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K. Tanaka 1) , H. Takenaga 2) , K. Muraoka 3) , C. Michael 4) , L. N. Vyacheslavov 5) ,

Comparison study of particle transport and role of fluctuation in low collisionality regime in LHD and JT-60U. K. Tanaka 1) , H. Takenaga 2) , K. Muraoka 3) , C. Michael 4) , L. N. Vyacheslavov 5) , A. Mishchenko 6) , M. Yokoyama 1) , H. Yamada 1) , N. Oyama 2) , H. Urano 2) , Y. Kamada 2) ,

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K. Tanaka 1) , H. Takenaga 2) , K. Muraoka 3) , C. Michael 4) , L. N. Vyacheslavov 5) ,

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  1. Comparison study of particle transport and role of fluctuation in low collisionality regime in LHD and JT-60U K. Tanaka1), H. Takenaga2), K. Muraoka3), C. Michael4), L. N. Vyacheslavov5), A. Mishchenko6), M. Yokoyama1), H. Yamada1), N. Oyama 2), H. Urano2), Y. Kamada2), S. Murakami7),A. Wakasa8), T. Tokuzawa1), T. Akiyama1), K. Kawahata1), M. Yoshinuma1), K. Ida 1),I. Yamada1), K. Narihara1), N. Tamura1) 1)National Institute for Fusion Science, Toki 509-5292, Japan 2)Japan Atomic Energy Agency, 801-1 Mukouyama, Naka, Ibaraki 311-0193, Japan 3)Chubu University, 1200 Matsumoto, Kasugai, Aichi 487-8501, Japan 4) EURATOM/UAKEA Fusion Association, Oxfordshire OX14 3 DB, United Kingdom 5) Budker Institute of Nuclear Physics, 630090, Novosibirsk, Russia 6) Max-Planck-Institute fur Plasmaphysik, EURATOM-Association, D-17491, Greifswald, Germany 7) Department of Nuclear Engineering, Kyoto University, Kyoto 606-8501, Japan 8) Graduate School of Engineering, Sapporo Hokkaido University, 060-8628, Japan

  2. Outline • General comparison of density profile in JT-60U and LHD • Density profiles and turbulence in JT-60U • Density profile and turbulence in LHD • Summary and Discussion • (Possibility of curvature pinch)

  3. Outline • General comparison of density profile in JT-60Uand LHD • Density profiles and turbulence in JT-60U • Density profile and turbulence in LHD • Summary and Discussion • (Possibility of curvature pinch)

  4. The particularity of helical/stellarator is enhanced neoclassical transport in low collision regime tokamak helical/stellarator Future operation regime of reactor Future operation regime of reactor Experimental De,ce Experimental De,ce Around one order Around one order Neoclassical Transport coefficient Neoclassical Transport coefficient 1/n regime Banana regime Plateau regime Plateau regime nei nei Plateau regime 1/n regime

  5. Magnetic axis position change magnetic helical ripple and higher ripple results in larger neoclassical transport Helical coil Plasma B contour HC-I Shifts by external vertical field and Shafranov shifts Flux Surface Orbit of guiding center

  6. Density profile is Clear difference of density profiles were observed in JT-60U and LHD LHD JT60U Elmy H mode Both NBI heated plasma In both devices, the effect of particle fueling is small, the observed difference is due to the difference of particle transport

  7. Similar nb* dependence with tokamak at Rax=3.5m, opposite nb* dependence at Rax=3.6m were observed Larger neoclassical Larger anomalous This is more important.

  8. Outline • General comparison of density profile in JT60-U and LHD • Density profiles and turbulence in JT-60U • Density profile and turbulence in LHD • Summary and Discussion • (Possibility of curvature pinch)

  9. In tokamak, particle transport is dominated by anomalous one Ware pinch is negligible in the present data set of JT-60U. Linear Gyro kinetic theory (Angioni Nucl. Fusion 2004) and non linear gyro fluid theory (Garbet, P.R.L. 2003) predicts peaked density profile in ion dominant heating. These are caused by ion temperature gradient (ITG) mode. In the dataset of JT-60U,hi=Ln/Lt>1, this suggests ITG is lenaerly unstable. Role of turbulence was experimentally studied by using correlation reflectometry.

  10. Omode correlation reflectmetry was used to measure radial correlation for different peaked density profiles f2 f1 f3 ne3 ne2 ne1 Freq. Two frequency channels One is fixed at 47.3GHz (Cut off density (nc) 2.78x1019m-3) The other is scanned from 42.3 -46.8GHz (nc=2.23-2.73x1019m-3) Six frequencies were scanned in step. Each frequency was 20msec duration. 120ms t

  11. Radial correlation was analyzed from correlation reflectometry Representative values were averaged one for -200 - -100kHz. Error was standard deviation for this frequency regime 2~5 scans were accumulated for constant Ne and PNB duration. Accumulated For quantitative estimation of radial correlation, coherence at dR=20mm was used for parameter dependence.

  12. Density peaking factor increased with decrease of collisionality as reported previously ITG induce density peaking for neff<1 Data used for analysis

  13. Ln decreased with coherence. Coherence was higher for more peaked profile. Lt does not show any systematic trend with coherence Peaked Longer correlation Longer correlation Ln and Lt was estimated from two YAG points (r-0.15 and 0.5) indicated by arrow.

  14. Radial correlation shows clearer dependence on density peaking factor more than collisionality

  15. Particle flux is given by For steady state Density peaking Smaller Ln Enhancement of inward pinch Larger radial coherence Larger radial diffusion

  16. Outline • General comparison of density profile in JT-60U and in LHD • Density profiles and turbulence in JT-60U • Density profile and turbulence in LHD • Summary and Discussion • (Possibility of curvature pinch)

  17. Density profile of LHD changes from peaked to hollow. Change of density profile in N-NBI heated plasma at Rax=3.6m PNBI= Last closed flux surface Last closed flux surface These differences are not due to particle fueling but due to transport characteristics.

  18. Magnetic axis position changes density profile as well. Inward shifted Small magnetic helical ripple and reduced neoclassical transport Outward shifted Large magnetic helical ripple and enhanced neoclassical transport

  19. Density modulation experiments shows Dcore is anomalous, outward Vcore is comparable with neoclassical one (K.Tanaka FUSION SCIENCE AND TECHNOLOGY VOL. 51 JAN. 2007 97) Dedge Vcore Dcore 1.0 r 0.7 r Vedge 0.7 Dneo 1/n Plateau n*h Vneo is dominated by thermo diffusion.

  20. With increase of PNB, density pump out and increase of core turbulence were observed. 6MW 1MW Ne Ne Te Te

  21. Comparison between non linear GKV simulation and PCI measurement shows rough agreement. Preliminary r=0.6 r=0-0.7 kyri-0.3 kyrs-0.4 Measurement by 2dimensional phase contrast imaging (2D-PCI) Te/Ti-2, so, kyri-0.3 T.H. Watanabe, H.Sugama Non linear GKV simulation hi=3 Nucl. Fusion 47 (2007) 1383–1390 Further confirmation is necessary.

  22. Outline • General comparison of density profile in JT-60U and in LHD • Density profiles and turbulence in JT-60U • Density profile and turbulence in LHD • Summary and Discussion • (Possibility of curvature pinch)

  23. General formulation ( both for tokamak and stellarator/heliotron) of curvature pinch was developed (A. Mishchenko et al, POP 14,102308 (2007) The calculation is based on Isichenko’s model (M,B, Isichenko et al., Pjys. Plasma 3,1916 (1995)) It was assumed that the anomalous pinch is only curvature pinch and profile is in the steady state. Only trapped electron was taken into account (wb>>w) For large aspect ratio (r/R<<1) approximation, canonical density profile is given by For larger aspect ration, curvature pinch becomes smaller. Sign of lnq (positive for tokamak, negative for stellarator/heliotron ) change the profile peaked or hollow.

  24. Comparison between JT60-U density profile and curvature pinch model (data set of density scan) high density,low density Model Exp. Both exp. and model profile are peaked for higher density The modeled curvature pinch is not large enough to account for observed profile.

  25. Comparison between LHD density profile and curvature pinch model (data set of b scan) b=0.11%, b=1.0% Model Exp. Both exp. and model profiles are more peaked for lower b. Curvature pinch is not large enough. Neoclassical effect may be necessary.

  26. Summary I

  27. Summary II

  28. Neo classical ambipola condition predict weak positive Er field in core (r<0.5) before and after density pumping out. If this is correct, phase velocity increases to i-dia direction in plasma frame. This is against GLF23 prediction in tokamak. t=4.0sec Before pump out t=4.5sec After pump out • Are there different role between tokamak and helical plasma? • Are there different propagation direction between linear and non linear status? • Does larger contribution of neoclassical cause different role of turbulence? • Plasma poloidal rotation should be measured.

  29. Summary • Different collisionality dependence of density peaking was observed in JT-60U and LHD. • At Rax=3.5m with larger anomalous contribution, collisionality dependence of density peaking is similar to tokamak one (peaking factor increases with decrease of collisionality). • At Rax=3.6m with smaller anomalous contribution, collisionality dependence was opposite to Rax=3.5m and JT-60U. • With increase of NB power, density profile becomes more peaked in JT-60U. • Radial correlation becomes higher for more peaked density profile • With increase of PNB, density profile become hollow in Rax=3.6m of LHD. • Peak wavenumber did not change with low and high PNB. This suggests correlation length did not change. • Fluctuation power increased with increase of PNB. • Both in JT-60U and LHD, fluctuation characteristics changed for different density profiles. • In JT-60U, fluctuation may induce both diffusion and convection. • In LHD, fluctuation may induce diffusion, convection may be due to neoclassical process.

  30. Additional considerations are necessary. • 1. Qualitative tendencies were agreed both in JT-60U and LHD • i) Peaked profile for positive lnq in JT-60U and hollow profile for negative lnq. • ii) JT-60U; more peaked profile in smaller density (lower collisionality) • iii) LHD; more hollow profile in higher beta • 2. In both case, curvature pinch is not strong enough. • 3. Is situation really stationary? • Anomalous thermo diffusion should be considered in JT-60U • Neoclassical thermo diffusion should be considered I LHD.

  31. Larger fluctuation power induce larger diffusion according to quasi linear theory Density flattening Larger Ln Smaller V (V is reversed. This may casused by neoclassical process Larger fluctuation power Larger radial diffusion

  32. Shape of density profile does not require saturated level of fluctuation. <>a is averaged for trapped electron D0 is canceled out.

  33. What can we measure from correlation reflectometer? The interpretation of the reflectometer signal is not simple. The change of signal power does not represent fluctuation power (may indicate change of fluctuation power in some stage but sensitive to density gradient and curvature of the magnetic surface). In the present system, we looked correlation of the signal assuming signal correlation represent correlation of fluctuation.

  34. Density peaking factor increases with decrease of Ln. Cleaer tred is seen between peaking factor and neff(0.5) more than between peaking facotr and neff(0.35)

  35. In both tokamak and helical/stellarator, turbulence driven transport is important for density profiles. Therefore, it is essential to investigate characteristics of turbulence for different density profiles. from the measurements.Comparison study between turbulence and density profiles will give a god guidance for numerical simulation.

  36. The particularity of helical/stellarator is enhanced neoclassical transport in low collision regime tokamak helical/stellarator Future operation regime of reactor Future operation regime of reactor Experimental De,ce Experimental De,ce Around one order Around one order Neoclassical Transport coefficient Neoclassical Transport coefficient 1/n regime Banana regime Plateau regime Plateau regime nei nei Plateau regime 1/n regime S. Murakami Nucl. Fusion 42 (2002) L19–L22 In 1/n, neoclassical transport is minimum at Rax=3.53m In Plateau, neoclassical transport is smaller at more inward axis. Dneo/Dtokamak plateu Dneo/Dtokamak plateu Axis Position Axis Position Outward shifted Inward shifted Inward shifted Outward shifted

  37. Role of neoclassical transport in tokamak and heliotron/stellarator in low collisionality regime In tokamak , neoclassical effect (Ware pinch) is negligible in low collsionality regime In LHD, diffusion is anomalous but convection is comparable with neoclassical thermo-diffusion in certain configuration. ( K.Tanaka 2007 Fusion Sci. Tech. , K.Tanaka 2008 Plasma Fusion Research )

  38. More systematic trend was observed between Ln and coherence more than neff and coherence Radial coherence might be more essential parameter for density peaking more than neff.

  39. Core fluctuation may play role on density profile shaping.Most of fluctuation components exists in ITG/TEM unstable region Helical particular. Inward turbulence driven flux can be balanced with outward neoclassical Tokamak like. Turbulence transport produce peaked profile

  40. Strong magnetic shear helps as well. Measured by 2D detector Decomposed by FFT and MEM toroidal Propagation direction tells local field angle. Local field angle tells local position. Shear techniques was done by Truc on Tore Supra (RSI (1992)) and Kado on Heliotron E (JJAP (1996))

  41. Rax=3.5m →Peaked density profile Rax=3.6m→Peaked ~ hollow density profileRax>3,75m→hollow density profile Anomalous contribution becomes larger Vexp is comparable with Vneo. Both are minimum at Rax=3.5m Minimum Rax is different between experimental (~anomalous) and neoclassical diffusion coefficient→It is a contrast to energy confinement ceff∝1/te is minimum at neoclassical minimum. K. Tanaka et al., Journal of Plasma Fusion and Research 2008

  42. Rax=3.5m →Peaked density profile→stronger Te dependence of D Rax=3.6m→Peaked ~ hollow density profile→weaker Te dependence of D Dedge Dcore r 0.7

  43. Rax=3.5m →Peaked density profile→negative Te dependence of VcoreRax=3.6m→Peaked ~ hollow density profile→positive Te dependence of Vcore V Vcore r rv

  44. In LHD, anomalous and neoclassical contribution depends on magnetic configuration. The biggest configuration effect is magnetic ripple.Inward-> Smaller ripple, Outward -> larger ripple Diffusion; Anomalous contribution is larger at more inward shifted configuration. Convection; More or less comparable with neoclassical, but direction becomes inward against neoclassical prediction at more inward shifted configuration. Rax=3.6m was compared with JT-60U data

  45. At more outwardly Rax, neoclassical transport becomes larger and density profile becomes more hollow. Dneo 1/n Plateau n*h Larger neoclassical Smaller neoclassical

  46. Summary • Different collisionality dependence of density peaking was observed in JT-60U and LHD. • At Rax=3.5m with larger anomalous contribution, collisionality dependence of density peaking is similar to tokamak one (peaking factor increases with decrease of collisionality). • At Rax=3.6m with smaller anomalous contribution, collisionality dependence was opposite to Rax=3.5m and JT-60U. • With increase of NB power, density profile becomes more peaked in JT-60U. • Radial correlation becomes higher for more peaked density profile • With increase of PNB, density profile become hollow in Rax=3.6m of LHD. • Peak wavenumber did not change with low and high PNB. This suggests correlation length did not change. • Fluctuation power increased with increase of PNB. • Both in JT-60U and LHD, fluctuation characteristics changed for different density profiles. • In JT-60U, fluctuation may induce both diffusion and convection. • In LHD, fluctuation may induce diffusion, convection may be due to neoclassical process.

  47. Density profiles were scanned from scan of NB power Change of power spectrum suggest the change of fluctuation property.

  48. Ln decreased with coherence. Coherence was higher for more peaked profile. Lt does not show any systematic trend with coherence Ln and Lt was estimated from two YAG points (r-0.15 and 0.5) indicated by arrow.

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