Laboratory Excitation of Chirped EMIC Waves

The Electromagnetic Ion Cyclotron (EMIC) wave is a ubiquitous and consequential plasma wave mode in the Earth's magnetosphere. It possesses electric field components both perpendicular and parallel to the ambient magnetic field. As such, it interacts effectively with both ambient plasma ions and electrons. Importantly, it can scatter such particles trapped in the radiation belts into the loss cone.

Preliminary experiments are conducted at the Basic Plasma Science Facility (BaPSF) at UCLA using the Large Plasma Device (LaPD). The goal is to model a subset of conditions relevant to the generation of energetic-ion-driven EMIC waves in the Earth's magnetosphere and to observe the effects of such waves on the background plasma (ions and electrons) as well as other energetic, injected electron test particle populations.

Energetic ions (v_beam ~ v_A ) are injected at a variety of energies and pitch angles to excite the EMIC waves. This is achieved using a 15 keV, 10 A fast ion source mounted at the end of LAPD, opposite the plasma source. Either protons or helium (He⁺) ions can be injected into mixtures of He, H, Ne, or Ar plasmas. In these experiments, a variety of gradients in the downstream background magnetic field are used to investigate the conditions under which chirping, time-frequency signatures in the wave magnetic field spectra can best be achieved. Such chirping waves are believed to efficiently scatter energetic electrons into the loss cone to help deplete the Earth's radiation belts.