Finnish-Russian Collaboration: Reflectometry Turbulence Measurements & ELMFIRE Validation on FT-2 Tokamak in St.Petersburg.

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1 Finnish-Russian Collaboration: Reflectometry Turbulence Measurements & ELMFIRE Validation on FT-2 Tokamak in St.Petersburg Established in 1918 Fusion research started in 1957 Alexey Gurchenko

2 Tokamaks in Ioffe Institute FT-2 TUMAN-3M Globus-M circular limiter R = 55 cm, a = 8 cm A = 7, B = 3 T circular limiter R = 53 cm, a = 22 cm A = 2.4, B = 1 T divertor configuration and significant elongation and triangularity R = 36 cm, a = 24 cm A = 1.5, B =.4 T The research activity on these tokamaks is concentrated around fast-ions physics, methods of L current drive, anomalous turbulent tokamak transport and the development of fusion plasma diagnostics. 2of 19

3 iagnostics for ITER developed in Ioffe Institute The high level of expertise led to the participation in the ITER project, in the frame of the Russian domestic team activity. Three diagnostic systems for ITER are developed in the Ioffe Institute: Tandem neutral particle analyser (NPA) [Afanasyev V.I. et al. 21 Nucl. Instrum. Methods Phys. Res. A ] Gamma-ray spectrometry (GS) [Shevelev A. et al. 213 Nucl. Fusion ] ivertor Thomson scattering (TS) [Mukhin E.E. et al. 214 Nucl. Fusion ] 3of 19

4 iagnostics for ITER: : TS The ITER TS diagnostic measures the electron temperature and density in the outer leg of the ivertor. Tests of technical solutions and prototyping of the equipment is being performed on Globus-M tokamak. 4of 19

5 iagnostics for ITER: : GS The vertical gamma camera for a tomographic reconstruction of gamma-ray emissivity profiles together with the radial gamma-ray spectrometers developed by the European team. The GS consists of two systems: A high-resolution gamma-ray spectrometer built around detectors inside the NPA neutron dump for line integrated measurements of gamma-ray and hard x-ray emission in the equatorial plane. The diagnostic will supply information on fuel ratio in the plasma core, alpha particle and fast-ios energy distributions, maximum energy of runaway electrons and ICRF heating optimization in and e phases of ITER operation. 5of 19

6 iagnostics for ITER: NPA Two important issues for NPA on ITER: The distribution functions of the fast-ions generated as a result of additional heating and nuclear fusion reactions. The hydrogen isotope composition of the plasma on the basisofmeasurementsoftheneutralizedfluxes of the corresponding hydrogen ions, namely protons, deuterons, and tritons. igh energy neutral particle analyser (ENPA):.1 4MeV energy range Low energy neutral particle analyser (LENPA): 1 2 kev Both are covering plasma core and periphery and will be able to discriminate hydrogen (,, T) and helium (e3, e4 ) isotopes. It has to be one of the main tasks of the ITER control system to provide an optimal /T ratio in the plasma for themosteffectiveplasmaburning. 6of 19

7 The isotope effect in anomalous transport of energy and particles Besides the diagnostics development the general studies on anomalous transport of magnetized plasmas are in progress in Ioffe Institute. The problem of anomaly high transport of energy and particles is one of the last unsolved fundamental problems in fusion-research. The isotope effect in tokamak anomalous transport is a longstanding puzzle for physicists. It was first reported almost 3 years ago [ugill J. & Sheffield J Nucl. Fusion 18 15] and since that time observed in many machines. Already in the TFTR [Ernst.R., Coppi B., Scott S.., Porkolab M. and TFTR Group 1998 Phys. Rev. Lett ] it was shown that coming from hydrogen to deuterium and then to the mixture of deuterium and tritium the energy transport goes down for the heavy isotopes. 7of 19

8 The isotope effect puzzle The typical orbit s widths for circulation of particles in a tokamak go in the opposite direction: the Larmor radius and the banana orbit are larger for heavy isotopes. In terms of turbulent transport, the typical width of the drift-wave turbulent eddy scales like an ion Larmor radius, and therefore for heavier isotopes larger eddies are predicted. Based on these arguments one could expect growing transport with increasing isotope mass, nevertheless, in numerous experiments an opposite direction of effect was observed [Wagner F. and Stroth U Plasma Phys. Control. Fusion ], [Stroth U Plasma Phys. Control. Fusion 4 9]. 8of 19

9 Motivation of the present collaboration Predictions for ITER are based on scaling laws for -mode taking into account the isotope effect, which is promising for fusion applications, but the reason why it happens and possible limitations are still unclear. For instance, it was shown that the isotope effect is much stronger in tokamaks compared to stellarators. That is why revealing and investigation of the physical mechanisms of the isotope effect are among the main aims of the present Finnish-Russian collaboration. Recently it was proposed that the ion mass dependence of the multi-scale turbulence component with long-range correlation could be responsible for the isotope effect in tokamak transport [Xu Y. et al. 213 Phys. Rev. Lett ]. Investigation of just such multi-scale objects is one of the basic skills of research groups involved in this collaboration. Therefore, the comparative investigation of the isotope effect in multi-scale anomalous transport phenomena was performed both experimentally in FT-2 tokamak and theoretically by global gyrokinetic ELMFIRE modeling in Aalto University [Gurchenko A.. et al. 215 EPL ], [Askinazi L.G. et al. 215 Nucl. Fusion ], [Gurchenko A.. et al. 216 Plasma Phys. Control. Fusion ]. 9of 19

10 Experimental approach (backscattering/reflectometry) UR BS X-mode reflectometry O-mode reflectometry [Gurchenko A.. et al. 213 Plasma Phys. Control. Fusion ] Antennae Correlative measurements with horns two-frequency probing in FT-2 1 of 19

11 Theoretical approach (Elmfire global GK modeling) [eikkinen J.A. et al. 28 J. Comput. Phys ], [Leerink S et al. 21 Contrib. Plasma Phys ], [Korpilo T. et al. 213 J. Comput. Phys ] Poloidal FT-2 cross-section 11 of 19

12 Multi-scale benchmarking of experimental FT-2 2 data and GK simulations [Gusakov E.Z. et al. 24 IAEA FEC (San iego, USA) 212 T/6-3], [Leerink S. et al. 212 Phys. Rev. Lett ] 12 of 19

13 Turbulence radial correlation length poloidal dependence [Altukhov A. et al. 25 IAEA FEC 214 EX/P1-3] L r (cm) GK simul. X-RCR O-RCR (degree) The turbulence radial correlation length both measured by Radial Correlation oppler Reflectometry and simulated by GK modeling quickly decreases at high field side 12 o < θ < 21 o and then steadily grows in direction of plasma rotation. 13 of 19

14 The intensive electric field wave associated with the GAM [Gusakov E.Z. et al. 213 Plasma Phys. Control. Fusion ], [Gurchenko A.. et al. 215 EPL ] r ~ 5.5 cm At the meso-scale the GAM frequency distribution (b) as well as its wavelength and phase velocity (c) are reproduced by the code cross-phase ( /2) (c) E r ELMFIRE f ES k GAM r 2.6 cm -1 F ~ 5 kz -1 1 r (cm) 14 of 19

15 An evidence of the isotope effect in FT [Gurchenko A. 42nd EPS Conf. on Plasma Phys. I5.J23] r (cm).1 n e (1 19 m -3 ) P rad (W/cm 3 ) r (cm) 6 4 T i (kev) p (arb. un.) T e (kev) ASTRA r (cm) 3 2 Energy fluxes Q e (1 3 Jm -2 s -1 ) Q i (1 3 Jm -2 s -1 ) r (cm) t (ms) 27 ms: 19.5 ka; 2.25 T; Z eff = 2.3; Z eff = dn e /dt = const / 1 ASTRA r (cm) 15 of 19

16 The isotope effect in the mean particle and ion energy fluxes and diffusivity in ELMFIRE simulations e (1 2 m -2 s -1 ) i (1 2 m -2 s -1 ) Q e (1 3 Jm -2 s -1 ) Q i (1 3 Jm -2 s -1 ) (m 2 /s) r (cm) Electron energy mean fluxes in - and - discharges are comparable, whereas ion energy mean fluxes and particle fluxes are systematically higher in -case. [Gurchenko A.. et al. 216 Plasma Phys. Control. Fusion ] 16 of 19

17 Turbulence level modulation at the GAM frequency <E r > (kv/m) GK modeling t ( s) < n 2 > (1 35 m -6 ) f (Mz) f (Mz) Experimental measurements t ( s) P IQ (arb. un.) P IQ (arb. un.) This modulation which is more coherent in at larger GAMs level provides the reason for the modulation of particle and energy fluxes investigated experimentally and theoretically now. [Gurchenko A.. et al. 215 EPL ], [Gurchenko A.. et al. 216 Plasma Phys. Control. Fusion ] 17 of 19

18 Conclusions The comparative investigation of the isotope effect in multi-scale tokamak anomalous transport phenomena was performed both experimentally by highly localized turbulence diagnostics in comparable - and - FT-2 tokamak discharges and theoretically with the help of the global GK modeling. A self-organized multi-scale turbulence behaviour, more coherent in the -case, was visualized by both methods. The exact mechanism of this effect and the role of GAMs in it are not clear yet. Nevertheless the obtained experimental and computational results possess potential for explanation of the transport isotope effect in tokamaks. Results were presented in oral talks on the 24 th IAEA Fusion Energy Conf. (San-iego 212), the 41 st EPS Conf. on Plasma Physics (Berlin 214), the 25 th IAEA Fusion Energy Conf. (St.Petersburg 214) and in invited talks on the 4 th EPS Conf. on Plasma Physics (Espoo 213), the 42nd EPS Conf. on Plasma Physics (Lisbon, 215). 18 of 19

19 Plans Further GK investigation of the turbulent fluxes modulated by GAMs in - and - regimes. Additional comparative investigation of the isotope effect in the FT-2 discharge with higher current and better confinement both in experiment and in global GK simulations. Creating of the radial velocity fluctuations diagnostic in FT-2 for verification of the GK code predictions, concerning the phase difference between velocity and density fluctuations in and plasmas. GK modeling of L- and -mode regimes in TUMAN-3M tokamak. Presentation in 216 of invited talks on the 43 rd EPS Conference on Plasma Physics ( Physics of GAM-initiated L- transition in a tokamak ) and the Joint Varenna-Lausanne International Workshop Theory of Fusion Plasmas ( Coupling experimental and computational studies of the isotope effect in turbulent particle transport ). 19 of 19