Transport

1
Transport

• Jan Weiland
• Recent results from
• IAEA Geneva October 2008
• TF-T JET February 2009
• ITPA Naka March-April 2009
• RU work 2008-2009

2
Main areas in International transport research

• Momentum transport
• Particle transport
• Transport barriers
• Transient transport
• Scaling studies
• These areas are all covered in the new Transport
  Topical Group, chaired by Carlos Hidalgo

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TTG-overview
4
ITER Physics RD

• Modelling. Substantial advances in the
  theoretical understanding of plasma behaviour and
  modelling capabilities are still needed in order
  to complement the present semi empirical
  extrapolations to ITER
• Gyrokinetic codes are now in use and have been
  rather successful in comparison with experiment.
  However, they can still not be run on the
  transport timescale. Apparent succes running on
  shorter timescales still needs to be understood
• Significant progress has been made on momentum
  transport, both toroidal and poloidal. Prandtl
  numbers (ratio of toroidal momentum and ion heat
  diffusivities) agree roughly with experiments
  both for diagonal and effective diffusivities.
  Also the anomalous spinup of poloidal rotation in
  JET is recovered by theory based models.

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Hybride mode

• A strong interest in the Hybrid mode scenario
  (Hybride mode is an H-mode with a broad q profile
  everywhere above 1). Hybride modes have slightly
  better confinement than usual H-modes but show
  degradation of confinement with beta. They have
  higher beta than ordinary H-modes because the
  lowest order NTM mode has been stabilized.
  However, higher order NTM modes are still
  present, making simulations with drift wave
  models difficult.

6
ITER issues

• New issues in ITER modelling are the current
  rampup and current rampdown phases. They may be
  critical since large ELMs (Edge Localized Modes)
  or even disruptions may be difficult to avoid.
  ITER walls will be considerably more sensitive to
  ELMS than the walls in present day tokamaks.
• Since present theory based transport models
  have problems with the current dependence,
  empirical models are mainly used.

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Current ramping

• Simulations using the empirical Coppi-Tang model
  have indicated that the current ramp rate should
  be below 0.5 MA/s for impurity, electron
  temperature and inductance control.
• The fastest density drop was found to be t_p 5
  t_E and the slowest the same rate as the current
  in order to maintain the same ratio (0.85) to the
  Greenwald density.
• Density pump-out was needed in order to
  control the H-L transition during rampdown as
  well as for avoiding radiative collapse.
• Hidalgo emphasized the need to understand the
  L-H transition better for the current rampup
  phase.

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Fluid - Kinetic models

• Generally accepted that kinetic models can still
  not be run on the transport timescale, i.e. can
  not be used in predictive transport codes.
• It seems that nonlinear frequency shifts often
  detune kinetic resonances on a shorter timescale.
  However, it is difficult to give general criteria
  for this and when this happens also a reactive
  fluid model must be valid.
• What can be proven is that also the strongly
  nonlinear perpendicular dynamics relaxes on the
  confinement timescale in the case of maximum
  phase mixing.
• Thus we need to assume that the fact that
  nonlinear effects initially are stronger (more
  coherent state) will phase mix all kinetic
  resonances before the turbulence is phase mixed
  since then the timescale increases to the
  confinement timescale.
• The actual times for these different phase
  mixings are complicated functions of the strength
  of the instabilities, the correlation length,
  frequency mismatches in the mode coupling, level
  of first maximum etc.

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Fluid kinetic models cont.

• A new gyrofluid model, TGLF uses quasilinear
  kinetic theory, normalized to nonlinear kinetic
  simulations (Gyro). Also this model has problems
  with particle pinches. Results close to
  quasilinear kinetic.
• Improved quasilinear kinetic models are under
  development

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Particle transport

• Particle transport
• Very good agreement between our model and Gyro
  for particle transport in ITER-like plasmas.
  (Candy Nordman Fülöp et. al, IAEA 2008) (see
  below)
• This indicates again that nonlinear gyrokinetic
  codes may relax linear kinetic resonances on
  timescales shorter than the confinementtime as
  discussed above.

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Databases, physical mechanisms, methods and
general fusion physics

• It is important to further develop the
  comprehensive understanding of fusion physics and
  the theoretical-computational tools
• The further elucidation of physical mechanisms
  such as reconnection, non-local transport and
  turbulence suppression has high importance for
  key questions on fusion plasmas and needs to be
  compared with experiments on a range of fusion
  devises with a sufficiently broad range of
  parameters
• An expansion of the first principle basis of
  modelling codes would enhance the confidence in
  their use for extrapolating from present day
  devices towards a reactor

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Transient transport

• Electron transport
• Mantica Our model better than GLF 23 and GS2
  for several JET discharges studied
• Momentum transport, Torq modulation
• Tala Studies of diagonal Prandtl numbers and
  peaking factors for GS2 indicates good agreement
  with JET experiments.
• We have made full simulations which now give good
  agreement with modulation phases and amplitudes
  in the inner 50

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Frameworks for international collaboration

• EFDA-JET Transport work at JET is mainly
  organized by Task Force T (transport)
  (participation from Chalmers) Activities on Core
  heat transport, Transport of main particle
  species, Impurities, Transient transport, Edge
  turbulence
• ITPA (International Tokamak Physics Activities)
• Swedish RU participates in several groups.
  Within Confinement and Modelling and also in
  Transport we have participation from Chalmers.
  This activity is a continuation of the previous
  ITER Expert Group activities and is focused on
  problems of special interest for the next step
  large tokamak.

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Frameworks, cont

• ITM (European Task Force on Integrated Modelling,
  TFL Pär Strand) A new well funded project is
  EUFORIA.
• TTG The accompanying programmes in the
  associations are focusing on more basic aspects
  of the high priority tasks
• In particular Momentum transport and Particle
  transport

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Simulation of Transport barrier dynamics

• A new model for toroidal momentum transport
  has been derived from fluid theory including
  toroidal effects from the stress tensor (J.
  Weiland, R. Singh, H. Nordman et. al. Proc. IAEA
  2008 TH/P8.29) Accepted for Nuclear Fusion)
• With the new model it has been possible to
  simulate four channels simultaneously, Ion and
  Electron temperatures and Poloidal and Toroidal
  momentum
• Using all these channels the formation of a
  transport barrier could be simulated from initial
  profiles without barrier. The agreement with
  experiment was good including also the strong
  spinup of poloidal momentum (J. Weiland, P.
  Mantica, T.Tala et al. Presentation at the ITPA
  meeting in Naka March-April 2009)

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Drift Waves in Tokamaks and Stellarators

• Study of ion-temperature gradient (ITG) modes
  in 3D configurations
• Disagreements found between numerical and
  analytical equilibria
• The growthrate of the ITG mode is smaller in
  Stellarators than in tokamaks
• Also electron trapping included 2008

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Intrinsic Rotation
A. Kritz, G. Bateman, F. Halpern et. al. US TTF
2009

• Nine time slices from four DIII-D discharges are
  plotted
• NBI torque is varied from co to counter with
  other parameters fixed
• MMM08 model reproduces observed angular momentum
  variation of with torque
• Positive toroidal angular momentum at zero torque
  (intrinsic rotation) is observed
• Caused by inward convection of momentum from
  boundary to plasma core
• Negative torque is needed to produce zero total
  angular momentum

Discharges described in paper by W. M. Solomon,
K. H. Burrell, J. S. deGrassie, R. Budny, R. J.
Groebner, J. E. Kinsey, G. J. Kramer, T. C. Luce,
M. A. Makowski, D. Mikkelsen, et al., Plasma
Physics and Controlled Fusion 49(12B), B313 (2007)
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Model comparisons

• Comparisons between nonlinear gyrokinetic
  simulations (GYRO), TGLF and Weiland model for
  ITER-like plasma (ref scenario 3).
• Fluid results obtained for k??0.2.
• Comparison between Weiland model and nonlinear
  GENE simulations for JET discharges planned for
  2009 (330 kCPU hours allocated in HPC-FF).
• J. Candy, H. Nordman, T. Fülöp et al, Proc of
  IAEA Fusion Energy Conf TH/P8-28, Geneva (2008).

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Trace versus self-consistent treatment

• Weiland model treats impurities
• self-consistently. The often used trace impurity
  approximation is not adequate in TE dominated
  regimes.
• Carbon peaking factor R/LnC in (a) ITG dominated
  regime and (b) TE dominated regime versus
  normalised temperature gradient for standard
  parameters.
• T. Fülöp, H. Nordman, PoP 16, 032306 (2009).

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COllisional Model of Electrostatic Turbulence

• Semi-analytical gyrokinetic model of long
  wavelength electrostatic microinstabilities.
• Shear dependent model ballooning potential
• The electron-ion collisions are modeled by a
  Lorentz operator
• Simple analytic expressions for the quasilinear
  particle and heat fluxes
• See poster of I. Pusztai

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Stiffness with rotation
Weiland Grey norot, Green Wexb1.1104,
Purple Wexb 2.1 104, Dimits shift included
in calc. but no effect
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Summary

• Increased emphasis on ITER relevance and
  collaborations in the new EU programme
• A new framework for collaboration in basic
  transport problems , TTG, is supposed to connect
  Accompanying programmes in the Associations and
  is expected to produce new physics results that
  can be transferred to more applied activities .
• Both the TF-T meeting at JET and the ITPA meeting
  in Naka have shown that a large number of basic
  physics problem remain and that we need to apply
  a combination of experimental, numerical and
  analytical techniques in order to make progress.
• At the ITPA meeting in Naka plans were made for
  combined activities of the new European TTG, The
  TTTF activities in Europé and the US and ITPA.

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Summary cont.

• New areas of interest
• Current rampup and rampdown experiments
• Transport in Hybride discharges. This may require
  more detailed geometry effects since
  electromagnetic effects appear to be important
• Transient transport for comparison of kinetic and
  fluid models
• Transient momentum transport (torq modulation)