1. M. Hron IAEA RCM, Beijing, China 23/10/2006 Edge plasma physics and relevant diagnostics development on the CASTOR tokamak Presented by M Hron for the CASTOR team Institute of Plasma Physics, Academy of Sciences of the Czech Republic EURATOM Association IPP.CR, Prague, Czech Republic and collaborators EURATOM Associations: ENEA Padova (Padua, Italy), CEA (Cadarache, France), Etat Belge (Ghent University, Belgium),

2. M. Hron IAEA RCM, Beijing, China 23/10/2006 CASTOR tokamak 1960 built in Kurchatov Institute, Moscow 1977 put in operation in IPP Prague 1985 reconstructed (new vessel) 31.12.2006 shutdown

3. M. Hron IAEA RCM, Beijing, China 23/10/2006 CASTOR tokamak MAIN PARAMETERS major radius0.4 m minor radius85 mm plasma volume0.1 m 3 plasma current10 kA toroidal magnetic field1.3 Tesla pulse length30 ms plasma density 1-2*10 19 m -3 plasma temperature150 eV edge plasma density2*10 18 m -3 edge plasma temperature15 eV Manpower20 My MAIN PHYSICS TOPICS Edge plasma physics fluctuation measurements, biasing Wave plasma interaction fast particle generation, wave propagation Diagnostics development SXR spectroscopy advanced probes

4. M. Hron IAEA RCM, Beijing, China 23/10/2006 Diagnostics

5. M. Hron IAEA RCM, Beijing, China 23/10/2006 Edge plasma diagnostics Electric probes Classical Langmuir probes IV characteristics, local Te, ne, Ufl at the plasma edge, routine measurements Radial & Poloidal & 2D arrays of Langmuir probes for spatially / temporaly resolved measurements of plasma fluctuations Oriented probes Rotating Mach probe, Gundestrup probe for flow measurements during biasing experiments Advanced probes Tunnel probe - a quite novel concept for fast T e measurements ball-pen probe

6. M. Hron IAEA RCM, Beijing, China 23/10/2006 60 mm Poloidal array of 124 probes Poloidal resolution  = 2.9 deg (3 mm) 64 fast channels available - signals of one half of the ring can be monitored simultaneously. Rake probe Distance between the tips 2.5 mm Total length 35 mm Movable on the shot to shot basis U float or I sat mode of operation Probe arrays

7. M. Hron IAEA RCM, Beijing, China 23/10/2006 Poloidal distribution Radial distribution at the top of the torus Measured by the rake probe in a single shot Measured by the poloidal ring in four shots Floating potential profiles

8. M. Hron IAEA RCM, Beijing, China 23/10/2006 Ring represents the poloidal limiter Plasma is not centered, but downshifted Separatrix is not defined by the limiter Tips at the top – localized in the SOL Connection length >> 2  R to a material surface (shield) depends on the local helicity of magnetic field lines - q(a) Tips at the bottom - Closed Magnetic Field Lines Respective position of separatrix and probes

9. M. Hron IAEA RCM, Beijing, China 23/10/2006 Turbulence in the SOL

10. M. Hron IAEA RCM, Beijing, China 23/10/2006 Poloidally periodic patterns (bipolar) propagating poloidally are evident. Poloidal direction LFS TOP HFS Bottom Time 0.5 ms Potential “valley”Potential “hill” U fl ( , t) – raw data

11. M. Hron IAEA RCM, Beijing, China 23/10/2006 Poloidal direction Time lag [ms] Poloidal periodicity as confirmed by cross-correlation analysis The reference probe is located at the top of the torus Poloidal periodicity

12. M. Hron IAEA RCM, Beijing, China 23/10/2006 Dominant poloidal mode number is found to be m = 6-7 (standard discharge conditions on CASTOR) Poloidal mode analysis

13. M. Hron IAEA RCM, Beijing, China 23/10/2006 The safety factor q(a) was increased in time by ramping down the plasma current. q(a) Time [ms] Dominant mode number m clearly follows the evolution of the edge safety factor q(a) m 8765487654 8765487654 Poloidal mode analysis

14. M. Hron IAEA RCM, Beijing, China 23/10/2006 Conclusion - Turbulence in SOL Flute-like structure elongated along the magnetic field lines Radial dimension~ 1 cm Poloidal dimension~ 1 cm Lifetime~ 1-40  s Poloidal wavelength~ 5-15 cm Only a single (bipolar) turbulent structure exists in the SOL. Snakes q-times around the torus m=q, n=1 mode Starts (and ends) on the Ion (and Electron) side of the poloidal limiter Propagates poloidally due to the local ExB drift experimental data folded on the toroidal surface (toroidal angle = time)

15. M. Hron IAEA RCM, Beijing, China 23/10/2006 Biasing

16. M. Hron IAEA RCM, Beijing, China 23/10/2006 Motivation  Generate electric fields in the edge plasma  manipulate with ion flows via ExB drift  reduce plasma fluctuations  improve particle&heat confinement Massive electrode is inserted in the edge plasma and biased with respect to the vessel Biasing experiments density H_alpha U_bias I_bias biasing phase 1050152025 t [ms]

17. M. Hron IAEA RCM, Beijing, China 23/10/2006 Biased flux tube - originates at the electrode and extends upstream and downstream Peaks - Intersection of the biased flux tube with the poloidal ring Electrode is localized within the SOL and biased with respect to the vessel Poloidal distribution of floating potential SOL biasing

18. M. Hron IAEA RCM, Beijing, China 23/10/2006 Poloidal position of the biased flux tube versus the local safety factor (#14076 &14077) PROJECTION OF THE ELECTRODE 4 3 2 1 5 Position of peaks 2 and 3 is independent on q- value, but determined by the poloidal extent of the biasing electrode. Peaks 1,4,5 vary with the edge safety factor as expected SOL biasing

19. M. Hron IAEA RCM, Beijing, China 23/10/2006 Terminates on the electron and ion side of the poloidal limiter at the bottom part of the torus. Intersects q-times a poloidal cross section Originates at the electrode Extends upstream and downstream along the magnetic field lines Unfolded torusPoloidal cross section SOL biasing

20. M. Hron IAEA RCM, Beijing, China 23/10/2006 E pol xB tor drift in radial direction I sat Bias /I sat OH E pol Convective cells BIAS ohmic Electrode A significant modification of density profile is observed during the SOL biasing

21. M. Hron IAEA RCM, Beijing, China 23/10/2006 E r (r) during V fl peaks 10  s Sudden rise of oscillating behaviour during the biasing phase The effect involves a wide radial region Edge plasma biasing

22. M. Hron IAEA RCM, Beijing, China 23/10/2006 Creation and collapse of sheared region U fl E rad Huge radial electric fields characterize the edge region in between Ufl oscillations High sheared region (transport barrier) propagates towards the wall at about 200 m/s becoming progressively thinner before being destroyed

23. M. Hron IAEA RCM, Beijing, China 23/10/2006 More clear evidence of a periodic radial propagation of high density structures is provided by the fluctuating part of I sat signal U fl I sat Ejection of particles

24. M. Hron IAEA RCM, Beijing, China 23/10/2006 Highly time resolved (1 MHz) measurement of H  allowed a detailed investigation of it behavior during bias: a quite clear periodic oscillation is observed also on H  The H  periodic increase exhibit a good correlation with the radial propagations of density streams H  response

25. M. Hron IAEA RCM, Beijing, China 23/10/2006 Mach numbers show an equivalent behaviour with the 10 kHz poloidal and toroidal flows swap during the relaxations. M II MM ~100  s 0.1 0.2 0.3 0.4 0.5 11.611.812.0 time [ms] 0 Modification of flows

26. M. Hron IAEA RCM, Beijing, China 23/10/2006 Summary - Biasing Biasing experiments resulted in effective inducing of an improved plasma confinement, characterized by steeper gradients of density and radial electric field. SOL biasing creation of a bised flux tube in the SOL radial drift of particles (E pol x B tor ) modification of the density profile Edge plasma biasing periodic creation and collapse of a transport barrier (high shear region) at  10 kHz critical gradients achieved both on floating potential and plasma density radial propagation of high density structures response of the neutral particle influx from the wall

27. M. Hron IAEA RCM, Beijing, China 23/10/2006 Summary and future plans

28. M. Hron IAEA RCM, Beijing, China 23/10/2006 Summary EDGE PHYSICS Edge plasma polarization Convective cells Relaxation phenomena Emissive electrode – late 2006 M. Hron et al: Detailed measurements of momentum balance during the periodic collapse of a transport barrier, 33rd EPS Plasma Physics Conference, Roma, Italy, 19-23 June, 2006 P.Devynck et al: Plasma Phys. Control. Fusion 47 (2005) 269-280 J.Stockel et al.: Plasma Phys. Control. Fusion 47 (2005) 635-643 Electro-magnetic properties of the turbulence A Bencze et al: Observation of zonal flow-like structures using autocorrelation-width technique, Plasma Phys. Control. Fusion 48 (2006) S137-S153 P. Devynck et al: Dynamics of turbulent transport in the Scrape-off-Layer of the CASTOR tokamak, accepted for publication in Physics of Plasmas, in October 2006

29. M. Hron IAEA RCM, Beijing, China 23/10/2006 Summary Density fluctuations Fluctuations of density and turbulent particle flux P. Peleman et al: Highly resolved measurements of periodic radial electric field and associated relaxations in edge biasing experiments, PSI Conf., Hefei China, 2006, P3-23, accepted for publication in Journal of Nuclear Materials

30. M. Hron IAEA RCM, Beijing, China 23/10/2006 Summary DIAGNOSTICS DEVELOPMENT Electric probes Further experiments and modelling: Tunnel probe for Te measurements Ball pen probe R. Dejarnac et al.: Study of SOL plasma by advanced oriented Langmuir probes on the CASTOR tokamak, to be submitted to PPCF J. Stöckel et al: Advanced probes for edge plasma diagnostics on the CASTOR tokamak, submitted to Journal of Physics, Conference Series. Hydrogen absorption in metallic membranes Experiments performed in late 2005 prepared for publication M.E. Notkin et al: Measurements of the suprathermal hydrogen flux on the CASTOR tokamak, to be published in Nuclear Instruments and Methods in Physics Research Section B 2006

31. M. Hron IAEA RCM, Beijing, China 23/10/2006 Summary CORE TRANSPORT AND TURBULENCE Transport of non-intrinsic impurities Experiments performed on CASTOR Participation on T-10 experiments V.Piffl et al: Measurements of line radiation power in the CASTOR tokamak, 33nd EPS Conference on Plasma Physics, Roma, 19/6- 23/6/2006, P-2.126 V.Weinzettl et al: Snake-like structures after pellet injection in the T-10 tokamak, 33nd EPS Conference on Plasma Physics, Roma, 19/6- 23/6/2006, P-4.080 EDUCATION Experimental training course on tokamak physics July 2006, 16 participants from 9 countries

32. M. Hron IAEA RCM, Beijing, China 23/10/2006 Summary EXPERTISE EXCHANGE Turbulence and biasing experiments – a)Ghent University, Ghent, Belgium b)RFX, ENEA Padova, Italy c)CEA Cadarache, France d)LPMI, Nancy University, France e)IST Lisbon, Portugal f)Nuclear Fusion Institute, Kurchatov Institute, Moscow, Russia g)ERM/KMS Brussels, Belgium Diagnostics development and improvement – a)CEA Cadarache, France b)Innsbruck University, Austria Core transport and and turbulence – a)Budker Institute of Nuclear Physics, Novosibirsk, Russia

33. M. Hron IAEA RCM, Beijing, China 23/10/2006 Future plans CASTOR shut down at the end of 2006 negative biasing using emissive electrode Magnetic properties of turbulence probe head prepared for TJ-II Simulations of plasma deposition in tile gaps modelling of plasma penetration into castellated tile gaps Educational activities Education of stuents of Czech Universities Experimental training course on tokamak physics organized by IPP Prague and KFKI Budapest

34. M. Hron IAEA RCM, Beijing, China 23/10/2006 Publications J. Stockel et al.: Dynamics of the edge transport barrier at plasma biasing on the CASTOR tokamak, Invited talk at 11th International Conference on Plasma Physics and Technology, Alushta, Ukraine, September 11-16, 2006, submitted to Voprosy Atomnoj Nauki I Tekhniky: (Problems of Atomic Science and Technology: Plasma Physics) R. Dejarnac et al.: Study of SOL plasma by advanced oriented Langmuir probes on the CASTOR tokamak, to be submitted to PPCF P. Peleman et al: Highly resolved measurements of periodic radial electric field and associated relaxations in edge biasing experiments, PSI Conf., Hefei China, 2006, P3-23, accepted for publication in Journal of Nuclear Materials A Bencze et al: Observation of zonal flow-like structures using autocorrelation- width technique, Plasma Phys. Control. Fusion 48 (2006) S137-S153 P. Devynck et al: Dynamics of turbulent transport in the Scrape-off-Layer of the CASTOR tokamak, accepted for publication in Physics of Plasmas, in October 2006

35. M. Hron IAEA RCM, Beijing, China 23/10/2006 Publications M.E. Notkin et al: Measurements of the suprathermal hydrogen flux on the CASTOR tokamak, to be published in Nuclear Instruments and Methods in Physics Research Section B 2006 T. Van Rompuy et al: Sensitivity of electron temperature measurements with the tunnel probe to a fast electron component, submitted to PPCF. Tsv. K. Popov, J. Stöckel, R. Dejarnac, M. Dimitrova, P. Ivanova, Tsv. Naydenova, Advanced Probe Measurements of Electron Energy Distribution Functions in CASTOR Tokamak Plasma, to be published in Journal of Physics, Conference Series, 2006 J. Stöckel et al: Advanced probes for edge plasma diagnostics on the CASTOR tokamak, submitted to Journal of Physics, Conference Series. G. Van Oost et al: Joint Experiments on Small Tokamaks, submitted to Nuclear Fusion. J. Sentkerestiová: Systematic measurements of plasma position on CASTOR tokamak using magnetic coils and Hall sensors, diploma thesis, CTU Prague (2006). V.Weinzettl et al: Snake-like structures after pellet injection in the T-10 tokamak, 33nd EPS Conference on Plasma Physics, Roma, 19/6-23/6/2006, P-4.080

36. M. Hron IAEA RCM, Beijing, China 23/10/2006 Publications M. Spolaore et al: Relaxation phenomena induced by edge biasing experiments in the CASTOR tokamak, Czechoslovak Journal of Physics, Vol. 55 (2005), No.12, 6104C. K. Kovařík et al: Measurement of safety factor using Hall probes on CASTOR tokamak, Czech. J. Phys. Vol. 56 (2006), Suppl. D. J. Sentkerestiová et al: Comparative measurements of plasma position using coils, Hall probes and bolometers on CASTOR tokamak, Czech. J. Phys. Vol. 56 (2006), Suppl. D. Schrittwieser R et al: Direct measurements of the plasma potential by katsumata – type probes, Czech. J. of Phys. 56 (2006), Suppl. B M. Kočan et al: Ion temperature measurements in the tokamak scrape-off layer, submitted to Journal of Nuclear Materials M. Hron et al: Detailed measurements of momentum balance during the periodic collapse of a transport barrier, 33rd EPS Plasma Physics Conference, Roma, Italy, 19-23 June, 2006 V.Piffl et al: Measurements of line radiation power in the CASTOR tokamak, 33nd EPS Conference on Plasma Physics, Roma, 19/6-23/6/2006, P-2.126