toroidal momentum transport in limited and diverted tcv ohmic plasmas

Alessandro Bortolon 12th ITPA 2007 Lausanne 8 May 2007 1/18

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


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


Outline of the talk

• Stationary regimes observed

in Limited L-mode and Diverted L-mode

• Description and modeling of rotation profile evolution


• Conclusions


Limited L-mode: stationary u profileIp=340 kA, =0.3, =1.4, B=1.4T

Typically counter current rotation is observed(Scarabosio PPCF 2006)

• Core region (<inv): convex u(r) due to

sawteeth (ST~ 5 ms)

• Intermediate region (inv<<0.85): u Ti()

• Edge region (>0.85): u


Limited L-mode: stationary u profile

For ne0>6x1019 m-3 and Ip>290kAco-current rotation profile

(Bortolon PRL 2006)• Similar core velocity u0~10-15 km/s• Same effect of sawtooth• Reverse gradient• Similar u(0.85)

Typically counter current rotation is observed(Scarabosio PPCF 2006)

• Core region (<inv): convex u(r) due to

sawteeth (ST~ 5 ms)

• Intermediate region (inv<<0.85): u Ti()

• Edge region (>0.85): u

Ip=340 kA, =0.3, =1.4, B=1.4T


Diverted L-mode: stationary u profile

2 regimes observed

nn

ee

• ne0>6x1019 m-3 hollow profile

• ne0<6x1019 m-3 peaked profile

• Rigid shift of profile with density

• Large variation of u(0.85) with ne

Stationary profile in shot by density scan Ip=250kA, =0.5, =1.6

Lower Single Null, B>0


Diverted L-mode: stationary u profile (2)

• Rotation profile reverses (but at different densities)• Different edge behavior for changing B ion drift direction

IIpp>0, B>0, B>0, LSN, UNFAV>0, LSN, UNFAV IIpp<0, B<0, B<0, LSN, FAV<0, LSN, FAV

nnee


Diverted L-mode: edge u dependence on ne

• u(0.85) decreases with ne

• 10 km/s offset between

FAV and UNFAV

configurations

• saturation of u(0.85) at low

density for FAV

u(0.85) independent on

the core rotation regime


Outline of the talk

• Stationary regimes observed


• Description and modeling of rotation profile evolution


• Conclusions


Limited L-mode: u profile evolution

Rotation inversion obtainedwith a density ramp at Ip=const

Ip=340 kA, =0.3, =1.4, B=1.4T


Limited L-mode: u profile evolution

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

Ip=340 kA, =0.3, =1.4, B=1.4T


Diverted L-mode: u profile evolution

For low ne stationary profile is reached 250 ms after the divertor formation.

LIM. DIV.

Ip=250 kA, =0.5, =1.6, B=1.4T


Diverted L-mode: u profile evolution

For low ne stationary profile is reached 250 ms after the divertor formation.

• Inversion of rotation profileInversion of rotation profile• Counter edge acceleration

Inward momentum flux

LIM. DIV.

Ip=250 kA, =0.5, =1.6, B=1.4T


Model description

• D(r) = constant

• ND(r):

– for r<rinv

• ND= ST<0, accounts for sawteeth effect

– for r>rinv

• ND = 1>0 before inversion

• ND = 2<0 after

NDd

duD

1D cylindrical model used to simulate inversions to co-current regime

pinch like term(not v·u convection)

0dt

du

1

2

b.c.(0.85) = -k [ u(0.85) – u,stat.]edge dissipation, determining dynamic of the total momentum variation


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

Flow flux inversion Flow flux inversion regionregion

Sawteeth Sawteeth regulated regulated

regionregion

Fit parameters:– D = 0.25 m2/s >100 D,Neo

– 1 = +6.3×104 m2/s2

– 2 = -7.3×104 m2/s2

– ST = -4.3×104 m2/s2

– ustat = -4 km/s

– kb.c. = 6 m/s


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

Mom. flux inversion Mom. flux inversion regionregion

Sawteeth Sawteeth regulated regulated

regionregion

Fit parameters:– D = 0.20 m2/s >100 D,Neo

– (1 = +3.2×104 m2/s2)

– 2 = -3.7×104 m2/s2

– ST = -2.7×104 m2/s2

– ustat = 8.3 km/s

– kb.c. = 3 m/s


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


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?

toroidal momentum transport in limited and diverted tcv ohmic plasmas

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