Justin Ball
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View article: On the interplay between plasma triangularity and micro-tearing turbulence
On the interplay between plasma triangularity and micro-tearing turbulence Open
In this work, we study the interplay between triangularity and micro-tearing turbulence using linear and nonlinear flux tube GENE simulations. We consider scenarios with negative and positive triangularity (PT) plasma shaping taken from ex…
View article: On the feasibility of Ohmically heated negative triangularity tokamak power plants
On the feasibility of Ohmically heated negative triangularity tokamak power plants Open
Negative triangularity (NT) plasmas achieve enhanced confinement without edge localized modes nor the need to exceed the L-H heating power threshold. Removing this H-mode accessibility constraint opens a new region of parameter space: scen…
View article: Global electromagnetic gyrokinetic simulations of internal transport barriers in reversed-shear tokamaks
Global electromagnetic gyrokinetic simulations of internal transport barriers in reversed-shear tokamaks Open
Internal transport barriers (ITB) form through turbulence suppression, often observed when the safety factor profile exhibits an off-axis minimum. This work aims at improving our understanding of the conditions enabling the development of …
View article: Reducing turbulent transport in tokamaks by combining intrinsic rotation and the low momentum diffusivity regime
Reducing turbulent transport in tokamaks by combining intrinsic rotation and the low momentum diffusivity regime Open
Based on the analysis of a large number of high-fidelity nonlinear gyrokinetic simulations, we propose a novel strategy to improve confinement in spherical tokamak plasmas by combining up-down asymmetric flux surface shaping with the Low M…
View article: A quasilinear model for momentum transport including rotation and electron-scale turbulence
A quasilinear model for momentum transport including rotation and electron-scale turbulence Open
In a previous paper, a new gyrokinetic quasilinear model was proposed to study turbulent momentum transport in tokamaks with up-down asymmetric plasma shaping and toroidal flow shear [H. Sun et al., Nuclear Fusion 64, 036026 (2024)]. In th…
View article: Electromagnetic instability and turbulence in plasmas with positive and negative triangularity
Electromagnetic instability and turbulence in plasmas with positive and negative triangularity Open
While a number of studies exist comparing positive triangularity (PT) and negative triangularity (NT) δ, the nature of how the normalized electron pressure β affects microinstabilities and turbulence in fusion devices with substantial δ ha…
View article: Intrinsic momentum transport driven by almost-rational surfaces in tokamak plasmas
Intrinsic momentum transport driven by almost-rational surfaces in tokamak plasmas Open
We demonstrate that a symmetry of the local gyrokinetic model is broken when the safety factor q is almost (but not exactly) a rational number and magnetic shear is $\hat{s} \approx 0$. Tokamaks with such a q profile will spontaneously rot…
View article: Doubling fusion power with volumetric optimization in magnetic confinement fusion devices
Doubling fusion power with volumetric optimization in magnetic confinement fusion devices Open
A technique, volumetric power optimization, is presented for enhancing the power output of magnetic confinement fusion devices. Applied to a tokamak, this approach involves shifting the burning plasma region to a larger plasma volume while…
View article: Turbulence-Generated Stepped Safety Factor Profiles in Tokamaks with Low Magnetic Shear
Turbulence-Generated Stepped Safety Factor Profiles in Tokamaks with Low Magnetic Shear Open
Nonlinear local and global gyrokinetic simulations of tokamak plasmas demonstrate that turbulence-generated currents flatten the safety factor profile near low-order rational surfaces when magnetic shear is low, even when the plasma $β$ is…
View article: Global electromagnetic gyrokinetic simulations of internal transport\n barriers in reversed-shear tokamaks
Global electromagnetic gyrokinetic simulations of internal transport\n barriers in reversed-shear tokamaks Open
This work aims at improving our understanding of the conditions enabling the\ndevelopment of an Internal transport barriers (ITB), using a more comprehensive\nphysical model, including low-$\\beta$ electromagnetic flux-driven simulations.\…
View article: Turbulence-Induced Safety Factor Profile Flattening at Rational Surfaces in Tokamaks with Low Magnetic Shear
Turbulence-Induced Safety Factor Profile Flattening at Rational Surfaces in Tokamaks with Low Magnetic Shear Open
In this paper, we investigate the effects of ion-scale turbulence-generated currents on the local safety factor profile under conditions of low magnetic shear and proximity to rational surfaces, relevant to Internal Transport Barrier (ITB)…
View article: Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part I: Linear simulations
Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part I: Linear simulations Open
This study examines the impact of low and zero magnetic shear, along with rational values of safety factor, on linear mode behavior in tokamak plasmas. We focus on how magnetic field line topology and parallel domain length influence linea…
View article: Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part II: Nonlinear simulations
Numerical study of turbulent eddy self-interaction in tokamaks with low magnetic shear. Part II: Nonlinear simulations Open
Using local nonlinear gyrokinetic simulations and building up on linear results from a companion paper (Volčokas 2024 Submitted for publication), we demonstrate that turbulent eddies can extend along magnetic field lines for hundreds of po…
View article: Reducing turbulent transport in tokamaks by combining intrinsic rotation and the low momentum diffusivity regime
Reducing turbulent transport in tokamaks by combining intrinsic rotation and the low momentum diffusivity regime Open
Based on the analysis of a large number of high-fidelity nonlinear gyrokinetic simulations, we propose a novel strategy to improve confinement in spherical tokamak plasmas by combining up-down asymmetric flux surface shaping with the Low M…
View article: Physics of the low momentum diffusivity regime in tokamaks and its experimental applicability
Physics of the low momentum diffusivity regime in tokamaks and its experimental applicability Open
Strong $E\times B$ plasma flow shear is beneficial for reducing turbulent transport. However, traditional methods of driving flow shear do not scale well to large devices such as future fusion power plants. In this paper, we use a large nu…
View article: Negative triangularity scenarios: from TCV and AUG experiments to DTT predictions
Negative triangularity scenarios: from TCV and AUG experiments to DTT predictions Open
Experiments, gyrokinetic simulations and transport predictions were performed to investigate if a negative triangularity (NT) L-mode option for the Divertor Tokamak Test (DTT) full-power scenario would perform similarly to the positive tri…
View article: On the feasibility of Ohmically heated negative triangularity tokamak power plants
On the feasibility of Ohmically heated negative triangularity tokamak power plants Open
Negative triangularity tokamak plasmas feature naturally enhanced confinement in the so-called L-mode regime, irrespective of the power of external heating. This is in contrast to conventional scenarios, which require exceeding a given hea…
View article: Study of impurity C transport and plasma rotation in negative triangularity on the TCV tokamak
Study of impurity C transport and plasma rotation in negative triangularity on the TCV tokamak Open
Carbon impurity transport is studied in the TCV tokamak using a charge exchange recombination diagnostic. TCVs flexible shaping capabilities were exploited to extend previous impurity transport studies to negative triangularity ( δ < 0). A…
View article: Physical insights from the aspect ratio dependence of turbulence in negative triangularity plasmas
Physical insights from the aspect ratio dependence of turbulence in negative triangularity plasmas Open
In this work, we study the impact of aspect ratio (the ratio of major radius R 0 to minor radius r) on the confinement benefits of negative triangularity (NT) plasma shaping. We use high-fidelity flux tube gyrokinetic GENE simula…
View article: Experiments and gyrokinetic simulations of TCV plasmas with negative triangularity in view of DTT operations
Experiments and gyrokinetic simulations of TCV plasmas with negative triangularity in view of DTT operations Open
Negative triangularity (NT) scenarios in TCV have been compared to positive triangularity (PT) scenarios using the same plasma shapes foreseen for divertor tokamak test tokamak operations. The experiments provided a NT/PT L-mode pair and a…
View article: Self-interaction of turbulent eddies in tokamaks with low magnetic shear
Self-interaction of turbulent eddies in tokamaks with low magnetic shear Open
Using local nonlinear gyrokinetic simulations, we demonstrate that turbulent eddies can extend along magnetic field lines for hundreds of poloidal turns in tokamaks with weak or zero magnetic shear $\hat{s}$. We observe that this parallel …
View article: Reducing transport via extreme flux-surface triangularity
Reducing transport via extreme flux-surface triangularity Open
Based on a gyrokinetic analysis of and extrapolation from TCV discharges with large negative and positive triangularity δ , the potential of extreme in reducing turbulent transport is assessed. Linearly, both positive and negative δ c…
View article: A new quasilinear model for turbulent momentum transport in tokamaks with flow shear and plasma shaping
A new quasilinear model for turbulent momentum transport in tokamaks with flow shear and plasma shaping Open
In tokamak experiments, sufficiently strong E × B flow shear reduces turbulent transport, thereby improving the prospects for fusion power plants. It is therefore of great importance to efficiently explore parameter space to find where str…
View article: A new quasilinear model for turbulent momentum transport in tokamaks with flow shear and plasma shaping
A new quasilinear model for turbulent momentum transport in tokamaks with flow shear and plasma shaping Open
In tokamak experiments, sufficiently strong $E\times B$ flow shear reduces turbulent transport, thereby improving the prospects for fusion power plants. It is therefore of great importance to efficiently explore parameter space to find whe…
View article: Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas
Study of fast-ion-driven toroidal Alfvén eigenmodes impacting on the global confinement in TCV L-mode plasmas Open
Following recent observations of unstable Toroidal Alfvén Eigenmodes (TAEs) in a counter-current Neutral Beam Injection (NBI) scenario developed in TCV, an in-depth analysis of the impact of such modes on the global confinement and perform…
View article: Analysis of edge transport in L-mode negative triangularity TCV discharges
Analysis of edge transport in L-mode negative triangularity TCV discharges Open
View article: Local gyrokinetic simulations of tokamaks with non-uniform magnetic shear
Local gyrokinetic simulations of tokamaks with non-uniform magnetic shear Open
In this work, we modify the standard flux tube simulation domain to include arbitrary ion gyroradius-scale variation in the radial profile of the safety factor. To determine how to appropriately include such a modification, we add a strong…
View article: A synthetic phase-contrast imaging diagnostic with spatial filtering for gyrokinetic simulations
A synthetic phase-contrast imaging diagnostic with spatial filtering for gyrokinetic simulations Open
A Phase-contrast imaging (PCI) diagnostic provides measurements of line-integrated electron density fluctuations. Localisation along the laser beam path can be achieved with a spatial filter that selects the wave-vector directions of the f…
View article: Ultra long turbulent eddies, magnetic topology, and the triggering of internal transport barriers in tokamaks
Ultra long turbulent eddies, magnetic topology, and the triggering of internal transport barriers in tokamaks Open
Local nonlinear gyrokinetic simulations of tokamak plasmas demonstrate that turbulent eddies can extend along magnetic field lines for hundreds of poloidal turns when the magnetic shear is very small. By accurately modeling different field…
View article: Local gyrokinetic simulations of tokamaks with non-uniform magnetic shear
Local gyrokinetic simulations of tokamaks with non-uniform magnetic shear Open
In this work, we modify the standard flux tube simulation domain to include arbitrary ion gyroradius-scale variation in the radial profile of the safety factor. To determine how to appropriately include such a modification, we add a strong…