Measurement of Radio-Frequency (RF) Heating Saturation in Ultracold Plasmas

Radiofrequency (RF) fields cause electron heating in ultracold neutral plasmas (UNPs) through electron-ion collisions. The RF field drives the electrons in the plasma at an oscillating center-of-mass velocity, v_cm, relative to the ions. As the RF amplitude is increased, the electron velocity increases and the collision cross-section decreases, which would cause the heating rate to saturate if it were the only change in the effective collision rate. However, the increased velocity of the electrons can also have effects on electron screening, which in turn can increase the electron-ion collision rate and mitigate saturation. We have made measurements of the heating saturation to better understand the net contribution of each of these effects for a particular set of ultracold neutral plasma experimental conditions. We will present our measurements, along with theory predictions of the heating saturation from binary collision theory and linear response theory.