Towards Stronger Coulomb Coupling in an Ultracold Neutral Plasma

Abstract

Ultracold neutral plasmas are strongly coupled Coulomb systems that are generated by photoionizing lasercooled atoms close to the ionization threshold. The strong coupling parameter Γ is limited at times later than ∼100 ns by disorder-induced heating. A recent simulation predicted that higher values of Γ can be realized in ultracold neutral plasmas if the plasma ions are excited to higher ionization states. In this paper we present recent results from an experiment that increases the strong coupling of an ultracold neutral plasma by promoting the plasma ions to the second ionization state. Using laser-induced fluorescence we map out the ion velocity distribution of the Ca + ions in a partially doubly ionized plasma and show that the heating due to the second ionization depends on the timing of the second ionization laser pulses. We compare our results to MD simulations, which estimate that Γ increases from approximately 2.5 to 3.6.

The physics and applications of strongly coupled plasmas levitated in electrodynamic traps

“…We also mention the book of Fortov et al [70] which explores the physics of strongly coupled plasmas. A new frontier in the study of neutral plasmas are the ultracold neutral plasmas [287,288,289,290,291,292,293].…”

Disorder-induced heating of ultracold neutral plasmas created from atoms in partially filled optical lattices

“…A UCNP created from the above example SC lattice with σ/a = 0.087, at the typical experimental limit of f = 0.5, would have eq = 6.7, compared to eq = 2.2 for disordered atoms. Our results show that by creating UCNP from opticallattice trapped atoms, even with imperfect filling fraction, an increase in eq may be achieved that is comparable to the expected increases using doubly ionized [33] or Rydbergblockade correlated atoms [9,16]. Achieving an increase in eq by greater than an order of magnitude compared to disordered ions would require f > 0.8 and cooling of the atoms to near the vibrational ground state of the lattice trapping potential.…”

Calibrated heating rate measurements using electric-field-induced electron extraction in ultracold neutral plasmas

“…Their cold and tuneable temperatures, dilute and adjustable densities, and known ionization states mean that UNPs are very classical (i.e. quantum effects are expected to be very small), their dynamics have time scales that are accessible to conventional electronics, they do not have detectable collisions with neutral atoms, their ions and electrons can have an adjustable amount of strong coupling (Ichimaru 1982;Lyon & Bergeson 2015;Chen, Witte & Roberts 2017;Langin, Gorman & Killian 2019) and because of their cold temperatures they can be strongly magnetized at easily accessible laboratory magnetic fields (Baalrud & Daligault 2017;Sprenkle et al 2022). Through scaling relations, the experimentally measured or theoretically determined properties of UNPs can be related to more complicated plasmas at higher temperatures and densities (Bergeson et al 2019), including plasmas used for fusion (Betti & Hurricane 1999), having conditions like those of fusion plasmas (Frenje et al 2015) and dense astrophysical plasmas (Paquette et al 1986;van Horn 1991;Paxton et al 2015).…”

“…Their cold and tuneable temperatures, dilute and adjustable densities, and known ionization states mean that UNPs are very classical (i.e. quantum effects are expected to be very small), their dynamics have time scales that are accessible to conventional electronics, they do not have detectable collisions with neutral atoms, their ions and electrons can have an adjustable amount of strong coupling (Ichimaru 1982; Lyon & Bergeson 2015; Chen, Witte & Roberts 2017; Langin, Gorman & Killian 2019) and because of their cold temperatures they can be strongly magnetized at easily accessible laboratory magnetic fields (Baalrud & Daligault 2017; Sprenkle et al. 2022).…”