BO Non-Local Heat Transport, Rotation Reversals and Up/Down Impurity Density Asymmetries in Alcator C-Mod Ohmic L-mode Plasmas. J.E.

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1 BO7-5 Non-Local Heat Transport, Rotation Reversals and Up/Down Impurity Density Asymmetries in Alcator C-Mod Ohmic L-mode Plasmas J.E.Rice with thanks to Plasma Science and Fusion Center, MIT M.L.Reinke, C.Gao, N.T.Howard, Y.A.Podpaly, M.J.Greenwald, J.L.Terry, M.Chilenski, P.C.Ennever, D.Ernst, C.L.Fiore, R.S.Granetz, A.E.Hubbard, J.W.Hughes, J.H.Irby, Y.Ma, E.S.Marmar, M.Porkolab, N.Tsujii, A.E.White, S.M.Wolfe, C-Mod Team H.J.Sun SWIP P.H.Diamond, I.Cziegler CMTFO UCSD R.M.McDermott, C.L.Angioni IPP Garching L.Delgado-Aparicio, D.Mikkelsen PPPL W.L.Rowan IFS UT B.P.Duval, A. Bortolon EPFL APS Providence Oct. 29, 212

2 Motivation Several long-standing mysteries: Up/down impurity density asymmetries J.L.Terry et al., Phys. Rev. Lett. 39 (1977) Ohmic energy confinement saturation A.Gondhalekar et al., 7th IAEA (1978) Vol.I 199. Non-local heat transport K.Gentle et al., Phys. Rev. Lett. 74 (1995) 362. Rotation reversals A.Bortolon et al., Phys. Rev. Lett. 97 (26) electron transport dominated Outline Cold pulse propagation and connection to rotation reversals Relation with / transition, up/down impurity asymmetries Associated turbulence changes during reversals Discussion, role of ν * τ E (ms) τ 89-P 5.2 T.81 MA neo-alcator n e (1 2 )/m 3 : linear Ohmic confinement : saturated Ohmic confinement (L-mode scaling) Rotation velocities, impurity densities and T i from imaging x-ray spectrometers Cold pulses from LBO CaF 2 injection No external momentum sources Ohmic plasmas only

3 Comparison of Non-local and Local Heat Transport (1 2 /m 3 ) Below a critical collisionality in, cold pulse propagation is non-diffusive, core rotation is co-current and impurity density profiles are up/down symmetric core edge V Tor () electron density (1 2 /m 3 ) Above a critical collisionality in, cold pulse propagation is diffusive, core rotation is counter-current and impurity density profiles are up/down asymmetric core edge V Tor () electron density 2.5 edge (r/a~.9) up/down impurity brightness ratio t (s) edge (r/a~.9) up/down impurity brightness ratio t (s)

4 Is the core rise in due to a transient drop in χ e or evidence of a heat pinch? (1 2 /m 3 ) Repetitive cold pulses Chi Gao Poster JP8.8 Tuesday Afternoon electron density core ln[amplitude(ev)] Fourier analysis indicates a rise in amplitude inside of the inversion radius, suggestive of a heat pinch. 1 Hz phase (deg) edge t (s) R (m)

5 Cold Pulse Temperature Flex Point and Rotation Reversal Anchor Point Similar temperature profiles before and during cold pulse. R/L Te changes from 11.5 to 14.. R/L Ti changes from 5.9 to 8.2. T i profile develops more slowly. 3 r/a Comparison of and velocity profiles. Rotation anchor point close to flex point in. r/a s cold pulse at 1. s.7x1 2 /m s T i 1.3 s V Tor 1.99 s.9x1 2 /m s R (m) R (m)

6 (ms) (%) Rotation Reversal, / Transition, Non-Local Heat Transport and Up/Down Impurity Density Asymmetry All Related For.8 MA, reversal and non-local transition at exact same density. τ e 5 non-local -5 change at R =.78 m -1 1 co -1 V Tor () R/L 4.5 n (.79 m) local counter 2. up/down edge z brightness ratio n e (1 2 /m 3 ) (ms) (1/keV 2 ) At / transition, /T i ~, Z/T 2 ~.8 for.8 MA. τ I T i /T i Z eff Z/T n e (1 2 /m 3 )

7 Scalings of Critical Densities and Characteristic Radii with Plasma Current Critical densities for temperature inversion, rotation reversal, / transition and up/down impurity asymmetries scale similarly with plasma current. n x q = const. Rotation reversal anchor points and temperature flex points located just inside of q =3/ inv.7 rot rev.82 q=3/2 (EFIT) 1. /.6 (1 2 /m 3 ).8.6 up-down asymmetry R (m).8.78 inv rot rev.5 r/a critical densities /q q=1 (EFIT) /q 95.3

8 Turbulence Characteristics Very Different in and.99x1 2 /m 3 Core density fluctuations from PCI. J.E.Rice et al., Phys. Rev. Lett. 17 (211) x1 2 /m 3 6 Difference between and 5 5 Frequency (khz) = Frequency (khz) 2 Frequency (khz) k R (cm -1 ) Edge density fluctuations from GPI k R (cm -1 ) k R (cm -1 ) k θ ρ s up to1 TEM? Edge turbulence propagation direction reverses at / transition. Significant fluctuations seen in (previous talk)

9 Rotation Reversals, / Transition, Non-Local Heat Transport, Density Profile Peaking and Up/Down Impurity Density Asymmetries Correlated Pieces of the puzzle have been around for many years: / transition occurs at a critical density A.Gondalekar et al., Proc. 7th IAEA Conf., Innsbruck (1978) which depends on current Y.Shimomura et al., JAERI-M Report 87-8 (1987) and is correlated with turbulence changes. R.L.Watterson et al., Phys. Fluids 28 (1985) Non-local heat transport K.W.Gentle et al., Phys. Rev. Lett. 74 (1995) 362. occurs below a critical density. P.Mantica et al., Phys. Rev. Lett. 82 (1999) 548. Density profile peaking saturates at / transition. C. Angioni et al., Phys. Plasmas 12 (25) 471. Up/down impurity density asymmetries seen at low density. J.L.Terry et al., Phys. Rev. Lett. 39 (1977) Rotation reversal is the most sensitive indicator of the / transition: Rotation reversals occur at a critical density A.Bortolon et al., Phys. Rev. Lett. 97 (26) which depends on q 95 and is associated J.E.Rice et al., Nucl. Fusion 51 (211) 835. with turbulence changes and the / transition. J.E.Rice et al., Phys. Rev. Lett. 17 (211) 2651.

10 Is Collisionality ν * the Determining Parameter? at q=3/2 surface Machine size scaling of / density 1.62 MA V Tor () V Tor () 1. MA density at confinement saturation (1 2 /m 3 ) FT C-Mod TCV TEXT JFT-2M 1/R T < q < 3.8 ASDEX, AUG Tore Supra DIII-D JT ν * ν * =.18 n e q R Z eff / 2 ε 3/2 ~ nqr = const. J.E.Rice et al., Phys. Plasmas 19 (212) Unifying ansatz: R (m) low collsionality,, co- rotation, TEM turbulence, non-local heat transport, peaking density profiles high collisionality,, counter- rotation, ITG turbulence, diffusive heat transport, stable density profiles JET

11 Conclusions and Discussion Non-diffusive, non-local heat transport has been observed below a critical density. profile flex point coincides with the rotation reversal anchor point, inside of the q = 3/2 surface. Critical densities for inversion, rotation reversal and / transition are very close. Critical densities for inversion, rotation reversal, / transition and up/down impurity density asymmetries scale with 1/q. Reversals from the co- to counter-current direction are correlated with a sharp decrease in core density fluctuations with 2 cm -1 < k θ < 11 cm -1 and frequencies above 7 khz. Propagation direction of edge turbulence switches at / transition. Unifying ansatz: At low collisionality, in the regime, the rotation is co-current, TEMs dominate, heat transport is non-local, density profiles peak and impurity density profiles are up/down symmetric. At high collisionality, in the regime, the rotation is counter-current, ITG modes dominate, heat transport is diffusive, density profile peaking saturates and impurity density profiles are up/down asymmetric. The transition occurs at a particular collisionality, near ν * ~.4. Save Alcator C-Mod: