10th itpa tp meeting - 24 april 2006 - a. scarabosio 1 spontaneous stationary toroidal rotation in...

10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio1

Spontaneous stationary toroidal rotation in the TCV tokamak

A. Scarabosio, A. Bortolon, B. P. Duval, A. Karpushov and A. Pochelon

10th ITPA TP Group Meeting


Layout of the talk

• Stationary toroidal rotation in H-mode

- Ohmic regime with small and frequent ELM’s

- ECH heated H-mode with large ELM

1 A. Scarabosio et al., Plasma Phys. Control. Fusion 48 (2006) 663–6832 A. Bortolon et al., to be submitted to PRL

• The DNBI and CXRS diagnostic on TCV

- The effect of the DNBI on toroidal rotation

• Stationary toroidal rotation in limited ohmic L-mode:1

- Plasma current scan and effect of sawteeth- Density dependence, basic scaling and Ti-v similarity- Comparison with neoclassical predictions- Inverted rotation regime at high Ip and ne

2


The TCV DNBI-CXRS system


CXRS: the TCV rotation diagnosticDoppler shift of CVI 529 nm charge exchange recombination line is measured

Diagnostic Neutral Beam Injector (H0)• Extracted current 3A, acceleration voltage

50 kV

• Injected power < 80 kW (20-70% absorbed)

• Small injection angle: 11.25º

Monochromator• Czerny-Turner (f/7.5, 5.5Å/mm) • 2400 l/mm holographic grating• CCD front illuminated detector

Magnetic axisis moved verticallyto change radial coverage


TCV parameters and conventions

• Plasma height max. 1.44m

• Plasma width max. 0.48m

• Plasma major radius0.875m

• Plasma current1.2MA

• Plasma elongation max. 3

• Aspect ratio3.6

• Toroidal magnetic field max.1.43T


CXRS signals analysisCharge exchange background subtraction by means of DNBI modulation

• Typical uncertainty: ±2 km/s in the core ±5 km/s in the edge

Standard set up:tNBI pulse=tint = 30 ms sample rate 90 ms(It may reduced to 45 ms)

• Wavelength calibration from reference Ne spectrum (Ne lamp) after each shot.


The effect of the DNBI on rotation

• 1-2 km/s beam induced velocity for 30 ms beam pulse length

• Simple 3 three forces one-dimensional model:

• Exponential solution with characteristic time on~ off~60-80 ms

NBIplasma FFdt

d

vv

• Experiments with 180 ms NBI pulse length

• Sawtooth precursors frequency is modulated by the neutral beam!

• Max. excursion of ~1 kHz 6 km/s


Spontaneous rotation in limited L-mode ohmic plasmas


Plasma current scan: typical exp.

qE = 2.4 - 8Ip =-350 - +320 kA<ne> =1.4 - 71019 m-3

= 1.15 - 1.5 = -0.4 - 0.4Te = 500 -1600 eVTi = 150 - 700 eVp = 0.2 - 1li = 0.8 - 2

Database of ohmic limited L-mode

• Very basic experiments in steady state condition and ohmic limited L-mode regime

• Average over several profiles (~10) to minimize errors

• No simultaneous high ne

and low qE!

# 27098


Plasma current scan: rotation profiles

• Counter-current carbon rotation also confirmed by MHD spectroscopy.(electron diamagnetic drift) ofseveral tens of km/s

• Central rotation increases withqE.

• Peak profile in the outer regionand flat or hollow central profile.

• Knee in profiles correlates withposition of the sawtooth inversion radius from SXR.

• Expected (from neoclassical theory) deuterium rotation (dashed lines) differs significantly in the low current case


Negative plasma current scanNegative current scan Comparison positive-negative Ip

• co-current rotation (ion diamagnetic drift) with similar velocities and profile shape with respect to Ip>0

qE~6

• Same profile within the errors:

- same absolute rotation velocity in the core plasma.

- some difference in outer part profile (not due to the beam!

- radial shift of ~1cm (ex. error in equilibrium reconstruction) can explain difference in outer

region (>0.4)

# 27098

# 27484


Edge profiles with Zaxis scan

• By varying (from shot to shot) the axis vertical position we get the edge rotation profile too!

• Data consistent with

being a flux function

• Inverted (co-current) edge rotation =+3 km/s as suggested by current scan experiments (but large error bar!!)

qE=4.4ne=2.5


Sawteeth flatten core rotationRotation profiles response to a flattened current profile by off-axis ECH

# 27677

• Rotation profile peaks when inv is reduced

• 500 kW of off-axis ECH power.

• The temperature and current profiles flattened inv from 0.35 to 0.15.


v-Ti similarity

# 27098 • Strong similarity (same gradient) between the rotation and temperature profile from CXRS outside inv.


Scaling law of toroidal rotation

• v,Max (~v(inv)) scales linearly with the plasma current and ion temperature

• Averaged values on steady state discharges

• For qE3.2 deviate from this scaling

v,Max [km/s]=-12.5 Ti,0/Ip [eV/kA]


Neoclassical prediction: effect of Er

Er and diamagnetic contribution• Neglecting E

1:

1,//,/1 ,2,1, OKnTrnTL Ii

nT

• In this configuration TCV rotation dominated by EB flow

1Kim Y B et al 1991 Phys. Fluid B 3 2050–60


Neoclassical prediction

0 r

• In neoclassical theory the radial angular momentum flux has a diffusive part (velocity gradient) and a non-diffusive part related with gradients in plasma parameters.1,2

1Catto P J and Simakov A N 2005 Phys. Plasmas 12 0125012Wong S K and Chan V S 2005 Phys. Plasmas 12 092513

• The steady state condition in absence of external momentum input:


Spontaneous rotation in limited L-mode ohmic plasmas (2)

High density- high current plasma

A new rotation regime


Inverted core rotation at high Ip and ne

0 0.2 0.4 0.6 0.8 1

-20

0

20

vi profiles

km/s

3

4

5

6

7

8x 10

19

ne0 [

m-3

]

Rotation inversion shot #28355

0.6 0.8 1 1.2 1.4 1.6 1.8

-10

0

10

v i0 [

km/s

]

t [s]

coreedge

• t = 1.1s (ne0 = 6x1019 m-3)carbon toroidal velocity flips from -12 to +12 km/s

• change in toroidal rotation also observedon MHD mode rotation frequency

Ip ~ 340 kA, qe ~ 3.5

• see next presentation of A. Bortolon for details!

Low ne or low Ip counter-current rotation

High ne and high Ip core co-current rotation


Spontaneous rotation in H-mode ohmic and ECH plasmas


Toroidal rotation in ohmic H-mode

• Ohmic, diverted H-mode with frequent ELM’s. (Ti(0.6)=600 eV, q95=2.5)

• Standard H-mode at Zaxis=20 cm limited radial coverage

• Co-current rotation in the observed region

• Only outer region available no core rotation measurements


Toroidal rotation in ECH H-mode

• Central X3 ECH increases stored energy. Ti(0.6)~1000 eV!!

• New ELM regime, less frequent but more energy released.

• Co-current rotation increases with stored energy and Ti

• MHD mode rotation frequency confirms co-current rotation


Conclusions• Carbon toroidal rotation, with negligible external input

(spontaneous), is routinely measured in TCV L-mode and recently in H-mode discharges.

• Toroidal rotation shows a rich phenomenology:1. Counter-current rotation in limited L-mode at low

ne or Ip

2. Core co-current rotation in limited L-mode at high ne and high Ip

3. Co-current rotation in ohmic and ECH heated H-mode (core and edge)

• Similarity between v and Ti (in L-mode v [km/s]=-12.5Ti/Ip [eV/kA]

• Neoclassical predictions of radial flux of angular momentum does not agree with L-mode TCV data (H-mode??)


Directions of future researches

• Effect of divertor on edge and core plasma rotation• Central rotation in H-mode plasmas• Establish a scaling law for H-mode plasmas• Study toroidal rotation in plasmas with ITB’s

• Up-grades of the DNBI - New arc source (full energy fraction 60 → 85%)- Reduced beam divergence (0.8 → 0.5 degrees )- A/P ratio increased by a -factor of 2.5-3 without increasing deposited power

• Up-grades of CXRS:- New back illuminated CCD detector (QE X4)

- New bundle of optic fibers (8 to 20 measurement points)

• New vertical CXRS view to measure poloidal rotation is under commissioning

Hardware improvements

Physics issues


Extra slides


Density scan at low Ip


Empirical momentum flux

k~1


MHD Spectroscopy

0.1 0.2 0.3 0.4 0.5 0.6 0.7-10

-5

0

5

10

Fre

q. [

kHz]


Sawteeth flatten core rotationinv vs. s = width of the flat region in the rotation profile

• Good correlation between inv and the outer position of the flat rotation region.• For large inv profile is hollow even outside inv.• Existence of a co-current torque?

Negative Ip

Positive Ip


MHD spectroscopy

#29500


Neoclassical prediction: effect of E

E contribution to C rotation

)/(1019.42/3

2 skmn

T

R

VZZfV

i

ilieff

ITor

• The neoclassical drive1 from E to V//

is negligible for TCV ohmic plasmas

1Kim Y B et al 1991 Phys. Fluid B 3 2050–60


Overview on #29475


Temporal evolution #29475


Vertical CXRS

• 40 vertical chords for poloidal velocity measurement

• Czerny-Turner monochromator

• Back illuminated CCD


0 0.1 0.2 0.3 0.4 0.5 0.612

14

16

18

20

22

24

26

28

30

*e

E,T

S+

CX

RS [m

s]

Energy confinement time as a function of *e

(ne,Ip) *e No power degradation oror Ip effect!

Rotation inversion depends on collisionality and plasma current!

370 kA

340 kA

320 kA290 kA

Collisionality at rotationinversion

Time

10th itpa tp meeting - 24 april 2006 - a. scarabosio 1 spontaneous stationary toroidal rotation in...

Documents

kms spontaneous rotation

core plasma

absolute rotation velocity

plasma current1

plasma width

limited ohmic

ohmic regime

conventions plasma height