eu transport topical group under efda ( efda ttg ) … · 2008-05-06 · eu transport topical group...

EU TRANSPORT TOPICAL GROUP under EFDA

( EFDA TTG )

Organization, Research Areas and Projects

Carlos Hidalgo (Chair)

Clemente Angioni and Clarisse Bourdelle (vice-Chairs)

presented by Clemente Angioni

Kick-off meeting of the French research federation on magnetic confinement fusion Paris, 29.04.2008

OUTLINE

Kick-off mtg. French Research Fed. on Magnetic Confinement Fusion C. Angioni Paris, 29.04.2008

➤ Rationale and Organization

➤ Main Research Areas

➤ Task Oriented Research Projects

➤ Related open issues

➤ Specific research projects for Priority Support

RATIONALE of the EFDA TTG


➤ A broad and open organization providing a framework for exchanging results and tools, and promoting interaction and collaboration among different EU experiments and theory groups

➤ Main Goal is to bring an "added value" with respect to individual efforts in the different EU countries

➤ Right balance to be found between large freedom to be left to individual groups to develop independent research lines, and the requirement of coordinating the efforts in specific high priority topics ( ITER needs )

ADDED VALUE of the EFDA TTG


➤ Motivate cross-EU collaboration by the identification of specific task oriented projects (proposed for priority support)

➣ To be created by voluntary agreement of scientists involved and to focus on agreed specific questions on limited time

➣ PS covers also new hardware required by the physics program

➣ ITM TF, PWI TF, MHD TG, Diagnostics TG, Heating and CD TG

➤ Provide an interface at EU level with other connected fields through the EU collaborations under EFDA

➤ EU interface with transport research worldwide➣ ITPA , US Transport Task Force

➣ Edge and SOL transport physics

➣ Core heat and particle transport

➣ Core and edge momentum transport

➣ MHD and fast particles interactions with transport

RESEARCH AREAS


➤ Research program for 2008 / 09 organized on the basis of four main research areas

( identified in concert with previous EU TTF Scientific Committee )

➣ Edge and SOL transport physics

➣ Core heat and particle transport

➣ Core and edge momentum transport

➣ MHD and fast particles interactions with transport

4 TASK ORIENTED PROJECTS ARE IDENTIFIED WITHIN THE RESEARCH AREAS


➣ Pedestal and H-mode transport physics

➣ Physics of edge intermittent transport and link with particle sources

➣ Test of ITG/TEM/ETG models by joint profile, impurity transport and fluctuation investigations

➣ Physics of (spontaneous) rotation in plasmas

EDGE and SOL TRANSPORT PHYSICS


➤ Main open issues in the confinement of the standard scenario (actually of all ITER scenarios ) are related to the knowledge of the edge behaviour

➣ Empirical statistical approaches delivered uncertainties over large ranges

➤ Parametric dependences of the pedestal top pressure and of the edge transport barrier width

➤ Power threshold for the L-H transition ➣ Still uncertainties in the empirical description, complex

dependences on some parameters➣ Scalings in terms of local edge parameters rather than global parameters more effective for comparison with theory

Pedestal and H-mode transport physics

EDGE and SOL TRANSPORT PHYSICS (2)


General Fundamental Theoretical Issues on H-mode physics

➤ Local models of turbulence generated ExB velocity shear layer formation have been tested and found to work in slab geometry but not in toroidal geometry

➤ No first principles code has predicted yet self-consistently a L-H transition

➤ First principles approach required in which all relevant physical ingredients are to be included (challenge from both theory and numerical standpoints)

➤ Requires accurate and specific verification efforts, any assumption leading to simple (toy) models has to be verified against more complete theories before looking at experimental data

PEDESTAL and H-mode transport physics: critical test of transport mechanisms


➣ Impact of orbit ion losses across the separatrix

➣ Role of equilibrium/neoclassical flows

➣ Role of turbulence driven flows based on 2nd order and 1st order phase transitions

➣ Role of SOL boundary conditions

➤ Possible combination of different mechanisms

( Task Oriented Research Project )



➤ Possible goals ( experimental side )➣ Critical test of turbulence driven flows by the experimental investigation of long range correlations and the structure of the turbulence at the L-H transition and link with the pedestal structure, in both small and large devices

➣ Role of plasma boundary conditions (SOL flows, importance of recycling at the X-point) in the power threshold to trigger edge transport barriers

➣ Multi-machine experiments with simultaneous profile and fluctuation measurements to quantify the importance of turbulence and neoclassical mechanisms for the pedestal structure (width & height)

➣ ELM mitigation: Influence of external magnetic perturbations on edge / pedestal transport



➤ Possible related specific modelling goals➣ Role of long range correlations in turbulence driven sheared flows as 2nd order transition (simulations of externally induced transport barrier development )➣ Magnetic field perturbations ( bootstrap current and rotation)

➤ Edge codes should include realistic geometry, hot ions (Ti, ∇Ti ) and be electromagnetic to be experimentally relevant

➤ General fundamental theoretical issues

➣ nonlocal edge / core interface effects ( global description )➣ gyrofluid and/or gyrokinetic

➣ turbulence + neoclassical flow equilibrium problem➣ consistent inclusion of a X-point

Physics of edge intermittent transport and link with particle sources


➤ Bridge between plasma-wall interaction and turbulent cross-field transport

➤ Development of test particle experiments (impurities) in low temperature plasmas

➣ Fast visible cameras ( ~10 µs ) in laboratory plasmas

➤ Systematic investigations of the statistical properties of intermittent events and their link with edge particle sources

➣ 2D visualisation of transport events in the plasma boundary ( turbulence/ELMs ) and impurity sources in the plasma wall and divertor regions

➣ Diagnostics for edge transport / particle source with time resolution ~ 10 ms to access relevant physics

(Task Oriented Research Project )


Physics of edge localized modes

➤ Requires investigation of radial / parallel transport of both particles and energy and its dependence with ELM size / type and filamenary structure

➣ For a theoretical description of the ELM evolution and prediction of the distribution of energy losses in space and time, understand the ELM behaviour beyond the peeling / ballooning description (the latter might stiull remain the relevant triggert mechaniusm)

➤ not solely an MHD problem, but a turbulence + MHD problem➣ ELMs are not established to be just an instability onset phenomenon (because of the lack of a first prinicples description of the H-mode )

Density limit physics➤ Plasma region determining the limit ( is it just edge density), role of turbulence in SOL

CORE HEAT and PARTICLE TRANSPORT


➤ Theoretical framework of core micro-instabilities ( ITG, TEM, ETG ) allowed significative progress in the understanding of core transport phenomenology in recent years

➤ Still, real conclusive demonstrations that ITG / TEM / ETG are at the origin of the experimentally observed core anomalous transport are hard to obtain and very important theoretical predictions did not find yet an experimental validation (e.g. existence of the ion temperature gradient threshold )

Test of ITG/TEM/ETG model by joint profile,impurity transport and fluctuation investigations


➣ Combine as many experimental evidences as possible (different transport channels, different kind of diagnostics) for a as conclusive as possible validation of the ITG/TEM/ETG paradigma

➣ Direction of particle (impurity) convection can depend on type of instability (can be used for "consistency checks" w.r.t. other measurements and modelling )

➣ Turbulence models/codes cannot be validated only in terms of profiles (although profiles play already a crucial role ) ⇒ critical role of fluctuation measurements

➣ Experimental investigation of wave number spectra for more complete comparisons with codes ( role of ETGs )


Goal: To consolidate predictive capability of core turbulent theories

Test of ITG/TEM/ETG model by joint profile,impurity transport and fluctuation investigations


➣ Joint investigation of the structure of plasma profiles and fluctuations: Characterization of the level of fluctuations and correlation length in different plasma conditions (e.g. varying the heat flux vs R/LT, collisionality, Te/Ti, momentum input/rotation shear, etc ) ➣ Requires implementation of synthetic diagnostics in turbulence codes ( measure in codes same quantities in the same ways as in real experiments )

➣ Joint studies of various Z impurity transport in different plasma conditions (ITG, TEM)


Possible experimental / modelling actions

Open Issues in Core Transport Physics for Advanced Tokamak Scenarios


➤ Source of residual turbulent transport inside barriers (el. transport, ETG ? ) experimental study of barrier disappearance

➤ Internal transport barrier trigger and sustainment mechanismsRole on electron and ion transport barriers of :

➣ ExB ( toroidal and poloidal rotation ) ➣ magnetic shear ( current profile ) and MHD α (Shafranov shift )

➣ Temperature ratio Ti / Te

➣ Fast particles, impurities (dilution)

➣ β➣ Rational surfaces

➤ Particle transport in the presence of a barrier (density profiles ⇒ bootstrap current, impurity accumullation )

➤ Momentum transport ... requires specific research area

Core and Edge Momentum Transport


➤ Toroidal momentum

➣ Experimental determination of the relation between momentum conductivity and ion heat conductivity

➣ Experimental determination of existence and role of momentum pinch➣ Room for further theoretical developments

➤ Poloidal rotation

➣ anomalous or neoclassical ? how applicable is standard neoclassical theory in the presence of steep gradients in transport barriers

Physics of rotation in plasmas


➣ Characterization of momentum transport in plasmas with low momentum input

➣ Systematic investigations of the coupling of momentum transport with other transport channels

➣ Role of poloidal / toroidal rotation in ITB trigger and sustainment

➤ Improvement of the diagnostic possibilities is crucial Time resolution ( to enable transient experiments ) Toroidal rotation measurements in absence of NBI Direct measurements of poloidal rotation


MHD and Fast Particles interactions with transport


➤ Interplay between MHD and microturbulence➣ Effect of macroinstabilities ( islands ) and stochastic regions on plasma microturbulence ( usually considered in the presence of fixed nested magnetic flux surfaces )

➤ Fast particle transport ➣ Are fast particles transported by the plasma background microturbulence ( electrostatic, electromagnetic, stochasticity ) Possible effects on alpha particle profiles, as well as on efficiency of heating and current drive schemes

➤ For Priority Support, specific short term research projects within the high priority research areas have to be defined

➣ Scientists of the whole EU transport community are invited to consider this interesting possibility, intended to favour their own research and their collaborations within EU

➣ Identify and propose a specific research project of your interest, and labs / colleagues who share this interest and wish to contribute ( with experimental facilities, expertize ... )

➤ Just let us know ( Carlos, Clarisse and myself ), our main goal is just to favour your research

Research Projects for Task Agreements


eu transport topical group under efda ( efda ttg ) … · 2008-05-06 · eu transport topical group...

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