Numerical simulation of ultracold plasmas

Kuzmin, S. G.; O’Neil, T. M.

doi:10.1063/1.1497166

Cited by 101 publications

(197 citation statements)

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“…A variety of fascinating phenomena has been observed in these initially well characterized plasmas, including the expansion of the plasma and recombination to form Rydberg atoms, both of which occur on the time scale of tens of microseconds [6,7]. The fact that such clean experiments can be done has stimulated theoretical interest, and many theoretical papers on the subject have appeared [8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Evolution dynamics of a dense frozen Rydberg gas to plasma

Noel

Robinson

et al. 2004

Phys. Rev. A

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Dense samples of cold Rydberg atoms have previously been observed to spontaneously evolve to a plasma, despite the fact that each atom may be bound by as much as 100 cm −1 . Initially, ionization is caused by blackbody photoionization and Rydberg-Rydberg collisions. After the first electrons leave the interaction region, the net positive charge traps subsequent electrons. As a result, rapid ionization starts to occur after 1 s caused by electron-Rydberg collisions. The resulting cold plasma expands slowly and persists for tens of microseconds. While the initial report on this process identified the key issues described above, it failed to resolve one key aspect of the evolution process. Specifically, redistribution of population to Rydberg states other than the one initially populated was not observed, a necessary mechanism to maintain the energy balance in the system. Here we report new and expanded observations showing such redistribution and confirming theoretical predictions concerning the evolution to a plasma. These measurements also indicate that, for high n states of purely cold Rydberg samples, the initial ionization process which leads to electron trapping is one involving the interactions between Rydberg atoms.

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Section: Introductionmentioning

confidence: 99%

Evolution dynamics of a dense frozen Rydberg gas to plasma

Noel

Robinson

et al. 2004

Phys. Rev. A

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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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“…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].…”

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confidence: 99%

“…Collisions form and then ionize Rydberg atoms, most of which have a binding energy roughly equal to k B T . This collisional equilibrium gives rise the so-called "thermal bottleneck," which is a minimum in the Rydberg state distribution near −4k B T [17]. A collision occasionally occurs that puts the atom in a Rydberg state below the bottleneck.…”

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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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Numerical simulation of ultracold plasmas

Cited by 101 publications

References 15 publications

Evolution dynamics of a dense frozen Rydberg gas to plasma

Evolution dynamics of a dense frozen Rydberg gas to plasma

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

Recombination Fluorescence in Ultracold Neutral Plasmas

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