Kinetic Energy Spread Research Articles

Subdiffusion of heavy quarks in hot QCD matter by the fractional Langevin equation

The subdiffusion phenomena are studied for heavy quarks dynamics in the hot QCD matter. Our approach aims to provide a more realistic description of heavy quark dynamics through detailed theoretical analyses and numerical simulations, utilizing the fractional Langevin equation framework with the Caputo fractional derivative. I present numerical schemes for the fractional Langevin equation for subdiffusion and calculate the time evolution mean squared displacement and mean squared momentum of the heavy quarks. My results indicate that the mean squared displacements of the heavy quarks for the subdiffusion process deviate from a linear relationship with time. Further, I calculate the normalized momentum correlation function, kinetic energy, and momentum spread. Finally, I show the effect of subdiffusion on experimental observables, the nuclear modification factor. Published by the American Physical Society 2024

Coupled Space- and Velocity-Focusing in Time-of-Flight Mass Spectrometry-a Comprehensive Theoretical Investigation.

A comprehensive theoretical calculation that couples space- and velocity-focusing is developed for optimizing the design of a time-of-flight (TOF) mass spectrometer. Conventional designs for ion sources of TOF mass spectrometers deviate from the optimal condition because the velocity- and space-focusing conditions are considered separately for two ions with simplified equations. The result of a reexamination taking into account all essential ions reveals that the conventional ion source design, especially the length of the ion extraction region, results in poor resolving power. The comprehensive calculation demonstrates that the resolving power increases when the length of the extraction region is shorter than that of the conventional ion source. A numerical analysis indicates that the resolving power dramatically increases when the effective extraction potential compensates for the initial kinetic energy spread of ions. With typically used extraction potentials, the newly optimized ion source improves the resolving power by more than two orders of magnitude compared with the conventional design. This new theoretical interpretation can also be used to predict the optimal extraction potential and extraction delay in conventional ion sources to substantially improve the resolving power. This comprehensive calculation method is effective not only for designing new high-resolution instruments but also for optimizing commercial products.

Investigation on Mechanically Bistable MEMS Devices for Energy Harvesting From Vibrations

In this paper, mechanically bistable microelectromechanical systems devices are investigated for energy harvesting from mechanical vibrations. This approach is particularly suitable when random, weak, and broad-band vibrations in the low-frequency range are considered. These working conditions are, in fact, quite challenging and are often approached via arrays of linear resonant microdevices. Our approach allows, with a single device, to efficiently collect kinetic energy in the whole spectrum of frequencies of the incoming signal. Bistable behaviors are achieved through purely mechanical and fully compliant micromechanisms. Different structures have been analytically and numerically investigated, both in static and dynamic working conditions, and optimized results are proposed. The advantages of the proposed device, which exploit bistable dynamic behaviors, over linear and monostable strategies are presented in this paper: In the case of the incoming kinetic energy spread over a large bandwidth and confined at low frequencies, a larger fraction of the input mechanical energy is transferred to the mechanical-to-electrical conversion section of the harvester and, therefore, to the final user. A complete device design is proposed in this paper by taking into account a dedicated fabrication process which allows to obtain large inertial masses; electrostatic conversion has been considered and embedded into the device to evaluate the device performances in terms of the electric energy scavenged.

Measurement of Ion Kinetic-energy Distributions in Electron-impact Ion Sources of a Quadrupole Mass Spectrometer

An ideal ion source should create stable ion beams of sufficient intensity with an ion energy spread as low as possible. Most electron-impact ion sources used in mass spectrometers have been based on the design by Nier. Calculation of the potential distribution in the ion source revealed that the ion extraction efficiency could be improved by applying a positive repeller potential to the ionization chamber, which is normally at ground potential in a Nier-type ion source. Ion kinetic-energy distributions were measured in a Nier-type ion source and in a modified ion source by applying a retarding pole bias potential to the quadrupole at various emission currents and chamber pressures. As the emission current or the chamber pressure was increased, the most probable energy was shifted to a higher energy in both ion sources. However, the ion kinetic-energy spread was smaller and varied less in the modified ion source while it was larger in the conventional Nier-type ion source.

Computer simulation of electron and ion trajectories in electron-impact ion sources of a quadrupole mass spectrometer

Electron and ion trajectories have been simulated in electron-impact ion sources of a quadrupole mass spectrometer. The ion trajectories in the conventional Nier-type ion source show poor extraction efficiency of the generated ions into the quadrupole. Based on the electron and ion trajectory simulation results, the Nier-type ion source has been modified to improve the ion extraction efficiency. The modified ion source exhibits much better ion extraction efficiency and smaller kinetic energy spread than the Nier-type ion source.

A deceleration system at the Heidelberg EBIT providing very slow highly charged ions for surface nanostructuring

Recently, it has been demonstrated that each single-impact of a slow (typically 1–2 keV/u) highly charged ion (HCI) creates truly topographic and non-erasable nanostructures on CaF 2 surfaces. To further explore the possibility of nanostructuring various surfaces, using mainly the potential energy stored in such HCIs, projectiles with kinetic energies as low as possible are required. For this purpose a new apparatus, capable of focusing and decelerating an incoming ion beam onto a solid or gaseous target, has been installed at the Heidelberg electron beam ion trap (EBIT). An X-ray detector and a position-sensitive particle detector are utilized to analyze the beam and collision products. First experiments have already succeeded in lowering the kinetic energy of HCIs from 10 keV/q, down to ∼30 eV/q, and in focusing the decelerated beam to spot sizes of less than 1 mm 2, while maintaining the kinetic energy spread below ∼20 eV/q.

The tripole linear ion trap with highly efficient orthogonal ion ejection designed by computer simulations

An ion guide, consisting of three rods carrying three alternating current (AC) voltages symmetrically delayed, called a tripole, was used as a linear ion trap (LIT) and studied by computer simulations. Radial containment of ions was also demonstrated with the pseudopotential which was calculated by approximating the tripole electric potential to the multipoles expansion. This work found a new analyte concentrator, which performs effective ion ejection, and is suitable for use with time-of-flight mass spectrometry. The efficiency of the overall process from the trapping until the ejection was higher than 90%, although some degree of ion spatial and kinetic energy spread which can be corrected with a reflectron was obtained. The reason for the ejection of this tripole linear ion trap (tLIT) lies in the high space available between the rods. The ejection is optimized with the application of focusing voltages, especially suitable for a tripole symmetry (one electrode has a pulse offset voltage and the other two have a fraction of that pulse). The beam is finally well parallelized with a rectangular Einzel lens.

Matrix-assisted laser desorption/ionization fourier transform ion cyclotron resonance mass spectrometry with pulsed in-source collision gas and in-source ion accumulation.

A new matrix-assisted laser desorption/ionization (MALDI) source for Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been developed. The new source is equipped with a hexapole ion guide. The sample on the laser target is one millimeter from the hexapole ion guide, so that ions are desorbed directly into the guide. A device for pulsing collision gas in direct proximity to the laser target makes it possible to cool the ions, which have a kinetic energy spread of several electron volts when produced by the MALDI process. These ions are trapped in the hexapole where positive potentials at the laser target and at an extraction plate help trap ions along the longitudinal axis. After a pre-defined trapping time the voltage of the extraction plate is reversed and the trapped ions are extracted for transmission to the ion cyclotron resonance cell. Accumulation of ions from multiple laser shots in the hexapole before mass spectrometric analysis increases sensitivity. Preliminary sensitivity studies with substance P show that 10 attomoles of analyte applied on the target can be detected with a signal-to-noise (S/N) ratio >15.

Prediction of artifact peak intensity in linked scans for dissociations occurring in the first field-free region of sector mass spectrometers

Linked scans are commonly used on double-focusing mass spectrometers to obtain tandem mass spectrometry (MS/MS) spectra. The appearance of artifact peaks in linked scan MS/MS spectra from dissociations occurring in the first field-free region are a result of poor parent ion resolution, and they often can complicate the interpretation of the MS/MS spectra. The kinetic energy release associated with dissociation of ions of similar m/z to the “selected” parent ion is the main factor in determining the intensity of artifact peaks. A means of predicting the intensities of these artifact peaks in product ion and constant neutral loss scans is presented here. The method requires straightforward calculations based on Lacey-Macdonaldion intensity diagrams. The exact calculations require knowledge of the kinetic energy release of a particular dissociation, the kinetic energy spread of the main beam, and the parent ion and product ion mass-to-charge ratios. Adequate predictions, however, can be made by assuming a general kinetic energy release for any given reaction and a typical instrument energy resolution. Theoretical predictions are in good agreement with experimental data obtained from the product ion scans of unlabeled and isotopically labeled tirilazad and unlabeled and labeled leucine enkephalin methyl ester. There is also excellent agreement between experiment and theory in the constant neutral loss scans of rubidium bromide clusters.

Observation of Two-Atom Correlation of an Ultracold Neon Atomic Beam.

The intensity correlation spectrum of an ultracold ${}^{20}\mathrm{Ne}$ atomic beam in the ${1s}_{3}[{3s:}^{1}{P}_{0}]$ state is experimentally studied. The spectrum shows a peak around the origin with the width corresponding to the kinetic energy spread of atoms in the beam source.

REMPI in a focusing rf-quadrupole: a new source for mass-, energy-, and state-selected ions

Abstract Using resonance enhanced multiphoton ionization (REMPI), ions are created in a small volume centred on the axis of an rf-quadrupole. The pulsed beam of neutral molecular precursors is injected coaxially. This combination leads to high collection efficiency without the need of strong electrostatic extraction fields. The quadrupole is operated in the adiabatic limit. Therefore, the influence of the oscillatory rf-field on the ion trajectories can be described by an effective harmonic potential, which has focusing properties. Using these energy and mass dependent focusing properties, a primary H2 + beam of well-defined kinetic energy (< 5 meV (fwhm) at a mean of 50 meV) is prepared. In a typical case of multiphoton ionization of polyatomic molecules using C2H2, suppression of fragment ions by more than a factor of 10 is achieved, without losing the narrow kinetic energy spread of the parent ion beam.

Guided ion beam measurement of the product branching ratios for the ion-molecule reaction N++O2 as a function of collision energy

A quadrupole-octopole-quadrupole mass spectrometer has been constructed for comparing ion-molecule reaction product intensities as both the internal excitation and the kinetic energy of the reactant ion are varied. Such comparisons require an ion beam with a known kinetic energy distribution and, most importantly, they require product intensity measurements made without significant bias in detection of the different product channels. To assess the characteristics of our instrument, we have studied the ion-molecule reaction N++O2 that is known to yield three different product channels: N+O+2, NO++O, and NO+O+. Ion beam trajectory simulations combined with experimental measurements show that the spread in the kinetic energy of the reagent ions has a fixed value in the range of 0.6 to 1.1 eV full width at half maximum in the center of mass (c.m.). Relative cross sections for the three different product channels are reported as a function of c.m. collision energy. A comparison of the observed product branching ratios with those determined previously by other workers shows that no serious product discrimination occurs over the collision energy range of 1.5 to 10.0 eV c.m. Discrepancies in the product branching ratios below 1.5 eV c.m. are believed to be caused by the overall collision energy uncertainty that results from both the ion beam kinetic energy spread and the thermal motion of the O2 reactant.

Ionization of fast rydberg atoms in longitudinal and transverse electric fields

The main properties of longitudinal and transverse electric field ionizers for fast Rydberg atoms n=21–40 have been investigated. The dispersion and the background due to collisional processes between fast atoms and residual gas molecules have been measured and calculated. The kinetic energy spread of ions formed by field ionization of Rydberg atoms and their trajectories have been calculated. The potassium beam energy was 3.9 keV.

The infrared photofragmentation of Ar+2. Evidence of excited state population from dimer and cluster ionization

Argon dimer ions have been generated via three different techniques: (1) autoionization; (2) vertical ionization of neutral Ar2; (3) ionization and subsequent fragmentation of argon cluster ions. In experiments (2) and (3) the dimers and clusters are formed via the adiabatic expansion of argon in a supersonic beam. In each case Ar+2 ions have been mass selected and subjected to single-photon infrared excitation (912–1094 cm−1) using a line-tunable carbon dioxide laser in a crossed-beam arrangement. Only those Ar+2 ions with internal energies within 1000 cm−1 of a dissociation limit yield Ar+ photofragments, the kinetic energy spread of which has been measured using an electrostatic analyzer. The photofragment kinetic energy spectra of dimer ions formed by autoionization do not exhibit any dependence on the angle of laser polarization; it is proposed that such behavior is due to the presence of a high thermal rotational temperature (500 K). In contrast, the corresponding spectra of Ar+2 formed via vertical ionization, exhibit two quite distinct features, one of which shows a strong dependence on laser polarization angle. Calculations show that the latter behavior is most probably due to photodissociation out of an excited spin–orbit state of Ar+2. A very pronounced increase in Ar+2 infrared photodissociation signal is observed as a function of increasing nozzle stagnation pressure. To account for such behavior it is proposed that, following ionization, argon cluster ions fragment to give dimer ions in excited vibrational/rotational levels both in the electronic ground and an excited spin–orbit state.

Surface-induced dissociation of protonated peptides: implications of initial kinetic energy spread.

Surface-induced dissociation (SID) has been used to produce daughter ion spectra of small protonated peptides generated by fast atom bombardment (FAB). The relative abundances of daughter ions depends critically upon the energy of the ion/surface collision. A wide array of decomposition processes may be observed using ELAB collision energies in the range 10-20 eV. At approximately 13-eV collision energy, the variety of decomposition processes is maximized for the small peptides studied; hence, maximum structural information may be deduced. Collisionally-activated dissociations (CAD) using argon gas and the identical protonated peptides could not produce as large an array of daughter ions in a constant condition experiment. An apparent contradiction is thereby posed because SID is known to produce a narrow distribution of ion internal energies relative to CAD. This apparent contradiction is resolved by considering the rather large kinetic energy spread of ions leaving the FAB source. For the SID process, this large initial kinetic energy distribution is converted into a significantly wider spread in center-of-mass collision energy, leading to a broader variety of decomposition processes (high and low energy) compared to CAD.

Electron bombardment ion source with small energy spread and high brightness

The design and the operating conditions of a new electron bombardment ion source are described. The ion source produces an ion beam with a small kinetic energy spread of 0.1-0.5 eV (full width at half maximum) and a relatively high brightness of up to 50 A sr-1 m-2 for a kinetic energy of 200 eV.

Kinetic Energy Distributions of Positive Ions in an Inductively Coupled Plasma Mass Spectrometer

A simple method is described for the approximate measurement of the ion energy distribution in an inductively coupled plasma-mass spectrometer (ICP-MS) with a continuum flow sampling interface. The average ion kinetic energy, kinetic energy spread, and maximum kinetic energy are evaluated from a plot of ion signal as a function of retarding voltage applied to the quadrupole mass analyzer. The effects of plasma operating parameters on ion signals and energies are described. In particular, kinetic energy is a sensitive function of aerosol gas flow rate. This behavior is attributed to a nonthermal, possibly electrical, interaction between the plasma and the sampling interface, which is induced by the presence of the axial channel in the ICP.

Deconvolution of the effect of apparatus broadening and the kinetic energy spread of the parent ion beam from metastable peak shapes

A procedure is described, based on fast Fourier transformations, which allows the effect of the velocity spread of the parent ion beam to be deconvoluted out of an experimentally obtained metastable peak. The fast Fourier deconvolution procedure is described and details concerning the computer programming involved are given. Examples of the techniques are shown where considerable enhancement of fine structure in metastable peaks is demonstrated. Also it is shown that in the case of narrow metastable peaks, this technique provides the only precise means of obtaining kinetic energy release data.

Molecular ion source having low energy spread and single-electron-impact excitation

A cylindrically symmetric electron-bombardment ion source is described that has been useful in beam experiments with molecular ions. Measurements indicate that the ions have a kinetic-energy spread (full-width at half-maximum) of 0.5-1.0 eV, a current of several microamperes, and a population distribution that is consistent with vibrational and rotational factors resulting from single-electron-impact ionization. The source exhibits low noise ( less, similar twice the theoretical shot-noise limit) and has a compact and easily serviceable construction.

The time-focusing principle: A double-focusing design for time-of-flight mass spectrometers

Conventional non-magnetic time-of-flight mass spectrometers use the simplest form of mass analyser, a field-free drift tube. Because such an analyser is completely passive any time spread caused by the initial kinetic energy spread of the ions cannot easily be removed. A first order theory is presented which shows that a conventional analyser (the field-free drift tube) can be combined with a radial electric analyser in such a way that the time dispersion is opposite and equal in the two analysers giving complete time-focusing.