Helicity Injection by Knotted Antennas into Electron Magnetohydrodynamical Plasmas

Rousculp, C. L.; Stenzel, R. L.

doi:10.1103/physrevlett.79.837

Cited by 13 publications

(6 citation statements)

References 21 publications

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“…The role of magnetic helicity -the scalar product of the magnetic field with the magnetic vector potential -on electron MHD has been investigated experimentally through the production of electron MHD heat pulses and the study of their transport (Stenzel et al 1995;Stenzel and Urrutia 1996;Rousculp and Stenzel 1997). In turbulence, the first effect reported in the literature is from two-dimensional direct numerical simulations.…”

Section: Introductionmentioning

confidence: 99%

Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence

Galtier

Meyrand

2014

J. Plasma Phys.

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International audienceThe role of magnetic helicity is investigated in kinetic Alfvén wave and oblique whistler turbulence in presence of a relatively intense external magnetic field b ₀ e _||. In this situation, turbulence is strongly anisotropic and the fluid equations describing both regimes are the reduced electron magnetohydrodynamics (REMHD) whose derivation, originally made from the gyrokinetic theory, is also obtained here from compressible Hall magnetohydrodynamics (MHD). We use the asymptotic equations derived by Galtier and Bhattacharjee (2003 Phys. Plasmas 10, 3065-3076) to study the REMHD dynamics in the weak turbulence regime. The analysis is focused on the magnetic helicity equation for which we obtain the exact solutions: they correspond to the entanglement relation, n ñ = -6, where n and ñ are the power law indices of the perpendicular (to b ₀) wave number magnetic energy and helicity spectra, respectively. Therefore, the spectra derived in the past from the energy equation only, namely n = -2.5 and ñ = -3.5, are not the unique solutions to this problem but rather characterize the direct energy cascade. The solution ñ = -3 is a limit imposed by the locality condition; it is also the constant helicity flux solution obtained heuristically. The results obtained offer a new paradigm to understand solar wind turbulence at sub-ion scales where it is often observed that -3 < n < -2.5

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Section: Introductionmentioning

confidence: 99%

Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence

Galtier

Meyrand

2014

J. Plasma Phys.

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“…Directional whistler antennas are not reciprocal for transmitting and receiving. 21,22 An antenna with rotating field produces no directionality.…”

Section: Discussionmentioning

confidence: 99%

“…Earlier experiments have reported antenna directionality. 21,22 The antennas consisted of a current knot or a torus with a linked loop through the center. Such antennas produced helical fields matching the helicity of whistler waves.…”

Section: Directional Radiation From Two Loop Antennasmentioning

confidence: 99%

Magnetic antenna excitation of whistler modes. I. Basic properties

Urrutia

Stenzel

2014

Physics of Plasmas

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Properties of magnetic loop antennas for exciting electron whistler modes have been investigated in a large laboratory plasma. The parameter regime is that of large plasma frequency compared to the cyclotron frequency and signal frequency below half the cyclotron frequency. The antenna diameter is smaller than the wavelength. Different directions of the loop antenna relative to the background magnetic field have been measured for small amplitude waves. The differences in the topology of the wave magnetic field are shown from measurements of the three field components in three spatial directions. The helicity of the wave magnetic field and of the hodogram of the magnetic vector in space and time are clarified. The superposition of wave fields is used to investigate the properties of two antennas for small amplitude waves. Standing whistler waves are produced by propagating two wave packets in opposite directions. Directional radiation is obtained with two phased loops separated by a quarter wavelength. Rotating antenna fields, produced with phased orthogonal loops at the same location, do not produce directionality. The concept of superposition is extended in a Paper II to generate antenna arrays for whistlers. These produce nearly plane waves, whose propagation angle can be varied by the phase shifting the currents in the array elements. Focusing of whistlers is possible. These results are important for designing antennas on spacecraft or diagnosing and heating of laboratory plasmas.

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“…We can use to our advantage one of the properties of the wave, its helicity. This property is used in Rousculp antenna design [6]. The antennas are designed to have a preferred helicity injection direction, i.e., they couple to the plasma preferentially along one direction.…”

Section: Plasma Antennamentioning

confidence: 99%

Dynamic soaring as a means to exceed the solar wind speed

Larrouturou

Higgins

Greason

2022

Front. Space Technol.

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A technique by which a spacecraft can interact with flows of ionized gas in space (the solar wind or interstellar medium) in order to be accelerated to velocities greater than the flow velocity is explored. Inspired by the dynamic soaring maneuvers performed by sea birds and gliders in which differences in wind speed are exploited to gain velocity, in the proposed technique a lift-generating spacecraft circles between regions of the heliosphere that have different wind speeds, gaining energy in the process without the use of propellant and only modest onboard power requirements. In the simplest analysis, the spacecraft motion can be modeled as a series of elastic collisions between regions of the medium moving at different speeds. More detailed models of the spacecraft trajectory are developed to predict the potential velocity gains and the maximum velocity that may be achieved in terms of the lift-to-drag ratio of the vehicle. A lift-generating mechanism is proposed in which power is extracted from the flow over the vehicle in the flight direction and then used to accelerate the surrounding medium in the transverse direction, generating lift (i.e., a force perpendicular to the flow). Large values of lift-to-drag ratio are shown to be possible in the case where a small transverse velocity is imparted over a large area of interaction. The requirement for a large interaction area in the extremely low density of the heliosphere precludes the use of a physical wing, but the use of plasma waves generated by a compact, directional antenna to impart momentum on the surrounding medium is feasible, with the excitation of R-waves, X-waves, Alfven waves, and magnetosonic waves appearing as promising candidates. A conceptual mission is defined in which dynamic soaring is performed on the termination shock of the heliosphere, enabling a spacecraft to reach speeds approaching 2% of c within two and a half years of launch without the expenditure of propellant. The technique may comprise the first stage for a multistage mission to achieve true interstellar flight to other solar systems.

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Helicity Injection by Knotted Antennas into Electron Magnetohydrodynamical Plasmas

Cited by 13 publications

References 21 publications

Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence

Entanglement of helicity and energy in kinetic Alfvén wave/whistler turbulence

Magnetic antenna excitation of whistler modes. I. Basic properties

Dynamic soaring as a means to exceed the solar wind speed

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