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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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio2
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio3
The TCV DNBI-CXRS system
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio4
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio5
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio6
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.
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio7
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio8
Spontaneous rotation in limited L-mode ohmic plasmas
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio9
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio10
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio11
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio12
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio13
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.
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio14
v-Ti similarity
# 27098 • Strong similarity (same gradient) between the rotation and temperature profile from CXRS outside inv.
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio15
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]
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio16
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio17
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:
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio18
Spontaneous rotation in limited L-mode ohmic plasmas (2)
High density- high current plasma
A new rotation regime
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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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio20
Spontaneous rotation in H-mode ohmic and ECH plasmas
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio21
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio22
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio23
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??)
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio24
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio25
Extra slides
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Density scan at low Ip
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Empirical momentum flux
k~1
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MHD Spectroscopy
0.1 0.2 0.3 0.4 0.5 0.6 0.7-10
-5
0
5
10
Fre
q. [
kHz]
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio29
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio30
MHD spectroscopy
#29500
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio31
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
10th ITPA TP Meeting - 24 April 2006 - A. Scarabosio32
Overview on #29475
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Temporal evolution #29475
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Vertical CXRS
• 40 vertical chords for poloidal velocity measurement
• Czerny-Turner monochromator
• Back illuminated CCD
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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