Rydberg-atom formation in strongly correlated ultracold plasmas

Bannasch, G.; Pohl, Thomas

doi:10.1103/physreva.84.052710

Cited by 36 publications

(40 citation statements)

References 92 publications

(150 reference statements)

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“…Our experimental results were consistent with molecular dynamics modeling of our system. We report a measured electron strong coupling parameter as large as Γ = 0.35 (8), which demonstrates that experimental conditions at low density can achieve greater value of Γ than predicted in [24], consistent with other predictions [28,29]. In addition, we identify a previously unreported heating mechanism that occurs due to the presence of a DC electric field during UCP formation.…”

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confidence: 86%

Observation of a strong-coupling effect on electron-ion collisions in ultracold plasmas

2017

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Ultracold plasmas (UCPs) provide a well-controlled system for studying multiple aspects in plasma physics that include collisions and strong coupling effects. By applying a short electric field pulse to a UCP, a plasma electron center-of-mass (CM) oscillation can be initiated. For accessible parameter ranges, the damping rate of this oscillation is determined by the electron-ion collision rate. We performed measurements of the oscillation damping rate with such parameters and compared the measured rates to both a molecular dynamic (MD) simulation that includes strong coupling effects and a Monte-Carlo binary collision simulation designed to predict the damping rate including only weak coupling considerations. We found agreement between the experimentally measured damping rate and the MD result. This agreement did require including the influence of a previously unreported UCP heating mechanism whereby the presence of a DC electric field during ionization increased the electron temperature, but estimations and simulations indicate that such a heating mechanism should be present for our parameters. The measured damping rate at our coldest electron temperature conditions was much faster than the weak coupling prediction obtained from the Monte-Carlo binary collision simulation, which indicates the presence of a significant strong coupling influence. The density averaged electron strong coupling parameter Γ measured at our coldest electron temperature conditions was 0.35.Electron-ion collisions are a fundamental feature of plasmas that determine several plasma properties, such as electron-ion thermalization rates [1], transport coefficients (diffusion, electric conductivity) [2], and stopping power considerations that, for instance, influence achievable DT fusion [3,4]. For a weakly coupled plasma, the electron-ion collision rate is given by [5] where Z is the ion charge number, e is the elementary electron charge, n i is the ion density, ǫ 0 is the electric permittivity in vacuum, m e is the mass of an electron, v th = k b T e /m e , and ln Λ = ln (Cλ D /b 0 ) is called the Coulomb logarithm, where λ D is the Debye screening length, b 0 = e 2 /4πǫ 0 k b T is the characteristic large angle scattering impact parameter, where ǫ 0 is electric permittivity, and k b is Boltzmann constant, and C is a constant, suggested to be 0.765 in Ref. [1,6,7].The presence of the screening length in the collision rate shows collective effects are relevant in a plasma even for individual collisions. This comes about because of a logarithmic divergence in the computed collision rate arising from large impact parameter collisions. The screening in a plasma reduces the influence of such collisions by screening out the inter-particle Coulomb forces. When the screening length λ D is much larger than other scale lengths such as b 0 or the typical interparticle spacing given by the Wigner-Seitz radius a, the assumptions that go into the derivation of Eq. 1 are valid. For sufficiently cold and dense plasmas, however, λ D becomes on the order of...

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supporting

confidence: 86%

Observation of a strong-coupling effect on electron-ion collisions in ultracold plasmas

2017

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“…Moreover they show a nontrivial dependence on n. These features cannot be attributed to Doppler or saturation effects since, for the given experimental parameters, they are in the order of 100 kHz. Furthermore it has been repeatedly demonstrated that the bulk excitation of Rydberg atoms in the ultracold regime rapidly leads to a series of secondary effects such as fast ionization by collisions or radiation [9,12], production of plasmas [13][14][15], or blockade effects [16,17]. In our case, on the time scale of the excitation these secondary effects are certainly present and a complete understanding of the observed features necessarily requires one to take into account all of them.…”

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confidence: 79%

Continuous coupling of ultracold atoms to an ionic plasma via Rydberg excitation

et al. 2012

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We characterize the two-photon excitation of an ultracold gas of rubidium atoms to Rydberg states analyzing the induced atomic losses from an optical dipole trap. Extending the duration of the Rydberg excitation to several milliseconds, the ground-state atoms are continuously coupled to the formed positively charged plasma. In this regime we measure the n dependence of the plasma-induced blockade effect and we characterize the interaction of the excited states and the ground state with the plasma. We also investigate the influence of the quasielectrostatic trapping potential on the system, confirming the validity of the ponderomotive model for states with 20 n 120.

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“…(8). This is useful for plasmas that evolve from cold Rydberg gases, for example, where the initial electron temperature is not well defined.…”

Section: Discussionmentioning

confidence: 99%

“…These plasmas are typically generated by photo-ionizing lasercooled gases [1] or gases in an ultrasonic jet [2]. They are diagnosed using three-body recombination [3][4][5][6][7][8], thermalization rates [9][10][11][12], electron evaporation or rf absorption [3,[13][14][15][16][17][18], charged particle imaging and detection [2,19], and optical fluorescence [12,20,21] and absorption [22][23][24]. Theoretical calculations and simulations [25][26][27][28][29][30][31][32] give great insights into the properties of these plasmas.…”

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confidence: 99%

Limit of strong ion coupling due to electron shielding

2013

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We show that strong coupling between ions in an ultracold neutral plasma is limited by electron screening. While electron screening reduces the quasi-equilibrium ion temperature, it also reduces the ion-ion electrical potential energy. The net result is that the ratio of nearest-neighbor potential energy to kinetic energy in quasi-equilibrium is constant and limited to approximately 1 unless the electrons are heated by some external source. We support these conclusions by reporting new measurements of the ion velocity distribution in an ultracold neutral calcium plasma. These results match previously reported simulations of Yukawa systems. Theoretical considerations are used to determine the screened nearest-neighbor potential energy in the plasma.

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Rydberg-atom formation in strongly correlated ultracold plasmas

Cited by 36 publications

References 92 publications

Observation of a strong-coupling effect on electron-ion collisions in ultracold plasmas

Observation of a strong-coupling effect on electron-ion collisions in ultracold plasmas

Continuous coupling of ultracold atoms to an ionic plasma via Rydberg excitation

Limit of strong ion coupling due to electron shielding

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