Research activity on the T-10 tokamak

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Research activity on the T-10 tokamak
G. Kirnev on behalf of T-10 team
Nuclear Fusion Institute, RRC Kurchatov
Institute, Moscow 123182, Russia
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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.
?-10 R 1.5 m aL 0.3 m BT 2.5 T IP 300
kA tP 1sec ECRH 2.0 MW (0.4 sec. )
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eITB studies
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eITB formation in T-10 during ECR preheating phase

• ECR preheating vs. L-mode
• Te(0) ?
• ? Te ? at the same ?heat (? ?e?) ? eITB is formed
  inside of r/a0.4

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q(r) evolution, MHD behavior and ITB dynamics

• eITB appears when slt0, qmingt3
• Internal disruptions lead to ITB shrinkage (at
  qmin?3) and even to temporal disappearance (at
  qmin2)
• eITB deterioration starts when m1 appears in
  plasma

?Te ?s/LTe characteristics of eITB strength
-Tresset G. et al, Nucl.Fus. 42(2002)520 ?Te
0.013 T-10 L-mode level
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Mechanisms of eITB Formation
Linear electrostatic flux tube code KINEZERO C.
Bourdelle et al, Nucl. Fus. 42 (2002) 892 has
been used for calculations of drift turbulence
stability
Ion drift direction

• Drift turbulence is stable (or marginally stable)
  inside of ITB region during the initial stage of
  discharge until qmin2
• 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 qmin2 achievement is predicted
  to be close to L-mode inherent turbulence level
  (!)
• ETG mode is predicted to be stable inside of
  r/a0.6 in a whole region of investigated
  parameters

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Films and dust formation
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Formation of dust and globular structure.
SEM
Globular films and dust are observed at the
limiter cross-section (at high heat load).
10 ?m
100 ?m
Globular film has fractal structure. Diffusion
Limited Aggregation (DLA) model was applied to
describe growth of the film.
?
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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.
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Nonlinear processes at the edge
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Third order spectrum (Bispectrum).
Cumulant function of the third order
Bispectral density
Bispectrum
Bispectrum (two-dimensional instantaneous
spectrum ?i(?1, ?2)) triad of instantaneous
one-dimensional spectrum at frequencies ?1, ?2 ?
?1 ?2.
Necessary condition of non-zero value of
bispectrum
(1)
Sufficient condition of non-zero value of
bispectrum
(2)
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Fluctuations of floating potential. LCFS.
Ip300kA, Bt 2.4T, ltnegt 5x1013 cm-3
Power spectrum
Mode "20 kHz" is the large-scale mode. It is
poloidally symmetrical with poloidal wave number
k??0 (from phase shift measurements in poloidal
direction). It could be result of cascading
energy transfer from the small-scale broadband
turbulence.
Bispectrum
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Fluctuations of floating potential. LCFS.
Ip300kA, Bt 2.4T, ltnegt 5x1013 cm-3
20kHz
Mode "20 kHz" interacts with continuous spectrum
by dint of three wave mechanism in a frequency
range 20-150 kHz. (f1-f220kHz)
(20,20)
(10,10) (12,8) (17,3)
Mode "20 kHz" splits to a few pairs of components
(above and below 10 kHz). (f1f220kHz)
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Poloidal asymmetry of turbulence in the plasma
core
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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
  14.81019 m-3
• For typical discharges T-10 HFS reflectometer
  band coincides with ITER required.

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Poloidal asymmetry of turbulence

• Strong asymmetry in density perturbations
  amplitude
• Low amplitude of quasicoherent oscillations at HFS

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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)

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Threshold Effects in Pellet-Plasma Interaction
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Experimental results

• Ablation rates for different sizes of carbon
  pellets demonstrate bursts/drops of ablation
  near rational magnetic surfaces.
• Pellets with the diameter lt 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 (dgt0.4 mm).
• Width of the reconnection zones is few
  centimeters except the Kadomtsev reconnection
  zone about 10 cm at q1.

Ablation rate, a.u.
Pellet diameter 0.62 mm 0.58 0.55 0.50 0.47 0.4
5 0.40 0.35 0.30 0.20
-20 -10 0
10 20
Minor radius, cm
B. Kuteev, EPS2006, Roma, Italy, June 19-June 23,
2006
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Experimental results
Plasma center

• Cooling front propagation
• For pellets with the diameter lt 0.3 mm the
  cooling front velocity coincides with the pellet
  velocity (gVcool/Vpel1) .
• Pellets with a larger size provoke reconnections.
  At the reconnection zone the jumps of the g-ratio
  are observed.
• The highest g-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.

Vpel
B. Kuteev, EPS2006, Roma, Italy, June 19-June 23,
2006
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Joint Experiment on T-10
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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.
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Future plans.

• 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