Curvature transition and spatiotemporal propagation of internal transport barrier in toroidal plasmas

Transcription

1 Curvature transition and spatiotemporal propagation of internal transport barrier in toroidal plasmas K.Ida, JT- Team a and LHD experiment Group National Institute for Fusion Science, Toki Japan a) Japan Atomic Energy Agency, Naka, Ibaraki-ken, , Japan 1 st Asia-Pacific Transport Working Group (APTWG) meeting National Institute for Fusion Science 15 June 11

2 OUTLINE 1 Introduction : why curvature? spatiotemporally propagating? Curvature transition of ITB region (experimental & model) 3 spatiotemporally propagating of ITB (experimental & model) Summary

3 Why curvature? and why spatiotemporally propagating? 1 Why the curvature of ITB is important? If the transport is governed by the simple ExB turbulence suppression model, Ti profile in the ITB region should have significant curvature to have enough Er shear, because ω ExB ~ T i and (ω ExB ) ~ T i. Curvature is important parameter in understanding the transport improvement. Why the spatiotemporally propagation of ITB is important. If the transport is governed by the simple local ExB turbulence suppression model, the ITB region never propagates in space unless background (such as q-profile) is changed. spatiotemporally propagating of ITB front is a key of issue in the transport barrier formation Ti Er Simple model Ti q No curvature ITB is inconsistent with the concept of ω ExB turbulence suppression experiment Ti q

4 Modulation CXRS for curvature measurements T i (kev) 1 8 (a) time(sec) T i (kev) R(m) <R> (b) 3.5m 3.5m 3.79m 3.7m (c) <R>= 3.5m NBI gap for background time (sec) subtraction K.Ida et. al., Rev Sci Instrum 79 (8) m 3.71m 3.788m 3.815m 3.8m 3.87m T i (kev) poibts measurements every 5ms

5 Concave and Convex ITB transtion 1 8 t =.-.9s (a) dt i /dr (kevm -1 ) The transition to convex shaped ITB is spontaneous without any change in q- profiles suggest the change in transport not the movement of ITB location weak concave ITB t =.s t =.s strong convex ITB...8 d T i /dr (MeVm - ) weak concave ITB.s.s strong convex ITB...8 K.Ida Phys. Rev. Lett. 11 (8) 553 T i (kev) T e (kev) q 8 t =.-.9s t =.s t =.s t =.5s t =.s (b) (c)

6 Spontaneous non-local phenomena in the ion-itb plasma Increase of T near foot point ( =.7) and decrease of T near shoulder (=.53) take place simultaneously Transition from concave-shaped ITB to convex-shaped ITB Concave ITB foot unclear (shoulder clear ) Convex ITB foot clear (shoulder unclear) χ i (m /s) 5 3 coherence.8... slice A slice B. 1 f(khz) weak concave ITB (time slice A) δr= 3 i strong convex ITB (time slice B) 1 δr = 15 i ITB foot (1/a)dT i /d (kev m -1 ) Q i /n e (kev m s -1 ) χ i (m s -1 ) T i (kev) (b) (c) 1 t =5.775s t =5.78s (a) =.7 weak concave ITB =.7 =.53 weak concave ITB =.7 A t =5.85s n e (1 19 m 3 ) transition transition strong convex ITB =.53 strong convex ITB =.53 B weak strong concave ITB transition convex ITB time (sec) 5.85 t =5.85s

7 Possible picture of curvature transition Theoretical model : Transport flux landscape, in position-gradient Space P.Diamond Phys. Rev. Lett, 78 (1997) 17. Flux shoulder Concave ITB space gradient foot constant-γ contours Convex ITB gradient Good confinement region poor confinement region shoulder space foot K.Ida Phys. Rev. Lett. 11 (8) 553

8 Ion ITB in LHD plasmas ITB region expands inward in time The normalized ion temperature gradient exceeds 1, which is equivalent to that in the weak ITB in tokamak K.Ida et. al., Nucl. Fusion 9 (9) 95 Pivot point exists in the ion temperature profile

9 Ion ITB plasmas with positive and negative shear in JT-U positive shear Negative shear Positive shear ITB location moves outward with expanding Negative shear ITB location moves outward with localizing K.Ida et. al., Nucl. Fusion 9 (9) 95

10 reff/a spatiotemporally propagating transport barriers LHD ITB region 3 9keV/m The ITB front propagates inward in the Ion ITB in LHD. However, the ITB front propagates outward in the Ion ITB in JT-U. r/a..8.. ITB front Time(s) JT-U positive magnetic shear ITB front ITB rear dt/dr (kev/m) The ITB rear also propagates outward in the Ion ITB in JT-U. r/a JT-U negative magnetic shear.8.. ITB front qmin ITB rear dt/dr (kev/m) Time(s) Time(s)

11 Dynamic model of spatiotemporally propagating transport barriers Transport (Flux gradient relation) T gradient Fluctuation intensity Heat Flux Turbulence flow relation generation flow suppression shear Fluctuation intensity P.Diamond Phys. Plasmas (1995) 385 Fluctuation intensity Extension to non-local fluctuation model Turbulence energy flux Flow shear magnitude Flow shear flux gradient Barrier propagates inward Space structure determining relation Local relation Barrier front propagation observed can be understood by this model

12 Summary Key concept of non-local transport 1 Continuity of flux gradient relation (turbulence) in space Radial flux of fluctuation intensity Experimental observation 1 Curvature transition The curvature transition between the convex and concave shape ITBs is observed. The curvature transition can be understood by the transport flux landscape model which is based on the smooth flux gradient relation (turbulence) in space. The mechanism of the deformation of transport flux landscape is not well understood. Spatiotemporally propagating transport barriers The ITB region is propagating during the formation phase of ITBs, regardless the a_min location (although it stops at the q_min location). The propagation of barrier front can be understood by the spatiotemporally propagating transport barriers model, by introducing the radial flux of fluctuation intensity and velocity shear. Further understanding is necessary for the propagation of barrier rear. Please visit to see references