Exploring the Alfvén-wave acceleration of auroral electrons in the laboratory

Auroras take place only 100-400 kilometers overhead and are the culmination of space physics events beginning at the sun. Understanding the processes that cause auroras is therefore critical to our understanding of Earth’s interaction with its space environment. While auroras have drawn the attention of humankind for millennia, the last half-century of rocket and satellite borne experiments have revolutionized our understanding of auroral formation. The solar wind, a diffuse ionized gas in the plasma state of matter, emanates from the sun and distorts Earth’s magnetic field. The penultimate step in auroral formation occurs when electrons, guided along Earth’s magnetic field lines, “precipitate” onto the upper atmosphere and collide with neutral atoms. These collisions cause atomic excitations that relax and give off photons that make up auroras. However, the cause of electron precipitation is still debated. A growing body of satellite data indicates that plasma waves around the earth can transfer energy to electrons, accelerate them, and cause them to precipitate. One of the primary waves suspected in this process is the Alfvén wave. Unfortunately, because satellite measurements are taken along a moving trajectory, the data contain ambiguities, and there is not yet definitive evidence showing if Alfvén waves accelerate electrons.

In this thesis, the extra control afforded by laboratory experiments was used to study electron interactions with Alfvén waves. Experiments were performed in the Large Plasma Device, a premier facility for Alfvén wave research at UCLA. Alfvén wave interactions with electrons were recorded using a novel radio frequency diagnostic technique. Recent results have shown for the first time that Alfvén waves cause electrons to oscillate, an effect predicted to be associated with auroras that had never before been measured. Theory has been developed that accurately describes the measured effects. Additional experiments were performed, and initial analysis indicates the measurements captured more detailed interactions between Alfvén waves and electrons that are believed to play a direct role in producing auroras.