Confinement and transport properties during current ramps in the ASDEX Upgrade tokamak

Fable, E.; Angioni, C.; Hobirk, J.; Pereverzev, G.; Fietz, S.; Hein, T.

doi:10.1088/0029-5515/51/4/043006

Cited by 13 publications

(17 citation statements)

References 37 publications

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“…Collisions are treated by means of a linearized Landau-Boltzmann collision operator, which includes both pitch angle and energy scattering as well as modeling terms which ensure conservation of density, momentum, and energy. The flux surface geometry is extracted from SPIDER equilibria 4,24 (in the form of G-EQDSK files) via a field line tracing method (developed in Refs. 25 and 26, and first applied to AS-DEX Upgrade in Ref.…”

Section: Methodology a Description Of Gyrokinetic Simulation Methodsmentioning

confidence: 99%

Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

et al. 2013

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The nature and level of turbulent transport in the outer core of low-confinement (L-mode) discharges performed at the ASDEX Upgrade tokamak [A. Kallenbach et al., Nucl. Fusion 51, 094012 (2011)] are examined. Previously, it was found that for an L-mode discharge of the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] gyrokinetic simulations were unable to reproduce the experimental ion heat flux, underestimating it by almost an order of magnitude. In the present work, employing the GENE gyrokinetic turbulence code, an extensive nonlinear study is performed for L-mode discharges of ASDEX Upgrade in order to cross-check this observation. It is shown that no systematic underprediction can be found in these simulations-instead, discrepancies with respect to experimental transport levels are small enough to be resolved within the uncertainties of the experimental profiles. Moreover, it is shown that some turbulence properties resemble closely those of the underlying linear microinstabilities at least out to 90% of the minor radius, so that quasilinear transport models remain in principle applicable even for these parameters, provided that appropriate nonlinear saturation rules can be developed.

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Section: Methodology a Description Of Gyrokinetic Simulation Methodsmentioning

confidence: 99%

Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

et al. 2013

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“…These kind of simulations are becoming of importance for ITER operation design [11], and full-discharge modeling of ITER has already started [12]. Previous work at ASDEX Upgrade (AUG) on current ramp scenarios has been focused on transport properties and validation of transport models [13,14,15].…”

Section: Introductionmentioning

confidence: 99%

Novel free-boundary equilibrium and transport solver with theory-based models and its validation against ASDEX Upgrade current ramp scenarios

Fable

Angioni

Casson

et al. 2013

Plasma Phys. Control. Fusion

105

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Tokamak scenario development requires understanding of the properties that determine the kinetic profiles in non-steady plasma phases, and of self-consistent evolution of the magnetic equilibrium. Current ramps are of particular interest since many transport-relevant parameters explore a large range of values and their impact on transport mechanisms has to be assessed. To this purpose a novel full-discharge modeling tool has been developed, which couples the transport code ASTRA [1] and the free boundary equilibrium code SPIDER [2], utilizing a specifically designed coupling scheme. The current ramp-up phase can be accurately and reliably simulated using this scheme, where a plasma shape, position, and current controller is applied, which mimics the one of ASDEX Upgrade. Transport of energy is provided by theory-based models (e.g. TGLF [3]). A recipe based on edge-relevant parameters [4] is proposed to resolve the low current phase of the current ramps, where the impact of the safety factor on microinstabilities could make quasi-linear approaches questionable in the plasma outer region. Current ramp scenarios, selected from ASDEX Upgrade discharges, are then simulated to validate both the coupling with the free-boundary evolution and the prediction of profiles. Analysis of the underlying transport mechanisms is presented, to clarify the possible physics origin of the observed L-mode empirical energy confinement scaling. The role of toroidal micro-instabilities (ITG, TEM) and of non-linear effects is discussed.

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“…An alternative expression for the magnetic energy (7) as a function of poloidal fluxes at certain locations and the current density is [14] ( )…”

Section: Derivation Of Exact Tokamak Transformer Lumped Parametermentioning

confidence: 99%

Development and validation of a tokamak skin effect transformer model

Romero¹,

Moret²,

Coda³

et al. 2012

Nucl. Fusion

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A lumped parameter, state space model for the tokamak transformer including the slow flux penetration in the plasma (skin effect transformer model) is presented. The model does not require detailed or explicit information about plasma profiles or geometry. Instead, this information is lumped in system variables, parameters and inputs. The model has an exact mathematical structure built from energy and flux conservation theorems, predicting the evolution and non linear interaction of the plasma current and internal inductance as functions of the primary coil currents, plasma resistance, non-inductive current drive and the loop voltage at an specific location inside the plasma (equilibrium loop voltage). Loop voltage profile in the plasma is substituted by a three-point discretization, and ordinary differential equations are used to predict the equilibrium loop voltage as function of the boundary and resistive loop voltages. This provides a model for equilibrium loop voltage evolution, which is reminiscent of the skin effect. The order and parameters of this differential equation are determined empirically using system identification techniques. Fast plasma current modulation experiments with Random Binary Signals (RBS) have been conducted in the TCV tokamak to generate the required data for the analysis. Plasma current was modulated in Ohmic conditions between 200kA and 300kA with 30ms rise time, several times faster than its time constant L/R≈200ms. A second order linear differential equation for the equilibrium loop voltage is sufficient to describe the plasma current and internal inductance modulation with 70% and 38% fit parameters respectively. The model explains the most salient features of the plasma current transients, such as the inverse correlation between plasma current ramp rates and internal inductance changes, without requiring detailed or explicit information about resistivity profiles. This proves that lumped parameter modeling approach can be used to predict the time evolution of bulk plasma properties such as plasma inductance or current with reasonable accuracy; at least in Ohmic conditions without external heating and current drive sources.

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Confinement and transport properties during current ramps in the ASDEX Upgrade tokamak

Cited by 13 publications

References 37 publications

Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

Characterizing turbulent transport in ASDEX Upgrade L-mode plasmas via nonlinear gyrokinetic simulations

Novel free-boundary equilibrium and transport solver with theory-based models and its validation against ASDEX Upgrade current ramp scenarios

Development and validation of a tokamak skin effect transformer model

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