Analysis of a 0D multimachine database of hybrid discharges

20 Oct 20081/12<Working Group> D C McDonald et al, Analysis of a 0D multimachine database of hybrid discharges. ITPA meeting on confinement and transport, Milano, Italy

Analysis of a 0D multimachine database of hybrid discharges

D C McDonald, J C DeBoo, F Ryter, L Laborde, and JET EFDA contributors*

*see appendix of F Romanelli et al, Fusion Energy 2008 (Proc 22nd Int Conf, Geneva, 2008) IAEA, (2008)


Introduction

• High N in hybrid scenario– JET Hybrid scenario uses strong

Ip ramp and LHCD to shape target q-profiles to avoid N

limiting MHD.– Similar scenarios on ASDEX

Upgrade and DIII-D.– Recent experiments, N,MHD≈3.6.

• Comparison with ELMy H-mode– Studies of q-profile evolution

indicate that JET Hybrid evolve rapidly (≈1s) to q-profiles similar to ELMy H-modes with H≈1.0.

– Similar ne, Te and Ti profiles and confinement seen in the resulting discharges.

– Seems to contradict 2003-4 JET experiments which showed high was favourable for confinement.

E Joffrin, EPS 2007


JET Hybrid beta scan: global confinement

• Global confinement– In Hybrid, find a strong decrease

of confinement with N.

– Fit gives BE~-1.400.38

– Much stronger dependence than previous experiments:

• BE~-0.040.22 (JET)

• BE~-0.010.09 (DIII-D)

• BE~-0.6 (JT-60U)

• BE~-1.20.6 (ASDEX Upgrade)

• Core transport– Interpretative analysis of core

transport with TRANSP code.

– Ion channel dominant.

– /B~+1.00.5 in line with global confinement, but appears to contradict electrostatic transport models.


JET Hybrid beta scan: modelled plasmas

• Modelled global confinement– Integrate modelled profiles from

x=0-0.8 to get confinement.

– Modelling agrees well with data

• Ideal scan– Take central point and perform

ideal scan with Weiland model.

– Modelled E has weak scaling as expected from theory.

• Interpretation– Small boundary condition

mismatches from ETB can explain the core scaling.

– ETB will dictate strong or weak confinement scalings depending on edge conditions ie not an effect of scenario.


Multimachine Hybrid studies: dataset

• Multi-machine dataset– Similar Hybrid scenarios on

ASDEX-Upgrade, DIII-D and JET combined into a multi-machine Hybrid dataset

– Wide range of parameters explored and N,MHD up to 3.5 for each machine.

– Majority of DIII-D operation at 1.2MA/1.7T.

– As largest machine, JET has largest confinement time, but maximum H-factors are lower.

ASDEX Upgrade DIII-D JET

N 376 103 149

I (MA) 0.6-1.2 1.1-1.3 1.1-2.8

B (T) 1.4-2.8 1.7-1.9 1.4-3.5

ne (1019 m-3) 3.4-11.4 2.7-7.2 2.0-8.5

P (MW) 2.7-17.1 4.4-11.1 3.7-21.4

N,MHD 1.2-3.5 2.2-3.5 1.0-3.5

N,th 1.0-3.1 1.8-2.7 0.7-2.6

E (ms)

40-230 80-220 90-390

H98(y,2) 0.8-2.0 1.0-1.8 0.7-1.2


Multimachine Hybrid studies: residuals

• Confinement trends– Studied residuals with respect to

IPB98(y,2)

– Negative P-H98(y,2) present, but weaker for JET

– No consistent residual trends observed with engineering parameters or *, , N

– Highest confinement is not associated with highest N., particularly clear on ASDEX Upgrade.

– Some evidence of different density scaling, but no clear pattern between machines.

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5

N,th

H98

(y,2

)

ASDEX UpgradeDIII-DJET

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25Power (MW)

H98

(y,2

)

ASDEX UpgradeDIII-DJET


Multimachine Hybrid studies: ne scaling

• Density scaling– Conditioning and low density

seem to play a major role in reaching high H98Y2, as suggested in the figure below.

– This is the case for AUG and DIII-D, while JET is insensitive to it.

– The high sensitivity of very good confinement to density is related to edge density and edge Ti.

– 2008 JET shots show H=1.2-1.4 at low density, e.g. H=1.4 (transiently) at ne=3.3e19 m-3.

• ASDEX Upgrade

• DIII-D

• JET


Multimachine Hybrid studies: *, match

• Confinement trends– All three machines have one discharge with N=2.4 and *=0.07. – These shots show the general trend for * and confinement.– q-profile is clearly different, with lower q95 for JET and DIII-D.– Mach number of rotation seems well matched.– Could consider a detailed 1D study of these discharges, or take

more recent shots if better matches exist.

Tokamak shot t (s) I (MA) B (T) q95 NEL PLTH rho* fGr H98(y,2)

ASDEX Upgrade 17514 2.3 1.0 2.0 3.8 6.3 6.4 8.8 0.50 1.44

DIII-D 110004 1.8 1.2 1.7 3.3 5.9 6.9 8.3 0.56 1.43

JET 69463 25.6 1.7 1.7 3.3 4.8 16.1 5.9 0.72 1.09


Multimachine Hybrid studies: confinement

• Multi-machine dataset– ASDEX Upgrade and DIII-D data

deviate from IPB98(y,2) scaling with different magnitude and trend.

– DIII-D confinement scales as E~n0.310.04 P-1.030.04

– ASDEX Upgrade 1MA data as E~n0.390.04 P-0.940.03

– JET data appears to be IPB98(y,2), E~n0.41 P-0.69, like

– Are DIII-D and ASDEX Upgrade Hybrids in a different confinement mode to JET?

H98(y,2) = 1.5

H98(y,2) = 1


Multimachine Hybrid studies: size scaling

• Multi-machine dataset– Positive *-H98(y,2) correlation

within and between machines.

– Consistent with earlier DIII-D experiments which found Bohm-like transport for broad q-profiles.

– Thus, it may be possible to have unified scaling for all Hybrids, albeit one with a poor * scaling.

– For Hybrid scenarios to be extrapolated to H98(y,2)=1.5 on ITER would require breaking of * trend.

– On the available evidence, Hybrid scenario is suitable only for H98(y,2)=1 inductive ITER operation.


Improved JET Hybrid confinement in 2008

In 2008 JET studies the effect of broader q profile on confinement

Hybrid scenario in ITER requires up to 50% increase over the H-mode confinement

H98(y,2) = 1.5

H98(y,2) = 1

JET(NTH<2.6)

DIII-D(NTH<2.7)

AUG (NTH<3.1)

Multi-machine dataset 2003-2007

2008Strong current ramp-up then ramp down produces significant q profile broadening

EFIT reconstruction with MSE + MHD markers


R [m]


R [m]

q

Time [s]

Ip [MA]PNBI [MW]

74825 & 74826 (BT=2T)

Current ramp-up, ramp-down method has produced a set of shots with H>1.2 at Bt=1.7-2.4T.

F Romanelli + E Joffrin, IAEA 2008


Summary

• scan performed in Hybrid scenario with =0.45– Strong core and edge confinement degradation with N

– Modelling shows core effect can be explained by mismatches in parameters and bc’s rather than true dependent transport.

– Results consistent with ETB resulting in strong or weak confinement dependence on depending on edge conditions.

• Multi-machine global confinement dataset formed– Confinement differs from IPB98(y,2) for ASDEX Upgrade and DIII-D– JET confinement follows IPB98(y,2) for 2003-7 data.– ASDEX Upgrade and DIII-D both see strongly negative power scalings

and evidence for best confinement at low densities.– Positive *-E correlation suggests H98(y,2)≈1.5 unlikely for ITER.– * scaling could be investigated through 1D study of matched , *

shots.

• JET 2008 results– JET now achieves H=1.2-1.4 at N,MHD≥3.0, albeit transiently, due to

NTM limits. Key factor is q-profile shaping using tailored Ip ramps.

Date post:	22-Jan-2016
Category:	Documents
Upload:	vila
View:	37 times
Download:	0 times

Analysis of a 0D multimachine database of hybrid discharges

Documents