Wrick Sengupta
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View article: Periodic Korteweg–de Vries soliton potentials generate quasisymmetric magnetic field strength in a finite plasma-β equilibrium
Periodic Korteweg–de Vries soliton potentials generate quasisymmetric magnetic field strength in a finite plasma-β equilibrium Open
Quasisymmetry (QS) is a hidden symmetry of the magnetic field strength, B, that enables effective confinement of charged particles in a fully three-dimensional (3D) toroidal plasma equilibrium. Such equilibria are typically modeled by the …
View article: Periodic Korteweg-de Vries soliton potentials generate quasisymmetric magnetic field strength in a finite plasma-beta equilibrium
Periodic Korteweg-de Vries soliton potentials generate quasisymmetric magnetic field strength in a finite plasma-beta equilibrium Open
Quasisymmetry (QS) is a hidden symmetry of the magnetic field strength, B, that enables effective confinement of charged particles in a fully three-dimensional (3D) toroidal plasma equilibrium. Such equilibria are typically modeled by the …
View article: Enhanced collisional losses from a magnetic mirror using the Lenard–Bernstein collision operator
Enhanced collisional losses from a magnetic mirror using the Lenard–Bernstein collision operator Open
Collisions are crucial in governing particle and energy transport in plasmas confined in a magnetic mirror trap. Modern gyrokinetic codes model transport in magnetic mirrors, but some use approximate model collision operators. This study f…
View article: A Grad-Shafranov model for compact quasisymmetric stellarators
A Grad-Shafranov model for compact quasisymmetric stellarators Open
A Grad-Shafranov equation (GSE) valid for compact quasisymmetric stellarators is derived by an asymptotic expansion around a vacuum field carried to first order. We obtain an equation for the existence of flux surfaces leading up to the GS…
View article: Application of Lagrangian techniques for calculating the on-axis rotational transform
Application of Lagrangian techniques for calculating the on-axis rotational transform Open
The Floquet exponents of periodic field lines are studied through the variations of the magnetic action on the magnetic axis, which is assumed to be elliptical. The near-axis formalism developed by Mercier, Solov'ev and Shafranov is combin…
View article: A Grad-Shafranov model for compact quasisymmetric stellarators
A Grad-Shafranov model for compact quasisymmetric stellarators Open
A Grad-Shafranov equation (GSE) valid for compact quasisymmetric stellarators is derived by an asymptotic expansion around a vacuum field carried to first order. We obtain an equation for the existence of flux surfaces leading up to the GS…
View article: Sensitivity of the magnetic axis to variations in the magnetic field
Sensitivity of the magnetic axis to variations in the magnetic field Open
Lagrangian variational principles are used to locate the magnetic axis and to determine its sensitivity to variations in the magnetic field. Only the change in the magnetic field on axis is required to determine, to lowest order, the locat…
View article: An asymptotic Grad–Shafranov equation for quasisymmetric stellarators
An asymptotic Grad–Shafranov equation for quasisymmetric stellarators Open
A first-order model is derived for quasisymmetric stellarators where the vacuum field due to coils is dominant, but plasma-current-induced terms are not negligible and can contribute to magnetic differential equations, with $\beta$ of the …
View article: Universal Nonthermal Power-law Distribution Functions from the Self-consistent Evolution of Collisionless Electrostatic Plasmas
Universal Nonthermal Power-law Distribution Functions from the Self-consistent Evolution of Collisionless Electrostatic Plasmas Open
Collisionless systems often exhibit nonthermal power-law tails in their distribution functions. Interestingly, collisionless plasmas in various physical scenarios (e.g., the ion population of the solar wind) feature a v −5 tail in their ve…
View article: Enhanced Collisional Losses from a Magnetic Mirror Using the Lenard-Bernstein Collision Operator
Enhanced Collisional Losses from a Magnetic Mirror Using the Lenard-Bernstein Collision Operator Open
Collisions are crucial in governing particle and energy transport in plasmas confined in a magnetic mirror trap. Modern gyrokinetic codes model transport in magnetic mirrors, but some utilize approximate model collision operators. This stu…
View article: Universal non-thermal power-law distribution functions from the self-consistent evolution of collisionless electrostatic plasmas
Universal non-thermal power-law distribution functions from the self-consistent evolution of collisionless electrostatic plasmas Open
Distribution functions of collisionless systems are known to show non-thermal power law tails. Interestingly, collisionless plasmas in various physical scenarios, (e.g., the ion population of the solar wind) feature a $v^{-5}$ tail in the …
View article: Stellarator equilibrium axis-expansion to all orders in distance from the axis for arbitrary plasma beta
Stellarator equilibrium axis-expansion to all orders in distance from the axis for arbitrary plasma beta Open
A systematic theory of the asymptotic expansion of the magnetohydrostatics (MHS) equilibrium in the distance from the magnetic axis is developed to include arbitrary smooth currents near the magnetic axis. Compared with the vacuum and the …
View article: The Compelling Need for a Mid-Scale Stellarator Facility
The Compelling Need for a Mid-Scale Stellarator Facility Open
In the pursuit of the goal of commercial fusion as an abundant and safe source of energy, the stellarator is a leading concept with compelling attractiveness and demonstrated performance. In this white paper we, as a community of US resear…
View article: The Compelling Need for a Mid-Scale Stellarator Facility
The Compelling Need for a Mid-Scale Stellarator Facility Open
In the pursuit of the goal of commercial fusion as an abundant and safe source of energy, the stellarator is a leading concept with compelling attractiveness and demonstrated performance. A new mid-size stellarator is needed to retire risk…
View article: Phase-space entropy cascade and irreversibility of stochastic heating in nearly collisionless plasma turbulence
Phase-space entropy cascade and irreversibility of stochastic heating in nearly collisionless plasma turbulence Open
We consider a nearly collisionless plasma consisting of a species of “test particles” in one spatial and one velocity dimension, stirred by an externally imposed stochastic electric field—a kinetic analog of the Kraichnan model of passive …
View article: Asymptotic quasisymmetric high-beta three-dimensional magnetohydrodynamic equilibria near axisymmetry
Asymptotic quasisymmetric high-beta three-dimensional magnetohydrodynamic equilibria near axisymmetry Open
Quasisymmetry (QS), a hidden symmetry of the magnetic field strength, is known to support nested flux surfaces and provide superior particle confinement in stellarators. In this work, we study the ideal magnetohydrodynamic (MHD) equilibriu…
View article: An asymptotic Grad-Shafranov equation for quasisymmetric stellarators
An asymptotic Grad-Shafranov equation for quasisymmetric stellarators Open
A first-order model is derived for quasisymmetric stellarators where the vacuum field due to coils is dominant, but plasma-current-induced terms are not negligible and can contribute to magnetic differential equations, with $β$ of the orde…
View article: Stellarator equilibrium axis-expansion to all orders in distance from the axis for arbitrary plasma beta
Stellarator equilibrium axis-expansion to all orders in distance from the axis for arbitrary plasma beta Open
A systematic theory of the asymptotic expansion of the magnetohydrodynamic (MHD) equilibrium in the distance from the magnetic axis is developed to include arbitrary smooth currents near the magnetic axis. Compared to the vacuum and the fo…
View article: Asymptotic quasisymmetric high-beta 3D MHD equilibria near axisymmetry
Asymptotic quasisymmetric high-beta 3D MHD equilibria near axisymmetry Open
Quasisymmetry (QS), a hidden symmetry of the magnetic field strength, is known to support nested flux surfaces and provide superior particle confinement in stellarators. In this work, we study the ideal MHD equilibrium and stability of hig…
View article: Phase-space entropy cascade and irreversibility of stochastic heating in nearly collisionless plasma turbulence
Phase-space entropy cascade and irreversibility of stochastic heating in nearly collisionless plasma turbulence Open
We consider a nearly collisionless plasma consisting of a species of `test particles' in 1D-1V, stirred by an externally imposed stochastic electric field. The mean effect on the particle distribution function is stochastic heating. Accomp…
View article: FES 2023 Theory & Simulation Performance Target
FES 2023 Theory & Simulation Performance Target Open
The Report for the 2023 Theory & Simulation Performance Target (TSPT) is presented herein. The 1st, 2nd and 3rd Quarter Reports are given in Sec. I, Sec. II and Sec. III. These are unchanged from those previously submitted, except that in …
View article: Constructing the space of quasisymmetric stellarators through near-axis expansion
Constructing the space of quasisymmetric stellarators through near-axis expansion Open
A simplified view of the space of optimised stellarators has the potential to guide and aid the design efforts of magnetic confinement configurations suitable for future fusion reactors. We present one such view for the class of quasisymme…
View article: Constructing the space of quasisymmetric stellarators
Constructing the space of quasisymmetric stellarators Open
A simplified view of the space of optimised stellarators has the potential to guide and aid the design efforts of magnetic confinement configurations suitable for future fusion reactors. We present one such view for the class of quasisymme…
View article: Phases and phase-transitions in quasisymmetric configuration space
Phases and phase-transitions in quasisymmetric configuration space Open
We explore the structure of the space of quasisymmetric configurations identifying them by their magnetic axes, described as 3D closed curves. We demonstrate that this topological perspective divides the space of all configurations into we…
View article: Weakly quasisymmetric near-axis solutions to all orders
Weakly quasisymmetric near-axis solutions to all orders Open
We show that the equations satisfied by weakly quasisymmetric magnetic fields can be solved to arbitrarily high order in powers of the distance from the magnetic axis. This demonstration does not consider force balance. The existence of so…
View article: Steady plasma flows in a periodic non-symmetric domain
Steady plasma flows in a periodic non-symmetric domain Open
Steady plasma flows have been studied almost exclusively in systems with continuous symmetry or in open domains. In the absence of continuous symmetry, the lack of a conserved quantity makes the study of flows intrinsically challenging. In…
View article: Exact non-symmetric closed line vacuum magnetic fields in a topological torus
Exact non-symmetric closed line vacuum magnetic fields in a topological torus Open
Non-symmetric vacuum magnetic fields with closed magnetic field lines are of interest in the construction of stellarator equilibria. Beyond the result of D. Lortz, Z. Angew Math. Phys. 21, 196 (1970), few results are available. This work p…
View article: Near-axis expansion of stellarator equilibrium at arbitrary order in the distance to the axis
Near-axis expansion of stellarator equilibrium at arbitrary order in the distance to the axis Open
A direct construction of equilibrium magnetic fields with toroidal topology at arbitrary order in the distance from the magnetic axis is carried out, yielding an analytical framework able to explore the landscape of possible magnetic flux …
View article: Low-shear three-dimensional equilibria in a periodic cylinder
Low-shear three-dimensional equilibria in a periodic cylinder Open
We carry out expansions of non-symmetric toroidal ideal magnetohydrodynamic (MHD) equilibria with nested flux surfaces about a periodic cylinder, in which physical quantities are periodic of period $2\unicode[STIX]{x03C0}$ in the cylindric…
View article: Direct construction of optimized stellarator shapes. Part 2. Numerical quasisymmetric solutions
Direct construction of optimized stellarator shapes. Part 2. Numerical quasisymmetric solutions Open
Quasisymmetric stellarators are appealing intellectually and as fusion reactor candidates since the guiding center particle trajectories and neoclassical transport are isomorphic to those in a tokamak, implying good confinement. Previously…