A high-intensity metal ribbon ion beam was generated using plasma immersion extraction and the acceleration of the metal ions with their subsequent ballistic focusing using a cylindrical grid ...electrode under a repetitively pulsed bias. To generate the dense metal plasma flow, two water-cooled vacuum arc evaporators with Ti cathodes were used. The ion current density reached 43 mA/cm2 at the arc discharge current of 130 A. High-intensity ion implantation (HIII) with a low ion energy ribbon beam was used for the surface modification of the aluminium. The irradiation fluence was changed from 1.5 × 1020 ion/cm2 to 4 × 1020 ion/cm2 with a corresponding increase in the implantation temperature from 623 to 823 K. The structure and composition of the Ti-implanted aluminium were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The mechanical properties and wear resistance were measured using nanoindentation and “pin-on-disk” testing, respectively. It was shown that the HIII method can be used to form a deep intermetallic Al3Ti layer. It has been established that a thin (0.4 μm) modified layer with a hcp Ti(Al) structure is only formed on the surface at 623 K, while the formation of the ordered Al3Ti intermetallic phase occurs at the implantation temperatures of 723 and 823 K. Despite the significant ion sputtering of the surface, the thickness of the modified layer increases from ~1 μm to ~6 μm, and the implantation temperature rises from 723 to 823 K. It was found that the homogeneous intermetallic Al3Ti layer with a thickness of up to 5 μm was formed at 823 К. The mechanical and tribological properties of the aluminium were substantially improved after HIII. For the Ti-implanted aluminium, the hardness of the surface layer increases from 0.4 GPa (undoped Al) to 3.5–4 GPa, while the wear resistance increases by more than an order of magnitude.
•Metal ribbon ion beam was formed using cylindrical ballistic focusing system.•Aluminium was implanted with titanium at the maximum ion current density of 43 mA/cm2.•Phase composition and thickness of layer strongly depend on implantation temperature.•Homogeneous intermetallic Al3Ti layer with a thickness of 6 μm was formed at 823 K.•Surface modification leads to hardening of aluminium surface up to 4 GPa.
High-intensity low energy chromium ions implantation was used for surface modification of zirconium Zr-1Nb alloy. The Cr ions were extracted from cathodic arc plasma and focused ballistically using a ...negatively biased hemispherical grid electrode immersed in plasma. The microstructure, phase composition and elemental distribution of Cr-implanted alloy were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX), respectively. The results revealed the formation of ZrCr2 Laves phase of C15 polytype after Cr ions implantation. The content of Laves phase increases with implantation temperature up to 22 vol% (at 900 °C). The Laves phase precipitations are nucleated and grew alternately inside the α-Zr solid solution matrix. The high-temperature (HT) oxidation resistance of Cr-implanted samples was analyzed during HT oxidation test in steam at 1000 and 1200 °C for 10 min.
•Chromium high-intensity ion beam with current density up to 150 mA/cm2 was generated.•The formation of ZrCr2 Laves phase of C15 polytype after Cr ions implantation revealed•The content of Laves phase increases with implantation temperature.•The implantation of Cr enhances the oxidation resistance of the Zr-1Nb alloy.
This study focuses on the analysis of microstructural, elemental and phase compositions of surface and near-surface layers of titanium after the implantation of aluminium. A titanium alloy with a ...chemical composition close to commercially pure titanium (grade 2) was used as the target material. Ion implantation was performed using two modes of irradiation: 1. repetitively pulsed ion beams with a mean ion energy of 35 keV; 2. low-energy-focused ion beams of high intensity with a mean ion energy of 2.6 keV. The irradiation fluence reached 1.1 × 1018 ion/cm2 using the first mode and 1.6 × 1021 ion/cm2 using the second mode. In both cases, the beam itself heated the targets. The peak concentration of aluminium after the implantation of medium-energy ions was ~65 at.%, and the maximum depth of dopant penetration was 2.6 μm. On the contrary, in the case of high-intensity low-energy ion implantation, the surface concentration of dopant reached a maximum of 25 at.%, but the depth of penetration increased significantly and achieved 50 μm. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that fine-grained intermetallic phases, Ti3Al and TiAl, and solid solutions of various compositions were possibly formed after the medium-energy ion implantation. The mean grain size of the intermetallic phases was ~50 nm. XRD and TEM analyses in the case of low-energy high-intensity ion implantation demonstrated the formation of the ion-alloyed layer, which comprised intermetallic phase Ti3Al and solid solutions of aluminium in titanium. The grain size of Ti3Al phase can be 5 μm and more.
•Two types of ion sources used for high-intensity ion implantation•Higher current densities result in deeper ion-doped layers•An aluminium enriched titanium layer with a thickness of 50 mcm was obtained after 1 h of irradiation.•The formation of TiAl, Ti3Al, and solid solutions of aluminium in titanium was demonstrated.
Gamma-ray spectrometry on ITER can provide information both on confined fusion alpha particles for optimization of plasma heating and runaway electrons, which is important for safe reactor ...operations. For the purpose of deconvolution of gamma-ray spectra recorded in fusion plasma experiments the DeGaSum code has been developed. The code can be applied for processing of both spectra of monoenergetic gamma rays, which are born in nuclear reactions produced by alpha particles and other fast ions, and continuous bremsstrahlung spectra generated by runaway electrons in the MeV range in the plasma and reactor structure materials. Gamma-ray spectrometer response functions and bremsstrahlung spectra generated by electrons in the MeV energy range are calculated and used in the DeGaSum code. The deconvolution of the discrete spectra allows the identification of nuclear reactions, which give rise to gamma rays, and the calculation of their intensities. By applying the code for continuous hard x-ray spectra, the runaway electron energy distribution can be inferred. It can provide the maximal energy of runaway electrons with accuracy, which satisfies the ITER project requirements. The code has been used for processing of spectra recorded in JET experiments. An application of the deconvolution technique for gamma-ray emission measurements on ITER is discussed.
The results of experimental investigations on plasma-immersion formation of ballistically focused beams of low-energy titanium ions with the pulse duration up to 30 μs are presented. The processes of ...neutralization of the space charge of high-intensity beams upon increasing the ion-current density by a few orders of magnitude during their focusing are addressed. The conditions of preliminary injection of the metal plasma, its parameters, the formation of the beam plasma during residual-gas ionization and secondary and thermionic emissions are shown to be of critical importance for an effective transport of these beams in the equi-potential drift space. It is demonstrated that the use of a disc electrode, preventing the macroparticles from penetrating the region of the ballistic beam focusing, increases the efficiency of long-pulse titanium ion beam transport and simultaneously reduces the probability of instability development.
One of the main requirements to the Disruption Mitigation System (DMS) in International Thermonuclear Experimental Reactor (ITER) is a reliable capability to avoid/suppress a detrimental runaway ...electron (RE) generation during disruptions. An understanding of the physics of RE is a key factor for design of ITER DMS with necessary properties on RE suppression. RE interacting with plasma particles and hitting the plasma-facing components (PFCs) produce a bremsstrahlung in MeV energy range (hard X-rays (HXR) and γ-rays) and photo-neutrons. Measurements of produced HXR/γ-rays and photo-neutrons provide detailed information on RE generation and serve as a main tool for runaway physics study in JET. This report presents recent progress in development of the JET diagnostic techniques for registering of the HXR/γ-rays emission and improvement of HXR data analysis methods for RE studies. The HXR spectra have been measured with the sets of HXR spectrometers. This data was numerically processed using special de-convolution procedure allowing a study of evolution of the RE Distribution Function (REDF). Maximal and mean energies of RE populations have been calculated. As well, the detection of spatial distribution of HXR sources in JET plasmas with the JET neutron/γ-rays profile monitor allowed the mapping of RE beams spatial evolution during RE plateaus. In order to increase the HXR/γ-rays diagnostic performance in future JET experiments, the vertical slow spectrometers will be replaced by high-speed LaBr3(Ce) spectrometers allowing measurements with counting rate up to 5*106 sec−1. Also spectrometer with tangential LoS will be replaced by a couple of LaBr3(Ce) and CeBr3 spectrometers. CsI(Tl) detectors in γ-cameras will be substituted by LaBr3(Ce) and CeBr3 crystals coupled with up-to-date SiPM light detectors, which allowed increasing the counting rate of the γ-camera detectors by an order of 10.
The diagnostic complex of the Globus-M2 spherical tokamak (
R
= 36 cm,
a
= 24 cm), the only operating tokamak in Russia with a divertor plasma configuration, which operates in the range of ...subthermonuclear temperatures (
T
e
to 1.6 keV,
T
i
to 4.5 keV) and densities (
n
e
to 2 × 10
20
m
–3
), is described. The Globus‑M2 tokamak is the unique scientific facility, which is a part of the Federal Center for Collective Use of the Ioffe Institute, Russian Academy of Sciences “Materials Science and Diagnostics in Advanced Technologies.” This allows third parties to perform their research using it. The work contains a list of all diagnostics currently available on the tokamak. The description of the diagnostics is structured in such a way that the reader gets an idea of their capabilities for measuring plasma parameters with an emphasis on the limits and accuracy of the measured values, and also spatial and time resolution. At the same time, many technical details are omitted in order to save space; references are given to papers with a more detailed description of individual diagnostics.
The standardization of DNA fragment assembly methods for many tasks of synthetic biology is crucial. This is necessary for synthesizing a wider repertoire of sequences, as well as for further ...automation and miniaturization of such reactions. In this work, we proposed conditions for the assembly of DNA fragments from chemically synthesized oligonucleotides and we identified the errors occurring in the sequence under these conditions. Additionally, we proposed conditions for further combining synthetic fragments into larger DNA fragments. We showed that the optimized conditions are suitable for the assembly of a wide range of sequences.
NBI-assisted plasma heating with one or two injectors of fast neutral atoms was studied at the Globus-M2 spherical tokamak at the toroidal magnetic fields of 0.8–0.9 T and plasma currents of 0.35–0.4 ...MA. Measurements of the spatial temperature and electron density distributions, performed using the Thomson scattering diagnostics, showed a twofold increase in heating of plasma electrons during the injection of neutral particles with energies of up to 45 keV at the beam power of 0.75 MW, as compared to the ohmic heating regime. Switching on the second additional beam with the particle energy of up to 30 keV and power of up to 0.5 MW resulted in obtaining the hot ion mode in the range of mean plasma densities of (1.6–10) × 10
19
m
−3
. According to the data of active spectroscopy and neutral particle analyzer diagnostics, in the hot zone, the ion temperature reached 4 keV at the plasma density of 8 × 10
19
m
−3
, which is more than 2.5 times higher than the electron temperature.
