scholarly journals Effect of ionospheric depth on the ionospheric feedback instability: cutoff and subsequent <I>E</I><sub>||</sub> modes

2010 ◽  
Vol 28 (9) ◽  
pp. 1777-1794 ◽  
Author(s):  
R. Cosgrove ◽  
R. Doe
Keyword(s):  
Growth Rate ◽  
Electric Fields ◽  
Finite Thickness ◽  
Higher Order ◽  
Plasma Structure ◽  
Higher Order Modes ◽  
Order Of Magnitude ◽  
E Region ◽  
The One ◽  
Two Fluid

Abstract. The ionospheric feedback instability (IFI), which involves feedback between ionospheric modifications and waves reflected off the magnetosphere, has up to this point been analyzed in terms of field line integrated (FLI) ionospheric quantities, that is, with the assumption that the ionospheric thickness can be ignored. In this work we test this assumption by solving the two-fluid equations for a representative ionospheric slab of finite thickness. We find that the results are for the most part incompatible with a description in terms of FLI quantities, and that their use can easily lead to an order of magnitude overestimation of the growth rate. This occurs because the first eigenmode, which is the one compatible with an FLI description, is cutoff above a certain frequency, leaving only higher order modes with wavelengths along B that are subsumed by the slab. Taking the results at face value, the parallel electric fields associated with the higher order modes are a possible contributor to electron heating and plasma structure in the E-region ionosphere.

scholarly journals Two-fluid tokamak equilibria with reversed magnetic shear and sheared flow

2007 ◽  
Vol 73 (3) ◽  
pp. 347-366 ◽  
Author(s):  
G. POULIPOULIS ◽  
G. N. THROUMOULOPOULOS ◽  
H. TASSO
Keyword(s):  
Pressure Gradient ◽  
Electric Fields ◽  
Fluid Model ◽  
Radial Electric Field ◽  
Plasma Phys ◽  
Magnetic Shear ◽  
Sheared Flow ◽  
Order Of Magnitude ◽  
The Impact ◽  
Two Fluid

AbstractThe aim of the present work is to investigate tokamak equilibria with reversed magnetic shear and sheared flow, which may play a role in the formation of internal transport barriers (ITBs), within the framework of the two-fluid model in cylindrical geometry. The study is based on exact self-consistent solutions by means of which the impact of the magnetic shear, s, and the ‘toroidal’ (axial) and ‘poloidal’ (azimuthal) ion velocity components, viz and viθ, on the radial electric field, Er, its shear, |dEr/dr|, and the shear of the E×B velocity, ωE×B≡|d/dr(E× B/B2)|, is examined. For a wide parametric regime of experimental concern it turns out that the contributions of the viz, viθ and pressure gradient (∇ Pi) terms to Er, |Er′| and ωE×B are of the same order of magnitude. The contribution of the ∇ Pi term is missing in the framework of magnetohydrodynamics (MHD) (G. Poulipoulis et al. 2004 Plasma Phys. Control. Fusion46, 639). The impact of s on ωE×B through the ∇ Pi term is stronger than that through the velocity terms; in particular for constant Bz the ion pressure gradient contribution to ωE×B at the point where dEr/dr=0 scales as (1−s)(2−s), whereas the ion flow contributions to ωE×B scale as (1−s). The results indicate that, like MHD, the magnetic shear and the sheared toroidal and poloidal velocities act synergetically in producing electric fields and therefore ωE×B profiles compatible with the ones observed in discharges with ITBs; owing to the ∇ Pi term, however, the impact of s on Er, |Er′| and ωE×B is stronger than that in MHD.

scholarly journals Influence of uncertainties of the empirical models for inferring the E-region electric fields at the dip equator

2016 ◽  
Vol 68 (1) ◽  
Author(s):  
Juliano Moro ◽  
Clezio Marcos Denardini ◽  
Laysa Cristina Araújo Resende ◽  
Sony Su Chen ◽  
Nelson Jorge Schuch
Keyword(s):  
Electric Fields ◽  
Empirical Models ◽  
E Region ◽  
Dip Equator

scholarly journals Electrical characterisation of higher order spin wave modes in vortex-based magnetic tunnel junctions

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Alex. S. Jenkins ◽  
Lara San Emeterio Alvarez ◽  
Samh Memshawy ◽  
Paolo Bortolotti ◽  
Vincent Cros ◽  
...  
Keyword(s):  
Spin Wave ◽  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Higher Order ◽  
Spin Torque ◽  
Micromagnetic Simulations ◽  
Higher Order Modes ◽  
Spin Diode ◽  
Super High Frequency ◽  
Wave Modes

AbstractNiFe-based vortex spin-torque nano-oscillators (STNO) have been shown to be rich dynamic systems which can operate as efficient frequency generators and detectors, but with a limitation in frequency determined by the gyrotropic frequency, typically sub-GHz. In this report, we present a detailed analysis of the nature of the higher order spin wave modes which exist in the Super High Frequency range (3–30 GHz). This is achieved via micromagnetic simulations and electrical characterisation in magnetic tunnel junctions, both directly via the spin-diode effect and indirectly via the measurement of the coupling with the gyrotropic critical current. The excitation mechanism and spatial profile of the modes are shown to have a complex dependence on the vortex core position. Additionally, the inter-mode coupling between the fundamental gyrotropic mode and the higher order modes is shown to reduce or enhance the effective damping depending upon the sense of propagation of the confined spin wave.

scholarly journals Preserving the Shape of Functions by Applying Multidimensional Schoenberg-Type Operators

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1016
Author(s):  
Camelia Liliana Moldovan ◽  
Radu Păltănea
Keyword(s):  
Applied Sciences ◽  
Degree Of Approximation ◽  
Higher Order ◽  
Second Order ◽  
Dimensional Case ◽  
Moduli Of Continuity ◽  
One Dimensional ◽  
Multidimensional Generalization ◽  
The One

The paper presents a multidimensional generalization of the Schoenberg operators of higher order. The new operators are powerful tools that can be used for approximation processes in many fields of applied sciences. The construction of these operators uses a symmetry regarding the domain of definition. The degree of approximation by sequences of such operators is given in terms of the first and the second order moduli of continuity. Extending certain results obtained by Marsden in the one-dimensional case, the property of preservation of monotonicity and convexity is proved.

scholarly journals Design of large mode area all-solid anti-resonant fiber for high-power lasers

2021 ◽  
Vol 9 ◽  
Author(s):  
Xin Zhang ◽  
Shoufei Gao ◽  
Yingying Wang ◽  
Wei Ding ◽  
Pu Wang
Keyword(s):  
High Power ◽  
Single Mode ◽  
Higher Order ◽  
Coupling Scheme ◽  
Resonant Coupling ◽  
Higher Order Modes ◽  
Mode Loss ◽  
Fiber Mode ◽  
Power Needs ◽  
Mode Area

Abstract High-power fiber lasers have experienced a dramatic development over the last decade. Further increasing the output power needs an upscaling of the fiber mode area, while maintaining a single-mode output. Here, we propose an all-solid anti-resonant fiber (ARF) structure, which ensures single-mode operation in broadband by resonantly coupling higher-order modes into the cladding. A series of fibers with core sizes ranging from 40 to 100 μm are proposed exhibiting maximum mode area exceeding 5000 μm2. Numerical simulations show this resonant coupling scheme provides a higher-order mode (mainly TE01, TM01, and HE21) suppression ratio of more than 20 dB, while keeping the fundamental mode loss lower than 1 dB/m. The proposed structure also exhibits high tolerance for core index depression.

scholarly journals Electron Symmetry Breaking during Attosecond Charge Migration Induced by Laser Pulses: Point Group Analyses for Quantum Dynamics

Symmetry ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 205
Author(s):  
Dietrich Haase ◽  
Gunter Hermann ◽  
Jörn Manz ◽  
Vincent Pohl ◽  
Jean Christophe Tremblay
Keyword(s):  
Laser Pulse ◽  
Symmetry Breaking ◽  
Electric Fields ◽  
Quantum Dynamics ◽  
Point Group ◽  
Laser Pulses ◽  
Charge Migration ◽  
Laser Control ◽  
The One ◽  
Superposition States

Quantum simulations of the electron dynamics of oriented benzene and Mg-porphyrin driven by short (<10 fs) laser pulses yield electron symmetry breaking during attosecond charge migration. Nuclear motions are negligible on this time domain, i.e., the point group symmetries G = D6h and D4h of the nuclear scaffolds are conserved. At the same time, the symmetries of the one-electron densities are broken, however, to specific subgroups of G for the excited superposition states. These subgroups depend on the polarization and on the electric fields of the laser pulses. They can be determined either by inspection of the symmetry elements of the one-electron density which represents charge migration after the laser pulse, or by a new and more efficient group-theoretical approach. The results agree perfectly with each other. They suggest laser control of symmetry breaking. The choice of the target subgroup is restricted, however, by a new theorem, i.e., it must contain the symmetry group of the time-dependent electronic Hamiltonian of the oriented molecule interacting with the laser pulse(s). This theorem can also be applied to confirm or to falsify complementary suggestions of electron symmetry breaking by laser pulses.

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