the « hybrid » scenario in jet: towards its validation for ... · emmanuel joffrin xxth fusion...

Emmanuel Joffrin XXth Fusion Energy Conference, November 2004 1

The « hybrid » scenario in JET:towards its validation for ITER

E. Joffrin, A. C. C. Sips, J. F. Artaud, A. Becoulet, R. Budny, P. Buratti, P. Belo, C. D. Challis, F. Crisanti, M. de Baar, P. de Vries, C. Gormezano, C. Giroud,

O. Gruber, G.T.A. Huysmans, F. Imbeaux, A. Isayama, X. Litaudon, P. J. Lomas, D. C. McDonald, Y. S. Na, S. D. Pinches, A. Staebler, T. Tala,

A. Tuccillo, K.-D. Zastrow and JET-EFDA Contributors to the Work Programme.

Outline:

- Introduction to the hybrid scenario in JET

- Physics analysis (MHD, current, transport)

- Projections to ITER burning plasma for the hybrid scenario


ITER scenario for steady state burning conditions Maximise: G = βN . H / q95

2 Iboot / Ip ~ βN . q95 n ~ 0.85 nGreenwald

AUG: A. Staebler EX/4-4DIII-D: M. Wade EX/4-1

Ip

q95

βN . H98 y2

Burn time

Q

15MA

3

1.8 x 1.0

400s

10

NTM with sawteeth High Ip disruptions

Current controlHigh β MHD

9MA

5.3

2.95x1.6

>3000s

6

Non-inductive RS

12MA

~4

~3 x 1.0

~2000s

~10

Hybrid scenario

0 0.5 1

q-profileH-mode inductive scenario

Normalised radius

2

1

3

4

5

JET has started the study of the « hybrid » regime in the 2003 campaign


JET hybrid regime (1.7T, 1.4MA)

10

2

4

0.4

0.5

0 5 10 150

4

0.2

Ip [MW]

PNBI [MW]

4 x liH89

βN

G=H89.βN / q952

Fishbones n=1

Mild 3/2(NTM)

Pulse 58323 (q95=4, δ=0.22)

Dα

0

2.0

PLH [MW]

Times [s]

Identity experiment with ASDEX Upgrade:

1. Matched magnetic configurations.

2. Similar ρ* & q (qo ~1 and q95=4).Bo τIPB98(y,2) α ρ*-2.70 β-0.90 υ*-0.01 q-3.0 ε0.73 κ3.3

3. βN controlled in real time with PIN

4. ν*(JET)=0.08 ≠ ν*(AUG) = 0.15

Hybrid scenario reproduced in JET with similar phenomenology than in AUG.


Hybrid regimes in JETDevelopment of the hybrid regime towards the ITER domain

The hybrid regime has been achieved in JET:

• with AUG configuration δ=0.45

• with ITER configuration δ=0.45

• at 2.4T (lower ρ*) and δ=0.22

• at 2.4T (lower ρ*) and δ=0.45

1 2 3 4 5 6 7 8 9 100

0.5

1

1.5

2

2.5

3

x 103

βN

ρ*

1.7 TFor q95~4

AUGJET

2.4T

δ=0.2 (circles) δ=0.45 (triangles)

3.4T

DIII-D

(AUG & DIII-D from ITPA database)

MHD limited

ITER

3.1T

With more available power, future experiments are planning to explore the low ρ* region reachable by ITER

JET-AUG Identiy

JET can bridge the gap between machines like ASDEX Upgrade and ITER


NTM control in hybrid regimeIn JET, NTM are avoided by tuning the target q profile above 1 in the preheat phase

1.4

2/1 NTM

Sawteeth

0

10

20

0

1

2

0 5 10 150

2

βN

Ip [MA]

PNBI [MW]

Times [s]

PLH [MW] (x5) Pulse 58323 & 58324

In JET, the hybrid scenario can operate at β

Benign NTMs in main heating phase at high βN Wisland~3-4cm impact on confinement ~5%

N>2.5 with moderate NTM activity as in other devices (ASDEX Upgrade & DIII-D)

1/1 mode & fishbones

4/3 mode

3/2 mode


Ideal MHD in hybrid regimeJET has reached ~95% of the ideal kink limit so far.

Ideal m=1 kink mode behaviour predicted in JET using MISHKA code.

q(0)=1.07βp=1.25q(0)=1.07βp=1.25

m=1

m=3

m=2

0.002

0.004

βp0.4 0.6 0.8 1 1.2

q(0)=1.01

q(0)=1.03

q(0)=1.05

q(0)=1.07

q(0)=1.07(no wall)

Growth rate

Strong increase of the ideal kink growth rate as plasma pressure increases.

Also suggests that control of the q profile is necessary to keep q away from unity

Mode localisation


Current balance in the hybrid regimeINBCD / Ip=35%; Iboot / Ip=25% Current diffusion analysis with the CRONOS code

0 0.2 0.4 0.6 0.8 10.0

0.1

0.2

0.3

0.4

0.5 JTOT[MA/mJTOT[MA/m2]

JNBCD2JNBCD [MA/m]2

JBOOT [MA/m2]JBOOT

Pulse 58323, βN=2.8From TRANSP

Normalised radius

q contours from the CRONOS code (58323)

0

0.2

0.4

0.6

0.8

2 4 6 8 10 12 140

0.20.40.60.8

Vloop [V]

PNBI [MW]

q=1

q=4/3

q=3/2

q=2q=5/2

q=3q=4

Times [s]

At βN=2.8, non-inductive current sources are sufficient to maintain a steady state q profile


Confinement in the hybrid regime

• In JET at high βN hybrid regime have an improved confinement of up to 20 % with respect to IPB98y2.

• IPB98(y,2): ρ*-2.70 β-0.90 ν*-0.01 q-3.0

• Recent dedicated studies have shown that confinement has a weaker negative dependence on β:

1 1.5 2 2.5 31

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8Wth exp [MJ](for BT=1.7T & βN>2)

Wth scaling [MJ]

IPB98y2

+20%

Pure gyro-Bohm

• Pure gyro-Bohm scaling: ρ*-3 β0 ν*-0.1 q-1.7

Gives a reasonable fit to the data.

(Cordey et al., IT/P3-32

At high βN, he higher confinement observed in hybrid regime could be related to the β-0.90 dependence of the IPB98(y,2) scaling

& McDonald, EX/6-6)


Comparative transport property of the hybrid regime

15

For s>0.2 & R/Ln<2

0 5 100

5

10

15

20

25ITB regimeELMy H-modeHybrid regime

R/LTi critical from theory

R/LTi (exp)

(Jenko et al., PoP, 2002)

1. As expected, ITB discharges areshowing ion temperature gradients well above the predicted criticalgradients for ITGs

2. Hybrid scenario are behaving in the same way as the standard ELMy H-mode.

Supported by turbulence measurements with reflectometry.

In JET, it appears that the confinement in hybrid regimes is notsignificantly different than in the standard ELMy H-mode scenario.


Tritium and impurity transportParticle and impurity diffusion and convection inferred from the SANCO +

UTC codes constrained by experimental data

D [m2/s]

V [m/s]

Pulse 61389 (βN=2.7)

3

2

1

0

-5

-10

Dneo[m2/s]

Normalised radius0 10.5

Vneo[m/s]

Tritium and impurity diffusion and convection in hybrid regime are dominated by turbulent transport.

Trace tritium injection Tritium

Normalised radiusNormalised radius

62490 (B T=2.4T ; δ=0.45)60932 (B T=2.4T ; δ=0.20)

Neoclassical -----

0 0.2 0.4 0.6 0.8 1.0

5

4

3

2

1

2

1

-1

-2

0

D [m2/s]

V [m/s]

62490 (B T=2.4T ; δ=0.45)60932 (B T=2.4T ; δ=0.20)

Neoclassical -----

0 0.2 0.4 0.6 0.8 1.0

5

4

3

2

1

2

1

-1

-2

0

D [m2/s]

V [m/s]

Neon (Z=10)( Neutron monitor + fit )

(D. Stork, OV/4-1 & McDonald, EX/6-6)


ITER projections with the hybrid scenario Projections for burning hybrid regime in ITER with the integrated 1D code CRONOS

Hypothesis: - HH=1

- Gyro-Bohm transport normalised to scaling laws.

- Pedestal height from pedestal database scaling law.

- Zeff=1.8, He concentration 3%

Scaling used Pfus

[MW]Paux

[MW]βN Density

peakingQfus q95 Ip

[MA]

IPB98y2 (PPA) 400 73 1.9 0 5.4 3.3 13.8

IPB98y2 570 73 2.1 0 7.8 3.3 13.8Comparison

with PPA

IPB98y2 160 73 1.6 0 2.2 4 11.3

Pure Gyro-Bohm 285 73 2.25 0 3.9 4 11.3

Scaling comparison

Pure Gyro-Bohm 337 73 2.4 neo=1.5 x neped 4.6 4 11.3With ne peaking

Pure Gyro-Bohm 600 50 2.85 neo=1.5 x neped 12 3.5 13Lower q95

Reaching high βN requires the fine tuning of plasma current


Conclusions1. The steady state “hybrid” scenario has been successfully reproduced in JET

by the mean of an identity experiment approach with ASDEX-Upgrade.

2. In JET, current control is a key factor in avoiding NTM activity during the main heating phase of the scenario.

3. The JET hybrid scenario does not show any obvious sign of improved heat and particle confinement with respect to standard ELMy H-modes. On the other hand, its improved stability allows operation at higher βN close to the ideal limit.

4. The maximisation of confinement and stability properties provides to the hybrid regime a good probability for achieving high fusion gain at reduced current (~13MA) for more than 2000s.


Performance overview towards ITER

Bootstrap fraction from TRANSP data

(q95=4)

0.20.40.60.81

1.21.41.61.8

0.3 0.4 0.5 0.6 0.7 0.8

Ti(0)/Te(0)

ne/ne GREENWALD

ITER

δ=0.22δ=0.45

JET Hybrid regime are situated in the right ball park in terms of Ti/Te, density and plasma performance


NTM in hybrid regime

1/1 mode & fishbones

Spectrogram of magnetic fluctuations

4/3 mode

3/2 mode

CoupledIslands size is 3 to 4cm located at r/a=0.3-0.4

Limited impact on global confinement

few percent

Neoclassical tearing mode behaviour in the hybrid regime

1 < q < 1.3 in plasma core

ELMs ~40Hz

In JET, the hybrid scenario can operate at βN>2.5 with moderate NTM activity as in other devices (ASDEX Upgrade & DIII-D)


Summary of advanced modes development

ITER (PPA Q=5.4, Tburn=1000s): δ= 0.48 q95=3.5 fGW=0.85 H=1 βN=1.9 fBS=17%

ITER (Q=5 Steady State): δ=0.49 q95=5.5 fGW=0.8 H=1.5 βN=3 fBS=50%

Hybrid Mode or improved H-mode (new on JET)

Plasmas with ITBs

the « hybrid » scenario in jet: towards its validation for ... · emmanuel joffrin xxth fusion...

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