Search results for "impurities"
showing 10 items of 22 documents
Impurity analysis of JET DiMPle pulses
2021
Divertor monitoring pulses (DiMPle) have been run in JET from the C35 campaign onwards. They provide an opportunity to study the impurity contamination of the plasma when it is limited by different surfaces within the machine, as well as the longer term behaviour of the impurities. In these discharges the plasma is first limited on the outer wall, then on the inner wall and, subsequently, in the X-point configuration the outer strike point is positioned on the horizontal tile 5 of the machine followed by tile 6 and then the vertical tile 7. The present study details the impurity behaviour in the DiMPle pulses from JET-ILW campaigns C35 to C38, which ran from 2015 to 2019. The impurities can…
Existence of zero-energy impurity states in different classes of topological insulators and superconductors and their relation to topological phase t…
2015
We consider the effects of impurities on topological insulators and superconductors. We start by identifying the general conditions under which the eigenenergies of an arbitrary Hamiltonian H belonging to one of the Altland-Zirnbauer symmetry classes undergo a robust zero energy crossing as a function of an external parameter which can be, for example, the impurity strength. We define a generalized root of \det H, and use it to predict or rule out robust zero-energy crossings in all symmetry classes. We complement this result with an analysis based on almost degenerate perturbation theory, which allows a derivation of the asymptotic low-energy behavior of the ensemble averaged density of st…
Properties of dirty two-band superconductors with repulsive interband interaction: Normal modes, length scales, vortices, and magnetic response
2018
Disorder in two-band superconductors with repulsive interband interaction induces a frustrated competition between the phase-locking preferences of the various potential and kinetic terms. This frustrated interaction can result in the formation of an $s+is$ superconducting state, that breaks the time-reversal symmetry. In this paper we study the normal modes and their associated coherence lengths in such materials. We especially focus on the consequences of the soft modes stemming from the frustration and time-reversal-symmetry breakdown. We find that two-bands superconductors with such impurity-induced frustrated interactions display a rich spectrum of physical properties that are absent i…
Effect of spatial distribution of impurity ions on the signal of ‘C/O monitor for Wendelstein 7-X’ - an indicator of plasma wall interactions
2022
The ‘C/O monitor’ is a dedicated diagnostic system designed to monitor light impurities (B, C, N and O) in the Wendelstein 7-X (W7-X) stellarator. Its main goal is to provide fast (∼1 ms) information about the impurity level which is measured from a large plasma volume (high throughput). Its first subsystem dedicated to measure Lyman-α lines of H-like carbon (C5+ − 3.4 nm – used as PFC material) and oxygen (O7+ − 1.9 nm – common impurity absorbed by inner vessels’ walls) is going to be commissioned during the next Operational Phase of W7-X. Since the radiated photon intensity of a given impurity depends strongly on plasma kinetic parameters (Te, ne) and impurity transport, it is important t…
Vacancies and Carbon Impurities in Iron
1981
Point defects in electron-irradiated high-purity α-iron have been studied by positron lifetime measurements. We show that the migration stage of monovacancies occurs already as low as at 220 K, which results in agglomeration of small three-dimensional vacancy clusters. Furthermore, we irradiated carbon-doped iron specimens, where formation of highly asymmetric monovacancycarbon atom pairs was detected during the migration stage of monovacancies at 220 K.
Change of the vortex core structure in two-band superconductors at the impurity-scattering-driven s±/s++ crossover
2017
We report a nontrivial transition in the core structure of vortices in two-band superconductors as a function of interband impurity scattering. We demonstrate that, in addition to singular zeros of the order parameter, the vortices there can acquire a circular nodal line around the singular point in one of the superconducting components. It results in the formation of the peculiar ``moat''-like profile in one of the superconducting gaps. The moat-core vortices occur generically in the vicinity of the impurity-induced crossover between ${s}_{\ifmmode\pm\else\textpm\fi{}}$ and ${s}_{++}$ states.
Overview of first Wendelstein 7-X high-performance operation
2019
Abstract The optimized superconducting stellarator device Wendelstein 7-X (with major radius , minor radius , and plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. This paper reports on the results from the first high-performance plasma operation. Glow discharge conditioning and ECRH conditioning discharges in helium turned out to be important for density and edge radiation control. Plasma densities of with central electron temperatures were routinely achieved with hydrogen gas fueling, frequently terminated by a radiative collapse. In a first stage, plasma densities up to were reached with hydrogen pellet injec…
Ethanol-Based Post-processing of Generator-Derived 68Ga Toward Kit-Type Preparation of 68Ga-Radiopharmaceuticals
2014
Post-processing by means of a cation-exchanger–based protocol is an efficient strategy for purification and concentration of generator-derived 68Ga. It ensures the removal of 68Ge before 68Ga-radiopharmaceutical preparation and high labeling yields of 68Ga-labeled radiopharmaceuticals for routine medical application. Methods: In an effort to overcome the problem associated with acetone in the currently applied method, we have investigated the feasibility of replacing it with ethanol. The purification of 68Ga from coeluted metallic impurities (68Ge4+, Fe3+, Zn2+, and Ti4+) on various cation-exchange columns has been investigated with a variety of post-processing solutions. As a proof of prin…
Purification of Nano-Porous Silicon for Biomedical Applications
2011
Recently, various bio-medical applications of nanoporous silicon (np-Si) have been suggested. This work investigates the biocompatibility of np-Si particles taking into account hazardous residua confined in the pores after preparation. The emphasis is on the potential application of such particles as oxygen photosensitizer for photodynamic therapy of cancer, which requires both negligible toxicity of np-Si particles in darkness and a high photo-cyto-toxic effect due to generation of singlet oxygen under illumination. Considerable amounts of water soluble toxic impurities are found to be present in the nanoporous shell of micrometer-sized np-Si particles immediately after their preparation b…
Field-induced coexistence of s++ and s± superconducting states in dirty multiband superconductors
2018
In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. For example, a dirty two-band system with interband impurity scattering undergoes a sharp crossover between the s± state (which favors phase antilocking) and the s++ state (which favors phase locking). We discuss here that the situation can be much more complex in the presence of an external field or superconducting currents. In an external applied magnetic field, dirty two-band superconductors do not feature a sharp s±→s++ crossover but rather a washed-out crossover to a finite region in the parame…