Coexistence of Lightning Generated Whistlers, Hiss and Lower Hybrid Noise Observed by e-POP (SWARM-E)–RRI

Whistler mode waves play a major role in regulating the lifetime of trapped electrons in the Earth’s radiation belts. Specifically, interaction with whistler mode hiss waves is one of the mechanisms that maintains the slot region between the inner and outer radiation belts. The generation mechanism of hiss is a topic still under debate with at least three prominent theories present in the literature. Lightning generated whistlers in their ducted or non-ducted modes are considered to be one of the possible sources of hiss. We present a study of new observations from the Radio Receiver Instrument (RRI) on the Enhanced Polar Outflow Probe (ePOP: also known as SWARM-E). RRI consists of two orthogonal dipole antennas, which enables polarization measurements, when the satellite boresight is parallel to the geomagnetic field. Here we present 105 ePOP - RRI events from 2014–2018, in which lightning whistlers(75) and hiss waves(39) were observed. In more than 50% of those whistler observations, hiss found to co-exist. Moreover, the whistler observations are correlated with observations of wave power at the lower-hybrid resonance. The observations and a whistler mode ray-tracing study suggest that multiple-hop lightning induced whistlers can be a source of hiss and plasma instabilities in the magnetosphere.

Co-Existance of Lightning Generated Whistlers, Hiss and Lower Hybrid Noise Observed by e- POP (SWARM-E) –RRI

Whistler mode waves play a major role in regulating the lifetime of trapped electrons in the Earth's radiation belts. Specifically, whistler mode hiss waves are one of the mechanisms that maintains the slot region between the inner and outer radiation belts. The generation mechanism of hiss is a topic still under debate with at least three prominent theories present in the literature. Lightning generated whistlers in their ducted or non-ducted modes, are considered to be one of the possible sources of hiss. We present a study of new observations from the Radio Receiver Instrument (RRI) on the Enhanced Polar Outflow Probe (ePOP: currently known as SWARM-E). RRI consists of two orthogonal dipole antennas, which enables polarization measurements, when the satellite boresight is parallel to the geomagnetic field. Here we present 75 passes of ePOP - RRI from 2014 - 2018, in which lightning whistlers and hiss waves were observed. In more than 50% of those passes hiss is found to co-exist with the lightning whistlers. Moreover, the whistler observations are correlated with observations of wave power at the lower-hybrid resonance. The observations and a whistler mode ray-tracing study suggest that multiple-hop lightning induced whistlers can be a source of hiss and plasma instabilities in the magnetosphere.

Parameter study of ICRH wave propagation in IShTAR

A crude first assessment of how waves behave is commonly made relying on decoupled dispersion equation roots. In the low density, low temperature region behind the last closed flux surface in a tokamak – where the density decays exponentially and where the lower hybrid resonance is crossed but where the thermal velocity is small enough to justify dropping kinetic (hot plasma) effects – the study of the wave behaviour requires the roots of the full cold plasma dispersion equation. The IShTAR (Ion cyclotron Sheath Test ARrangement) device will be adopted in the coming years to shed light on the dynamics of wave–plasma interactions close to radio frequency (RF) launchers and in particular on the impact of the waves on the density and their role in the formation of RF sheaths close to metallic objects. As IShTAR is incapable of mimicking the actual conditions reigning close to launchers in tokamaks; a parameter range needs to be identified for the test stand to permit highlighting of the relevant wave physics. Studying the coupled dispersion equation roots allowed us to find a suitable operation domain for performing experiments.