Laboratory study of spiky potential structures associated with multi-harmonic shear-driven EIC waves

A ubiquitous feature of electric fields observed in the Earth's auroral region is their spiky, repetitive nature, and appearance as either unipolar or bipolar pulses. They have been observed on a number of satellites including S3-3, Polar, Viking, and FAST. These spiky structures have been associated with regions of upward ion flows with transverse shear, and multi-harmonic electrostatic ion cyclotron (EIC) waves. The occurrence of these spiky structures has been attributed to various nonlinear processes, e.g., solitary waves. We will present results of a laboratory experiment performed in a double-ended Q machine, in which spiky potential waveforms were observed in association with coherent multi-harmonic EIC waves in a current-less plasma having a region of parallel ion flow with transverse shear. The spiky waveforms are shown to result from the linear superposition of phase-coherent EIC waves.