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Analysis of a 0D multimachine database of hybrid discharges

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 b N in hybrid scenario

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Analysis of a 0D multimachine database of hybrid discharges

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  1. 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) <Working Group>

  2. Introduction • HighbNin hybrid scenario • JET Hybrid scenario uses strong Ip ramp and LHCD to shape target q-profiles to avoid bN limiting MHD. • Similar scenarios on ASDEX Upgrade and DIII-D. • Recent experiments, bN,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 b was favourable for confinement. E Joffrin, EPS 2007 <Working Group>

  3. JET Hybrid beta scan: global confinement • Global confinement • In Hybrid, find a strong decrease of confinement withbN. • Fit gives BtE~b-1.400.38 • Much stronger dependence than previous experiments: • BtE~b-0.040.22 (JET) • BtE~b-0.010.09 (DIII-D) • BtE~b-0.6 (JT-60U) • BtE~b-1.20.6 (ASDEX Upgrade) • Core transport • Interpretative analysis of core transport with TRANSP code. • Ion channel dominant. • c/B~b+1.00.5in line with global confinement, but appears to contradict electrostatic transport models. <Working Group>

  4. 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 b scan with Weiland model. • Modelled tE has weak b scaling as expected from theory. • Interpretation • Small boundary condition mismatches from ETB can explain the core b scaling. • ETB will dictate strong or weak b confinement scalings depending on edge conditions ie not an effect of scenario. <Working Group>

  5. 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 bN,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. <Working Group>

  6. 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*, b, bN • Highest confinement is not associated with highest bN., particularly clear on ASDEX Upgrade. • Some evidence of different density scaling, but no clear pattern between machines. <Working Group>

  7. 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 <Working Group>

  8. Multimachine Hybrid studies: n*, b match • Confinement trends • All three machines have one discharge with bN=2.4 and n*=0.07. • These shots show the general trend for r* 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. <Working Group>

  9. 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 tE~n0.310.04 P-1.030.04 • ASDEX Upgrade 1MA data as tE~n0.390.04 P-0.940.03 • JET data appears to be IPB98(y,2), tE~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 <Working Group>

  10. Multimachine Hybrid studies: size scaling • Multi-machine dataset • Positive r*-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 r* scaling. • For Hybrid scenarios to be extrapolated to H98(y,2)=1.5 on ITER would require breaking of r* trend. • On the available evidence, Hybrid scenario is suitable only for H98(y,2)=1 inductive ITER operation. <Working Group>

  11. Improved JET Hybrid confinement in 2008 74825 & 74826 (BT=2T) Ip [MA] PNBI [MW] Time [s] EFIT reconstruction with MSE + MHD markers q Hybrid scenario in ITER requires up to 50% increase over the H-mode confinement In 2008 JET studies the effect of broader q profile on confinement Multi-machine dataset 2003-2007 H98(y,2) = 1.5 Strong current ramp-up then ramp down produces significant q profile broadening 2008 DIII-D (bNTH<2.7) JET (bNTH<2.6) AUG (bNTH<3.1) F Romanelli + E Joffrin, IAEA 2008 H98(y,2) = 1 Current ramp-up, ramp-down method has produced a set of shots with H>1.2 at Bt=1.7-2.4T.

  12. Summary • b scan performed in Hybrid scenario with d=0.45 • Strong core and edge confinement degradation with bN • Modelling shows core effect can be explained by mismatches in parameters and bc’s rather than true b dependent transport. • Results consistent with ETB resulting in strong or weak confinement dependence on b 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 r*-tE correlation suggests H98(y,2)≈1.5 unlikely for ITER. • r* scaling could be investigated through 1D study of matched b, n* shots. • JET 2008 results • JET now achieves H=1.2-1.4 at bN,MHD≥3.0, albeit transiently, due to NTM limits. Key factor is q-profile shaping using tailored Ip ramps. <Working Group>

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