

ITG growth rate, g , reduced in outer region (r/a>0.5) of Ar shot

• gETG reduced everywhere• wExB much smaller than gITG

• Rotation not a factor

core edge

Reference (no Ar)

kq rs = 0.5 - 0.6

0.00.20.40.60.81.0

01020304050

kq rs = 35 - 40

g

wExB

0.0 0.2 0.4 0.6 0.8 1.0r/a

rate

(10

5 s-1

)ITG/TEM

ETG

Ar seeded

0.00.20.40.60.81.01.20.0

0.2

0.4

0.6

0.8

grow

th ra

te (1

05 s-1

)

0.0 0.2 0.4 0.6 0.8 1.0 r/a

reference (no Ar)

reference + Ar

kq rs = 0.0 - 0.6

ArAr removed

Dilution does not significantly change ITG growth rate

Adding argon to reference discharge

Removing argon from Ar-seeded discharge

02468

1002

4

68

0 0.2 0.4 0.6 0.8 1

• Shear effects not significant

T i (k

eV)

T e (k

eV)

IFS-PPPL

Measurement

Multimode

RLWB

Models qualitatively different in core for Ar discharge

Argon, dome top

39532b01

PRINCETON PLASMA PHYSICS LABORATORY

PPPL

Summary – Argon seeded discharges

Part I

• Near reactor requirements of high confinement, density, radiatedpower fraction, and fuel purity achieved simultaneously in JT-60U.

• Transient ELM heat load reduced by factor ~1/5 – 1/3 in dome-topconfiguration

• Particle confinement increased.

Part II

• Confinement enhancement with argon seeding is consistent withgyrokinetic microstability calculations.

• Reduced ITG growth rate in outer region is largely a Ti-profileeffect; dilution causes a smaller effect.

• Effect of rotation is small.

PRINCETON PLASMA PHYSICS LABORATORY

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Future work

• Increased ExB shearing, as well as impurity-induced reductionin drift-wave turbulence important in DIII-D (Murakami); particlepinch a factor leading to density peaking in RI mode, accordingto modeling (Tokar)

• Analyze JT-60U discharges for effect of ExB shearing duringevolution to final, high density discharges.

• Evaluate particle fluxes with FULL code for JT-60U discharges.

0

0.5

1

1.5

2

0 0.2 0.4 0.6 0.8 1

g (10

5 sec

-1)

r / a

JT-60U E39532A07, t = 7.35 selectrostatic toroidal drift modewith carbon and argon impuritiesand slowing-down beam; k

qri = 0.66

no rotation

with rotation (noeigenfunction shearing)

FULL Code

Rotation has little Effect on ITG growth rate

0.000

0.010

0.020

0.030

0.040[M

rad/

s]

0.0 0.2 0.4 0.6 0.8 1.0

Maximum ITG growth rate is near kq rs ~ 0.5

36349r = 0.61No Ar Growth rate

Real frequency / 10

kq rs

0 5 10 15 200

1

2

3

4

5

6

R / LTe

r/a = 0.47kq rs = 35

Ar

Critical Te gradient for ETG mode is higher in Ar-seeded discharge

reference

measured

critical

grow

th ra

te (1

06 s-1

)

0.0 0.5 1.0 1.5 2.0 2.5-0.02

0.00

0.02

0.04

0.06

0.08

0.10[M

rad/

s]

36349r = 0.73No Ar Growth rate

Real frequency / 10

kq rs

TEM/ETG mode dominates near edge

0 20 40 60 80-0.5

0.0

0.5

1.0

1.5[M

rad/

s]

36349r = 0.61No Ar

kq rs

Growth rate

Real frequency / 10

Maximum ETG growth rate is near kq rs ~ 40

R/LTecrit

R/LTe

20

15

10

5

00.0 0.2 0.4 0.8 1.00.6

Normalized Minor Radius (r/a)

20

15

10

5

0

R/LTe

R/LTecrit

No Argon

With Argon

36349

39532

ETG Stabilized Over Significant Region In Ar-Seeded Discharge