rotation inversion vs density and current in limited and diverted l mode plasmas on c mod
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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

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

introduction polemic
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….
goal can you see reversal elsewhere
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
tcv slightly increase ne velocity inversion
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)

r sum of tcv observations
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
time line
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)
shot plan
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)
core rotation decreasing ne
Core Rotation, decreasing ne

Even Lower ne, transition absent !

Change in core rotation observed

Lower ne, transition later

compare with tcv results
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)
slide14
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 ?
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