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Sapphire Surface Layer Structure and Transmission in Visible after Sputtering in H.sub.2-N.sub.2 RF Discharge
Leucosapphire (c-LS) structure and transmission in visible after surface treatment in 90%H.sub.2-10%N.sub.2 RF discharge are studied. According to AFM, the number of scratches of the mechanically polished surface decreased significantly after removal of about a 300 nm layer (exposure time of 12 h) under unchanged rms of roughness. According to TEM, a two-layer structure formed in the near-surface region consists of an outer 10 nm amorphous layer followed by a crystalline layer of 40-50 nm with a high defect density. The c-LS transmission in the angle of 400-1000 nm either slightly increased or remained unchanged. The demonstrated transmission stability during exposure in 90%H.sub.2-10%N.sub.2 RF discharge allows us to consider the plasma sputtering as a promising technique for cleaning contaminated windows protecting first mirror of divertor Thomson scattering being developed for ITER divertor.
Journal Article
Tungsten Material Behavior under Hsub.2, Dsub.2, and He Plasma Interaction Conditions in the Framework of Fusion-Relevant Studies
In the current study, bulk tungsten material surfaces are exposed to hydrogen, deuterium, and helium plasmas in the radiofrequency domain (13.56 MHz) at an input power of 250 W using the hollow-cathode configuration. The ejected material is collected on titanium substrates at various distances (from 6 mm up to 40 mm). Therefore, the exposed tungsten materials are investigated for surface changes (blister occurrence, dust formation, or nano-structuration), along with the crystallinity, depending on the plasma’s exposure times (from 30 min up to 120 min for each plasma type). Also, the collected materials are analyzed (morphological, structural, and statistical investigations) for dust and dust film-like appearance. Plasma discharges are analyzed using two methods: optical emission spectroscopy, and single Langmuir probes, to emphasize the nature of the used plasmas (cold discharges, ~2 eV), along with the presence of tungsten emission (e.g., WI 406.31 nm, WI 421.31 nm) during the plasma lifetime. By using a dedicated protocol, a method was established for obtaining fusion-relevant tungsten surfaces in the hydrogen and deuterium plasma discharges. By using the implemented method, the current paper introduces the possibility of obtaining a new tungsten morphology, i.e., the dandelion-like shape, by using helium plasma, in which the W[sub.18]O[sub.49] compound can be found.
Journal Article
Advancements in Tokamak Technology for Fusion Energy: A Bibliometric and Patent Trend Analysis (2014–2024)
Tokamak technology, as the cornerstone of nuclear fusion energy, holds immense potential in achieving efficient plasma confinement and high energy densities. To comprehensively map the rapidly evolving landscape of this field, this study employs bibliometric analysis to systematically examine the research and development trends of tokamak technology from 2014 to 2024. The data are drawn from 7702 academic publications in the Scopus database, representing a global research effort. Additionally, the study incorporates 2299 tokamak-related patents from Google Patents over the same period, analyzing their technological trends to highlight the growing significance of tokamak devices. Using the R language and the Bibliometric package, the analysis explores research hotspots, institutional influences, and keyword evolution. The results reveal a multifaceted global landscape: China leads in publication output, and the United States maintains a leading role in citation impacts and technological innovation, with other notable contributions from Germany, Japan, South Korea, and various European countries. Patent trend analysis further reveals the rapid expansion of tokamak applications, particularly with significant innovations in high-temperature superconducting magnets and plasma control technologies. Nevertheless, the study identifies major challenges in the commercialization process, including plasma stability control, material durability, and the sustainability of long-term operations. To address these, the study proposes concrete future directions, emphasizing international collaboration and interdisciplinary integration. These efforts are crucial in accelerating tokamak commercialization, thereby providing a strategic roadmap for researchers, policymakers, and industry stakeholders to advance the global deployment of clean energy solutions.
Journal Article
SYSTEMS OF IN SITU DIAGNOSTICS OF PLASMA-SURFACE INTERACTION IN A MEPHIST-1 TOKAMAK
At the Institute for Laser and Plasma Technologies of NRNU MEPhI, a compact spherical tokamak MEPhIST (MEPhI-Spherical Tokamak) has been developed and constructed for educational, demonstrational and research purposes. The creation of plasma diagnostic systems involves several stages, determined by a successive complication of the plasma research tasks, the device upgrading and the development of educational and methodological materials for the laboratory works to be performed at the tokamak. Testing of the in situ methods for analyzing the plasma-surface interaction is one of the main scientific and technological goals set for this tokamak. The diagnostic complex described in the paper provides cumulative information on the processes occurring after the plasma-surface contact; it represents a set of very informative and well-tested diagnostic tools that allow the students to obtain visual reliable information on the processes occurring in the tokamak vacuum vessel.
Journal Article
Plasma parameters comparison using different probes on WEST tokamak before and during N2 seeding
In this paper, a comparison is presented of the plasma parameters values as obtained by different Langmuir probe measurements in the WEST tokamak. The probes used in the divertor were as follows: a magnetically-driven “mousetrap” probe, “pop-up” probes and “wafer” (flush-mounted) probes. The agreement concerning the main parameters is good. It was also found that the divertor cooled down during nitrogen seeding, but the scrape-off layer was not affected substantially.
Journal Article
The Impact of Superconducting Properties of Micron-Scale Masked Proton Irradiation on BaTiOsub.3-Doped YBCO Film
This study investigates the effects of 60 keV proton irradiation on BaTiO[sub.3]-doped YBa[sub.2]Cu[sub.3]O[sub.7−δ] (YBCO) films using masks with micron-scale holes to create controlled defect patterns aimed at enhancing superconducting properties. Contrary to expectations, masked irradiation resulted in a reduction in the critical current density (J[sub.c]), while unmasked irradiation demonstrated improvement, consistent with previous studies. Notably, no improvement was observed at 2 T around liquid nitrogen temperature. These observations highlight the challenges of employing micron-scale masks in defect engineering and underscore the need for further refinement to achieve the desired performance enhancement. Insights from this study contribute to advancing defect engineering techniques for improving YBCO’s performance in high-field applications, including fusion energy systems.
Journal Article
Terahertz Absorption Spectroscopy in Bicrystal Josephson Junctions Formed from Mutually Tilted Ic/I-Axes YBasub.2Cusub.3Osub.7−x Films
Spectral analysis of terahertz (THz) and sub-THz emission from quantum cascade lasers has been recently demonstrated using conventional YBa[sub.2]Cu[sub.3]O[sub.7−x] bicrystal Josephson junctions made from c-axes thin films. Josephson frequencies of alternative bicrystal junctions made from YBa[sub.2]Cu[sub.3]O[sub.7−x] films with mutually tilted c-axes extend further into the THz range. However, these THz oscillations can weaken due to new absorption channels in the junction environment. Here, using Josephson admittance spectroscopy, THz losses in YBa[sub.2]Cu[sub.3]O[sub.7−x] bicrystal junctions with mutually tilted c-axes are studied. Absorption maximizes at a reproducible set of THz frequencies close to those of collective modes in bulk YBa[sub.2]Cu[sub.3]O[sub.7−x] recovered by Fourier spectroscopy. Annealing junctions in atomic oxygen reduces the losses at frequencies of 2.7 and 3.6 THz, while the losses increase at frequencies of 2.3 and 4.6 THz. Thus, as a THz spectrum analyzer, YBa[sub.2]Cu[sub.3]O[sub.7−x] bicrystal junctions require post-fabrication correction of the oxygen content. In addition, the fine structure of the absorption spectrum appears at frequencies near 4.6 THz. Significant absorption near 2.3 THz may be due to effects associated with the second Josephson harmonic or second-order nonlinearity of the susceptibility in YBa[sub.2]Cu[sub.3]O[sub.7−x]. This work paves the way towards probing collective modes in high-Tc materials in situ using the Josephson oscillations.
Journal Article