A5019260412- Magnetic confinement fusion research
- Ionosphere and magnetosphere dynamics
- Solar and Space Plasma Dynamics
- Superconducting Materials and Applications
- Laser-Plasma Interactions and Diagnostics
- Particle accelerators and beam dynamics
- Fusion materials and technologies
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Geomagnetism and Paleomagnetism Studies
- Plasma Diagnostics and Applications
- Stellar, planetary, and galactic studies
- Spacecraft and Cryogenic Technologies
- Nuclear physics research studies
- Fluid Dynamics and Turbulent Flows
- Atomic and Molecular Physics
- Nuclear reactor physics and engineering
- Astronomy and Astrophysical Research
- Inertial Sensor and Navigation
- Atomic and Subatomic Physics Research
- Laser-Matter Interactions and Applications
- Advanced Fiber Laser Technologies
- Adaptive optics and wavefront sensing
- Geophysics and Gravity Measurements
- Dust and Plasma Wave Phenomena
University of Maryland, College Park
2016-2025
United States University
2024
Los Alamos National Laboratory
2024
Max Planck Institute for Plasma Physics
2017-2018
Max Planck Society
2017-2018
The Graduate University for Advanced Studies, SOKENDAI
2018
Auburn University
2018
Princeton Plasma Physics Laboratory
2018
National Institute for Fusion Science
2018
Chalmers University of Technology
2016
Quasisymmetry is an unusual symmetry that can be present in toroidal magnetic fields, enabling the confinement of charged particles and plasma. Here it shown both quasiaxisymmetry quasihelical achieved to a much higher precision than previously thought over significant volume, resulting exceptional confinement. For 1 Tesla mean field far from axisymmetry (vacuum rotational transform >0.4), symmetry-breaking mode amplitudes throughout volume aspect ratio 6 made as small typical ∼50 μT...
We apply a continuation method to recently optimized stellarator equilibria with excellent quasi-axisymmetry generate new wide range of rotational transform profiles. Using these equilibria, we investigate how the affects fast-particle confinement, maximum coil–plasma distance, growth rate in linear gyrokinetic ion-temperature gradient simulations and ion heat flux corresponding nonlinear simulations. find values two-term quasi-symmetry error comparable or lower than those similar...
After completing the main construction phase of Wendelstein 7-X (W7-X) and successfully commissioning device, first plasma operation started at end 2015. Integral start-up using electron cyclotron resonance heating (ECRH) an extensive set diagnostics have been completed, allowing initial physics studies during operational campaign. Both in helium hydrogen, breakdown was easily achieved. Gaining experience with vessel conditioning, discharge lengths could be extended gradually. Eventually,...
The optimized, superconducting stellarator Wendelstein 7-X went into operation and delivered first measurement data after 15 years of construction one year commissioning. Errors in the magnet assembly were confirmend to be small. Plasma was started with 5 MW electron cyclotron resonance heating (ECRH) power five inboard limiters. Core plasma values keV, keV at line-integrated densities achieved, exceeding original expectations by about a factor two. Indications for core-electron-root found....
A stellarator is a magnetic field configuration used to confine plasma, and it candidate for fusion energy, as well general charged particle trap.A stellarator's typically produced using electromagnetic coils, the shaping of coils must be optimized achieve good confinement.SIMSOPT collection software components carrying out these optimizations.These include • Interfaces physics codes, e.g. magnetohydrodynamic (MHD) equilibrium.• Tools defining objective functions parameter spaces...
We present a novel method for numerically finding quasi-isodynamic stellarator magnetic fields with excellent fast-particle confinement and extremely small neoclassical transport. The works particularly well in configurations only one field period. examine the properties of these newfound configurations, including their transport coefficients, particle available energy trapped-electron-instability-driven turbulence, as degree to which they change when finite pressure profile is added....
Abstract The separation between the last closed flux surface of a plasma and external coils that magnetically confine it is limiting factor in construction fusion-capable devices. This plasma-coil must be large enough so components such as breeding blanket neutron shielding can fit coils. Plasma-coil affects reactor size, engineering complexity, particle loss due to field ripple. For some plasmas difficult produce desired shaping with distant coils, for other infeasible altogether. Here, we...
Selective enhancement ($>{10}^{3}$) of harmonics extending to the water window ($\ensuremath{\sim}4\text{ }\text{ }\mathrm{nm}$) generated in an argon gas filled straight bore capillary waveguide is demonstrated. This good agreement with modeling which indicates that multimode quasi-phase-matching achieved by rapid axial intensity modulations caused beating between fundamental and higher-order modes. Substantial pulse energies ($>10\text{ }\mathrm{nJ}$ per harmonic order) at wavelengths...
Several fast methods for computing stellarator coil shapes are compared, including the classical NESCOIL procedure (Merkel 1987 Nucl. Fusion 27 867), its generalization using truncated singular value decomposition, and a Tikhonov regularization approach we call REGCOIL in which squared current density is included objective function. Considering W7-X NCSX geometries, any desired level of regularization, find simultaneously achieves lower surface-averaged maximum values both (on winding...
The confinement of the guiding-centre trajectories in a stellarator is determined by variation magnetic field strength $B$ Boozer coordinates $(r,\unicode[STIX]{x1D703},\unicode[STIX]{x1D711})$ , but $B(r,\unicode[STIX]{x1D703},\unicode[STIX]{x1D711})$ depends on flux surface shape complicated way. Here we derive equations relating and rotational transform to surfaces cylindrical coordinates, using an expansion distance from axis. A related was done Garren ( Phys. Fluids B, vol. 3, 1991...
Quasi-symmetry can greatly improve the confinement of energetic particles and thermal plasma in a stellarator. The magnetic field quasi-symmetric stellarator at high pressure is significantly affected by bootstrap current, but computational cost accurate calculations has precluded use inside optimization. Here, new efficient method demonstrated for optimization configurations such that current profile consistent with geometry. approach based on fact all neoclassical phenomena quasi-symmetry...
Abstract We introduce a novel approach for the simultaneous optimization of plasma physics and coil engineering objectives using fixed-boundary equilibria that is computationally efficient applicable to broad range vacuum finite pressure scenarios. Our treats boundary shapes as independently optimized variables, penalizing mismatch between two quadratic flux term in objective function. Four use cases are presented demonstrate effectiveness approach, including simple complex stellarator...
We present new stellarator equilibria that have been optimized for reduced turbulent transport using nonlinear gyrokinetic simulations within the optimization loop. The routine involves coupling pseudo-spectral GPU-native code GX with equilibrium and DESC . Since allows fast simulations, we directly optimize heat fluxes. To handle noisy flux traces returned by these employ simultaneous perturbation stochastic approximation (SPSA) method only uses two objective function evaluations a simple...
Joint experiment/theory/modelling research has led to increased confidence in predictions of the pedestal height ITER. This work was performed as part a US Department Energy Research Target FY11 identify physics processes that control H-mode structure. The study included experiments on C-Mod, DIII-D and NSTX well interpretation experimental data with theory-based modelling codes. provides ability models for peeling–ballooning stability, bootstrap current, width scaling make correct...
In this work, we examine the validity of several common simplifying assumptions used in numerical neoclassical calculations for nonaxisymmetric plasmas, both by using a new continuum drift-kinetic code and considering analytic properties kinetic equation. First, phenomena are computed LHD W7-X stellarators versions equation, including commonly incompressible-ExB-drift approximation two other variants, corresponding to different effective particle trajectories. It is found that electric...
Quasisymmetric stellarators are appealing intellectually and as fusion reactor candidates since the guiding center particle trajectories neoclassical transport isomorphic to those in a tokamak, implying good confinement. Previously, quasisymmetric magnetic fields have been identified by applying black-box optimization algorithms minimize symmetry-breaking Fourier modes of field strength $B$. Here instead we directly construct cylindrical coordinates that leading order distance from axis,...
A method is given to rapidly compute quasisymmetric stellarator magnetic fields for plasma confinement, without the need call a three-dimensional magnetohydrodynamic equilibrium code inside an optimization iteration. The based on direct solution of equations and quasisymmetry using Garren & Boozer’s expansion about axis ( Phys Fluids B, vol. 3, 1991, p. 2805), it several orders magnitude faster than conventional approach. work here extends Landreman et al. J. Plasma Phys. , 85, 2019,...
The results from the investigation of neoclassical core transport and role radial electric field profile (Er) in first operational phase Wendelstein 7-X (W7-X) stellarator are presented. In plasmas, details Er expected to have a strong effect on both particle heat fluxes. Investigation is important understanding validation calculations. closely related perpendicular plasma flow (u⊥) through force balance equation. This allows be inferred measurements velocity, which can measured using x-ray...
Magnetic fields with quasi-symmetry are known to provide good confinement of charged particles and plasmas, but the extent which can be achieved in practice has remained an open question. Recent work [M. Landreman E. Paul, Phys. Rev. Lett. 128, 035001, 2022] reports discovery toroidal magnetic that quasi-symmetric orders-of-magnitude higher precision than previously fields. We show these accurately produced using electromagnetic coils only moderate engineering complexity, is, have low...
A linear array of n calcite crystals is shown to allow the generation a high contrast (>10:1) train 2n energy (>100 μJ) pulses from single ultrafast laser pulse. Advantage taken pulse-splitting properties birefringent crystal, where an incident pulse can be split into two with orthogonal polarizations and equal intensity, separated temporally in proportion thickness crystal traversed difference refractive indices optic axes. In work presented here seven sequentially doubled used produce 128...
The impurity transport in magnetically confined plasmas under some conditions finds neither quantitatively nor qualitatively a satisfactory theory-based explanation. This compromises the successful realization of thermo-nuclear fusion for energy production since accumulation is known to be one causes that limits plasma performance through radiative losses and dilution. Under stellarator reactor-relevant conditions, supported by negative (inwards pointing) radial electric field which must...
Collisionless physics primarily determines the transport of fusion-born alpha particles in 3D equilibria. Several mechanisms have been implicated stellarator configurations, including stochastic diffusion due to class transitions, ripple trapping, and banana drift-convective orbits. Given guiding center dynamics a set six quasihelical quasiaxisymmetric equilibria, we perform classification trapping states mechanisms. In addition drift convection transport, observe substantial...
A method is demonstrated to rapidly calculate the shapes and properties of quasi-axisymmetric quasi-helically symmetric stellarators. In this approach, optimization applied equations magnetohydrodynamic equilibrium quasisymmetry, expanded in small distance from magnetic axis, as formulated by Garren & Boozer [ Phys. Fluids B, vol. 3, 1991, p. 2805]. Due reduction expansion, computational cost significantly reduced, times order 1 cpu second, enabling wide high-resolution scans over...