Radiative Recombination in the presence of a few-cycles light pulse

Two-color ionization of hydrogen by short intense pulses

Photoelectron energy spectra resulting by the interaction of hydrogen with two short pulses having carrier frequencies, respectively, in the range of the infrared and XUV regions have been calculated. The effects of the pulse duration and timing of the X-ray pulse on the photoelectron energy spectra are discussed. Analysis of the spectra obtained for very long pulses show that certain features may be explained in terms of quantum interferences in the time domain. It is found that, depending on the duration of the X-ray pulse, ripples in the energy spectra separated by the infrared photon energy may appear. Moreover, the temporal shape of the low frequency radiation field may be inferred by …

PHOTODETACHMENT OF F- BY SHORT LASER PULSE. COMPARISON BETWEEN EXPERIMENTS AND NUMERICAL RESULTS

Hydraulic assessment of an upgraded pipework arrangement for the DEMO divertor plasma facing components cooling circuit

Abstract In the context of the Work Package DIVertor (WPDIV) of the EUROfusion action, a research campaign has been carried out by University of Palermo in cooperation with ENEA to assess the thermal-hydraulic performances of the DEMO divertor cooling system, concentrating the attention on its 2019 Plasma Facing Components (PFCs) configuration, relevant to DEMO baseline 2017. The research activity has been performed following a theoretical-numerical technique based on the finite volume method and adopting the well-known ANSYS CFX CFD code. The PFCs cooling circuit thermal-hydraulic performances under nominal steady-state conditions, assessed mainly in terms of coolant total pressure drop, c…

ENERGY- AND ANGLE-RESOLVED ELECTRON DISTRIBUTION IN THE PHOTODETACHMENT OF F

We report calculations of energy- and angle-resolved photoelectron distribution of F(-) irradiated by a linearly strong short infrared pulse, performed by evaluating the photoelectron ejection probability in the framework of a modified Keldysh theory, taking into account the temporal behavior of the pulse and the spatial inhomogeneity of the laser intensity. Results of the calculations are compared with the measurements of the photoelectron angular distribution recently appearing in the literature. The oscillations found in the experimental data are explained in terms of quantum interference effects.

CONTROL OF RADIATIVE RECOMBINATION BY A STRONG LASER FIELD

Strong-field laser-assisted radiation recombination is investigated: (a) to explore the control possibilities with two laser fields having commensurable frequencies and (b) to get some insight into the influence of the medium (a plasma) in which recombination occurs. It is found that by varying the relative phase of the two fields it is possible to control enhancement, broadening and symmetry properties of the recombination differential emitted power. In the case of an anisotropic two-temperature plasma, an interesting interplay is found between the shape of the laser-modified electron velocity distribution function and the shape of the emitted X-ray photon power spectrum. The novel feature…

Analysis of 7Be and 210Pb concentration and 7Be/210Pb activity ratio in ground level air in Palermo (Italy).

Recently a renewed interest has been put on the use of radioactive tracers to study transport and mixing processes in the atmosphere. Among the most commonly used radioactive tracers in the atmosphere, 7Be and 210Pb have assumed an ever-increasing importance. Beryllium-7 is the product of the interaction of cosmic rays with Nitrogen and Oxygen nuclei. Its cosmogenic origin makes the measured concentrations strongly dependent on the geographical position and seasonal cycles. It emits 478 keV gamma photons and has a half-life of about 53 days.

Control of multiphoton radiative recombination through the action of two low-frequency fields

Interference effects caused by the simultaneous action of a two low frequency fields with commensurate frequencies during laser assisted radiative recombination (LARR) are investigated theoretically. Varying the relative phase of the two fields the following LARR features may be controlled: a) location of the maxima in the total emitted power; b) enhancement of the total emitted power; c) polar shape of the differential emitted power; d) shape of the emitted power spectra.

Enhancement and control of radiative recombination by a strong laser field

Seasonal ARIMA Models for Wind Speed Time Series

Modeling harmonic generation by a degenerate two-level atom

An analytical theory of the generation of high-order harmonics of laser radiation has been developed on the basis of a two-level model atom with degenerate levels. Among other parameters, onset, width, and cutoff of the plateau in the harmonic spectrum are obtained in simple analytical forms that connect the basic problem parameters and permit a transparent interpretation of the mechanism underlying the spectrum formation for this specific case. Selected numerical calculations are reported to corroborate the analytical findings and to investigate other harmonic-spectrum features.

Radiative recombination in the presence of a few cycle laser pulse.

We have investigated the laser-assisted radiative recombination in the presence of a few-cycle pulse with the aim of demonstrating means of controlling such process. Within the Coulomb-Volkov approach already employed to describe the radiative recombination assisted by a monochromatic laser field, we have found that the emitted photon spectrum is affected by both the cycle number nc and the carrier-envelope relative phase phi . In particular, it has been shown that the minimum and the maximum values of the emitted photon energy may be controlled by varying nc and phi . Finally, it has been found that the enhancement of radiative recombination occurring in the presence of a monochromatic fie…

Electron energy distribution in the photodetachment ofH−by two radiation fields

We report on the energy distribution of the electrons emitted in two-color photodetachment of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ in a highly nonlinear regime, and compare these results with the ones found by averaging the cross section obtained in the presence of a static field over the values taken by the low-frequency field in a cycle. Similarities and differences are discussed.

Radiative recombination in a strong laser field: low-frequency approximation

A theoretical treatment of the laser-assisted radiative recombination (LARR) is presented in which the low-frequency (LF) assumption is exploited. The merit of the proposed LF approximation is twofold. First, the LF approximation considerably simplifies the calculations of the transition rates, whereas the results obtained within this approximation are only slightly different from those obtained without resorting to it. Second, the LF approximation gives more insight into the physical picture of the process, which may be viewed as a two-step process. In the first step, the free electron propagates toward the ion, and its motion is described classically with motion changes ascribed mainly to…

On the numerical assessment of the thermal-hydraulic operating map of the DEMO Divertor Plasma Facing Components cooling circuit

Abstract Within the framework of the Work Package DIV 1 - “Divertor Cassette Design and Integration” of the EUROfusion action, a research campaign has been jointly carried out by University of Palermo and ENEA to investigate the thermal-hydraulic behaviour of the DEMO divertor cassette cooling system, focussing the attention on the 2018 configuration of the Plasma Facing Components (PFCs) circuit consistent with the DEMO baseline 2017. The research campaign has been carried out following a theoretical-computational approach based on the finite volume method and adopting the commercial Computational Fluid-Dynamic (CFD) code ANSYS CFX. A steady-state CFD analysis has been carried out for the …

Symmetries in harmonic generation by a two-color field: an application to a simple model atom

We show that the parity of the order of the harmonics generated by a bichromatic field with commensurate frequencies may be related to the invariance properties of the time-dependent Hamiltonian with respect to some suitable transformations. To simplify the mathematical treatment, we have used a simple model atom to perform calculations that show the effects of the relative phase of the driving fields. Harmonic generation has been described as a two-step process that involves replicas of the Stark levels. In agreement with other previous treatments in which other model atoms were used, we have found that a small contamination of the fundamental harmonic can produce significant modifications…

Probing Rydberg atoms through collisions with helium in the presence of static electric and magnetic fields

We report on field induced inelasticity effects in state-to-state transitions caused by collisions of helium with Rydberg atoms in the presence of parallel static electric and magnetic fields. Due to the phases accumulated by the wavefunctions of the states involved into the collision events, the transition cross sections plotted as a function of the external fields exhibit modulations. When the relative velocity of the colliding atoms is high enough, these modulations are wiped out, while sizable modifications of the cross sections may take place due to the alteration of the wavefunctions' spatial localization. The possibility of using the field-assisted collisions as a probe giving inform…

Influence of a Plasma Medium on Laser Assisted Multiphoton Radiative Eecombination

Wind Speed Forecasting by Box-Jenkins Models

The possibility of modelling observed wind speed time series and forecasting their future values is presented in this paper. Seasonal autoregressive integrated moving average (SARIMA) models are applied to time series formed by four years hourly average wind speed measurements in thirty sites of Sicily. Our approach is considerably different from the original one (the Box-Jenkins approach) since it is completely automatic. We use a peculiar feature of wind speed on a land area, its daily period, to identify a class of SARIMA models within which to find the best fitting model by information criteria (here we employ AICC). Here we report the results, concerning the fit and forecast accuracy, …

Wind Speed Forecasting

This paper aims at providing a general class of stochastic models for hourly average wind speed time series taking into account all the main features of wind speed data, namely autocorrelation, non-Gaussian distribution, seasonal and diurnal nonstationarity. It will be shown that the methodology developed in this study, tested using the data recorded in two sites of Italy, attains valuable results in terms both of modelling and forecasting.

Analytical evaluation of integrals occurring in bound-free transitions.

A class of three-dimensional integrals on spatial coordinates of the type occurring in treatments of multiphoton ionization of atoms and of other bound-free transitions is evaluated in closed form for both hydrogenic and Slater-type wave functions. The reported method of evaluation is illustrated with a number of examples, including the multiphoton ionization of hydrogen by a very intense laser field, when the ejected electrons have absorbed more photons than the minimum required to reach the continuum.

Controlling laser assisted radiative recombination with few-cycle laser pulses

We report on the radiative recombination of a free electron with a hydrogenic ion in the presence of a few-cycle pulses. It has been shown that the main features of the emission spectra may be described in the framework of a semiclassical model in which the recombination is viewed as a two-step process. The spectra width of the emitted photon energy is practically confined in a range of values in which the emission is classically allowed. Moreover, it has been found that spectra width can be controlled by varying the carrier envelope phase and/or the pulse peak intensity.

Signature of quantum interferences in above-threshold detachment of negative ions by a short infrared pulse

Numerical calculations of photodetachment of ${\mathrm{F}}^{\ensuremath{-}}$ irradiated by a linearly polarized strong short infrared pulse have been performed by evaluating the photoelectron ejection probability in the framework of a Keldysh-type approach modified to account for the temporal behavior of the pulse. The results of the calculations are in good agreement with measurements of energy spectra recently appearing in literature, and show features that may be explained in terms of quantum interferences in time domain.

Asymmetries in the momentum distributions of electrons stripped by a XUV chirped pulse in the presence of a laser field

The ionization of hydrogen by a chirped XUV pulse in the presence of a few cycle infrared laser pulse has been investigated. The electron momentum distribution has been obtained by treating the interaction of the atom with the XUV radiation at the first order of the time-dependent perturbation theory and describing the emitted electron through the Coulomb-Volkov wavefunction. The results of the calculations agree with the ones found by solving numerically the time-dependent Schr¨odinger equation. It has been found that depending on the delay between the pulses the combined effect of the XUV chirp and of the steering action on the infrared field brings about asymmetries in the electron momen…

Field-assisted photodetachment process to observe the ponderomotive shift

Two-color photodetachment of a negative ion in the presence of a constant magnetic field is proposed as a process in which to observe the ponderomotive shift. Appropriate calculations are reported of the process under consideration based on a simple one-electron model and with the basic physical parameters well within the experimental state of the art.

Stochastic models for wind speed time series: a case study

Stochastic models for wind speed forecasting

Abstract This paper is concerned with the problem of developing a general class of stochastic models for hourly average wind speed time series. The proposed approach has been applied to the time series recorded during 4 years in two sites of Sicily, a region of Italy, and it has attained valuable results in terms both of modelling and forecasting. Moreover, the 24 h predictions obtained employing only 1-month time series are quite similar to those provided by a feed-forward artificial neural network trained on 2 years data.

Signature of Quantum Interferences in Above Threshold Detachment of Negative Ions by a Short Infrared Pulse

The effect of an intense external linearly polarized radiation field on the angular distributions and polarization states of the photons emitted during the radiative capture of a free electron by a bare nucleus into the ground state of the bound system is investigated. On symmetry grounds it is predicted that emission of elliptically polarized photons occurs when the momentum of the electron beam is not aligned to the direction of the oscillating field. The predictions are corroborated by numerical calculations of recombination rates carried out within a modified Keldysh-type treatment, in order to account for Coulomb effects. It is found that strong modifications to the angular distributio…

Radiative Recombination in a Strong Laser Field

Recent advances of radiative recombination in the presence of strong laser fields are reported. The intense laser radiation is found to introduce new relevant features, among which enhancement and control of the emitted X-ray spectra are the most important. The influence of the plasma medium in which the process generally takes place is considered as well. The results of the recent investigations shed new light on the laser assisted radiative recombination physics and give relevant indications concerning the possibilities to have effective slow electrons and to balance the plasma heating, as needed in important applications.

Misure di radioattività ambientale a Palermo: analisi statistica delle concentrazioni in aria di 7Be e 210Pb

In questo lavoro sono presi in considerazione gli andamenti delle concentrazioni in aria di 7Be e, per un più limitato periodo di tempo di 210Pb, e si è proceduto ad una analisi statistica dei dati, prendendo in esame le serie temporali (integrandole per i dati mancanti) dei valori medi mensili e settimanali al fine di operare confronti omogenei con dati disponibili di altre zone geografiche. Sono state studiate le correlazioni fra le serie di dati per i due radionuclidi ed è stata effettuata l’analisi in frequenza al fine di evidenziare ciclicità stagionali. Le analisi effettuate mostrano l’importanza dei processi di trasporto in atmosfera e l’influenza dei parametri meteo-climatici (in pa…

Influence of a plasma medium on laser assisted radiative recombination

The problem of laser assisted radiation recombination, taking into account the influence of the plasma in which the elementary process takes place, is investigated theoretically. Among the reported results, remarkable broadening and enhancement of the X-ray photon emission spectrum is found, provided some conditions are met. First, a sufficiently intense laser field must assist the process. For enhancement, the intensity must be such that the amplitude of the quiver electron velocity be comparable or slightly larger than the electron thermal velocity. For broadening it is important that at the level of the elementary act of recombination several multiphoton channels be open. A judicious com…

Joint probability distributions for wind speed and direction. A case study in Sicily

In this study we analyze data of hourly average wind speed and direction measured at three different sampling stations located in Sicily (Italy) and provide a statistical model for their joint probability density function. Singly truncated from below Normal Weibull mixture distribution and a linear combination of von Mises distributions are used to model wind speed and direction. Sites with heterogeneous local conditions (prevailing wind direction and/or elevation) have been considered in order to investigate the reliability of the model here taken into consideration.

Radiative Recombination in strong laser field

A theoretical treatment of the laser-assisted radiative recombination (LARR) is presented in which the low-frequency (LF) assumption is exploited. The merit of the proposed LF approximation is twofold. First, the LF approximation considerably simplifies the calculations of the transition rates, whereas the results obtained within this approximation are only slightly different from those obtained without resorting to it. Second, the LF approximation gives more insight into the physical picture of the process, which may be viewed as a two-step process. In the first step, the free electron propagates toward the ion, and its motion is described classically with motion changes ascribed mainly to…

Instantaneous hourly and daily radiation on tilted surfaces

A simple model to evaluate the irradiance incident on tilted surfaces of various orientations is proposed in this paper. It is based on the knowledge of the monthly daily average values of global and diffuse radiation on horizontal surfaces and their distributions over a period of a day. These distributions are approximated by a modified Gaussian expression with two parameters, which take into account the morning-to-afternoon asymmetries. Integrating the irradiance over a period of an hour or a day, values of monthly hourly average and daily on variously oriented surfaces have been calculated for the locations of Barcelona, Genoa, and Montreal. The calculated values are generally in good ag…

control and enhancement of radiative recombination by a strong laser field

Laser assisted atomic ionization by a short XUV pulse

We report on numerical results of energy spectra of photoelectrons emitted by irradiating an hydrogen atom with a relatively weak single attosecond XUV pulse in the presence of a two-color IR laser pulse. The densities of probabilities have been obtained by treating the interaction of the atom with the XUV radiation at the first order of the time-dependent perturbation theory and describing the emitted electron through the Coulomb-Volkov wavefunction. The results of the calculations agree with the ones found by numerically solving the time-dependent Schrödinger equation. Specifically, we use an algorithm that implements an high precision variant of the Cranck Nicolson integration method and…

Instantaneous distribution of global and diffuse radiation on horizontal surfaces

Abstract The aim of this paper is to obtain a general expression for estimating both the instantaneous global and diffuse radiations on horizontal surfaces from the respective daily values. The proposed expression is a modified Gaussian distribution with two parameters which take into account its width and the asymmetries between morning and afternoon hours. The performance of the method has been tested by comparing the theoretical hourly results with the experimental data of six actinometric stations with different geographical location and climatic conditions. The comparison has shown that the method here proposed is accurate for both the diffuse and global radiation.

Analysis and modeling of wind directions time series

This work aims at studying some aspects of wind directions in Italy and supplying appropriate models. A comparison is presented between independent mixture and Hidden Markov models, which seem to be appropriate as far as the series we studied.

Probing Rydberg Atoms in the Presence of Static Electric and Magnetic Fields Through Collisions with Helium Atoms

Analisi statistica delle concentrazioni in aria di 7Be e 210Pb misurate a Palermo.

Vengono analizzati e discussi i risultati delle misure, effettuate con cadenza quasi giornaliera, delle concentrazioni in aria a Palermo di 7Be (1982-2005) e 210Pb (1995-2005). In particolare è esaminato l’andamento dei rapporti di attività dei due radionuclidi relativamente al periodo di disponibilità congiunta dei dati al fine di evidenziare possibili correlazioni tra i due radionuclidi e con i dati meteo-climatici locali. Il 7Be (tempo di dimezzamento 53,29 giorni) è il prodotto dell’interazione dei raggi cosmici con nuclei di azoto ed ossigeno. La sua origine cosmogenica rende le concentrazioni misurate fortemente dipendenti dalla posizione geografica e dai cicli stagionali. Esso emette…

Photodetachment ofH−in the presence of a low-frequency laser field

The photodetachment of a model one-electron ion simulating ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ in the presence of a low-frequency field is analyzed. Two different geometries are considered in order to get information on the effect of the ponderomotive energy shift \ensuremath{\Delta} on the photodetachment cross section. Our calculations suggest that a correspondence may be established between the ponderomotive shift and the photodetachment cross section, when the ejected electron may exchange only a few low-frequency photons. This is in qualitative agreement with recent experimental observations. When a large number of processes are open in which the detached electron may exchange low…

Probing Rydberg Atoms in the Presence of Static Electric and magnetic Fields Through Collisions with Helium Atoms. International Workshop and Seminar on Rydberg Physics. May 2004 (Dresden)

Multiphoton Radiative Recombination

Controlling laser assisted radiative recombination with few-cycle laser pulse.

Polarization and angular distribution of the radiation emitted in laser-assisted recombination

The effect of an intense external linear polarized radiation field on the angular distributions and polarization states of the photons emitted during the radiative recombination is investigated. It is predicted, on symmetry grounds, and corroborated by numerical calculations of approximate recombination rates, that emission of elliptically polarized photons occurs when the momentum of the electron beam is not aligned to the direction of the oscillating field. Moreover, strong modifications to the angular distributions of the emitted photons are induced by the external radiation field.

Photoionization of hydrogen by a chirped, short X-ray pulse in the presence of a laser field

The ionization of hydrogen by a chirped XUV pulse in the presence of a few cycle infrared laser pulse is investigated. It is found that the combined action of the chirped pulse and the laser eld brings about asymmetries in the photoelectron momentum distribution that may be exploited for obtaining information on both the chirp and XUV pulse duration.

Wind speed stochastic models: a case study for the mediterranean area

Energy- and angle-resolved electron distribution in the photodetachment ofF−

We report calculations of energy- and angle-resolved photoelectron distribution of ${\text{F}}^{\ensuremath{-}}$ irradiated by a linearly strong short infrared pulse, performed by evaluating the photoelectron ejection probability in the framework of a modified Keldysh theory, taking into account the temporal behavior of the pulse and the spatial inhomogeneity of the laser intensity. Results of the calculations are compared with the measurements of the photoelectron angular distribution recently appearing in the literature. The oscillations found in the experimental data are explained in terms of quantum interference effects.

Interference Effects in Photodetachment of F- in a Strong Circularly Polarized Laser Pulse

A numerical simulation of photodetachment of F{sup -} by a circularly polarized laser pulse has been accomplished by using a Keldysh-type approach. The numerical results are in agreement with measurements of photoelectron energy spectra recently reported in the literature. The features exhibited by the spectra are traced back to quantum interference effects, in the same spirit as in a double-slit experiment in the time doma0008.

Photodetachment of F− by short laser pulses. Comparison between experiments and numerical results

Recently, angle-resolved photoelectron spectra have been measured by exposing negative F− ions to linearly or circularly polarized infrared femtosecond laser fields. We compare the experimental results with numerical calculations carried out in the framework of a Keldysh-type theory modified to account for both the time shape and the spatial inhomogeneity of the pulse. In order to account for the finite duration of the laser pulse, our results have been obtained through calculations of photodetachment probabilities. By using the saddle-point method it is possible to show that the transition amplitude may be written as a coherent sum of terms giving rise to interferences. This circumstance s…

Laser Assisted Atomic Ionization by a Short XUV Pulse

We report on numerical results of energy spectra of photoelectrons emitted by irradiating an hydrogen atom with a relatively weak single attosecond XUV pulse in the presence of a two-color IR laser pulse. The densities of probabilities have been obtained by treating the interaction of the atom with the XUV radiation at the first order of the time-dependent perturbation theory and describing the emitted electron through the Coulomb-Volkov wavefunction. The results of the calculations agree with the ones found by numerically solving the time-dependent Schrödinger equation. Specifically, we use an algorithm that implements an high recision variant of the Cranck Nicolson integration method and …

Collisions of Helium with Rydgerg Atoms in the Presence of Static and Magnetic Field

Photodetachment o F- by a few-cycle circularly polarized laser field

We report on calculations of the above threshold detachment of F(-) by a few-cycle circularly polarized laser field, discussing the effects of both the carrier-envelope relative phase and the number of the cycle contained in a pulse on the angular distribution of ejected photoelectron. The results are analyzed in terms of a two-step semiclassical model: after the electrons are detached through tunnelling their motion is determined by the electric field pulse according to the classical dynamics laws. Anisotropies in the angular distributions of the electrons ejected on the plane perpendicular to the laser propagation direction are found that depend on the number of cycle of the laser pulse.

statistical modeling of wind velocity: individual and collective perspective

Taxonomy of correlations of wind velocity;an application to the Sicilian area.

Abstract We present an algorithm that allows us to analyze the cross-correlation of wind velocity measured in different locations; this algorithm is applied to 29 recording stations in Sicily. The results show that such correlations present a significant and persistent ultrametric structure that is influenced by the geographical neighborhood as well as by the presence of mountain and the sea. The algorithm presented, that is also able to reveal weak correlations, can be used as a starting point for the development of multivariate models of wind.

Radiative recombination in the presence of a few cycle light pulse

Analysis of 7Be and 210Pb concentration and 7Be/210Pb activity ratio in ground level air in Palermo (Italy)

A series of measurements of particulate samples collected on paper filters in Palermo (Italy) during 1995–2005 has been performed to detect 210Pb air activity concentration and, along with previous similar data on 7Be, to evaluate their activity ratio. Average values for the daily activity concentrations of 7Be and 210Pb are found to be 4.7 and 0.6 mBq/m3 , respectively, 9.8 being the average activity ratio. Data confirm a seasonal behavior for both radionuclides. A correlation between 7Be and 210Pb air activity concentrations seems to exist, despite their different origins. The time behaviors of both 7Be and 210Pb air concentrations and 7Be/ 210Pb activity ratio have been compared with som…

Radiation controlled energy of photoelectrons produced by two-color short pulses.

We report on numerical results of energy spectra of photoelectrons emitted by irradiating a hydrogen atom with the superposition of two pulses. The spectra have been obtained by numerical integration of the time dependent Schr¨odinger equation. The highest frequency component of the pulse has been assumed to have low intensity and such a frequency that a single photon may ionize the atom. Its duration has been assumed to lie in the range of subfemtoseconds. The lowest frequency component that redistribute the energy of the ionized electrons has an higher intensity and duration of few femtoseconds. We find that when the field are aligned, the electron energy spectra strongly depend on the ti…

Univariate and multivariate properties of wind velocity time series

We analyze the time series of hourly average wind speeds measured at 29 different stations located in Sicily, a region with a complex morphology. The investigation, performed from the univariate as well as the multivariate point of view, evidences that the statistical properties of wind at the single sites have features that are not reproduced by standard models and, thus, require specific modeling. Moreover, the synchronous evolution of wind velocity presents a cluster structure, obtained with different algorithms, that persists in the standard deviation too.