Ne Ions Research Articles

Transient analysis of high-Z impurity screening by additional injection of low-Z impurity using integrated divertor code SONIC

The dynamics of the screening effect of Ar impurity by the injection of additional Ne has been studied through time-dependent analysis with the integrated divertor code SONIC. In the preceding study (Yamoto et al 2020 Plasma Phys. Control. Fusion 62 045006), the predictive simulation of JT-60SA plasma by SONIC has shown that the injection of additional Ne into Ar-seeded plasma results in lower Ar density and radiation power in the SOL and core edge than in the Ar-only seeded case. The results have demonstrated that the mixed impurity seeding of Ar and Ne may be advantageous for maintaining a high core plasma performance with a low divertor heat load. It was found that the friction force induced by the high D+ flow in the SOL towards the inner divertor (ID) region in the Ar + Ne seeded case pushes Ar impurities to the ID. However, the dynamics of D+ flow acceleration cannot be interpreted in the previous study because SONIC was a steady state code. In this study, we have developed the time-dependent version of SONIC and applied it to the transient analysis of the injection of additional Ne into Ar-seeded plasma in JT-60SA. When additional Ne is injected, Ne ions stay in the ID plasma near the X-point. As a result, the Ne radiation power increases near the X-point. The electron pressure then decreases due to the radiation cooling and the D+ flow is accelerated by the electron pressure gradient. The ion pressure also decreases due to the convection by the accelerated D+ flow by electron pressure gradient. The resulting ion pressure gradient further accelerates the D+ flow velocity towards the ID. The results suggest that both the high-performance core plasma and the low divertor heat load can be achieved by the Ar + Ne mixed impurity seeding.

Electron density and temperature in a diffuse nanosecond pulse discharge in air at atmospheric pressure

This work presents the first experimental results on the electron properties of a nanosecond diffuse fast ionisation wave generated in synthetic dry air at atmospheric pressure under very strong overvoltage. Both density and mean temperature of electrons are investigated by incoherent Thomson scattering. The electron density is also derived from the Stark broadening of oxygen lines resolved by optical emission spectroscopy. The extreme voltages applied question some common hypothesis of the diagnostics implemented. The solutions adopted and the remaining limitations are discussed in the paper. Each diagnostic covers a specific region of interest within the discharge and they show good agreement in conditions where they overlap. It is shown that most of the volume of the pin-to-plane discharge is quite representative of a quasi-steady state glow discharge dominated by the emission of the first and second positive systems of nitrogen. Once its propagation completed within the first two nanoseconds and until the end of the 10 ns pulse, it is characterized by rather homogeneous properties close to the axis. The electron density is of the order of 1015 cm−3 and the mean temperature is about 3 eV within the whole air gap. About 6 ns after the start of the discharge from the pin, a sub-millimetric region of strong ionization develops at the pin, which is consistent with the observation of a continuum of emission spreading from the UV to the near-IR spectral range. Within this part of the discharge, the electron density reaches values greater than 1017 cm−3 with an ionization degree higher than 1%. The radiative recombination of nitrogen ions N2 + and the three-body recombination of N+ with a large number of electrons could help to explain the continuum.

Data-driven ion-independent relative biological effectiveness modeling using the beam quality Q

Beam quality Q = Z2/E (Z = ion charge, E = energy), an alternative to the conventionally used linear energy transfer (LET), enables ion-independent modeling of the relative biological effectiveness (RBE) of ions. Therefore, the Q concept, i.e. different ions with similar Q have similar RBE values, could help to transfer clinical RBE knowledge from better-studied ion types (e.g. carbon) to other ions. However, the validity of the Q concept has so far only been demonstrated for low LET values. In this work, the Q concept was explored in a broad LET range, including the so-called overkilling region. The particle irradiation data ensemble (PIDE) was used as experimental in vitro dataset. Data-driven models, i.e. neural network (NN) models with low complexity, were built to predict RBE values for H, He, C and Ne ions at different in vitro endpoints taking different combinations of clinically available candidate inputs: LET, Q and linear-quadratic photon parameter α x/β x. Models were compared in terms of prediction power and ion dependence. The optimal model was compared to published model data using the local effect model (LEM IV). The NN models performed best for the prediction of RBE at reference photon doses between 2 and 4 Gy or RBE near 10% cell survival, using only α x/β x and Q instead of LET as input. The Q model was not significantly ion dependent (p > 0.5) and its prediction power was comparable to that of LEM IV. In conclusion, the validity of the Q concept was demonstrated in a clinically relevant LET range including overkilling. A data-driven Q model was proposed and observed to have an RBE prediction power comparable to a mechanistic model regardless of particle type. The Q concept provides the possibility of reducing RBE uncertainty in treatment planning for protons and ions in the future by transferring clinical RBE knowledge between ions.

Analysis of elastic scattering of 6,7Li and 20Ne from 24Mg nucleus using microscopic potentials

The experimentally available angular distributions (ADs) for [Formula: see text]Li and [Formula: see text]Ne ions elastically scattered from a [Formula: see text]Mg target are reanalyzed using various nuclear potentials based on phenomenological as well as microscopic approaches. The considered data are [Formula: see text] ADs at [Formula: see text], 88 and 240[Formula: see text]MeV; [Formula: see text] ADs at [Formula: see text], 34 and 88[Formula: see text]MeV; and [Formula: see text] ADs at [Formula: see text], 60, 80, 90 and 100[Formula: see text]MeV. Special emphasis is given on the ([Formula: see text]) and ([Formula: see text]) cluster structures of the 6Li and 7Li weakly bound projectiles, which appear at relatively low energies of [Formula: see text] and 2.468[Formula: see text]MeV, respectively. Furthermore, the [Formula: see text]Ne stable nucleus is a candidate to reveal the [Formula: see text]O cluster structure at an energy of 4.73[Formula: see text]MeV. These systems are analyzed within the framework of the cluster folding model by taking into consideration the aforementioned cluster nature of the 6Li, 7Li and [Formula: see text]Ne projectiles. The adopted approaches fairly reproduced the experimental ADs.

Computational study on the discharge dynamics of atmospheric pressure He plasma driven by high frequency AC voltage

A two dimensional self-consistent fluid model has been established to investigate the discharge dynamics of double-ring electrode He atmospheric pressure plasma jet (APPJ) driven by high frequency AC voltage. The difference of the internal stream and external jet and the influence of the change of applied voltage polarity on plasma discharge characteristics has been discussed. It has been discovered that the capacitive breakdown characteristic of the double ring electrode significantly enhances the intensity of the APPJ. The discharge intensity of the external jet is stronger than that of the internal stream and the propagation speed of the external jet is faster than that of the internal stream due to the ionization and Penning ionization of N2 and O2. Therefore, the density of reactive species in the external jet is greater than that in the internal stream. When the negative voltage is applied to the downstream electrode, the propagation direction of the internal stream changes to the downstream electrode. The ionization of the external jet is also concentrated near the downstream electrode and in the streamer head. The radial propagation distance of the external jet on the dielectric surface continues to increase and the peak value of the radial electric field is concentrated at the streamer head. When the applied voltage changes from negative to positive, the propagation direction of the internal stream turns to the upstream electrode and the upstream jet is formed above the electrode. At the beginning of the positive cycle, the radial propagation distance of the external jet is shortened due to the effects of the electron attachment of O2 and the radial electric field. With the increase of applied voltage, the ionization in the streamer head gradually increases, which promoted the radial propagation of external jet.

Изучение влияния энергии ионов неона на шероховатость поверхности основных срезов монокристаллического кремния при ионном травлении

The paper presents the results of studying the energy dependences of the sputtering coefficient and the effective surface roughness of single-crystal silicon irradiated with neon ions with an energy of 100-1000 eV. As a result of the work, the parameters of ion-beam etching with accelerated Ne ions were determined, providing a high sputtering coefficient (etching rate) and an effective roughness value in the spatial frequency range 4.9∙10-2-6.3∙101 μm-1 less than 0.3 nm for the main cuts of single-crystal silicon (<1 0 0>, <1 1 0> and <1 1 1>).

Воздействие плазмы N-=SUB=-2-=/SUB=- на монослои дисульфида молибдена

Based on ab initio DFT simulation results, the main processes of the interaction of thermal N atoms with MoS2 monolayers are revealed, potential mechanisms of defect formation by low-energy ions N2+ are described, and the ion threshold energy required to sulfur removal is estimated.

Investigation Ne ions scattering from the stepped InP(001) surface

We present in this paper possibility of using glancing incidence ions scattering process for the determination of surface atomic step. We study the grazing scattering of Ne+ stepped InP(001)<ī10> surface in small angle of incidence ions. Additionally, we elaborate on the spectra of energy some intensive maximums formed by ions scattered from the monoatomic surface steps. Based on concrete examples, we also observe the effect of the atomic mass of the stepped atoms on the process of ion scattering. We study the trajectories of ions which scattered from stepped InP(001)<ī10> surface and found that the track of scattered ions have a zig-zag shape. An ion Ne trapped in a channel formed by an atomic step, after passing some distances, dechannels due to a hard collision of one of the atoms forming the basis of the channel. The physical settings of dechannelized Ne ions were analyzed and calculated, and this calculation makes it possible to understand the mechanism of ion dechanneling.

Nonsequential double ionization of Ne with elliptically polarized laser pulses

We show through simulation that the improved quantitative rescattering model (QRS) can successfully predict the nonsequential double ionization (NSDI) process by intense elliptically polarized laser pulses. Using the QRS model, we calculate the correlated two-electron and ion momentum distributions of NSDI in Ne exposed to intense elliptically polarized laser pulses with a wavelength of 788 nm at a peak intensity of $5.0\ifmmode\times\else\texttimes\fi{}{10}^{14}$ W/${\mathrm{cm}}^{2}$. We analyze the asymmetry in the doubly charged ion momentum spectra observed by Kang et al. [Phys. Rev. Lett. 120, 223204 (2018)] in going from linearly to elliptically polarized laser pulses. Our model reproduces the experimental data well. Furthermore, we find that the ellipticity-dependent asymmetry arises from the drift velocity along the minor axis of the elliptic polarization. We explain how the correlated electron momentum distributions along the minor axis provide access to the subcycle dynamics of recollision. From these findings, we expect that we can extend the QRS model for NSDI toward more complicated laser fields in the future.

Strong-field ionization of N2 and CO molecules using two-color laser field

Two-color strong-field photoionization of two diatomic molecules (N2, CO) is studied using a velocity map imaging (VMI) spectrometer. The fundamental frequency, along with the second harmonic (800 + 400 nm) at different phases, with the two different polarization schemes viz, orthogonal and parallel, is employed for measuring the ion yields and photoelectron momentum distributions. The yield of the parent ion and its charged fragments as a function of the phase difference between the two-color field has been studied thoroughly, and the results are presented here. The correlation trends of the parent ion with their fragments as a function of the relative phase are discussed. It is observed that the ionized CO and its fragments have different correlation trends at different polarization schemes. Additionally, the photoelectron momentum distribution of N2 and CO due to orthogonal two-color (OTC) and parallel two-color (PTC) is performed in order to understand the modulation of electron dynamics as a function of phase between 800 nm and 400 nm. Further, the asymmetry parameter as a function of electron momenta due to the two-color fields has been estimated and discussed.

Two-XUV-photon double ionization of neon

Two-XUV-photon double ionization of Ne, induced by an intense few-pulse attosecond train with a \ensuremath{\sim}4 fs envelope duration is investigated experimentally and theoretically. The experiment is performed at ELI-ALPS (Extreme Light Infrastructure Attosecond Light Pulse Source) utilizing the recently constructed 10 Hz gas phase high-order harmonic generation SYLOS GHHG-COMPACT beamline. A total pulse energy up to \ensuremath{\sim}1 \ensuremath{\mu}J generated in argon in conjunction with high-reflectivity optics in the XUV region allowed the observation of the doubly charged state of Ne induced by 40 eV central XUV-photon energies. The interaction of the intense attosecond pulse train with Ne is also theoretically studied via second-order time-dependent perturbation theory equations of motion. The results of this work, combined with the feasibility of conducting XUV-pump--XUV-probe experiments, constitute a powerful tool for many potential applications. Those include attosecond pulse metrology as well as time-resolved investigations of the dynamics underlying direct and sequential double ionization and their electron correlation effects.

The Effect of Ne+ Ion Implantation on the Crystal, Magnetic, and Domain Structures of Yttrium Iron Garnet Films

The mechanism of the influence of crystal inhomogeneities on the magnetic and domain microstructures of functional materials based on yttrium iron garnet heterostructures is an important subject of investigation due to the aim to predict parameters for manufacturingpurposes. A study of the structural and magnetic characteristics of a set of yttrium iron garnet films grown on gadolinium–gallium garnet substrate is presented. High-resolution X-ray diffractometry, Mössbauer spectroscopy, MFM, as well as ion implantation simulation and X-ray diffraction simulation were used together to determine the features of the effect of Ne+ ion implantation with different dose rates on the samples. The simulation of ion implantation with E = 82 keV showed energy loss profiles of Ne ions with subsequent defect formation up to amorphization of near-surface layers at high doses. Implantation creates two magnetically non-equivalent types of tetrahedrally located Fe3+ ions, which leads to a rotation of the total magnetic moment relative to the film surface and a change in the width of the magnetic domain stripes.

Revealing and controlling nuclear dynamics following inner-shell photoionization of N2

In this work, we apply the Monte Carlo wave packet method to study the ultrafast nuclear dynamics following inner-shell photoionization of N2 exposed to an ultrashort intense X-ray pulse. The photon energy of the X-ray pulse is large enough to remove a 1s electron from the N atom in N2. The intermediate state in N+2 is highly excited so that autoionization takes place from this state to the dissociative or non-dissociative electronic states of ungerade and gerade symmetries in N++2. The possible vibrational resonances allowed by the non-dissociative states prevents a direct extraction of the nuclear kinetic release (KER) spectrum from the nuclear wave packets in N++2. Therefore, we propose a hybrid technique by combining the advantages of two energy analysis strategies to obtain the final nuclear KER spectrum of the process. A femtosecond IR probe pulse, which couples the electronic states in N++2 together, is applied to achieve a time-resolved imaging and controlling of the ultrafast dynamics that takes place during double ionization of N2. The influence of the laser parameters including the peak intensity, pulse duration and pump-probe delay, on the nuclear dynamics is also investigated.

The Mayo Clinic Florida microdosimetric kinetic model of clonogenic survival: formalism and first benchmark against in vitro and in silico data

Objective. To develop a new model (Mayo Clinic Florida microdosimetric kinetic model, MCF MKM) capable of accurately describing the in vitro clonogenic survival at low and high linear energy transfer (LET) using single-event microdosimetric spectra in a single target. Methodology. The MCF MKM is based on the ‘post-processing average’ implementation of the non-Poisson microdosimetric kinetic model and includes a novel expression to compute the particle-specific quadratic-dependence of the cell survival with respect to dose (β of the linear-quadratic model). A new methodology to a priori calculate the mean radius of the MCF MKM subnuclear domains is also introduced. Lineal energy spectra were simulated with the Particle and Heavy Ion Transport code System (PHITS) for 1H, 4He, 12C, 20Ne, 40Ar, 56Fe, and 132Xe ions and used in combination with the MCF MKM to calculate the ion-specific LET-dependence of the relative biological effectiveness (RBE) for Chinese hamster lung fibroblasts (V79 cell line) and human salivary gland tumor cells (HSG cell line). The results were compared with in vitro data from the Particle Irradiation Data Ensemble (PIDE) and in silico results of different models. The possibility of performing experiment-specific predictions to explain the scatter in the in vitro RBE data was also investigated. Finally, a sensitivity analysis on the model parameters is also included. Main results. The RBE values predicted with the MCF MKM were found to be in good agreement with the in vitro data for all tested conditions. Though all MCF MKM model parameters were determined a priori, the accuracy of the MCF MKM was found to be comparable or superior to that of other models. The model parameters determined a priori were in good agreement with the ones obtained by fitting all available in vitro data. Significance. The MCF MKM will be considered for implementation in cancer radiotherapy treatment planning with accelerated ions.

The preparation and lubrication properties of a CrN/Cr multilayer using the double glow plasma surface alloying technique

Metal sealing rings with high hardness can improve wear resistance and reduce internal leakage. In this study, the double glow plasma surface alloying (DGPSA) technique was employed to produce the necessary conditions for a metallurgical bond and lubricant storage. Four primary stages are required in deposition processing: evaporation, destruction, atomization, and ionization. A Cr layer (including a 5 μm interdiffusion layer and a 45 μm pure metallic layer in thickness) and a thin (1–2 μm) CrN layer were prepared using the DGPSA technique. The obtained interdiffusion layer can reduce the mismatch in mechanical properties between the Cr layer and the substrate. When the atomic coverage of N atoms is higher than 1.5 ML, the stable adsorption structure is essentially nonexistent, indicating that improving the N2 ionization rate is more valuable than increasing the nitrogen partial pressure. When the Ar/N2 flow ratio is 2:1, the CrN/Cr multilayers provided microreservoirs for lubricants and improved wear and plastic deformation resistance. For the CrN/Cr multilayer, a higher contact pressure resulted in superior frictional properties.

Alignment dependence of photoelectron momentum distributions for diatomic molecule N2 in strong elliptical laser fields

The ionization dynamics of aligned N2 molecules are studied in strong elliptical laser fields experimentally and theoretically. The alignment-dependent photoelectron momentum distribution of N2 is measured for highlighting the molecular structure contribution by comparing to that of Ar measured synchronously. Our results show that the ionization of N2 depends strongly on the alignment of molecules, relative to the main axis of the polarization ellipse of the laser. In particular, the most-probable electron-emission angle which is often used in attosecond measurement changes remarkably when changing the relative angle between the molecular axis and the major axis of laser fields. The alignment-dependent rotation angles have been well reproduced by our theoretical calculations. We show that the interplay between molecular structure and the laser fields plays an important role in the rotation angles based on the strong-field approximation analysis and this interaction also influences remarkably on the photoelectron angle distribution of aligned N2.

Filming movies of attosecond charge migration in single molecules with high harmonic spectroscopy

Electron migration in molecules is the progenitor of chemical reactions and biological functions after light-matter interaction. Following this ultrafast dynamics, however, has been an enduring endeavor. Here we demonstrate that, by using machine learning algorithm to analyze high-order harmonics generated by two-color laser pulses, we are able to retrieve the complex amplitudes and phases of harmonics of single fixed-in-space molecules. These complex dipoles enable us to construct movies of laser-driven electron migration after tunnel ionization of N2 and CO2 molecules at time steps of 50 attoseconds. Moreover, the angular dependence of the migration dynamics is fully resolved. By examining the movies, we observe that electron holes do not just migrate along the laser polarization direction, but may swirl around the atom centers. Our result establishes a general scheme for studying ultrafast electron dynamics in molecules, paving a way for further advance in tracing and controlling photochemical reactions by femtosecond lasers.

Effects of the solid target on electronic excitations during binary atomic collisions in the interaction of Ne ions with Al surfaces

We report on measurements of the energy distribution of electrons emitted by Aluminum surfaces under the impact of low energy singly charged Neon ions, focusing on Auger decay of electronic excitations produced in both projectile and target atoms during binary atomic collisions. These excitations are well described by the Fano-Lichten molecular orbital promotion model adopted for gas-phase experiments, but the structural and electronic properties of the solid environment strongly influence the promotion process, resulting in Auger or photon emission that differs from the corresponding ones in gas targets. This work discusses the influence of solid target effects in studies of electronic energy loss and energy deposition by slow ions in solids.

Spot-scanning hadron arc (SHArc) therapy: A proof of concept using single- and multi-ion strategies with helium, carbon, oxygen, and neon ions.

To present particle arc therapy treatments using single and multi-ion therapy optimization strategies with helium (4 He), carbon (12 C), oxygen (16 O), and neon (20 Ne) ion beams. An optimization procedure and workflow were devised for spot-scanning hadron arc therapy (SHArc) treatment planning in the PRECISE (PaRticle thErapy using single and Combined Ion optimization StratEgies) treatment planning system (TPS). Physical and biological beam models were developed for helium, carbon, oxygen, and neon ions via FLUKA MC simulation. SHArc treatments were optimized using both single-ion (12 C, 16 O, or 20 Ne) and multi-ion therapy (16 O+4 He or 20 Ne+4 He) applying variable relative biological effectiveness (RBE) modeling using a modified microdosimetric kinetic model (mMKM) with (α/β)x values of 2, 5, and 3.1Gy, respectively, for glioblastoma, pancreatic adenocarcinoma, and prostate adenocarcinoma patient cases. Dose, effective dose, linear energy transfer (LET), and RBE were computed with the GPU-accelerated dose engine FRoG and dosimetric/biophysical attributes were evaluated in the context of conventional particle and photon-based therapies (e.g., volumetric modulated arc therapy [VMAT]). All SHArc plans met the target optimization goals (3GyRBE) and demonstrated increased target conformity and substantially lower low-dose bath to surrounding normal tissues than VMAT. SHArc plans using a singleion species (12 C, 16 O, or 20 Ne) exhibited favorable LET distributions with the highest-LET components centralized in the target volume, with values ranging from ∼80-170keV/μm, ∼130-220keV/μm, and ∼180-350keV/μm for 12 C, 16 O, or 20 Ne, respectively, exceeding mean target LET of conventional particle therapy (12 C:∼55, 16 O:∼75 20 Ne:∼95keV/μm). Multi-ion therapy with SHArc delivery (SHArcMIT ) provided a similar level of target LET enhancement as SHArc compared to conventional planning, however, with additional benefits of homogenous physical dose and RBE distributions. Here, we demonstrate that arc delivery of light and heavy ion beams, using either a single-ion species (12 C, 16 O, or 20 Ne) or combining two ions in a single fraction (16 O+4 He or 20 Ne+4 He) affords enhanced physical and biological distributions (e.g., LET) compared with conventional delivery with photons or particle beams. SHArc marks the first single- and multi-ion arc therapy treatment optimization approach using light and heavy ions.

Elucidation of formation mechanism responsible for charge-transfer reagent ions in microwave induced plasma desorption ionization (MIPDI) source

Charge transfer reagent ions NO+ and O2+ were major observed in microwave-induced plasma desorption ionization (MIPDI) source. Ions NO+ was prosperous in the discharge region while ions O2+ generated in the afterglow region. Fundamental aspects of conditions that controlled MIPDI were addressed here to help understand the specific role of atmospheric components for charge transfer reagent ions formation. In the presence of trace nitrogen in Ar-MIPDI plasma, the production of NO+ ions increased significantly, while ions N2+ were not observed. The controlled afterglow environment obtained by connecting the plasma source to the mass spectrometer using a quartz reaction chamber found that ions O2+ produced from the interaction between plasma-generated energy particles and oxygen molecules. With the aid of mass spectra and optical emissions spectra, the ionization capacity of Ar-MIPDI plasma was revealed. Both the discharge region and afterglow region are not energetic enough to ionize N2 molecules. Charge transfer reagent ions in the MIPDI source have vital ionization ability for aromatic compounds. A deeper understanding of fundamental aspects, especially of condition-controlled ionization in a MIPDI source, will be vital for future practical applications, particularly with regard to difficult to ionize (e.g., nonpolar) species.