Search NASA⌕ Search

SEARCH · Search NASA

Results for “plasma antenna”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Ionospheric effects to antenna impedance

The reciprocity between high power satellite antennas and the surrounding plasma are examined. The relevant plasma states for antenna impedance calculations are presented and plasma models, and hydrodynamic and kinetic theory, are discussed. A theory from which a variation in antenna impedance with regard to the radiated power can be calculated for a frequency range well above the plasma resonance frequency is give. The theory can include photo and secondary emission effects in antenna impedance calculations.

Bethke, K. H.↗
NASA NTRS1980

A note on antenna models in a warm isotropic plasma

The electron-transparent and electron-reflecting models of antennas in a warm isotropic plasma are reexamined. It is shown that a purely electrical treatment of both the models without an explicit use of the boundary condition on electron velocity yields the same results as those previously obtained through an electromechanical treatment. The essential difference between the two models is that for the electron-reflecting model, fields are nonzero only in the exterior region, while for the electron-transparent model, they are nonzero both in the exterior and interior regions of the antenna. This distinction helps in clarifying some misconceptions about these models of antennas in warm isotropic plasma.

Singh, N.↗
NASA NTRS1971

Waves along a cylindrical 'grid-like' antenna in an anisotropic compressible plasma.

The dispersion equation is obtained analytically of waves along an infinitely long cylindrical ?grid-like' antenna in an anisotropic compressible homogeneous plasma. Numerical solutions of this equation show that an external static magnetic field has great influence upon the anomalously dispersive region of the dispersion relation around the plasma frequency.

Yu, W.↗
NASA NTRS1994

Wave rectification in plasma sheaths surrounding electric field antennas

Combined measurements of Langmuir or broadband whistler wave intensity and lower-frequency electric field waveforms, all at 10-microsecond time resolution, were made on several recent sounding rockets in the auroral ionosphere. It is found that Langmuir and whistler waves are partically rectified in the plasma sheaths surrounding the payload and the spheres used as antennas. This sheath rectification occurs whenever the high frequency (HF) potential across the sheath becomes of the same order as the electron temperature or higher, for wave frequencies near or above the ion plasma frequency. This rectification can introduce false low-frequency waves into measurements of electric field spectra when strong high-frequency waves are present. Second harmonic signals are also generated, although at much lower levels. The effect occurs in many different plasma conditions, primarily producing false waves at frequencies that are low enough for the antenna coupling to the plasma to be resistive.

Boehm, M. H.↗
NASA NTRS2006

Simplified Fabrication of Helical Copper Antennas

A simplified technique has been devised for fabricating helical antennas for use in experiments on radio-frequency generation and acceleration of plasmas. These antennas are typically made of copper (for electrical conductivity) and must have a specific helical shape and precise diameter.

Petro, Andrew↗
DOE OSTI2024

Spatial decay of electromagnetic waves from hypervelocity impact plasmas

Due to the high kinetic energy of impactors in space, hypervelocity impacts on spacecraft can ablate spacecraft material and produce plasmas. These plasmas have been observed in ground-based experiments to produce electromagnetic pulses (EMPs) and are suspected to be a cause of spacecraft anomalies. The initial EMP that is produced after plasma formation is replicated using a 2D electromagnetic plasma simulation, consisting of a discontinuous Galerkin, particle-in-cell (DG-PIC) framework. The spontaneous formation of EMPs from an initial quasineutral plasma is consistent with previous works and show behavior similar to that of waves emitted by antennas. The EMP emits from the plasma with a frequency less than the plasma frequency associated with the point of maximum density, showing the importance of the density gradient, and the far-field region of the “plasma antenna” is estimated. From the proportionality between plasma frequency and EMP frequency, there is a direct correlation between plasma density and radiation. Finally, as the plasma density decreases, the EMP frequency decreases, which suggests that several observable phenomena, such as optical flashes, radio frequency emission, and microwave emission, all result from the same plasma-related mechanism within a single hypervelocity impact.

42 ENGINEERING↗
DOE OSTI2026

Modeling rf sheath formation in turbulent tokamak boundary plasma

During ICRF antenna operation, complex interactions between turbulent density profiles, nonlinear RF sheaths, and RF-induced convective transport are observed to alter plasma density in the tokamak edge [D’Ippolito et al., Nucl. Fusion 38, 1543 (1998)]. In this work, we explore the physics of such interactions via numerical modeling, using a nonlinear EM/plasma/sheath code (VSim) and profiles obtained from a fluid plasma turbulence code (Hermes) in a 3D slab domain containing biased side-wall limiters. RF-rectified sheath formation on antenna and limiter surfaces is observed as electromagnetic waves launched by the antenna are refracted through the turbulent density profile. On transport timescales, such sheath potentials have been shown to influence both the mean species density and its RMS fluctuation spectrum [Smithe et al., these proceedings]. On the faster RF timescales, we demonstrate that the converse is also true – regions of high plasma density near material surfaces give rise to the highest sheath potential amplitudes. When density is turbulent and spatially nonuniform, localized regions of high sheath potential (hotspots) may develop where high-density filaments intersect material surfaces. Such hotspots are of particular concern as sources of impurity sputtering, and we explore their behavior in response to changes both to the local plasma density and to antenna operating parameters and structure. Related results exploring the role of Faraday shields and/or enclosing structures in suppressing high sheath potentials for other devices (e.g. SPARC) will also be shown.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1987

Effects of space plasma discharge on the performance of large antenna structures in low Earth orbit

The anomalous plasma around spacecrafts in low Earth orbit represents the coma of an artificial comet. The plasma discharge is caused by an energetic disturbance of charged particles which were formerly in a state of equilibrium. The plasma can effect the passive and active radio frequency operation of large space antennas by inducing corona discharge or strong arcing in the antenna feeds. One such large space antenna is the 15-meter hoop column antenna which consists of a mesh membrane material (tricot knitted gold plated wire) reflector and carbon fiber tension cords. The atomic oxygen in the plasma discharge state can force the wire base metal particles through the gold lattice and oxydize the metal particles to build a Schottky-barrier contact at the point where the wires meet. This effect can cause strong deviations in the reflector performance in terms of antenna pattern and losses. Also, the carbon-fiber cords can experience a strength reduction of 30 percent over a 40-hour exposure time.

Blume, Hans-Juergen C.↗