Research activity on the T-10 tokamak

G. Kirnevon behalf of T-10 team

Nuclear Fusion Institute, RRC “Kurchatov Institute”, Moscow 123182, Russia

Main points.

1. Results obtained in 2005-2006.

2. Joint experiment at the T-10 tokamak.

3. Future plans of research activity on T-10.

Т-10R = 1.5 maL = 0.3 mBT = 2.5 TIP = 300 kAtP = 1secECRH – 2.0 MW (0.4 sec. )

eITB studies

eITB formation in T-10 during ECR preheating phase

0.0 0.2 0.4 0.6 0.8 1.00

1

2

0

100

200

01234

40539 40540

tL

t2

t1

Te, k

eVn e, 1

019 m

-3

time, s

Pab

/10, kWI p, kA

OH ECRH ei neut

effe e

q q q q

n T

ECR preheating vs. L-mode:

1) Te(0)

2) Te at the same heat ( e) eITB is formed inside of r/a~0.4

0

1

2

3

4 40539 t=t

L

40540 t=t1

40540 t=t2

Te,k

eV

0.0 0.2 0.4 0.6 0.80

2

4

6

eff ,

m2 /s

r/a

0 5 10 15 20012345 r/a ~0.3

~150 kW/m2

t2 t1

L-mode ef

f, m2 /s

R/LTe

0

1

2

3

4

1

2

3

4

0.014

T6

T4

T5

T3

T2

T1

1 3/22qmin

= 3Te(0

), k

eV q

qmin

qmin

from MHD

q(0)

0.2 0.4 0.60

5

10

15

*

Te:

ECRH

tITB

h, c

m

time, s

0.0070

0.010

0.013

0.017

0.020

q(r) evolution, MHD behavior and ITB dynamics

*Te =s/LTe – characteristics of eITB

strength -Tresset G. et al, Nucl.Fus.

42(2002)520; *Te =0.013 – T-10 L-mode level

– eITB appears when s<0, qmin>3

– Internal disruptions lead to ITB shrinkage (at qmin3) and even to temporal disappearance (at qmin~2)

– eITB deterioration starts when m=1 appears in plasma

Mechanisms of eITB FormationLinear electrostatic flux tube code KINEZERO [C. Bourdelle et al, Nucl. Fus. 42

(2002) 892] has been used for calculations of drift turbulence stability

0

5

10

0.1 0.2 0.3 0.4 0.5 0.6

1

2

3

ITG

-TE

M, 1

04 s-1

L-mode RS, q

min=3

RS, qmin

=2.5 RS, q

min=2

RS, qmin

=1

q min

r/a

Position of steep gradient (gradT

e)

max

0.01 0.1 1 100

2

4

6

0.01 0.1 1 10

-20

-10

0

max at r/a=0.3,

104 s-1

ki

sum of all r,

104 s-1

ki

– Drift turbulence is stable (or marginally stable) inside of ITB region during the initial stage of discharge until qmin~2

– Further evolution of plasma parameters leads to the development of long wavelength turbulence (mainly ITG mode)

– ITG turbulence level at the time instant corresponding to qmin~2 achievement is predicted to be close to L-mode inherent turbulence level (!)

– ETG mode is predicted to be stable inside of r/a~0.6 in a whole region of investigated parameters

Ion drift directionIon drift direction

Films and dust formation

10 m100 m

SEM

Globular film has fractal structure.Diffusion – Limited Aggregation (DLA) model was applied to describe growth of the film.

Formation of dust and globular structure.

?

Globular films and dust are observed at the limiter cross-section (at high heat load).

Possible mechanisms of dust formation.

1. Dust agglomeration in plasma.

2. Deposition of carbon atoms Grow of the globular particles (globular films) Separation of the dust particles from the films.

3. Formation of the quasi-homogeneous carbon film Fragmentation of the film and formation globular particles with different scales Separation of the dust particles from the films.

Nonlinear processes at the edge

Third order spectrum (Bispectrum).

Bispectrum

Cumulant function of the third order 3 1 2 1 2T0

1K ( , ) lim x(t)x(t )x(t )dt

T

)3 1 2 3 1 2 1 1 2 2 1 2G (j , j ) K ( , )exp j d d

Bispectral density

2

3 1 2 N 3 1 2

2(j , j ) G (j , j )

T

Bispectrum (two-dimensional instantaneous spectrum Фi(1, 2)) – triad of

instantaneous one-dimensional spectrum at frequencies 1, 2 и 1 + 2.

1 2 3 (1)

Necessary condition of non-zero value of bispectrum

1 2 3 const (2)

Sufficient condition of non-zero value of bispectrum

Fluctuations of floating potential. LCFS.

20406080100

120140

160

1.0x10-6

2.0x10-6

3.0x10-6

4.0x10-6

5.0x10-6

6.0x10-6

2040

6080

100120

140160

f 2 , k

Hzf 1 , kHz

Mode "20 kHz" is the large-scale

mode. It is poloidally symmetrical

with poloidal wave number k0

(from phase shift measurements in

poloidal direction).

It could be result of cascading

energy transfer from the small-

scale broadband turbulence.

Ip=300kA, Bt =2.4T, <ne> =5x1013 cm-3

0 10 20 30 40 500.0

2.0x10-3

4.0x10-3

6.0x10-3

8.0x10-3

1.0x10-2

Am

plit

ude

f , kHz

Power spectrum

Bispectrum

Fluctuations of floating potential. LCFS.

20 40

10

20

30

40

50

f 1 , kHz

f 2 ,

kHz

3.000E-7

9.400E-7

1.580E-6

2.220E-6

2.860E-6

3.500E-6

20 40 60 80 100 120 140 160

20

40

60

80

100

120

140

160

f 1 , kHz

f 2 ,

kHz

9.000E-8

1.720E-7

2.540E-7

3.360E-7

4.180E-7

5.000E-7

Mode "20 kHz" interacts with continuous spectrum by dint of three wave mechanism in a frequency range 20-150 kHz. (f1-f2=20kHz)

20kHz

(20,20)(10,10); (12,8) (17,3) …

Ip=300kA, Bt =2.4T, <ne> =5x1013 cm-3

Mode "20 kHz" splits to a few pairs of components (above and below 10 kHz). (f1+f2=20kHz)

Poloidal asymmetry of turbulence in the plasma core

HFS antenna array at T-10

• Operation above 13.6 GHz for X-mode and 27.3 GHz for O-mode

• Possible densities for Xl-mode from 1.4 up to 14.8×1019 m-3

• For typical discharges T-10 HFS reflectometer band coincides with ITER required.

Poloidal asymmetry of turbulence

• Strong asymmetry in density perturbations amplitude

• Low amplitude of quasicoherent oscillations at HFS

-400 -200 0 200 4000.0

0.1

0.2Shot 42412t = 600 ms = 0.54

LFS, n/n

e=0.77 %

HFS, n/n

e=0.37 %Y

(n/

ne)

[s]

Frequency [kHz]

Density fluctuations profile

• Fluctuations amplitude in Ohmic discharges at HFS is in a factor of 2-3 less then at LFS and do not increase during ECRH.

• Poloidal asymmetry is well correlate with theory predictions (unfavorable curvature)

1,2 1,3 1,4 1,5 1,6 1,7 1,80,0

0,5

1,0

1,5

2,0 OH ECRH

n/n [%

]

R [m]

HFS LFS

Threshold Effects in Pellet-Plasma Interaction

Experimental results

Ablation rates for different sizes of carbon pellets demonstrate bursts/drops of ablation near rational magnetic surfaces.

•Pellets with the diameter < 0.3 mm do not disturb the plasma significantly.

•Pellets with a larger size provoke the reconnections. •Pellet ablation in the core plasma zone is totally governed by the Kadomtsev reconnection forming “delayed” ablation curves (d>0.4 mm).

• Width of the reconnection zones is few centimeters except the Kadomtsev reconnection zone about 10 cm at q=1.

B. Kuteev, EPS2006, Roma, Italy, June 19-June 23, 2006

-20 -10 0 10 20

Minor radius, cm

Ablation rate, a.u.

Pellet

diameter

0.62 mm

0.58

0.55

0.50

0.47

0.45

0.40

0.35

0.30

0.20

Experimental results

Cooling front propagation

•For pellets with the diameter < 0.3 mm the cooling front velocity coincides with the pellet velocity (=Vcool/Vpel=1) .

•Pellets with a larger size provoke reconnections. At the reconnection zone the jumps of the -ratio are observed. •The highest -ratio is observed in the core plasma zone that is totally governed by the Kadomtsev reconnection.

• The time of the cooling fronts propagation is shorter or comparable with the reconnection time.

B. Kuteev, EPS2006, Roma, Italy, June 19-June 23, 2006

-30 -20 -10 0 10 20 300

5

10

15

20

= 1

ICII

#42358d=0.62mm

I CII

r, cm

0

5

10

15

20#42300d=0.3mm

ICII

= 1

= 1

ICII

= Vcool

/ Vpel

#42359d=0.2mm

I CII

0

5

10

15

20

25

30

0

10

20

30

40

50

0

5

10

15

20

I CII

0

5

10

15

20

Vpel

Plasma center

Joint Experiment on T-10

Joint Experiment: - 25 September – 6 October.- three experimental groups.

Group 1. Core turbulence investigations with correlation reflectometry.Group 2. Studies of plasma potential fluctuations and radial electric field with HIBP diagnostics.Group 3. Edge turbulence investigations with the electric probe technique.

Main objects:

- investigation of HFS turbulence with respect to total turbulence level, turbulence types and poioidal rotation.- comparison of LFS turbulence with HFS one.- comparison of turbulence rotation at HFS/LFS with the [ExB] poloidal drift - comparison of radial distribution of GAMs, measured with reflectometry and HIBP.- application of the high-order statistical analysis to the experimental data, calculation of the bispectrum of the plasma fluctuation, revelation of the nonlinear coupling between fluctuations in time and space, determination of regions of unstable mode excitation and turbulent energy dissipation.

Investigation of an anomalous plasma transport mechanisms-Turbulence measurements and identification in different confinement modes, including ohmically heated plasmas and regimes with Internal Transport Barrier-Investigation of LFS/HFS turbulence asymmetry, theoretical analysis of the peculiarities-Investigation of the plasma transport peculiarities at high densities -Analysis of MHD effects on heat and particle transport in different regimes-Investigation of the q(r) profile effects on transport (role of the magnetic shear, rational q surfaces)

Analysis of pellet fuelled discharges-Energy confinement in pellet fuelled discharges in comparison with gas-puffed discharges-Physics of pellet penetration, role of MHD reconnections in pellet penetration-Possibility of ITB and H-mode formation in pellet fuelled discharges

Investigation of periphery plasma behaviour-Analysis of peculiarities of SOL transport, poloidal asymmetry of heat and particle fluxes-Investigation of the radial electric field effects on SOL transport and behaviour of high density structures in different regimes

Investigation of plasma-wall interaction:-Investigation of dust and film generation in different operational regimes in T-10 tokamak-Peculiarities of dust and film structure; investigation of hydrogen retention -Experiments with liquid Li evaporator, effect of Li on recycling

Future plans.