Using Charged Particle Imaging to Study Ultracold Plasma Expansion

TL;DR

This paper introduces a new imaging technique to analyze ultracold plasma expansion by capturing charged particle distributions, enabling measurement of plasma velocities and dynamics over time.

Contribution

The study develops a projection imaging method for ultracold plasmas, providing direct measurements of plasma expansion velocities and electron behavior.

Findings

Ion image size initially dominated by Coulomb explosion

Plasma expansion velocities match previous oscillation-based results

Electron image size decreases due to Coulomb forces and electron loss

Abstract

We develop a projection imaging technique to study ultracold plasma dynamics. We image the charged particle spatial distributions by extraction with a high-voltage pulse onto a position-sensitive detector. Measuring the 2D width of the ion image at later times (the ion image size in the first 20 $\mu$s is dominated by the Coulomb explosion of the dense ion cloud), we extract the plasma expansion velocity. These velocities at different initial electron temperatures match earlier results obtained by measuring the plasma oscillation frequency. The electron image size slowly decreases during the plasma lifetime because of the strong Coulomb force of the ion cloud on the electrons, electron loss and Coulomb explosion effects.