Research activity on the T-10 tokamak

1. Research activity on the T-10 tokamak G. Kirnev on behalf of T-10 team Nuclear Fusion Institute, RRC “Kurchatov Institute”, Moscow 123182, Russia

2. 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-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. )

3. eITB studies

4. 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/a~0.4

5. q(r) evolution, MHD behavior and ITB dynamics • eITB appears when s<0, qmin>3 • Internal disruptions lead to ITB shrinkage (at qmin3) and even to temporal disappearance (at qmin~2) • eITB deterioration starts when m=1 appears in plasma *Te =s/LTe – characteristics of eITB strength -Tresset G.etal, Nucl.Fus.42(2002)520; *Te=0.013 – T-10 L-mode level

6. Linear electrostatic flux tube code KINEZERO [C. Bourdelle et al, Nucl. Fus. 42 (2002) 892] has been used for calculations of drift turbulence stability Mechanisms of eITB Formation Ion drift direction • 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 achievementis 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

7. Films and dust formation

8. Formation of dust and globular structure. SEM Globular films and dust are observed at the limiter cross-section (at high heat load). 100 m 10 m Globular film has fractal structure. Diffusion – Limited Aggregation (DLA) model was applied to describe growth of the film. ?

9. 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.

10. Nonlinear processes at the edge

11. Third order spectrum (Bispectrum). Cumulant function of the third order Bispectral density Bispectrum Bispectrum (two-dimensional instantaneous spectrum Фi(1, 2)) – triad of instantaneous one-dimensional spectrum at frequencies1, 2 и 1 + 2. Necessary condition of non-zero value of bispectrum (1) Sufficient condition of non-zero value of bispectrum (2)

12. Fluctuations of floating potential.LCFS. Ip=300kA, Bt =2.4T, <ne> =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

13. Fluctuations of floating potential.LCFS. Ip=300kA, Bt =2.4T, <ne> =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-f2=20kHz) (10,10); (12,8) (17,3) … (20,20) Mode "20 kHz" splits to a few pairs of components (above and below 10 kHz). (f1+f2=20kHz)

14. Poloidal asymmetry of turbulence in the plasma core

15. 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.

16. Poloidal asymmetry of turbulence • Strong asymmetry in density perturbations amplitude • Low amplitude of quasicoherent oscillations at HFS

17. 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)

18. Threshold Effects in Pellet-Plasma Interaction

19. 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. Pellet diameter 0.62 mm 0.58 0.55 0.50 0.47 0.45 0.40 0.35 0.30 0.20 Ablation rate, a.u. -20 -10 0 10 20 Minor radius, cm B. Kuteev, EPS2006, Roma, Italy, June 19-June 23, 2006

20. Experimental results Plasma center • Cooling front propagation • For pellets with the diameter < 0.3 mm the cooling front velocity coincides with the pellet velocity (g=Vcool/Vpel=1) . • 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

21. Joint Experiment on T-10

22. 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.

23. 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