Overview of 2006 – 2007 L-H transition studies on JET
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Overview of 2006 – 2007 L-H transition studies on JET. Y Andrew CDBM ITPA Meeting, Lausanne, Switzerland 7 – 10 th May 2007.

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Overview of 2006 – 2007 L-H transition studies on JET

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Overview of 2006 2007 l h transition studies on jet

Overview of 2006 – 2007 L-H transition studies on JET

Y Andrew

CDBM ITPA Meeting, Lausanne, Switzerland

7 – 10th May 2007


Overview of 2006 2007 l h transition studies on jet

Y Andrew1*, NC Hawkes1, Y Martin2, R Sartori3, V Parail1, TM Biewer4, K Crombe5, C Giroud1, A Korotkov1, E de la Luna6, V Naulin7, I Nunes8, G Saibene3, P de Vries1 and JET-EFDA contributors#

  • Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, UK

  • EPFL/CRPP Association Euratom, Lausanne, Switzerland

  • 3. EFDA Close Support Unit, Garching, 2 Boltzmannstrasse, Garching (DE) Germany

  • 4. Oak Ridge National Laboratory, Oak Rdige, TN 37831, USA

  • 5. Department of Applied Physics, Ghent University, Belgium

  • 6. Associacion Euratom/CIEMAT para Fusion, Madrid, Spain

  • 7. Risoe National Laboratory Technical University of Denmark, OPL-128, 4000 Roskilde, Denmark

  • 8. Centro de Fusão Nuclear, Associacão EURATOM-IST, Lisboa, Portugal

    * [email protected]

  • # See appendix of M Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chengdu, 2006) IAEA Vienna (2006)


Overview of 2006 2007 l h transition studies on jet

Outline

  • Background

  • Effect of new JET Divertor of H-mode Access

  • H-mode Access with ‘ITER-like’ magnetic configuration

  • Influence of X-point location

  • Ip scan

  • Bt scan

  • Effect of TF Ripple on H-mode access

  • Type-III to Type-I ELM access


Overview of 2006 2007 l h transition studies on jet

Experimental Method

L-mode

H-mode

  • H-mode threshold measurements performed on JET by ramping the input power by typically 1 MW/s to follow the L-H and H-L transitions

  • Power threshold is defined as:

  • Pth = Pin+POH-dWdia/dt

  • at the transition to H-mode

  • L-mode density is held constant using feedback control

Da

Power

Wdia

Edge ne

Edge Ti

Edge Vtor

Edge Vpol


Overview of 2006 2007 l h transition studies on jet

New Divertor

MkII LBSRP

MkII SRP

HT3

2003

HT3

2006


Overview of 2006 2007 l h transition studies on jet

New Divertor has no effect on Pth

  • Density scan repeated for HT3 configuration with new divertor


Overview of 2006 2007 l h transition studies on jet

Increasing dlower

Proximity of X-point to divertor wall increasing

V/SFE/LT

2003

HT3

2003/2006

ITER-like

2006


Overview of 2006 2007 l h transition studies on jet

ITER-like configuration

  • ITER-like configuration Pth demonstrates weaker density dependence


Overview of 2006 2007 l h transition studies on jet

X-point height scan

ITER-like configuration with X-point

(a) closer to inner wall and (b) reduced in height

(b)

(a)


Overview of 2006 2007 l h transition studies on jet

Reduction in Pth

#68299

ITER-like optimised

#68300

ITER-like innermost X-point

#68301

ITER-like lowest X-point

Total Input Power

Edge Density

dlower


Overview of 2006 2007 l h transition studies on jet

Ip scan

  • Some variation in density with increasing Ip, so observed trend most likely to be the result of density dependence

  • Need to account for ne dependence of Pth


Overview of 2006 2007 l h transition studies on jet

Bt scan at fixed q95

  • Some variation in density with increasing Ip/Bt

  • Need to account for ne dependence of Pth


Overview of 2006 2007 l h transition studies on jet

TF Ripple – low density

Ip/Bt = 2 MA/2.2 T, q95 = 3.7, d ~ 0.2

0.08 % - No Ripple

# 69638

1 % Ripple

# 69639

No significant difference between L-H transition for ‘No Ripple’ and 1 % Ripple shots at low density

4.3 MW

4.1 MW

Total Input Power

Edge ne

1.3x1019 m-3

3.70 m

3.83 m

Edge Ti


Overview of 2006 2007 l h transition studies on jet

Edge CXRS Lines of Sight

# 69638 @ 60s

3.70 m

3.66 m

3.83 m

Ti (eV)

Mid-plane Radius (m)


Overview of 2006 2007 l h transition studies on jet

TF Ripple – low density

Ip/Bt = 2 MA/2.2 T, q95 = 3.7, d ~ 0.2

0.08 % - No Ripple

# 69638

1 % Ripple

# 69639

Edge ne

  • ELM Da characteristics different for no-ripple and ripple shots

  • No significant difference in edge ne during evolution of H-mode between no-ripple and ripple case

  • Large differences in edge vtor are observed during the H-mode phase

  • Differences in vtor disappear following the transition back to L-mode

vtor

3.66 m

9 km s-1

3.70 m

-62 km s-1

vtor

3.83 m

vtor


Overview of 2006 2007 l h transition studies on jet

TF Ripple – higher density

4.7 MW

#69641

0.08 % ripple

#69640

4.6 MW

1 % ripple

4.2 MW

#69646

1.3 % ripple

Total Input Power

Ti

ne

edge ne


Overview of 2006 2007 l h transition studies on jet

Type-III Type I ELM Threshold

ITER-like configuration 2.5 MA/2.7 T

#68221

6.5 MW

#68221

#68218

7.2 MW

#68218

7.9 MW

#68220

8.8 MW

#68219

#68220

#68216

14.2 MW

#68216


Overview of 2006 2007 l h transition studies on jet

Type-III  ELM-free Type III ELMs

ELM-free phases

#68221 ITER-like

Outer Divertor Da

  • The plasma does not drop out of H-mode

  • It has ELM-free H-mode phases:

  • Da signals remains low

  • ne increases due to lack of ELMs

  • Wdia increases

Edge ne

Wdia


Overview of 2006 2007 l h transition studies on jet

Conclusions

  • Replacement of SRP has no influence on Pth

  • Pth of ITER-like configuration demonstrates much weaker density dependence

  • Lowering of X-point height shows more dramatic effect of Pth than inner wall proximity

  • Three point Ip scan carried out

  • Four point Bt scan carried out

  • Valuable set of data has been obtained on H-mode transitions on JET with different levels of Toroidal Field ripple at two different densities

  • Type-III to Type-I ELM transition studies started


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