Radiation cooling rates of a selenium plasma

Whitney, K. G.; Coulter, M. C.

doi:10.1109/27.8964

Cited by 11 publications

(6 citation statements)

References 31 publications

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“…Of interest is the sensitivity of the calculated gain coefficients to these free parameters, and, of particular interest, is the question, for what choice of these parameters will the gains from the Fe-like hole states be comparable to or exceed those from the Co-like hole states. One parameter choice, made to reduce the number of these free parameters, was to take the initial laser intensity in all of our calculations to be 3 × 10 18 W cm −2 by taking t = t 0 / − ln 3 × 10 18 /I max laser (5) in equation (3). By this choice, the initial ionization state of the cluster could be taken to be near, but not yet in, the Ni-like ground state, and in addition the intensity risetime becomes directly related to t 0 for a given I max laser .…”

Section: Gain Calculationsmentioning

confidence: 99%

“…Our atomic model has been constructed in two stages. To begin, a generalized average-atom-type xenon model was constructed [3], which consists of principal quantum number states in each ionization stage and which accounts for the correct degeneracy factors per state. The ionization dynamics in this approximation is described through the use of averageatom collisional and radiative rate formulae.…”

Section: Introductionmentioning

confidence: 99%

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X-ray amplification dynamics at ∼2.8 Å in intense laser irradiated xenon clusters: multiple hole dynamics

Petrova

Whitney²,

Davis

2011

J. Phys. B: At. Mol. Opt. Phys.

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In a series of experiments (Borisov et al 2008 J. Phys. B: At. Mol. Opt. Phys. 41 105602, and references 1 through 7 cited in this paper), the amplification of 2.71-2.88 Å x-rays was observed, gain coefficients between 27 and 104 cm −1 were measured, and a number of conjectures were made concerning the ionization stages that were involved in the x-ray amplification. It was conjectured, for example, that x-ray emissions from hole states in Cl-, K-, Ca-, and Ti-like xenon were being amplified. In this paper, our earlier xenon gain model (Petrova et al 2010 J. Phys. B: At. Mol. Opt. Phys. 43 025601) is extended to include singleand double-hole state production within the Fe-like ionization stage in addition to single-hole state production within the Co-like ionization stage in order to assess these conjectures. The gain model, based on flexible atomic code generated data (Gu 2008 Can. J. Phys. 86 675), includes Co-like and Fe-like hole-state generation in xenon through photoionization of 2s and 2p electrons. The hole-state dynamics is self-consistently coupled to an extensive collisional-radiative dynamics of the Ni-, Co-, and Fe-like ionization stages of xenon. In addition, the model includes tunnelling ionization rates that confirm the initial condition assumptions that were made in our earlier paper, and they are needed to support the interpretations of the measured broadband x-ray data. With the use of tunnelling ionization rates, we demonstrate how all of the N-shell, n = 4, electrons are striped from a xenon atom in less than a femtosecond at laser intensities larger than 10 19 W cm −2 . Our calculations also show that, under these initial conditions and with sufficiently high pumping rates ( 10 14 s −1 ), a range of gains larger than 50 cm −1 are achievable under select conditions from both Co-and Fe-like xenon single hole radiative decays, in conformity with experimental observations. However, the calculated gain coefficients are sensitive to the laser intensity, laser pulse risetime, the magnitude of the hole-state pumping rates, ion density, and electron and ion heating rates, and, in general, Co-like holes are found to have much higher gains than Fe-like hole states. These model calculations are also capable of producing gains from the double-hole states in Fe-like xenon, but they are much smaller than those generated in the Fe-like single-hole states in the cases included in this paper. Thus, our model calculations do not support the experimental data interpretation in which the measured gains were attributed to double holes in much higher ionization stages of xenon (Xe 32+ , Xe 34+ , Xe 35+ , and Xe 37+ ). Our calculations suggest that these ionization stages can be reached either early in time at much higher laser intensities (in excess of 1.5 × 10 20 W cm −2 for a 248 nm, ∼230 fs pulse) or later in time, and only because of tunnelling ionization.

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Section: Gain Calculationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

X-ray amplification dynamics at ∼2.8 Å in intense laser irradiated xenon clusters: multiple hole dynamics

Petrova

Whitney²,

Davis

2011

J. Phys. B: At. Mol. Opt. Phys.

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“…In all but the beryllium-like ionization stage of iron and the nickel-like ionization stage of tungsten, excited states with the same principal quantum number are combined into a single state with one average energy, [4] and averageatom rate coefficients [1] are used to couple the different principal-quantum-number states. In this modelling approach, degeneracy factors for the n-labelled states vary from one ionization stage to another [4]. Significantly more detailed level descriptions were employed for the beryllium-like ionization stage of iron and the nickel-like ionization stage of tungsten.…”

Section: Iron and Tungsten Ionization Modelsmentioning

confidence: 99%

“…The remainder of the ionization dynamics, into which the beryllium-like and nickel-like structures were placed for use in equations ( 4), was analytically constructed as described above and in [4]; it constitutes a first-step generalization of the average-atom modelling procedure [1]. Thus, the rate coefficients formulae defined in [1] are employed, but with degeneracy factors that vary as a function of both the principal quantum number of the state and the charge state of the ion.…”

Section: Iron and Tungsten Ionization Modelsmentioning

confidence: 99%

“…Such models ignore the large differences in state structure that exist throughout the different ionization stages of the L-, M-and N-shells (see [3] for example). Alternatively, when each ionization stage is separately treated and assigned the correct state structure [4], the approximation commonly used is to group or lump states by various quantum numbers, most simply the principal quantum number, n [4]. These lumped states are then coupled by averaging and summing over the rate coefficients that couple the substates within the lumped states.…”

Section: Introductionmentioning

confidence: 99%

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Effects of non-LTE multiplet dynamics on lumped-state modelling in moderate to high atomic number plasmas

Whitney¹,

Dasgupta

Davis

et al. 2007

J. Phys. B: At. Mol. Opt. Phys.

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Two atomic models of the population dynamics of substates within the n = 4 and n = 3 multiplets of nickel-like tungsten and beryllium-like iron, respectively, are described in this paper. The flexible atomic code (FAC) is used to calculate the collisional and radiative couplings and energy levels of the excited states within these ionization stages. These atomic models are then placed within larger principal-quantum-number-based ionization dynamic models of both tungsten and iron plasmas. Collisional-radiative equilibrium calculations are then carried out using these models that demonstrate how the multiplet substates depart from local thermodynamic equilibrium (LTE) as a function of ion density. The effect of these deviations from LTE on the radiative and collisional deexcitation rates of lumped 3s, 3p, 3d, 4s, 4p, 4d and 4f states is then calculated and least-squares fits to the density dependence of these lumped-state rate coefficients are obtained. The calculations show that, with the use of lumped-state models (which are in common use), one can accurately model the L- and M-shell ionization dynamics occurring in present-day Z-pinch experiments only through the addition of these extra, non-LTE-induced, rate coefficient density dependences. However, the derivation and use of low-order polynomial fits to these density dependences makes lumped-state modelling both viable and of value for post-processing analyses.

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Absolute intensity of a sodium-like resonance line for temperature diagnosis of neon-like X-ray laser plasmas

Coulter¹,

Apruzese

Whitney

1990

Appl. Phys. B

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Radiation cooling rates of a selenium plasma

Cited by 11 publications

References 31 publications

X-ray amplification dynamics at ∼2.8 Å in intense laser irradiated xenon clusters: multiple hole dynamics

X-ray amplification dynamics at ∼2.8 Å in intense laser irradiated xenon clusters: multiple hole dynamics

Effects of non-LTE multiplet dynamics on lumped-state modelling in moderate to high atomic number plasmas

Absolute intensity of a sodium-like resonance line for temperature diagnosis of neon-like X-ray laser plasmas

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