Density and temperature scaling of disorder-induced heating in ultracold plasmas

Abstract

We report measurements and simulations of disorder-induced heating in ultracold neutral plasmas. Fluorescence from plasma ions is excited using a detuned probe laser beam while the plasma relaxes from its initially disordered nonequilibrium state. This method probes the wings of the ion velocity distribution. The simulations yield information on time-evolving plasma parameters that are difficult to measure directly and make it possible to connect the fluorescence signal to the rms velocity distribution. The disorder-induced heating signal can be used to estimate the electron and ion temperatures ∼100 ns after the plasma is created. This is particularly interesting for plasmas in which the electron and ion temperatures are not known.

Ion temperature evolution in an ultracold neutral plasma

“…The oscillation frequency has been shown by particlein-cell Yukawa simulations, 7 tree-code algorithms 12 and full molecular dynamics simulations 57 to agree well with ω pi , although electron screening softens the ion-ion interaction and slows the oscillations. 7,58 This deviation is small but observable for our conditions. As seen in Fig.…”

“…It has been shown, 7 however, that the velocity distribution shows a non-Maxwellian, high-velocity tail that relaxes on the same timescale as the oscillations, so Voigt fits will underestimate the ion RMS kinetic energy until the ions have achieved local thermal equilibrium. Therefore, to interpret our early-time measurements we compare them to a library of ion velocity distributions from molecular dynamics simulations of a homogeneous plasma.…”

“…Wigner-Seitz radius) and T is the temperature of the particle species of interest. Ions in UNPs have Γ i ≈ 2 − 4, and they have been used to study the equilibration of strongly coupled Coulomb systems after a potential quench [2][3][4][5][6][7][8] and collision rates beyond the regime of validity of Landau-Spitzer theory. 9 Strong coupling is of interest in many different plasma environments, 10 and the equilibration dynamics observed in UNPs in particular has been connected to laser-produced plasmas formed from clusters and solids 11 and proposed as a possible limitation in the brightness of photoemitted electron beams.…”

An experimental approach for investigating many-body phenomena in Rydberg-interacting quantum systems

“…A 7 mm diameter pushing beam propagates along the symmetry axis of the glass cell and guides the pre-cooled atoms through the 800 µm diameter exit hole of the differential pumping stage into the science chamber. To minimize vacuum contamination in the glass cell, we use 98% enriched 87 Rb dispensers as our atom source. For routine operation of the 2D-MOT we use the following parameters which were found to maximize the 3D-MOT loading rate.…”

“…This is possible through the use of a high flux 2D-MOT cold atom source and a three-beam optical dipole trap. The latter allows for varying the atomic density over three-orders of magnitude, including all-optical preparation of 87 Rb Bose-Einstein condensates, and for generating quasi-one-dimensional and three dimensional Rydberg systems. A special electrode structure is used to control electric fields and to field ionize Rydberg atoms for detection, without limiting the optical access.…”