Electron–ion recombination in strongly coupled cold plasmas under nonequilibrium conditions

Pohl, Thomas; Pattard, Thomas

doi:10.1088/0305-4470/39/17/s41

Cited by 12 publications

(9 citation statements)

References 23 publications

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“…They are created by photoionizing laser cooled atoms and therefore have very precisely controlled initial temperatures and densities [1,2,3,4]. Photoionization causes an impulsive hardening of the interparticle potential [5], and the pathway to (non)equilibrium can be studied in detail [6,7].The electron system equilibrates on the shortest time scales and largely determines how the plasma expands [8,9,10,11,12]. Indirect measurements of the electron temperature agree well with simulations [9,13,14].…”

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Recombination Fluorescence in Ultracold Neutral Plasmas

Bergeson

Robicheaux

2008

Phys. Rev. Lett.

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We present the first measurements and simulations of recombination fluorescence in ultracold neutral plasmas. In contrast with previous work, experiment and simulation are in significant disagreement. Comparison with a recombination model suggests that the disagreement could be due to the high energy portion of the electron energy distribution or to large energy changes in electron/Rydberg scattering. Recombination fluorescence opens a new diagnostic window in ultracold plasmas because it probes the deeply-bound Rydberg levels, which depend critically on electron energetics.PACS numbers: 34.80. Lx, 52.27.Gr, 52.27.Cm Ultracold neutral plasmas can provide new insights into relaxation phenomena in strongly coupled Coulomb systems. They are created by photoionizing laser cooled atoms and therefore have very precisely controlled initial temperatures and densities [1,2,3,4]. Photoionization causes an impulsive hardening of the interparticle potential [5], and the pathway to (non)equilibrium can be studied in detail [6,7].The electron system equilibrates on the shortest time scales and largely determines how the plasma expands [8,9,10,11,12]. Indirect measurements of the electron temperature agree well with simulations [9,13,14]. Disorder-induced heating, three body recombination (TBR), and electron/Rydberg scattering are important heating mechanisms in the plasma. The latter two are thought to occur on times that are long compared to the electron plasma frequency. Thus TBR can probe the electron system at early times in the plasma evolution after disorder-induced heating has occurred [15].In higher temperature plasmas, the TBR picture is an electron and ion colliding in the presence of another electron. The TRB rate is the two-body collision frequency (nσv th ) multiplied by the probability that a third body is one collision distance away (nb 3 ). The collision distance and cross section depend on the electron temperature (b = e 2 /4πǫ 0 k B T and σ = πb 2 ), giving the well-known TBR rate α 3 = Rn 2 T −9/2 , where R is the TBR rate coefficient [16].In a strongly-coupled system, this binary collision picture breaks down.When the nearest-neighbor potential energy exceeds the kinetic energy (Γ ≡ e 2 n 1/3 /4πǫ 0 k B T > 1), the plasma is strongly coupled. The average distance between electrons becomes comparable to the collision distance b ∼ n −1/3 . The electrons are in a constant collision and TBR becomes, in a sense, many-body recombination. A numerical simulation of early-time recombination suggest that even moderate initial coupling in the electron system changes the recombination rate by perhaps a factor of two [17]. Other theoretical treatments suggest larger changes [18,19]. However, there is no experimental evidence that TBR departs from the standard formulas [20].In this paper we present a new study of three-body recombination in ultracold neutral plasmas. We measure the time-dependent fluorescence emitted by the plasma following electron/ion recombination for a range of initial plasma densities and electr...

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Recombination Fluorescence in Ultracold Neutral Plasmas

Bergeson

Robicheaux

2008

Phys. Rev. Lett.

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“…One of the most important atomic-physics processes in cold plasmas is three-body recombination (TBR), which scales in temperature as T −9/2 [59,60,61] and most likely dominates radiative recombination. While in strong magnetic fields TBR rates are somewhat reduced [9,22], the process still plays an important role in plasma decay, and it is a key process in efforts to form and trap anti-hydrogen [23,24,25].…”

Section: Recombination Experimentsmentioning

confidence: 99%

Atoms and plasmas in a high-magnetic-field trap

Raithel¹,

Knuffman²,

Shah³

et al. 2008

AIP Conference Proceedings

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We investigate cold rubidium plasmas in a particle trap that has the unique capability to simultaneously laser-cool and trap neutral atoms as well as to confine plasmas in magnetic fields of about three Tesla. The atom trap is a high-field Ioffe-Pritchard laser trap, while the plasma trap is a Ioffe-Penning trap that traps electrons and ions in separate wells. The observed plasma dynamics is characterized by a breathing-mode oscillation of the positive (ionic) plasma component, which feeds back on the behavior of the negative (electron) component of the plasma. At higher densities, the observed oscillations become nonlinear. The electron component has been found to undergo rapid cooling. We further report on the recombination of magnetized plasmas into Rydberg atoms in transient traps and quasi-steady-state traps. In transient traps, large numbers of recombined Rydberg atoms in high-lying states are observed. In quasi-steady-state traps, the measured numbers of recombined atoms are lower and the binding energies higher.

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“…The electron temperature can be tuned from approximately 0.5 K to 1000 K. At low initial electron temperature, space-charge effects prevent electrons from leaving, and the plasmas are charge neutral [1]. The electrons screen the ion-ion interactions, playing an important role in the rate at which the ions thermalize the the plasma evolves [5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29].…”

Section: Introductionmentioning

confidence: 99%

Measurement and simulation of laser-induced fluorescence from nonequilibrium ultracold neutral plasmas

2009

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We report new measurements and simulations of laser-induced fluorescence in ultracold neutral plasmas. We focus on the earliest times, when the plasma equilibrium is evolving and before the plasma expands. In the simulation, the ions interact via the Yukawa potential in a small cell with wrapped boundary conditions. We solve the optical Bloch equation for each ion in the simulation as a function of time. Both the simulation and experiment show the initial Bloch vector rotation, disorder-induced heating, and coherent oscillation of the rms ion velocity. Detailed modeling of the fluorescence signal makes it possible to use fluorescence spectroscopy to probe ion dynamics in ultracold and strongly coupled plasmas.

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Electron–ion recombination in strongly coupled cold plasmas under nonequilibrium conditions

Cited by 12 publications

References 23 publications

Recombination Fluorescence in Ultracold Neutral Plasmas

Recombination Fluorescence in Ultracold Neutral Plasmas

Atoms and plasmas in a high-magnetic-field trap

Measurement and simulation of laser-induced fluorescence from nonequilibrium ultracold neutral plasmas

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