Single Domain Nanoparticle Transmitters

Abstract

Recent magnetospheric missions have revolutionized our understanding of Relativistic Electron (RE) Radiation Belt (RB) precipitation. The old concepts were based on stationary wave-particle interactions with broadband whistler hiss. The models relied on stationary marginal stability theory and quasilinear analysis with the loss resembling quasi-static drizzle. The new missions revealed the dominant role of non-linear, dynamic Triggered Emissions (TE) especiall the omnipresent L-mode Electromagnetic Ion Cyclotron (EMIC) waves driving microbursts that precipitate more than 1026 RE/day. In addition to the presence of anisotropic particle distributions a necessary requirement for TE is a threshold amplitude of the triggering wave. The triggering wave can be monochromatic or broadband while the triggered wave is amplified by several tens of dB, has a rising frequency and is composed by a number of subpackets. A resonant interaction between the triggered wave and RE is repeated many times during the triggering period while a substantial number of RE is precipitated through nonlinear wave trapping by the rising-tone emission. While under natural conditions the triggering wave is driven by anisotropic instability of energetic particles, Artificially Stimulated Emissions (ASE) have been observed only in the whistler mode when a VLF wave was injected in the magnetosphere from ground-based facilities such as the Siple station in the Antarctic and the HAARP facility in Alaska. While serious and sophisticated theories supported by simulations have been developed, there lack of cause and effect verification of the physics underlying ASE in the EMIC mode in both space and laboratory. In this paper we argue that new artificial magnetic materials allow for the first-time space-based injection of EMIC waves from small satellites with amplitude in excess of the theoretical threshold for triggering ASE. Theoretical analysis supported by observations and computer modeling indicates that a threshold amplitude of approximately 1 nT is required for EMIC triggering in the RBs and the vicinity of the ring current. Given the fact that at EMIC frequencies close to .8–.9 of the proton gyrofrequency fcp the injection cone is of the order or less than 1° spanning 10−4 steradian, injection of 1 W radiated power will result in magnetic field exceeding 1 nT over distances of several hundred km, sufficient to ignite EMIC triggering and precipitation. The radiation resistance of a conventional magnetic loop with radius 15 meter in the RB plasma at a frequency .8 f pc is of the order 10−4 Ohm requiring 100 A current to radiate 1 Watt with efficiency less than 10−4. The new transmitter concept is based on Single Domain Magnetic Nanoparticles (SDMN) and referred here as Magnetic Nano-Transmitter (MNT). SDMNs are small (10–20 nm radius), single domain, noninteracting magnetic grains with uniaxial magnetic anisotropy, dispersed in liquid or solid non-conducting matrix. They can be described as ensembles of noninteracting magnetic moments that when driven by an AC magnetic field, behave in manner similar to ordinary paramagnets, with exception that SDMNs are composed by many thousands of magnetic atoms and as a result have susceptibilities comparable to ferromagnets but with very low coercivity and almost no hysteresis loss. Depending on the size and matrix viscosity they can have response time smaller than microsec. It will be shown that an assembly of 50–50 Co-Fe SMDN diluted to 10 % in epoxy and driven by 1A AC current will produce the required magnetic field amplitude with more than 70% radiation efficiency. Proof of principle laboratory experiments using Ferrite Loop Antenna (FLA) as a substitute for the SDMNs are presented.