Configuration and installation design of optical diagnostic systems on KSTAR

The optical diagnostic system of KSTAR consists of visible diagnostics including toroidal and poloidal Hα monitors, a visible survey spectrometer, and filterscopes. A re-entrant cassette made of stainless steel, containing five optical quartz windows has been developed to allow easy access of the visible diagnostics to the plasma. The configuration and manufacturing design of the diagnostic cassette and the installation of optical diagnostic systems within the cassette are described. The structural and thermal analysis of the diagnostic cassette and in situ calibration of optical diagnostics have also been performed. The optical lens system showed good image quality by spot diagram analysis.     

Ion source plasma parameters measurement based on Langmuir probe with commercial frequency sweep

Langmuir probe is one of the main diagnostic tools to measure the plasma parameters in the ion source. In this article, the commercial frequency power, which is sine wave of 50 Hz, was supplied on the Langmuir probe to measure the plasma parameters. The best feature of this probe sweep voltage is that it does not need extra design. The probe I-V characteristic curve can be got in less than 5 ms and the plasma parameters, the electron temperature and the electron density, varying with the time can be got in one plasma discharge of 400 ms.     

Imaging of optical diffraction radiation in pre-wave zone and spatial resolution of non-invasive beam size diagnostics

A simple model to evaluate the imaging shape of an optical diffraction radiation (ODR) source focused by a lens on a detector, taking into account the pre-wave zone effect has been developed. The characteristic size of an ODR image does not depend on the Lorentz-factor and is defined by the impact-parameter (minimal distance between a particle trajectory and ODR target edge) only. Using the ODR intensity component polarized parallel to the target edge it is possible to significantly improve the spatial resolution of an ODR beam profile monitor.     

Polymer processing by a low energy ion accelerator

Ion implantation is a process in which ions are accelerated toward a substrate at energies high enough to bury them just below the surface substrate in order to modify the surface characteristics. Laser-produced plasma is a very suitable and low cost technique in the production of ion sources. In this work, a laser ion source is developed by a UV pulsed laser of about 10⁸ W/cm² power density, employing a C target and a post ion acceleration of 40 kV to increase the ion energy. In this work, we implanted C ions on ultra-high-molecular-weight-polyethylene (UHMWPE) and low-density polyethylene (LDPE). We present the preliminary results of surface property modifications for both samples. In particular, we have studied the modifications of the surface micro-hardness of the polymers by applying the “scratch test” method as well as the hydrophilicity modifications by the contact angle measurements.     

Properties of the acrylic acid polymers obtained by atmospheric pressure plasma polymerization

Plasma polymers of acrylic acid were obtained using an atmospheric pressure discharge system. The plasma polymerization reactor uses a dielectric barrier discharge, with the polyethylene terephthalate dielectric acting as substrate for deposition. The plasma was characterized by specific electrical measurements, monitoring the applied voltage and the discharge current. Based on the spatially resolved optical emission spectroscopy, we analyzed the distribution of the excited species in the discharge gap, specific plasma temperatures (vibrational and gas temperatures) being calculated with the Boltzmann plot method. The properties of the plasma polymer films were investigated by contact angle measurements, infrared and UV-Vis spectroscopy, scanning electron microscopy. The films produced by plasma polymerization at atmospheric pressure showed a hydrophilic character, in correlation with the strong absorbance of OH groups in the FTIR spectrum. Moreover, the surface of the plasma polymers at micrometric scale is smooth and free of defects without particular features.     

Effect of swift heavy ion irradiation on nanocrystalline CaS:Bi phosphors: Structural, optical and luminescence studies

Luminescence studies of CaS:Bi nanocrystalline phosphors synthesized by wet chemical co-precipitation method and irradiated with swift heavy ions (i.e. O⁷⁺-ion with 100 MeV and Ag¹⁵⁺-ion with 200 MeV) have been carried out. The samples have been irradiated at different ion fluences in the range 1 × 10¹²-1 × 10¹³ ions/cm². The average grain size of the samples before irradiation was estimated as 35 nm using line broadening of XRD (X-ray diffraction) peaks and TEM (transmission electron microscope) studies. Our results suggest a good structural stability of CaS:Bi against swift heavy ion irradiation. The blue emission band of CaS:Bi³⁺ nanophosphor at 401 nm is from the transition ³P₁ → ¹S₀ of the Bi³⁺. We have observed a decrease in lattice constant (a) and increase of optical energy band gap after ion irradiation. We presume this change due to grain fragmentation by dense electronic excitation induced by swift heavy ion. We have studied the optical and luminescent behavior of the samples by changing the ion energy and also by changing dopant concentration from 0.01 mol% to 0.10 mol%. It has been examined that ion irradiation enhanced the luminescence of the samples.     

Time-of-flight detection of monoatomic ions generated by femtosecond laser ablation from large molecules

Single-shot femtosecond laser ablation (fsLA) was applied to large molecules to analyze elemental composition through out wide range of mass-to-charge ratio. Molecular samples such as Eu-DNA and cosmetic powders were atomized and ionized simultaneously by the single-shot fsLA and positive atomic ions were detected using a reflectron time-of-flight (TOF) mass spectrometer. The ratios among the signal intensity of the detected stable isotopes including ^151,153Eu and ^182-184,186W were consistent with the respective natural abundances of the isotopes. The results demonstrate the feasibility of the fsLA-TOF method as a high-throughput analytical technique for elemental microanalysis of large molecular samples in small quantities.     

Applications of parametric X-rays for X-ray diffraction analysis

Until now parametric X-rays (PXR) have not had practical applications because of the lack of a modern compact accelerator providing the required beam current and consequently high X-ray photon flux. PXR sources even with the intensities achievable at present may be applied to a number of X-ray reflectometry and diffractometry measurements which are important for the characterization of crystals and multi-layer nanostructures. In the paper we present some proposals for possible PXR applications for a number of X-ray measurements based on the smooth energy tuning, high monochromaticity and directed emission of this radiation. The theoretical background and numerical evaluations for PXR applications for determining ingredient concentration in a solid solution in the range of anomalous dispersion of the defect atoms, determination of the phase structure of a crystal, and selective PXR action in organic compounds, important for medical and biological research, are considered.     

Transition radiation in the pre-wave zone for an oblique incidence of a particle on the flat target

Backward transition radiation of an electron with an arbitrary energy is studied when an ideally-conducting target is flat and its normal is not collinear with the particle velocity (oblique incidence). A model for radiation registered with a small flat detector placed at a finite distance (including the radiation in the pre-wave zone) in the vicinity of specular reflection direction is developed. Characteristics of the radiation in the far-field zone are in complete agreement with well-known results. The calculations for pre-wave zone show that the angular distribution of the radiation intensity is distorted compared to the far-field case, and the radiation asymmetry (having a place in the far-field for moderately relativistic energies) is also preserved in the pre-wave zone. Some numerical estimations of the radiation asymmetry at a finite distance are also given. The technique developed may be used for estimations of coherent transition radiation intensity in the mm-wavelength range.     

Photoluminescence study of Ge nanocrystals irradiated by reactor neutron flux

Samples of Ge nanocrystals (Ge-ncs) embedded in amorphous SiO₂ film were prepared by Ge ion implantation and subsequent primary thermal annealing. These samples were irradiated by neutron flux in a nuclear reactor followed by the second annealing. Irradiation with thermal neutrons leads to doping of nanocrystals with Ga, As and Se impurities due to nuclear transmutation of isotope ⁷⁰Ge into ⁷¹Ga, isotope ⁷⁴Ge into ⁷⁵As, isotope ⁷⁶Ge into ⁷⁷Se, respectively (neutron transmutation doping, NTD). Irradiation with fast neutrons leads to appearance of radiation damages, which are expected to be removed after the second annealing. Photoluminescence (PL) measurements show that PL is quenched after neutron irradiation, and restored after annealing higher than 500 °C. The PL spectra of doped Ge-ncs samples show more intense exciton radiative luminescence than of undoped Ge-ncs sample, which is related to that the donor and acceptor impurities recombine the nonradiative centers in the interface of Ge-ncs and SiO₂ matrix, and enhance the probability of exciton recombination.     

Characterization and applications of a new tabletop confocal micro X-ray fluorescence setup

A tabletop confocal three-dimensional micro X-ray fluorescence (3D micro-XRF) setup was designed, based on polycapillary X-ray optics and a micro-focus X-ray source. This confocal setup consists of a polycapillary full lens to focus the incident beam and a polycapillary half lens to collect the X-ray fluorescence. The confocal volume was proved to be ellipsoidal. The full-width at half maximum (FWHM) of the confocal volume in three directions were measured with a “knife edge” scan method to obtain the spatial resolution of the confocal setup. The structure of multilayer samples was studied using the depth scan technique.     

Analysis of elemental maps from glaze to body of ancient Chinese Jun and Ru porcelain by micro-X-ray fluorescence

The reasons how the middle layer of Ru and Jun porcelain between the glaze and body came into being are still not completely understood. Here, elemental maps from the glaze to the body of pieces of ancient Chinese Ru and Jun porcelain were analyzed by micro-X-ray fluorescence. The results show the middle layer was probably formed by the chemical composition of the glaze turning into glassy states and undergoing complex physical-chemical reactions with the body. However, the middle layer of Jun porcelain was formed by the chemical composition of the glaze turning into glassy states and then infiltrating the body at high temperatures during the firing process.     

Ion-induced electron emission monitoring of the structure and morphology evolution in HOPG

The temperature dependences of the ion-induced electron emission yield γ of highly-oriented pyrolytic graphite (HOPG) under high-fluence (10¹⁸-10¹⁹ ions/cm²) 30 keV Ar⁺ ion irradiation at ion incidence angles from θ = 0^o (normal incidence) to 80^o have been measured to trace both the structure and morphology changes in the basal oriented samples. The target temperature has been varied during continuous irradiation from T = −180 to 400 ^oC. The surface analysis has been performed by the RHEED and SEM techniques. The surface microgeometry was studied using laser goniophotometry (LGF). The dependences of γ(T) were found to be strongly non-monotonic and essentially different from the ones for Ar⁺ and N₂⁺ ion irradiation of the polygranular graphites. A sharp peak at irradiation temperature T_p ≈ 150 ^oC was found. A strong influence of electron transport anisotropy has been observed, and ion-induced microgeometry is discussed.     

Temperature accelerated dynamics study of migration process of oxygen defects in UO2

We studied the migration dynamics of oxygen point defects in UO₂ which is the primary ceramic fuel for light-water reactors. Temperature accelerated dynamics simulations are performed for several initial conditions. Though the migration of the single interstitial is much slower than that of the vacancy, clustered interstitial shows faster migration than those. This observation gives us important insight on the formation mechanism of high-burnup restructuring, including planar defects and grain sub-division (the rim structure), found in UO₂.     

Effect of swift heavy ion irradiation on structure, optical, and gas sensing properties of SnO2 thin films

Swift heavy ion irradiation has been successfully used to modify the structural, optical, and gas sensing properties of SnO₂ thin films. The SnO₂ thin films prepared by sol-gel process were irradiated with 75 MeV Ni⁺ beam at fluences ranging from 1 × 10¹¹ ion/cm² to 3 × 10¹³ ion/cm². Structural characterization with glancing angle X-ray diffraction shows an enhancement of crystallinity and systematic change of stress in the SnO₂ lattice up to a threshold value of 1 × 10¹³ ions/cm², but decrease in crystallinity at highest fluence of 3 × 10¹³ ions/cm². Microstructure investigation of the irradiated films by transmission electron microscopy supports the XRD observations. Optical properties studied by absorption and PL spectroscopies reveal a red shift of the band gap from 3.75 eV to 3.1 eV, and a broad yellow luminescence, respectively, with increase in ion fluence. Gas response of the irradiated SnO₂ films shows increase of resistance on exposure to ammonia (NH₃), indicating p-type conductivity resulting from ion irradiation.     

Local field effect in diffraction radiation from a periodical system of dielectric spheres

We present a theory of diffraction radiation from a two-dimensional system that consists of small spherical particles on a metal substrate. The interaction between a moving charge and single particles is described in the frames of local field theory. The local field effects are proved to lead to a sharp increase of the radiation intensity at certain frequencies, similar to the effect of giant Raman scattering. The case of nanoparticles is explored and it is shown that the possible enhancement of radiation can reach some thousands of times in the THz range. The Smith-Purcell effect is investigated for the case when the system of particles is periodically arranged.     

A systematic study on MOS type radiation sensors

Radiation sensors based on metal oxide semiconductor (MOS) structure are useful because of their superior sensitivity as well as excellent compatibility with the existing microelectronic technology. In this paper, a systematic study of MOS capacitors built on p- and n-type Si substrates with different SiO₂ thicknesses (10 nm, 50 nm, 100 nm and 240 nm) is presented. MOS device response to gamma radiation up to 256 Gray have been studied from the sensor application point of view. Variation of the radiation induced device response with oxide thickness, substrate type, applied bias and post annealing have been measured and discussed. Radiation induced charge in MOS devices is shown to be a strong function of the oxide thickness as expected. Application of a positive bias to the gate is found to enhance the device sensitivity for both n- and p-type devices. This is explained in terms of the involvement of the interface states in the sensing process. Devices have also been studied after repeated cycles of irradiation and annealing treatment under hydrogen atmosphere. Each cycle consists of gamma irradiation with 60 Gray dose and an anneal at 200 °C for 30 min. The charging-discharging mechanism during these cycles is discussed.     

Cytocompatibility of Ar plasma treated and Au nanoparticle-grafted PE

Polyethylene (PE) was irradiated with inert Ar plasma, and the chemically active PE surface was grafted with Au nanoparticles. The composition and the structure of the modified PE surface were studied using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). Changes in the surface wettability were determined from the contact angle measured in a reflection goniometer. The changes in the surface roughness and morphology were followed by atomic force microscopy (AFM). The modified PE samples were seeded with rat vascular smooth muscle cells (VSMC) or mouse NIH 3T3 fibroblasts, and their adhesion and proliferation were studied. We found that plasma discharge and Au grafting lead to dramatic changes in the surface morphology and roughness of PE. The Au nanoparticles were found not only on the sample surface, but also in the sample interior up to the depth of about 100 nm. In addition, plasma modification of the PE surface, followed with grafting Au-nanoparticles, significantly increased the attractiveness of the PE surface for the adhesion and growth of VSMC, and particularly for mouse embryonic 3T3 fibroblasts.     

The inverse problem for the dipole field

The inverse problem for an electromagnetic field produced by a dipole is solved. It is assumed that the field of an arbitrary changing dipole is known. Obtained formulae allow calculation of the position and dynamics of the dipole which produces the measured field. The derived results can be used in investigations on radiative process in solids caused by changing of the charge distribution. For example, generation of the electromagnetic field caused by oscillations of atoms or electron gas at the trace of a particle channeling in a crystal, or fields arising at solids cracking or dislocation formation - in any case when one is interested in the details of the dipole field source.