Off-axis electron cyclotron heating and the sandpile paradigm for transport in tokamak plasmas

March, T. K.; Chapman, Sandra C.; Dendy, R. O.; Merrifield, J. A.

doi:10.1063/1.1639017

Cited by 9 publications

(12 citation statements)

References 25 publications

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“…However in Ref. 29, direct quantitative comparisons are not made between the model results and experimental profiles, and so these results are not included in Fig. 5.…”

Section: A Rtpmentioning

confidence: 96%

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Comparison of a radial fractional transport model with tokamak experiments

Kullberg¹,

Morales²,

Maggs³

2014

Physics of Plasmas

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A radial fractional transport model [Kullberg et al., Phys. Rev. E 87, 052115 (2013)], that correctly incorporates the geometric effects of the domain near the origin and removes the singular behavior at the outer boundary, is compared to results of off-axis heating experiments performed in the Rijnhuizen Tokamak Project (RTP), ASDEX Upgrade, JET, and DIII-D tokamak devices. This comparative study provides an initial assessment of the presence of fractional transport phenomena in magnetic confinement experiments. It is found that the nonlocal radial model is robust in describing the steady-state temperature profiles from RTP, but for the propagation of heat waves in ASDEX Upgrade, JET, and DIII-D the model is not clearly superior to predictions based on Fick's law. However, this comparative study does indicate that the order of the fractional derivative, a, is likely a function of radial position in the devices surveyed. V C 2014 AIP Publishing LLC.

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“…However in Ref. 29, direct quantitative comparisons are not made between the model results and experimental profiles, and so these results are not included in Fig. 5.…”

Section: A Rtpmentioning

confidence: 96%

“…29 using a simple sandpile model. The results of this model share similar qualitative features with the experimentally measured profiles, such as the hollow shape of the profiles, the presence of ears or sharp peaks at the power source, and consistency in the outboard profile regardless of deposition radius.…”

Section: A Rtpmentioning

confidence: 99%

Comparison of a radial fractional transport model with tokamak experiments

Kullberg¹,

Morales²,

Maggs³

2014

Physics of Plasmas

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“…The emergence, from a very simple system [16], of counterparts to several aspects of tokamak confinement phenomenology [18,35,36], is interesting. Insofar as the resemblance is close, there is more to be learned.…”

Section: Complex Systems Models For Global Tokamak Phenomenologymentioning

confidence: 99%

Fusion, space and solar plasmas as complex systems

Dendy

Chapman

Paczuski

2007

Plasma Phys. Control. Fusion

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Complex systems science seeks to identify simple universal models that capture the key physics of extended macroscopic systems, whose behaviour is governed by multiple nonlinear coupled processes that operate across a wide range of spatiotemporal scales. In such systems, it is often the case that energy release occurs intermittently, in bursty events, and the phenomenology can exhibit scaling, that is a significant degree of self-similarity. Within plasma physics, such systems include Earth's magnetosphere, the solar corona and toroidal magnetic confinement experiments. Guided by broad understanding of the dominant plasma processes-for example, turbulent transport in tokamaks or reconnection in some space and solar contextsone may construct minimalist complex systems models that yield relevant global behaviour. Examples considered here include the sandpile approach to tokamaks and the magnetosphere and a multiple loops model for the solar coronal magnetic carpet. Such models can address questions that are inaccessible to analytical treatment and are too demanding for contemporary computational resources; thus they potentially yield new insights, but risk being simplistic. Central to the utility of these models is their capacity to replicate distinctive aspects of observed global phenomenology, often strongly nonlinear, or of event statistics, for which no explanation can be obtained from first principles considerations such as the underlying equations. For example, a sandpile model, which embodies critical-gradient-triggered avalanching transport associated with nearest-neighbour mode coupling and simple boundary conditions (and little else), can be used to generate some of the distinctive observed elements of tokamak confinement phenomenology such as ELMing and edge pedestals. The same sandpile model can also generate distributions of energy-release events whose distinctive statistics resemble those observed in the auroral zone. Similarly, a multiple loops model, which embodies random footpoint motion combined with reconnection of intersecting loops (and little else), can generate global magnetic field structure resembling

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“…Several Soc models in the form of CA have been suggested for fusion plasmas that address different aspects of turbulent transport and that are able to reproduce a number of observed phenomena, including the transport suppressing role of sheared poloidal flows 21 , the scaling of transport characteristics with system size 4 , the power-law shape of waiting time distributions 29,30,33 , the occurrence of anomalous, super-diffusive transport events 5 , the appearance of enhanced confinement, edge pedestals, edge localized modes, and the L-to H-mode transition 6,10,11,31 , and the non-diffusive energy transport observed in off-axis heating experiments 20 .…”

Section: Introductionmentioning

confidence: 99%

A self-organized criticality model for ion temperature gradient mode driven turbulence in confined plasma

Isliker¹,

Pisokas²,

Strintzi³

et al. 2010

Physics of Plasmas

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A new Self-Organized Criticality (Soc) model is introduced in the form of a Cellular Automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the actual physical variable, the ion temperature, and that the temporal evolution of the CA, which necessarily is in the form of rules, mimics actual physical processes as they are considered to be active in the system, i.e. a heating process and a local diffusive process that sets on if a threshold in the normalized ion temperature gradient R/L T is exceeded. The model reaches the Soc state and yields ion temperature profiles of exponential shape, which exhibit very high stiffness, in that they basically are independent of the loading pattern applied. This implies that there is anomalous heat transport present in the system, despite the fact that diffusion at the local level is imposed to be of a normal kind. The distributions of the heat fluxes in the system and of the heat out-fluxes are of power-law shape. The basic properties of the model are in good qualitative agreement with experimental results.

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Off-axis electron cyclotron heating and the sandpile paradigm for transport in tokamak plasmas

Cited by 9 publications

References 25 publications

Comparison of a radial fractional transport model with tokamak experiments

Comparison of a radial fractional transport model with tokamak experiments

Fusion, space and solar plasmas as complex systems

A self-organized criticality model for ion temperature gradient mode driven turbulence in confined plasma

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