Plasma density effects on the three-body recombination rate coefficients

Hahn, Yukap

doi:10.1016/s0375-9601(97)00287-9

Cited by 68 publications

(62 citation statements)

References 12 publications

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“…However, the unphysical divergent behavior of the rate as T e → 0 indicates that this scaling must break down at sufficiently low temperatures. Modifications of the rate associated with the nonideality of strongly coupled plasmas have been demonstrated analytically [42][43][44][45] and with molecular dynamics simulations [46,47]. Quantum effects associated with the wave character of the electrons can also play a role at sufficiently low temperatures, if the electronic de Broglie wavelength becomes noticeable on the spatial scale of the TBR process [48].…”

Section: Three-body Recombinationmentioning

confidence: 99%

Heating mechanisms in radio-frequency-driven ultracold plasmas

2012

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Several mechanisms by which an external electromagnetic field influences the temperature of a plasma are studied analytically and specialized to the system of an ultracold plasma (UCP) driven by a uniform radiofrequency (rf) field. Heating through collisional absorption is reviewed and applied to UCPs. Furthermore, it is shown that the rf field modifies the three-body recombination process by ionizing electrons from intermediate high-lying Rydberg states and upshifting the continuum threshold, resulting in a suppression of three-body recombination. Heating through collisionless absorption associated with the finite plasma size is calculated in detail, revealing a temperature threshold below which collisionless absorption is ineffective.

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Section: Three-body Recombinationmentioning

confidence: 99%

Heating mechanisms in radio-frequency-driven ultracold plasmas

2012

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“…Modifications to eq. 2 to correct for low temperatures by using a density dependent cutoff for the Rydberg levels created by 3BR [4] do not apply to our plasma. The the-ory modifications are only applicable for a plasma denser than ours by several orders of magnitude (our plasma is still in the weakly-coupled regime).…”

Section: Pacs Numbersmentioning

confidence: 99%

Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas

2007

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Three-body recombination, an important collisional process in plasmas, increases dramatically at low electron temperatures, with an accepted scaling of T −9/2 e . We measure three-body recombination in an ultracold neutral xenon plasma by detecting recombination-created Rydberg atoms using a microwave-ionization technique. With the accepted theory (expected to be applicable for weakly-coupled plasmas) and our measured rates we extract the plasma temperatures, which are in reasonable agreement with previous measurements early in the plasma lifetime. The resulting electron temperatures indicate that the plasma continues to cool to temperatures below 1 K. PACS numbers:Three-body recombination (e − + e − + A + → e − + A * ) is a fundamental collisional process in plasmas that is dominant at sufficiently low electron temperatures due to its T −9/2 e dependence. In ultracold plasmas (UCPs), the observation of copious Rydberg atom production [1] and the observation of T e almost independent of initial energies [2] show that three-body recombination (3BR) and its associated heating play a critical role in the evolution of UCPs. Early-time T e measurements[2] and simulations [3] suggest that the electrons remain weakly coupled, so that traditional 3BR theory is still valid (in the strong-coupling regime, the 3BR rate is predicted to be reduced below the 9/2 scaling law to a T −1 e rule [4]). A measurement of 3BR in an UCP can thus be used to test 3BR theory by using existing T e measurements. This is less than ideal, given the paucity of measurements and the sensitivity of the rate constant to T e due to the 9/2 power. Conversely, using 3BR theory, T e can be extracted from the measured 3BR rate. This is relatively insensitive to the value of the rate constant (due to a 2/9 power law), and can be used to make the first measurement of T e throughout the life of the plasma. In addition, modifications of the rate constant due to strong-coupling will overestimate T e , i.e. our extracted T e are an upper limit. We note that in addition to furthering our understanding of UCPs, a study of 3BR may aid in using plasmas with similar parameters (albeit at high magnetic fields) to optimize production of anti-hydrogen [5].In this work, we measure the instantaneous Rydberg atom production rate in an expanding ultracold xenon plasma as a function of the time elapsed after plasma formation. By applying a short microwave pulse to the UCP, the Rydberg population for principal quantum numbers N>35 is ionized and subsequently detected by a micro-channel plate detector. Using two such pulses separated by up to a few microseconds, we measure the refilling of the depleted Rydberg levels that form during the interval between the two pulses. In this manner we determine the instantaneous Rydberg formation rate during the plasma expansion. There are several processes that may contribute to this refill rate, including 3BR, radiative recombination, blackbody-driven transitions from low Rydberg levels to higher (and thus microwave-ionizable) levels,...

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“…At lower temperatures the properties of plasmas are expected to differ significantly. For instance, three-body recombination which is prevalent in high temperature plasmas, should be suppressed [2]. If the thermal energy of the particles is less than the Coulomb interaction energy, the plasma becomes strongly coupled, and the usual hydrodynamic equations of motion and collective mode dispersion relations are no longer valid [3].…”

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confidence: 99%

Creation of an Ultracold Neutral Plasma

et al. 1999

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We report the creation of an ultracold neutral plasma by photoionization of laser-cooled xenon atoms. The charge carrier density is as high as 2 × 10 9 cm −3 , and the temperatures of electrons and ions are as low as 100 mK and 10 µK, respectively. Plasma behavior is evident in the trapping of electrons by the positive ion cloud when the Debye screening length becomes smaller than the size of the sample. We produce plasmas with parameters such that both electrons and ions are strongly coupled.The study of ionized gases in neutral plasma physics spans temperatures ranging from 10 16 K in the magnetosphere of a pulsar to 300 K in the earth's ionosphere [1]. At lower temperatures the properties of plasmas are expected to differ significantly. For instance, three-body recombination which is prevalent in high temperature plasmas, should be suppressed [2]. If the thermal energy of the particles is less than the Coulomb interaction energy, the plasma becomes strongly coupled, and the usual hydrodynamic equations of motion and collective mode dispersion relations are no longer valid [3]. Strongly coupled plasmas are difficult to produce in the laboratory and only a handful of examples exist [4], but such plasmas do occur naturally in astrophysical systems.In this work we create an ultracold neutral plasma with an electron temperature as low as T e = 100 mK, an ion temperature as low as T i = 10 µK, and densities as high as n = 2×10 9 cm −3 . We obtain this novel plasma by photoionization of laser-cooled xenon atoms. Within the experimentally accessible ranges of temperatures and densities both components can be simultaneously strongly coupled. A simple model describes the evolution of the plasma in terms of the competition between the kinetic energy of the electrons and the Coulomb attraction between electrons and ions. A numerical calculation accurately reproduces the data.Photoionization and laser-cooling have been used before in plasma experiments. Photoionization in a 600 K Cs vapor cell produced a plasma with T e ≥ 2000 K [5], and a strongly coupled non-neutral plasma was created by laser-cooling magnetically trapped Be + ions [6]. A plasma is often defined as an ionized gas in which the charged particles exhibit collective effects [7]. The length scale which divides individual particle behavior and collective behavior is the Debye screening length λ D . It is the distance over which an electric field is screened by redistribution of electrons in the plasma, and is given by λ D = ǫ 0 k B T e /e 2 n. Here, ǫ 0 is the electric permittivity of vacuum, k B is the Boltzmann constant, and e is the elementary charge. An ionized gas is not a plasma unless the Debye length is smaller than the size of the system [7]. In our experiment, the Debye length can be as low as 500 nm, while the size of the sample is σ ≈ 200 µm. The condition λ D < σ for creating a plasma is thus easily fulfilled.The atomic system we use is metastable xenon in the 6s [3/2] 2 state. This state has a lifetime of 43 s [8] and can be treated as the groun...

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Plasma density effects on the three-body recombination rate coefficients

Cited by 68 publications

References 12 publications

Heating mechanisms in radio-frequency-driven ultracold plasmas

Heating mechanisms in radio-frequency-driven ultracold plasmas

Using Three-Body Recombination to Extract Electron Temperatures of Ultracold Plasmas

Creation of an Ultracold Neutral Plasma

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