EFDA Transport Topical Group Research Activities Survey

EFDA Transport Topical Groupsurvey of research activities relation with ITER Scenario Modellingpresented by C. Angioni on behalf ofC. Hidalgo (Chair)C. Angioni,C. Bourdelle, P. de Vries (co-Chair) ISM meeting, March 15-26 (2010)

A Transport Topical Group under EFDA • Transport has critical impact on the development of ITER scenarios • Progress in this complex field requires close interaction among theory, modelling and experiments • EFDA TTG aims at providing a broad framework for exchanging tools and results, at promoting interaction and collaboration between different EU experiments and theory groups, in order to address critical open issues of particular relevance for the practical development of nuclear fusion • In addition, TTG provides a natural way for collaboration at EU level with other connected fields of research under EFDA, like the MHD TG, the Diagnostics TG, the ITM and PWI TFs, and the H&CD TG • Finally, at international level, TTG is the interface with other transport collaborations worldwide, in particular with US TTF and with the ITPA groups ISM meeting, March 15-26 (2010)

TTG is chaired by Carlos Hidalgo, co-chaired by C. Bourdelle, P. de Vries (JET co-Chair), and myself. TTG structure • It has a scientific committee, whose members also naturally ensure connections with other research fields and research activities B. Weyssow (EFDA), M. Beurskens, A. Fasoli, F. Imbeaux, A. Kirk, V. Naulin, A.G. Peeters, F. Ryter, H. Wilson, F. Zonca • The structure of the TTG research activities is divided at present in 5 areas, in which focus has been proposed on 5 projects, included in the EFDA work program and for which specific task agreements for priority support are foreseen in the calls for participation • Research projects have coordinators, who are appointed on the basis of the interest shown in the answer to the calls for participation • Today, opportunity for an open exchange about high priority topics to be considered in the TTG research for the goals of the development of ISM activities ISM meeting, March 15-26 (2010)

TTG Research projects TTG / 2010 programme Pilot TTG project: Long-range correlations and edge transport barriers (2008) / Coordinator C. Hidalgo L-H transition physics (2010) coordinator H. Meyer Role of neoclassical and turbulent mechanisms in plasma rotation (2009) Coordination B. Duval Core impurity transport in plasmas with different dominant core turbulence (2009) Coordination C. Giroud / C. Angioni Statistical properties of edge turbulent transport and impurity/particle sources (2009) chair A. Kirk Test particle experiments (2009) Coordination A. Fasoli /U. Stroth Turbulent electron transport (2010) coordinator P. Hennequin ISM meeting, March 15-26 (2010)

Long-range correlations and edge transport bifurcations in fusion plasmas Pilot project in WP 2008/09 delivered the following main results Discovery of low frequency long range correlations in potential fluctuations that are amplified during the development of radial electric field using electrode biasing (TJ-II and TJ-K stellarators, and TEXTOR and ISTTOK tokamaks) and during spontaneous development of edge sheared flows ( TJ-II stellarator ) Comparative studies in the level of long-range toroidal correlations in different magnetic configurations (tokamaks, stellarators, RFPs) with and without RMPs suggest role of magnetic perturbations in the level of long-range correlations Degree of long-range toroidal correlations reduced as approaching the plasma density limit in TEXTOR Experiments in AUG also show that long-range correlations due to GAMs strongly decrease when entering the H-mode ISM meeting, March 15-26 (2010)

TEXTOR, Y. Xu et al, PoP 2009 Amplification of long-range correlations in potential fluctuations during the development of radial electric fields • Langmuir probe arrays at almost opposite toroidal locations • Small cross-correlation observed during the OH phase before biasing, whereas during biasing a zonal flow structure with significant long range correlation appears ISM meeting, March 15-26 (2010)

L-H transition Triggering of the L-H transition: Investigation of the role of equilibrium and fluctuating electric fields on the L-H transition and transport barrier formation. Role of multi-scale mechanism in the L-H transition: Experimental and modelling studies of the underlying physics mechanisms linking equilibrium electric fields and the development of zonal flows. Previous studies (TTG WP 2008/09)have shown the amplification of multi-scale mechanisms by externally imposed electric fields in stellarators and tokamaks. Pedestal width physics: Multi-machine experiments with simultaneous measurements of profile and fluctuation, to quantify the importance of turbulence / neoclassical mechanisms in setting the pedestal structure with / without external resonant magnetic perturbations (RMPs). Development of pedestal structure modelling (role of turbulence spreading) L-H power threshold and ELM control techniques: Experimental investigation of L-H power threshold with ergodic divertor / resonant magnetic perturbation with different n number; density and Bt dependence. Hysteresis L-H versus H-L transition: Comparative studies in different plasma regimes and description of the transitions in terms of local / global plasma parameters. Role of atomic physics mechanisms: Investigation of the underlying mechanisms linking wall conditions (clean vs dirty plasmas, neutrals) and isotope effect on L-H transition conditions. ISM meeting, March 15-26 (2010)

Effect of RMPs on the L-H transition (tokamaks) JET No effect observed (2009 experimental campaign) MAST On MAST there is observation of the delay of the L-H transition time if the n=1 coils are applied before the L-H transition but not with n=3. DIII-D In Deuterium plasmas no effect observed for n=3 – increased PL-H with n=1 In Helium plasmas PL-H increased by >50% in the presence of n=3 RMP perturbations for q95~ 3.5-3.6. NSTX PL-H increases from ~1.4 to 2.6 MW with higher n=3 current (~65% increase for Pheat/ne) AUG (2010 / 11) ISM meeting, March 15-26 (2010)

Impact of L-H transition physics on ITER scenario modelling Pedestal physics … no need to say … Impact of L-H and H-L transitions during current ramps on plasma stability and control Evolution of pedestal parameters during transient phases Burning plasma, relatively fast change of plasma pressure at the H-L transition due to loss of alpha heating power (current ramp down) Importance of better understanding of H-L / H-L hysteresis Role of ELM control techniques (RMPs and pellets) on L-H transition and scenarios (plasma profiles) ISM meeting, March 15-26 (2010)

TTG Research projects TTG / 2010 programme Pilot TTG project: Multi-scale physics and edge transport barriers (2008) Coordination C. Hidalgo L-H transition physics (2010) coordinator H. Meyer Role of neoclassical and turbulent mechanisms in plasma rotation (2009) Coordination B. Duval Core impurity transport in plasmas with different dominant core turbulence (2009) Coordination C. Giroud / C. Angioni Statistical properties of edge turbulent transport and impurity/particle sources (2009) chair A. Kirk Test particle experiments (2009) Coordination A. Fasoli /U. Stroth Turbulent electron transport (2010) coordinator P. Hennequin ISM meeting, March 15-26 (2010)

Role of neoclassical and turbulent mechanisms in plasma rotation Diagnostics for plasma rotation: Develop diagnostics allowing systematic comparisons between experimental measurements of rotation with neoclassical and turbulent mechanisms (L-, H- and improved confinement modes). Experiments and theory of plasma rotation: Perform systematic comparisons between experimental measurements of rotation with neoclassical and turbulent mechanisms (L-, H- and improved confinement modes). ISM meeting, March 15-26 (2010)

Poloidal rotation measurements vs neoclassical predictions MAST, A. Field et al PPCF 2009 JET, K. Crombe et al., PRL 2006 ISM meeting, March 15-26 (2010)

Turbulent mechanisms producing toroidal momentum transport and intrinsic plasma rotation Toroidal momentum transport connected with the breaking of symmetry in the direction parallel to the magnetic field [Peeters PoP 05, Diamond PoP 08] • Finite radial gradient of the rotation • An ExB shearing (role of poloidal rotation) • The Coriolis force due to the plasma rotation • A finite particle flux in the presence of a toroidal rotation • The up-down asymmetry of flux surfaces [Mattor PF88] [Dominguez PF 93] [Peeters PRL 07, Hahm PoP 07] [Camenen PRL 09] Many other processes can be identified at higher order in rhostar ExB shearing mainly provides correction to the diagonal viscosity Large (non-neoclassical) poloidal rotation can give rise to toroidal momentum convection (otherwise higher order in rhostar) ISM meeting, March 15-26 (2010)

Rotation in ITER, some questions • Which level of toroidal rotation can be expected in ITER ? • Large uncertainties on the prediction come not only from the core, but even more from limited understanding of the plasma edge • Most of present simulations performed assuming no plasma rotation • But then, what about a situation in which some rotation is included in the simulations ( say with central Mach ~ 0.05 – 0.1 ) • Are steady operation conditions easily obtained ? (feedback through stabilization from ExB shearing, increase in heating power … ) • And what limits the rotation in the very center of the plasma column, where turbulence becomes stable ISM meeting, March 15-26 (2010)

Particle and impurity transport in standard and advanced tokamak scenarios Experiments on impurity transport: Coordinated experiments on impurity transport to validate the paradigm of the ITG / TEM / ETG theory, by performing impurity transport measurements, profile measurements and fluctuations. Internal heat transport barrier: Explore experimentally the behaviour of the electron density profile and impurity transport before, during and after internal heat transport barriers with different strength and at different temperature ratios. Central electron heating and plasma dynamics: Impact of central electron heating on both electron and ion temperatures as well as on particle and impurity densities, with emphasis to conditions with ITBs (2010) ISM meeting, March 15-26 (2010)

w d Role of Collisions Pure Convection Thermodiffusion ITG ITG ITG TEM TEM TEM in in out out electrons in resonance only out in impurities out in out in electrons in slab resonance limit in out impurities Particle and impurity transport and type of turbulence Framework for theory validation: Do experiment exhibit (qualititatively, quantitatively) the same pattern ISM meeting, March 15-26 (2010)

Non-boronized operation with 100% W PFCs demonstrated on AUG [ A. Kallenbach et al, NF 49, 045007 (2009) ] Role of central electron heatingExperience from W wall in ASDEX Upgrade Investigation of transport physics responsible for these observations among priorities in EFDA TTG project on impurity transport • Dedicated experiments performed on several devices [AUG, JET, TS] in a collaborative effort. • Comparison with theory (fluid, GK ) in progress ISM meeting, March 15-26 (2010)

Modelling of density profile and impurities in ITER scenarios was often neglected in the past: no anomalous inward convection expected to be at play close to the density limit, leading to the assumption of flat (box-like) electron density profiles [ IPB NF 99, Green et al PPCF 03 ] ITER modelling of Particle & Impurity transport • Today we know that this approach is not appropriate • A turbulent inward convection of electrons has to be expected at the low collisionalities of the current flat top phase of ITER SS • Interplay between neoclassical and turbulent transport critical for impurity transport • In contrast to neoclassical transport, turbulent impurity convection does not lead to mechanisms of strong accumulation of heavy impurities Turbulent convection of impurities observed to be close to that of main species (ExB transport) : no anomalous convection of impurities included in ITER modelling • In contrast to current flat top phases, transient phases (current ramps) can explore very broad and different parameter domains ISM meeting, March 15-26 (2010)

Relative role of turbulent and neoclassical transport • Actual size of turbulent diffusion is the key parameter • Ratio D / c is appropriate dimensionless parameter to describe this effect in theory / modelling and for comparisons with experiments Modelling of Impurity transport Direction of turbulent convection mechanisms can depend on the type of instability and turbulence at play • Outward (or weak inward) convection of heavy impurities is operationally attractive • Observations of outward convection of (heavy) impurities provide real challenge for the theory (can be obtained only by dominant role of specific transport processes) • In validation, look for consistency among all transport channels (electron particle transport and impurity transport, and beyond … ) ISM meeting, March 15-26 (2010)

Statistical properties of edge turbulent transport Turbulent structures and intermittency: Investigation of filamentary structures and nature (electrostatic and magnetic), the mechanisms behind their formation and propagation and their role in transporting energy and particles to the wall. Diagnostics for edge turbulence: Improving edge plasma diagnostics to characterize edge transport/particle sources to have access to the relevant physics, including the upgrade of edge diagnostics to allow ion temperature and/or plasma potential measurements Theory and modelling of edge turbulence: Theory and modelling (kinetic and fluid models) of edge turbulence, particle (including impurity and particles sources) transport and ELMs (eg kinetic vs fluid) and comparison with experimental results. Test particle experiments: Development of test particle approach to study thermal test particles (using gas-puffing and tracer pellets) and the supra-thermal test particles (using fast ion sources). ISM meeting, March 15-26 (2010)

[ Spolaore et al. PRL 2009 ] Current density filaments in RFX-mod (and tokamaks and stellarators) U-probe 50 mm  B r Coherent pressure structures detected within the turbulence background and exhibit both electrostatic patterns, vortices and magnetic patterns, localized current density filaments aligned with the edge magnetic field (B) and travelling according to the EB flow with a vortex like velocity pattern Electromagnetic measurements during type I ELMs in AUG [ Vianello et al. PRL subm.] Role of beta (TJ-II / 2010) ISM meeting, March 15-26 (2010)

Turbulent electron transport: experimental search of turbulence and transport at small scales H&CD mix effect on Electron transport: Perform experiments and analysis of experiments performed in view of understanding the role of H&CD mix on electron transport. Diagnostics for high-k and low-k instabilities: Perform feasibility studies of plasma diagnostics for high-k and low-k instabilities ETG threshold: Perform experiments and analysis of experiments to identify plasma conditions which exceed or not the predicted linear ETG thresholds, compare with levels of high-k fluctuations Simulation of multi-scale transport: Perform simulations of multi-scale transport. Develop simulation tools of turbulence and transport to characterize the role of small scales turbulence on electron transport. ISM meeting, March 15-26 (2010)

High-k instabilities expected to be of particular relevance in advanced tokamak scenarios Theory / modelling standpoint, electron heat transport produced at both ion and electron scales. At present, multi-scale simulations are one of the main challenges in the field of numerical simulations of plasma turbulence [e.g. Waltz et al PoP 07, Goerler, Jenko PoP 08 ] Present experiments with dominant electron heating often achieve conditions of Te >> Ti, where high-k modes (ETG) are stable, and allow experimental studies on TEM turbulence [ e.g. Ryter PRL 05 ] In ITER, plasma conditions with Te/Ti ~ 1 leat to a decrease of the threshold of high-k modes These can be expected to play an important role particularly in advanced scenarios for “steady-state” operation, where strong gradients required to increase the bootstrap fraction are likely to lead to a strong destabilization of the high-k part of the spectrum ISM meeting, March 15-26 (2010)

ISM meeting, March 15-26 (2010)

The End ISM meeting, March 15-26 (2010)

TTG diagnostic development as trigger for new physics MAST Beam Emission spectroscopy Aim of the diagnostic: Provide 2D density fluctuation measurement in 0-1 MHz frequency range with cm resolution. ISM meeting, March 15-26 (2010)

EFDA Transport Topical Group Research Activities Survey