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Rotation inversion vs density and current, in limited and diverted L-mode plasmas on C-MOD

Rotation inversion vs density and current, in limited and diverted L-mode plasmas on C-MOD. Presentation, bpd. Basil P. DUVAL, Alessandro Bortolon Centre de Recherches en Physique des Plasmas, EPFL J. Rice, A. Ince-Cushman, B. LaBombard et al. MIT. Introduction…Polemic ?.

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Rotation inversion vs density and current, in limited and diverted L-mode plasmas on C-MOD

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  1. Rotation inversion vs density and current, in limited and diverted L-mode plasmason C-MOD Presentation, bpd Basil P. DUVAL, Alessandro Bortolon Centre de Recherches en Physique des Plasmas, EPFL J. Rice, A. Ince-Cushman, B. LaBombard et al. MIT

  2. Introduction…Polemic ? • Intrinsic Rotation- Absence of External Torque-Is this closer to the ITER situation ? (Doyle et al 2007 ?) • Passive measurement (as far as our efforts are concerned) • TCV-DNBI… MIT- passive spectroscopy… Others ? • Other Definitions… Are these closer to ITER ? • Balanced Torque (DIII-D…) • Modulated Torque (JT60, JET) • Assuming you know everything.. (Fast Ions… ICH… ECH…) • Methods rely on • Knowing torque • Torque not affected by heating, braking, shaping….

  3. Goal- Can you see reversal elsewhere? • Use C-Mod’s rotation profile diagnostics to reproduce the TCV rotation scaling and reversal observations • Extend the published C-Mod data to lower plasma densities to seek correspondence with TCV data • If successful, see if any of the C-Mod diagnostics can provide some further clues in indentifying the momentum generation and transport mechanisms for rotation reversal… • Central Rotation with multichord X-ray spectroscopyEdge Rotation with DNBIHFS working gas rotation with GasJet

  4. TCV- Slightly increase ne: Velocity Inversion Ip=340 kA, d=0.3, k=1.4, Bj=1.4T Counter-Current rotation observed • Core region (r<rinv):convex uj(r) from sawteeth (tST~ 5 ms) • Intermediate region (rinv<r<0.85): uj(r)  Ti(r) • Edge region (r>0.85): uj(r)  0 #28355 qe~3.4 For ne0>6x1019 m-3and Ip>290kA Co-Current rotation profile • Similar core velocity uj0~10-15 km/s • Similar sawteeth effect (still “bulged” in the co-current direction) • Similar uj(0.85) • Small change in Te and Ti profiles A. Bortolon et al, Phys. Rev. Lett. 97, 235003 (2006)

  5. Résumé of TCV observations • L-mode discussed here • Configuration: Limited Counter-Current toroidal rotation Diverted Co-Currenttoroidal rotation • Max toroidal velocity scales linearly with Ti and 1/Ip.Ip scaling partially due to toroidal profile flattening in core by sawteeth. • Toroidal velocity “reversal” events observedLimited Counter -> CoDiverted Co -> Counter, with increasing density • Toroidal rotation inversions when qe approaches ~3 (limited configurations) • 3 zones: (more about this next time….)Core – flat toroidal profile within sawtooth inversion radiusIntermediate zoneEdge Zone: Limited ~0 km/s, Diverted freer to evolve

  6. C-Mod results 2005 (Diverted)

  7. Time-line • Velocity “reversal” a severe conundrum for theory- see Diamond, Peeters, Hahm, Gurcan, Callen…. • Following APS07, suggested trying to reproduce TCV results on C-MOD • Finally accepted for operation in Feb 2008 • Scheduled ITPA- one session May 2 2008 (morning !) • One session, 12 discharges (12:30 Boston time), then PS-failure until the end of the day- (we call this research) • Goal Kappa ~1.5, Delta ~0.4, q~3 (see Duval et al POP-2008 & EPS 2008) • (Breakdown at 5T, q~3 (Bphi 3T) only reached @ 0.8s)

  8. Shot-Plan • Discharges 1080502#004 -010 Diverted-Lower, qedge ~3.2, Bphi 3T (breakdown @5T, 3T only @0.5s) • Nothing really happened- Core rotates Co-current, decreasing with core density (Ne-av 1.2-0.3 e20) • Moved to limited (same kappa ~1.5, Delta ~0.4) • Density too high (1.1e20) • Lower slowly, finally reached low enough densities (much more difficult than for diverted configurations)

  9. Limited results

  10. Reconstruction (EFIT)

  11. Rotation (Only From X-ray (Ar))

  12. Core Rotation, decreasing ne Even Lower ne, transition absent ! Change in core rotation observed Lower ne, transition later

  13. Compare with TCV-results • As on TCV • “transition” depends V .Strongly on Density • Edge rotation does not change much • Toroidal rotation changes inside q~1.5 • Even at 3T, density at transition is not far from that seen on TCV • However ! • Rotation goes more “co-current” with decreasing Density • If we can believe zero-reference (from discharge #1080502003 with an induced locked-mode), not symmetrical across Vphi=0 • Their definition of “limited” and “diverted” may require some complementary TCV experiments (lift config off central column)

  14. So… • Really Promising ! • Analysis still very rudimentary- Hope to complete a more detailed analysis before end of 2008- • Bphi, as for TCV, does not appear to have too strong an effect.. • Can we operate at 5T ?

  15. Full Bphi (5T) #1080520026

  16. EFIT Bphi (5T) #1080520026

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