Linda Vahala

Thermal Lattice-Boltzmann Models (TLBM) for Compressible Flows

The progress and challenges in thermal lattice-Boltzmann modeling are discussed. In particular, momentum and energy closures schemes are contrasted. Higher order symmetric (but no longer space filling) velocity lattices are constructed for both 2D and 3D flows and shown to have superior stability properties to the standard (but lower) symmetry lattices. While this decouples the velocity lattice from the spatial grid, the interpolation required following free-streaming is just 1D. The connection between fixed lattice vectors and temperature-dependent lattice vectors (obtained in the Gauss–Hermite quadrature approach) is discussed. Some (compressible) Rayleigh–Benard simulations on the 2D octagonal lattice are presented for extended BGK collision operators that allow for arbitrary Prandtl numbers.

Superfluid Turbulence from Quantum Kelvin Wave to Classical Kolmogorov Cascades

The main topological feature of a superfluid is a quantum vortex with an identifiable inner and outer radius. A novel unitary quantum lattice gas algorithm is used to simulate quantum turbulence of a Bose-Einstein condensate superfluid described by the Gross-Pitaevskii equation on grids up to 5760(3). For the first time, an accurate power-law scaling for the quantum Kelvin wave cascade is determined: k(-3). The incompressible kinetic energy spectrum exhibits very distinct power-law spectra in 3 ranges of k space: a classical Kolmogorov k(-(5/3)) spectrum at scales greater than the outer radius of individual quantum vortex cores and a quantum Kelvin wave cascade spectrum k(-3) on scales smaller than the inner radius of the quantum vortex core. The k(-3) quantum Kelvin wave spectrum due to phonon radiation is robust, while the k(-(5/3)) classical Kolmogorov spectrum becomes robust on large grids.

Quantum lattice gas representation of some classical solitons

A quantum lattice gas representation is determined for both the non-linear Schrodinger (NLS) and Korteweg–de Vries (KdV) equations. There is excellent agreement with the solutions from these representations to the exact soliton–soliton collisions of the integrable NLS and KdV equations. These algorithms could, in principle, be simulated on a hybrid quantum-classical computer.

Electromagnetic Wave Scattering from Magnetic Fluctuations in Tokamaks

Cross sections are calculated for electromagnetic wave scattering and mode transformation from magnetic and density fluctuations in a homogeneous plasma. For the special case of scattering perpendicular to the magnetic field, density fluctuations scatter ordinary to ordinary and extraordinary to extraordinary modes—but cannot transform these modes. On the other hand, magnetic fluctuations perpendicular to the field can transform modes but cannot scatter on a single branch. For incident frequencies on the order of the electron plasma frequency or gyrofrequency, the cross sections for scattering and transformation due to field and density fluctuations have a similar value. Estimates are given for scattering in a tokamak plasma with special emphasis on the question of how to detect and localize magnetic field fluctuations. Ray tracing calculations, estimates of practical limitations on polarization technique, and lower bound estimates on density and magnetic fluctuation levels show that magnetic fluctuations can be detected and localized by this method.

Graphical and statistical analysis of airplane passenger cabin RF coupling paths to avionics

Portable wireless technology provides many benefits to modern day travelers. Over the years however, numerous reports have cited portable electronic devices (PEDs) as a possible cause of electromagnetic interference (EMI) to aircraft navigation and communication radio systems. PEDs may act as transmitters, both intentional and unintentional, and their signals may be detected by the various radio receiver antennas installed on the aircraft. Measurement of the radiated field coupling between passenger cabin locations and aircraft communication and navigation receivers, via their antennas is defined herein as interference path loss (IPL). IPL data is required for assessing the threat of PEDs to aircraft radios, and is very dependent upon airplane size, the interfering transmitter position within the airplane, and the location of the particular antenna for the aircraft system of concern. NASA Langley Research Center, Eagles Wings Inc., and United Airlines personnel performed extensive IPL measurements on several Boeing 737 airplanes. This paper provides a graphical and statistical analysis of IPL data measured onboard two Boeing 737 airplanes. The analysis reveals valuable insight into EMI field propagation characteristics, measurement repeatability, selection of test equipment, and interpretation of measurement data related to IPL.

Lattice Boltzmann and quantum lattice gas representations of one-dimensional magnetohydrodynamic turbulence

Abstract A simplified one-dimensional (1D) magnetohydrodynamics (MHD) is solved using a lattice Boltzmann and a quantum lattice gas model. It is shown that the magnetic field decreases the strength of the velocity shock fronts, with marked spikes in the magnetic field strength that gradually broaden in time. There is very good agreement between the lattice Boltzmann model—a representation of non-linear systems that circumvent the non-local non-linear advection by simple local non-linearities within the collision operator—and the quantum lattice gas—an algorithm that is unconditionally stable and appropriate for a hybrid quantum-classical computer.

Effects of alpha particles on the scattering function in CO2 laser scattering

It is shown that the alpha-particle contribution to the scattered power can be dominant in the coherent scattering of a CO2 laser in a Maxwellian plasma. For Ti = Te = 10 keV, the optimal forward-scattering angle is around 1.0°, with detection of the electron density fluctuation wavenumbers k⊥ >> k|| (relative to the toroidal magnetic field). A strong resonance occurs at the lower hybrid frequency. Because of the strong dependence of the scattered signal on the alpha-particle temperature and the alpha distribution function, it seems feasible that CO2 laser scattering, using heterodyne techniques, could give detailed local information on fusion alphas.

Wireless network simulation in aircraft cabins

An electromagnetic propagation prediction tool was used to predict electromagnetic field strength inside airplane cabins. A commercial software package, Wireless Insite/sup /spl reg//, was used to predict power levels inside aircraft cabins and the data was compared with previously collected experimental data. It was concluded that the software could qualitatively predict electromagnetic propagation inside the aircraft cabin environment.

Inelastic vector soliton collisions: a lattice-based quantum representation.

Lattice–based quantum algorithms are developed for vector soliton collisions in the completely integrable Manakov equations, a system of coupled nonlinear Schrödinger (coupled–NLS) equations that describe the propagation of pulses in a birefringent fibre of unity cross–phase modulation factor. Under appropriate conditions the exact 2–soliton vector solutions yield inelastic soliton collisions, in agreement with the theoretical predictions of Radhakrishnan et al. (1997 Phys. Rev. E 56, 2213). For linearly birefringent fibres, quasi–elastic solitary–wave collisions are obtained with emission of radiation. In a coupled integrable turbulent NLS system, soliton turbulence is found with mode intensity spectrum scaling as k−6.

Effect of magnetic and density fluctuations on the propagation of lower hybrid waves in tokamaks

Lower hybrid waves have been used extensively for plasma heating, current drive, and ramp‐up as well as sawteeth stabilization. The wave kinetic equation for lower hybrid wave propagation is extended to include the effects of both magnetic and density fluctuations. This integral equation is then solved by Monte Carlo procedures for a toroidal plasma. It is shown that even for magnetic/density fluctuation levels on the order of 10−4, there are significant magnetic fluctuation effects on the wave power deposition into the plasma. This effect is quite pronounced if the magnetic fluctuation spectrum is peaked within the plasma. For Alcator‐C‐Mod [I. H. Hutchinson and the Alcator Group, Proceedings of the IEEE 13th Symposium on Fusion Engineering (IEEE, New York, 1990), Cat. No. 89CH 2820‐9, p. 13] parameters, it seems possible to be able to infer information on internal magnetic fluctuations from hard x‐ray data—especially since the effects of fluctuations on electron power density can explain the hard x‐ray ...