Jonathan Citrin - Academia.edu (original) (raw)

Papers by Jonathan Citrin

2012 Abstracts IEEE International Conference on Plasma Science, 2012

ABSTRACT We present high-resolution observations of a magnetic-field front (peak magnitude ~ 8 kG... more ABSTRACT We present high-resolution observations of a magnetic-field front (peak magnitude ~ 8 kG) propagating through low-resistivity, multi-ion species plasma (mainly protons and carbon ions, electron density ~ 2.5×1014 cm-3 and temperature ~ 6 eV). Diagnostic methods are developed in order to reveal the details of the interaction, including the evolution of the magnetic-field front and plasma properties. These methods are based on controlled injection of trace-element ions (via an optimized laser blow-off) and new analysis approach that allows for obtaining the magnetic field from the velocity evolution of trace-element ions. A sub-mm resolution is achieved, which is comparable to the electron skin-depth. Moreover, the newly developed method enables the determination of relatively low-intensity fields of ~ 1 kG, otherwise impractical to measure spectroscopically by the common Zeeman method under such highly transient, low-density conditions. Here, we briefly describe the diagnostic method and the main results. The structure of the propagating magnetic field front is reconstructed and its width (~ 10 mm) is used for estimating the plasma conductivity. We find that the magnetic-field front structure and velocity remain nearly constant when the field propagates a length scale of the order of the front width. This allows the analysis of the associated electric potential hill in the moving frame of the magnetic field. Using the properties of the potential hill we derive the details of the ion dynamics according to their charge-to-mass (Z/m) ratios. Ions of relatively low Z/m ratios (C II-III) are penetrated by the magnetic field, whereas ions of high Z/m ratios (protons and C V-IV) are reflected off the field-front at different field magnitudes. The measured electron density evolution agrees with the predicted ion dynamics.

Plasma Physics and Controlled Fusion, 2012

ABSTRACT

Plasma Physics and Controlled Fusion, 2013

ABSTRACT The flux surfaces' layout and the magnetic winding number q are important quanti... more ABSTRACT The flux surfaces' layout and the magnetic winding number q are important quantities for the performance and stability of tokamak plasmas. Normally, these quantities are iteratively derived by solving the plasma equilibrium for the poloidal and toroidal flux. In this work, a fast, non-iterative and magnetics-free numerical method is proposed to estimate the shape of the flux surfaces by an inward propagation of the plasma boundary shape, as can be determined for example by optical boundary reconstruction described in Hommen (2010 Rev. Sci. Instrum. 81 113504), toward the magnetic axis, as can be determined independently with the motional Stark effect (MSE) diagnostic. Flux surfaces are estimated for various plasma regimes in the ITER, JET and MAST tokamaks and are compared with results of CRONOS reconstructions and simulations, showing agreement to within 1% of the minor radius for almost all treated plasmas. The availability of the flux surface shapes combined with the pitch angles measured using MSE allow the reconstruction of the plasma q-profile, by evaluating the contour-integral over the flux surfaces of the magnetic field pitch angle. This method provides a direct and exact measure of the q-profile for arbitrary flux surface shapes, which does not rely on magnetic measurements. Results based on estimated flux surface shapes show agreement with CRONOS q-profiles of better than 10%. The impact of the shape of the flux surfaces on the q-profile, particularly the profiles of elongation and Shafranov shift, and offsets in plasma boundary and the magnetic axis are assessed. OFIT+ was conceived for real-time plasma profile control experiments and advanced tokamak operation, and provides quickly and reliably the mapping of actuators and sensors to the minor radius as well as the plasma q-profile, independent of magnetic measurements.

We discuss a new approach to measure magnetic fields in situations where the magnetic-field prope... more We discuss a new approach to measure magnetic fields in situations where the magnetic-field properties and/or the plasma regime make the traditional Zeeman spectroscopy inapplicable. The approach is particularly useful when the field direction and/or magnitude vary significantly in the region viewed or during the diagnostic system's integration time, and hence no Zeeman splitting can be observed. Similar difficulty may also occur for high-energy-density conditions, where the Zeeman pattern is often completely smeared, regardless of the field distribution, due to the dominant contributions of the Stark and Doppler broadenings to the spectral-line shapes. In the new approach, the magnetic field is inferred from the comparison of the line-shapes of different fine-structure components of the same multiplet, which practically have the same Stark and Doppler broadenings, but different magnetic-field-induced contributions. Limitations of the new method are discussed.

Plasma Physics and Controlled Fusion, 2014

The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is inv... more The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low-β JET L-mode discharge illustrates the relation between ITG stabilization, and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high-β JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant, and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high-β generalization of comparable observations found at low-β at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

Nuclear Fusion, 2015

ABSTRACT The L to H mode transition occurs at a critical power which depends on various parameter... more ABSTRACT The L to H mode transition occurs at a critical power which depends on various parameters, such as the magnetic field, the density, etc. Experimental evidence on various tokamaks (JET, ASDEX-Upgrade, DIII-D, Alcator C-Mod) points towards the existence of a critical temperature characterizing the transition. This criterion for the L-H transition is local and is therefore easier to be compared to theoretical approaches. In order to shed light on the mechanisms of the transition, simple theoretical ideas are used to derive a temperature threshold (Tth). They are based on the stabilization of the underlying turbulence by a mean radial electric field shear. The nature of the turbulence varies as the collisionality decreases, from resistive ballooning modes to ion temperature gradient and trapped electron modes. The obtained parametric dependencies of the derived Tth are tested versus magnetic field, density, effective charge. Various robust experimental observations are reproduced, in particular Tth increases with magnetic field B and increases with density below the density roll-over observed on the power threshold.

37th European Physical Society Conference on Plasma Physics, Dublin, Ireland, June 21-25, 2010, P... more 37th European Physical Society Conference on Plasma Physics, Dublin, Ireland, June 21-25, 2010, P1.1047

Plasma Physics and Controlled Fusion

Hybrid scenarios in present machines are often characterized by improved confinement compared wit... more Hybrid scenarios in present machines are often characterized by improved confinement compared with the IPB98(y,2) empirical scaling law expectations. This work concentrates on isolating the impact of increased s/q at outer radii (where s is the magnetic shear) on core confinement in low-triangularity JET and ASDEX Upgrade (AUG) experiments. This is carried out by predictive heat and particle transport modelling using the integrated modelling code CRONOS coupled to the GLF23 turbulent transport model. For both machines, discharge pairs were analysed displaying similar pedestal confinement yet significant differences in core confinement. From these comparisons, it is found that s/q shaping at outer radii may be responsible for up to ~50% of the relative core confinement improvement observed in these specific discharges. This relative improvement is independent of the degree of rotational shear turbulence suppression assumed in the GLF23 model. However, employing the full GLF23 rotatio...

Nuclear Fusion, 2015

ABSTRACT

Nuclear Fusion, 2014

ABSTRACT The E x B shear stabilization of anomalous transport in JET hybrid discharges is studied... more ABSTRACT The E x B shear stabilization of anomalous transport in JET hybrid discharges is studied via self-consistent predictive modelling of electron and ion temperature, ion density and toroidal rotation velocity performed with the GLF23 model. The E x B shear stabilization factor (parameter alpha E in the GLF23 model) is adjusted to predict accurately the four simulated quantities under different experimental conditions, and the uncertainty in aE determined by 15% deviation between simulated and measured quantities is estimated. A correlation of aE with toroidal rotation velocity and E x B shearing rate is found in the low density plasmas, suggesting that the turbulence quench rule may be more complicated than assumed in the GLF23 model with constant alpha(E). For the selected discharges the best predictive accuracy is obtained by using weak/no E x B shear stabilization (i.e. alpha(E) approximate to 0) at low toroidal angular frequency (Omega < 60 krad s(-1)), even in the scenarios with the current overshoot, and alpha(E) = 0.9 at high frequency (Omega > 100 krad s(-1)). Interestingly, a weak E x B shear stabilization of anomalous transport is found in the medium density strongly rotating discharge. An importance of linear beta(e) stabilization in this discharge is estimated and compared to the low density discharge with equally high beta(e). The toroidal rotation velocity is well predicted here by assuming that the momentum diffusion coefficient is a fraction of thermal ion diffusivity. Taking into account the alpha(E) and Prandtl number with their uncertainties determined in the modelling of JET hybrid discharges, the performance of ITER hybrid scenario with optimized heat mix (33 MW of NBI and 20 MW of ECCD) is estimated showing the importance of toroidal rotation for achieving Q > 5.

Plasma and Fusion Research, 2012

Plasma Physics and Controlled Fusion, 2013

ABSTRACT Detailed experimental studies of ion heat transport are carried out in JET to explore th... more ABSTRACT Detailed experimental studies of ion heat transport are carried out in JET to explore the Te/Ti dependence of ion heat transport in ITER relevant range of parameters (Te/Ti ≥ 1) using low rotation plasmas with dominant ion cyclotron resonance heating to avoid the coupling of the effects of Te/Ti and rotation which affected previous experiments. This experimental setup has led to an accurate determination of the ion temperature gradient (ITG) threshold at varying Te/Ti, offering unique opportunities for validation of the well-established theory of ITG driven modes. A rather mild decrease in threshold with increasing Te/Ti in the interval of ITER interest was found. The new experimental result has found good agreement with theoretical predictions based on quasi-linear fluid and linear gyrokinetic models.

In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiment... more In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiments from several tokamaks have been analyzed by means of integrated modelling with the aim of determining relevant heat transport models for these operation phases. The results have implications on PF systems, H&CD methods for current profile shaping, and expected flux consumption in ITER.

Nuclear Fusion, 2014

ABSTRACT This letter reports on quasi-coherent (QC) modes observed in fluctuation spectra from To... more ABSTRACT This letter reports on quasi-coherent (QC) modes observed in fluctuation spectra from Tore Supra and TEXTOR reflectometers. QC modes have characteristics in between coherent and broad-band fluctuations as they oscillate around a given frequency but have a wide spectrum. They are ballooned at the LFS midplane and appear usually on a frequency ranging from 30 to 120 kHz. In ohmic plasmas from both tokamaks, QC modes are detected only in linear ohmic confinement (LOC) regime and disappear in saturated ohmic confinement (SOC) regime. Linear simulations from Tore Supra predict that the LOC and SOC regimes are dominated by electron and ion modes respectively. Measurements of the perpendicular velocity of density fluctuations have been made from the top of TEXTOR by poloidal correlation reflectometry. They suggest that QC modes have a phase velocity ∼400 m s−1 higher in the electron diamagnetic direction than lower frequency fluctuations. Additionally, the onset of QC modes during electron cyclotron resonance heating has been observed in a Tore Supra region where turbulence is suspected to be driven by electron modes. These experimental results and instability calculations show a correlation between onsets of QC modes and predictions of trapped electron modes.

Physics of Plasmas, 2012

ABSTRACT

Physical Review Letters, 2013

Nonlinear electromagnetic stabilization by suprathermal pressure gradients found in specific regi... more Nonlinear electromagnetic stabilization by suprathermal pressure gradients found in specific regimes is shown to be a key factor in reducing tokamak microturbulence, augmenting significantly the thermal pressure electromagnetic stabilization. Based on nonlinear gyrokinetic simulations investigating a set of ion heat transport experiments on the JET tokamak, described by Mantica et al. [Phys. Rev. Lett. 107, 135004 (2011)], this result explains the experimentally observed ion heat flux and stiffness reduction. These findings are expected to improve the extrapolation of advanced tokamak scenarios to reactor relevant regimes.

Nuclear Fusion, 2011

In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiment... more In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiments from various tokamaks have been analysed by means of integrated modelling in view of determining relevant heat transport models for these operation phases. A set of empirical heat transport models for L-mode (namely, the Bohm-gyroBohm model and scaling based models with a specific fixed radial shape

2012 Abstracts IEEE International Conference on Plasma Science, 2012

ABSTRACT We present high-resolution observations of a magnetic-field front (peak magnitude ~ 8 kG... more ABSTRACT We present high-resolution observations of a magnetic-field front (peak magnitude ~ 8 kG) propagating through low-resistivity, multi-ion species plasma (mainly protons and carbon ions, electron density ~ 2.5×1014 cm-3 and temperature ~ 6 eV). Diagnostic methods are developed in order to reveal the details of the interaction, including the evolution of the magnetic-field front and plasma properties. These methods are based on controlled injection of trace-element ions (via an optimized laser blow-off) and new analysis approach that allows for obtaining the magnetic field from the velocity evolution of trace-element ions. A sub-mm resolution is achieved, which is comparable to the electron skin-depth. Moreover, the newly developed method enables the determination of relatively low-intensity fields of ~ 1 kG, otherwise impractical to measure spectroscopically by the common Zeeman method under such highly transient, low-density conditions. Here, we briefly describe the diagnostic method and the main results. The structure of the propagating magnetic field front is reconstructed and its width (~ 10 mm) is used for estimating the plasma conductivity. We find that the magnetic-field front structure and velocity remain nearly constant when the field propagates a length scale of the order of the front width. This allows the analysis of the associated electric potential hill in the moving frame of the magnetic field. Using the properties of the potential hill we derive the details of the ion dynamics according to their charge-to-mass (Z/m) ratios. Ions of relatively low Z/m ratios (C II-III) are penetrated by the magnetic field, whereas ions of high Z/m ratios (protons and C V-IV) are reflected off the field-front at different field magnitudes. The measured electron density evolution agrees with the predicted ion dynamics.

Plasma Physics and Controlled Fusion, 2012

ABSTRACT

Plasma Physics and Controlled Fusion, 2013

ABSTRACT The flux surfaces' layout and the magnetic winding number q are important quanti... more ABSTRACT The flux surfaces' layout and the magnetic winding number q are important quantities for the performance and stability of tokamak plasmas. Normally, these quantities are iteratively derived by solving the plasma equilibrium for the poloidal and toroidal flux. In this work, a fast, non-iterative and magnetics-free numerical method is proposed to estimate the shape of the flux surfaces by an inward propagation of the plasma boundary shape, as can be determined for example by optical boundary reconstruction described in Hommen (2010 Rev. Sci. Instrum. 81 113504), toward the magnetic axis, as can be determined independently with the motional Stark effect (MSE) diagnostic. Flux surfaces are estimated for various plasma regimes in the ITER, JET and MAST tokamaks and are compared with results of CRONOS reconstructions and simulations, showing agreement to within 1% of the minor radius for almost all treated plasmas. The availability of the flux surface shapes combined with the pitch angles measured using MSE allow the reconstruction of the plasma q-profile, by evaluating the contour-integral over the flux surfaces of the magnetic field pitch angle. This method provides a direct and exact measure of the q-profile for arbitrary flux surface shapes, which does not rely on magnetic measurements. Results based on estimated flux surface shapes show agreement with CRONOS q-profiles of better than 10%. The impact of the shape of the flux surfaces on the q-profile, particularly the profiles of elongation and Shafranov shift, and offsets in plasma boundary and the magnetic axis are assessed. OFIT+ was conceived for real-time plasma profile control experiments and advanced tokamak operation, and provides quickly and reliably the mapping of actuators and sensors to the minor radius as well as the plasma q-profile, independent of magnetic measurements.

We discuss a new approach to measure magnetic fields in situations where the magnetic-field prope... more We discuss a new approach to measure magnetic fields in situations where the magnetic-field properties and/or the plasma regime make the traditional Zeeman spectroscopy inapplicable. The approach is particularly useful when the field direction and/or magnitude vary significantly in the region viewed or during the diagnostic system's integration time, and hence no Zeeman splitting can be observed. Similar difficulty may also occur for high-energy-density conditions, where the Zeeman pattern is often completely smeared, regardless of the field distribution, due to the dominant contributions of the Stark and Doppler broadenings to the spectral-line shapes. In the new approach, the magnetic field is inferred from the comparison of the line-shapes of different fine-structure components of the same multiplet, which practically have the same Stark and Doppler broadenings, but different magnetic-field-induced contributions. Limitations of the new method are discussed.

Plasma Physics and Controlled Fusion, 2014

The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is inv... more The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low-β JET L-mode discharge illustrates the relation between ITG stabilization, and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high-β JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant, and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high-β generalization of comparable observations found at low-β at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

Nuclear Fusion, 2015

ABSTRACT The L to H mode transition occurs at a critical power which depends on various parameter... more ABSTRACT The L to H mode transition occurs at a critical power which depends on various parameters, such as the magnetic field, the density, etc. Experimental evidence on various tokamaks (JET, ASDEX-Upgrade, DIII-D, Alcator C-Mod) points towards the existence of a critical temperature characterizing the transition. This criterion for the L-H transition is local and is therefore easier to be compared to theoretical approaches. In order to shed light on the mechanisms of the transition, simple theoretical ideas are used to derive a temperature threshold (Tth). They are based on the stabilization of the underlying turbulence by a mean radial electric field shear. The nature of the turbulence varies as the collisionality decreases, from resistive ballooning modes to ion temperature gradient and trapped electron modes. The obtained parametric dependencies of the derived Tth are tested versus magnetic field, density, effective charge. Various robust experimental observations are reproduced, in particular Tth increases with magnetic field B and increases with density below the density roll-over observed on the power threshold.

37th European Physical Society Conference on Plasma Physics, Dublin, Ireland, June 21-25, 2010, P... more 37th European Physical Society Conference on Plasma Physics, Dublin, Ireland, June 21-25, 2010, P1.1047

Plasma Physics and Controlled Fusion

Hybrid scenarios in present machines are often characterized by improved confinement compared wit... more Hybrid scenarios in present machines are often characterized by improved confinement compared with the IPB98(y,2) empirical scaling law expectations. This work concentrates on isolating the impact of increased s/q at outer radii (where s is the magnetic shear) on core confinement in low-triangularity JET and ASDEX Upgrade (AUG) experiments. This is carried out by predictive heat and particle transport modelling using the integrated modelling code CRONOS coupled to the GLF23 turbulent transport model. For both machines, discharge pairs were analysed displaying similar pedestal confinement yet significant differences in core confinement. From these comparisons, it is found that s/q shaping at outer radii may be responsible for up to ~50% of the relative core confinement improvement observed in these specific discharges. This relative improvement is independent of the degree of rotational shear turbulence suppression assumed in the GLF23 model. However, employing the full GLF23 rotatio...

Nuclear Fusion, 2015

ABSTRACT

Nuclear Fusion, 2014

ABSTRACT The E x B shear stabilization of anomalous transport in JET hybrid discharges is studied... more ABSTRACT The E x B shear stabilization of anomalous transport in JET hybrid discharges is studied via self-consistent predictive modelling of electron and ion temperature, ion density and toroidal rotation velocity performed with the GLF23 model. The E x B shear stabilization factor (parameter alpha E in the GLF23 model) is adjusted to predict accurately the four simulated quantities under different experimental conditions, and the uncertainty in aE determined by 15% deviation between simulated and measured quantities is estimated. A correlation of aE with toroidal rotation velocity and E x B shearing rate is found in the low density plasmas, suggesting that the turbulence quench rule may be more complicated than assumed in the GLF23 model with constant alpha(E). For the selected discharges the best predictive accuracy is obtained by using weak/no E x B shear stabilization (i.e. alpha(E) approximate to 0) at low toroidal angular frequency (Omega < 60 krad s(-1)), even in the scenarios with the current overshoot, and alpha(E) = 0.9 at high frequency (Omega > 100 krad s(-1)). Interestingly, a weak E x B shear stabilization of anomalous transport is found in the medium density strongly rotating discharge. An importance of linear beta(e) stabilization in this discharge is estimated and compared to the low density discharge with equally high beta(e). The toroidal rotation velocity is well predicted here by assuming that the momentum diffusion coefficient is a fraction of thermal ion diffusivity. Taking into account the alpha(E) and Prandtl number with their uncertainties determined in the modelling of JET hybrid discharges, the performance of ITER hybrid scenario with optimized heat mix (33 MW of NBI and 20 MW of ECCD) is estimated showing the importance of toroidal rotation for achieving Q > 5.

Plasma and Fusion Research, 2012

Plasma Physics and Controlled Fusion, 2013

ABSTRACT Detailed experimental studies of ion heat transport are carried out in JET to explore th... more ABSTRACT Detailed experimental studies of ion heat transport are carried out in JET to explore the Te/Ti dependence of ion heat transport in ITER relevant range of parameters (Te/Ti ≥ 1) using low rotation plasmas with dominant ion cyclotron resonance heating to avoid the coupling of the effects of Te/Ti and rotation which affected previous experiments. This experimental setup has led to an accurate determination of the ion temperature gradient (ITG) threshold at varying Te/Ti, offering unique opportunities for validation of the well-established theory of ITG driven modes. A rather mild decrease in threshold with increasing Te/Ti in the interval of ITER interest was found. The new experimental result has found good agreement with theoretical predictions based on quasi-linear fluid and linear gyrokinetic models.

In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiment... more In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiments from several tokamaks have been analyzed by means of integrated modelling with the aim of determining relevant heat transport models for these operation phases. The results have implications on PF systems, H&CD methods for current profile shaping, and expected flux consumption in ITER.

Nuclear Fusion, 2014

ABSTRACT This letter reports on quasi-coherent (QC) modes observed in fluctuation spectra from To... more ABSTRACT This letter reports on quasi-coherent (QC) modes observed in fluctuation spectra from Tore Supra and TEXTOR reflectometers. QC modes have characteristics in between coherent and broad-band fluctuations as they oscillate around a given frequency but have a wide spectrum. They are ballooned at the LFS midplane and appear usually on a frequency ranging from 30 to 120 kHz. In ohmic plasmas from both tokamaks, QC modes are detected only in linear ohmic confinement (LOC) regime and disappear in saturated ohmic confinement (SOC) regime. Linear simulations from Tore Supra predict that the LOC and SOC regimes are dominated by electron and ion modes respectively. Measurements of the perpendicular velocity of density fluctuations have been made from the top of TEXTOR by poloidal correlation reflectometry. They suggest that QC modes have a phase velocity ∼400 m s−1 higher in the electron diamagnetic direction than lower frequency fluctuations. Additionally, the onset of QC modes during electron cyclotron resonance heating has been observed in a Tore Supra region where turbulence is suspected to be driven by electron modes. These experimental results and instability calculations show a correlation between onsets of QC modes and predictions of trapped electron modes.

Physics of Plasmas, 2012

ABSTRACT

Physical Review Letters, 2013

Nonlinear electromagnetic stabilization by suprathermal pressure gradients found in specific regi... more Nonlinear electromagnetic stabilization by suprathermal pressure gradients found in specific regimes is shown to be a key factor in reducing tokamak microturbulence, augmenting significantly the thermal pressure electromagnetic stabilization. Based on nonlinear gyrokinetic simulations investigating a set of ion heat transport experiments on the JET tokamak, described by Mantica et al. [Phys. Rev. Lett. 107, 135004 (2011)], this result explains the experimentally observed ion heat flux and stiffness reduction. These findings are expected to improve the extrapolation of advanced tokamak scenarios to reactor relevant regimes.

Nuclear Fusion, 2011

In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiment... more In order to prepare adequate current ramp-up and ramp-down scenarios for ITER, present experiments from various tokamaks have been analysed by means of integrated modelling in view of determining relevant heat transport models for these operation phases. A set of empirical heat transport models for L-mode (namely, the Bohm-gyroBohm model and scaling based models with a specific fixed radial shape