Ion thermometry in ultracold neutral plasmas

Disorder-induced heating (DIH) is a well-known feature of ultracold neutral plasmas (UNPs). It occurs as excess electrical potential energy is converted to kinetic energy during a global relaxation of the plasma towards equilibrium. Fluorescence methods are used to measure the ion temperature. In this talk I will present three analysis methods for determining the ion temperature. PMT measurements give spatially-averaged temperatures with excellent time resolution. Except at very early times in the plasma expansion, these 'temperatures' are compromised by the hydrodynamic velocity. Spatially resolved fluorescence images can be analyzed pixel by pixel to produce a temperature map at a particular time. These high-resolution images often suffer from poor signal-to-noise characteristics. We demonstrate that ion temperatures can be obtained from a single image at late times in the plasma expansion. We will discuss ion temperature measurements in both magnetized and un-magnetized plasmas.