Toroidal momentum transport in limited and diverted TCV Ohmic plasmas

1. Toroidal momentum transport in limited and diverted TCV Ohmic plasmas A.Bortolon, B.P.Duval, A.Scarabosio, A.Pochelon and the TCV team. Centre de Recherche en Physique des Plasmas, EPFL Association EURATOM

2. TCV toroidal rotation measurements CXRS (CVI 529.1 nm) • Czerny-Turner (f/7.5, 5.5Å/mm) • 2400 l/mm holographic grating • CCD front illuminated detector Diagnostic Neutral Beam Injector (H0) • Injection angle 11o • Extracted current 3A, acceleration voltage 50 kV • Injected power < 80 kW • 20-70% absorption (mainly on the electrons) • Configuration for the presented experiments: • 8 measurement points along minor radius • sample frequency ~ 10 Hz • integration time = 30 ms • typical uncertainty: ±2 km/s in the core ±5 km/s in the edge

3. Outline of the talk • Stationary regimes observed in Limited L-mode and Diverted L-mode • Description and modeling of rotation profile evolution in Limited L-mode and Diverted L-mode • Conclusions

4. Limited L-mode: stationary uj profile Ip=340 kA, d=0.3, k=1.4, Bj=1.4T Typically counter current rotation is observed(Scarabosio PPCF 2006) • Core region (r<rinv): convex uj(r) due to sawteeth (tST~ 5 ms) • Intermediate region (rinv<r<0.85): uj(r)  Ti(r) • Edge region (r>0.85): uj(r)  0

5. Limited L-mode: stationary uj profile Ip=340 kA, d=0.3, k=1.4, Bj=1.4T Typically counter current rotation is observed(Scarabosio PPCF 2006) • Core region (r<rinv): convex uj(r) due to sawteeth (tST~ 5 ms) • Intermediate region (rinv<r<0.85): uj(r)  Ti(r) • Edge region (r>0.85): uj(r)  0 • For ne0>6x1019 m-3and Ip>290kA • co-current rotation profile • (Bortolon PRL 2006) • Similar core velocity uj0~10-15 km/s • Same effect of sawtooth • Reverse gradient • Similar uj(0.85)

6. ne Diverted L-mode: stationary uj profile 2 regimes observed Stationary profile in shot by density scan Ip=250kA, d=0.5, k=1.6 Lower Single Null, Bj>0 • ne0>6x1019 m-3 hollow profile • ne0<6x1019 m-3 peaked profile • Rigid shift of profile with density • Large variation of uj(0.85) with ne

7. Rotation profile reverses (but at different densities) Different edge behavior for changing B ion drift direction ne Diverted L-mode: stationary uj profile (2) Ip<0, Bj<0, LSN, FAV Ip>0, Bj>0, LSN, UNFAV

8. Diverted L-mode: edge uj dependence on ne • uj(0.85) decreases with ne • 10 km/s offset between FAV and UNFAV configurations • saturation of uj(0.85) at low density for FAV uj(0.85) independent on the core rotation regime

9. Outline of the talk • Stationary regimes observed in Limited L-mode and Diverted L-mode • Description and modeling of rotation profile evolution in Limited L-mode and Diverted L-mode • Conclusions

10. Limited L-mode: uj profile evolution Ip=340 kA, d=0.3, k=1.4, Bj=1.4T Rotation inversion obtainedwith a density ramp at Ip=const

11. Limited L-mode: uj profile evolution Ip=340 kA, d=0.3, k=1.4, Bj=1.4T Rotation inversion obtainedwith a density ramp at Ip=const • Core accelerates rigidly • Transient cnt-acceleration of the edge • Momentum conservation dynamic followed by edge dissipation

12. Diverted L-mode: uj profile evolution Ip=250 kA, d=0.5, k=1.6, Bj=1.4T For low ne stationary profile is reached 250 ms after the divertor formation. LIM. DIV.

13. Diverted L-mode: uj profile evolution Ip=250 kA, d=0.5, k=1.6, Bj=1.4T For low ne stationary profile is reached 250 ms after the divertor formation. LIM. DIV. • Inversion of rotation profile • Counter edge acceleration • Inward momentum flux

14. Model description 1D cylindrical model used to simulate inversions to co-current regime • D(r) = constant • GND(r): • for r<rinv • GND= GST<0, accounts for sawteeth effect • for r>rinv • GND = G1>0 before inversion • GND = G2<0 after pinch like term(not v·uj convection) G1 G2 Gb.c.(0.85) = -k [ uj(0.85) – uj,stat.]edge dissipation, determining dynamic of the total momentum variation

15. Sawteeth regulated region Flow flux inversion region Model results: inversion in limited L-mode • Reasonably good agreement • Main features are matched: • Stationary profiles before and after inversion • Rigid core acceleration • Inversion timescale • Transient counter acceleration of the edge • Fit parameters: • D = 0.25 m2/s >100 D,Neo • G1 = +6.3×104 m2/s2 • G2 = -7.3×104 m2/s2 • GST = -4.3×104 m2/s2 • uj,stat = -4 km/s • kb.c. = 6 m/s

16. Sawteeth regulated region Mom. flux inversion region Model results: inversion in diverted L-mode • Reasonably good agreement • Main features are matched: • Stationary profiles before and after inversion • Rigid core acceleration • Inversion timescale • Transient counter acceleration of the edge • Fit parameters: • D = 0.20 m2/s >100 D,Neo • (G1 = +3.2×104 m2/s2) • G2 = -3.7×104 m2/s2 • GST = -2.7×104 m2/s2 • uj,stat = 8.3 km/s • kb.c. = 3 m/s

17. Conclusions • Intrinsic rotation observed in Ohmic L-mode • Limited L-mode (2 regimes) • Low density counter current • High density co-current • Edge velocity fixed at slightly negative values • Diverted L-mode (2 regimes) • Low density co-current • High density counter current (limited behavior) • Edge velocity varies with density and acts as boundary condition • Co-current regimes can be sustained by non diffusive fluxes in intermediate region of profile

18. Future • 3 regions interpretation scheme: no model for the underlying physics • Core region: sawteeth • ECH for sawteeth modification effects • Edge region: physics of boundary condition • effect of plasma shape • parallel SOL fluxes, neutrals friction • Intermediate region: non diffusive fluxes • which mechanisms can provide the non diffusive fluxes with the required dependecies?