Dennis Papadopoulos

Generation of polarized shear Alfvén waves by a rotating magnetic field source

Experiments are performed in the Large Plasma Device at the University of California, Los Angeles to study the propagation of field-aligned, polarized kinetic shear Alfven waves radiated from a rotating magnetic field source created via a novel phased orthogonal loop antenna. Both right and left hand circular polarizations are generated at a wide range of frequencies from 0.21≤ω/Ωci<0.93. Propagation parallel to the background magnetic field near the Alfven velocity is observed along with a small parallel wave magnetic field component implying a shear mode. The peak-to-peak magnitude of the wave magnetic field, 33 cm away from the antenna, is on the order of 0.8% of the background field and drops off in the far field. The full width at half maximum of the wave energy changes little over a distance of 2.5 parallel wavelengths while the exponential decrease in wave energy as a function of distance can be attributed to collisional damping. Evidence of electron heating and ionization is observed during the pulse.

Highly efficient, megawatt-class, radio frequency source for mobile ionospheric heaters

Abstract A mobile heater for ionospheric modification studies requires a new megawatt (MW) class radio frequency (RF) source operating with an antenna array 1/20 the area of the High-Frequency Active Auroral Research Program (HAARP). To deliver an effective power density comparable to HAARP, the total source power must be in the range of 16 MW, thus demanding highly efficient sources. While the development of a whole multi-megawatt system for mobile ionospheric heaters is a complex engineering problem, in the present paper we describe only the work of our group on studying main features of a prototype MW-class vacuum electronics RF source for such system. The source design we are currently pursuing assumes class D operation using a modified version of the inductive output tube. The electron beam is a thin annular beam, switched on and off by a mod-anode as opposed to a grid. The beam is then passed through a decelerating gap, and its kinetic energy is extracted using a tunable resonant circuit that presents a constant impedance in the range of 3–10 MHz. With this design the beam is almost completely decelerated at all frequencies, thus achieving high efficiency.

Induced Alfvenic turbulence in the magnetosphere

Intense Alfvenic turbulence is artificially induced by the release of neutral gas in the equatorial plane perpendicular to the ambient magnetic field. The free energy associated with he orbital motion of the released neutral atoms is the energy source of the Alfvenic turbulence. Ions resulting from the photo ionized neutrals form a ring type distribution in velocity that is highly unstable to shear Alfven waves near the ion cyclotron harmonics of the released species. The nonlinear evolution of the primary waves leads to redistribution of the wave energy in k‐space and to excitation of secondary waves with characteristics appropriate for electron cyclotron resonance with the energetic electrons in the radiation belts that can induce intense pitch angle scattering of the trapped electrons.