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New Method to Evaluate Negative-Ion Density Using Conventional Langmuir Probe
Get PDFA new experimental method using a Langmuir probe to measure negative-ion density is introduced in an area that cannot use lasers, such as the extraction hole. An electron reduction Langmuir probe model is established to distinguish negative ions from electron density. A comparison between density measured by the Langmuir probe with the electron reduction model and a photo-detachment Langmuir probe is performed to verify the use of the newly developed model.journal articl
Development of an experimental system for cell viability assays of yeasts using gas-temperature controllable plasma jets
Get PDF0000-0002-0602-0665The characteristics of a gas-temperature-controllable atmospheric-pressure helium plasma jet and the development of an experimental system for cell viability assays of yeasts (fission yeast Schizosaccharomyces pombe and budding yeast Saccharomyces cerevisiae) are reported. The physicochemical properties of the plasma plume, which can maintain the temperature of the irradiated object at a temperature suitable for yeast, were not significantly different from those of a typical helium plasma jet. Furthermore, good reproducibility of cell viability was observed when gas temperature, gas flow rate, applied high voltage, and irradiation distance remained fixed, and only irradiation time was used as a parameter. This experimental system allows us to carry out various experiments, such as the search for plasma-resistant mutants that will contribute to the identification of genes involved in resistance to direct plasma irradiation.journal articl
Conference Report on the 7th International Symposium on Liquid metals Applications for fusion (ISLA-7)
Get PDFSupported by the world magnetic fusion research community, a series of International Symposia on Liquid metals Applications for fusion (ISLA) have been held biannually since 2010. The 7th edition (ISLA-7) was held for the period from 12 December through 16 December 2022, at Chubu University located in Kasugai, Aichi, Japan. For the first time in the history of this series of symposia, ISLA-7 was held in a hybrid fashion, due to the COVID-19 situation. The total number of the participants was 60, 34 out of whom attended the symposium in person, and the rest participated online. As to the presentation statistics, 29 papers were presented in person, whereas 21 presentations were delivered online but real-time by the presenters in China, Spain, the UK, and the USA. Both of the presentations delivered in person and online were recorded, and the video has been shared by all participants. These participants represent 11 countries: China, Czech, Italy, Japan, Latvia, Netherlands, Russia, Thailand, the UK, and the USA. All these numbers are among the largest in this series of symposia. Covered by these presentations are; in session-2, program overviews and liquid metal research review; in session-3, liquid metal flows, and MHD issues; in session-4, liquid metal facilities; in sessions-5 and 6, liquid metal experiments and modeling; in session-7, divertor physics and heat flux mitigation; in session-8, plasma and liquid metals interactions; in session-9 liquid metal plasma-facing components, erosion, and wettability. In addition, there were an opening session whereby several opening addresses were delivered and also a closing session where all technical session summaries were presented by the respective session chairs.journal articl
Simulation study of the harmonic structure of lower hybrid waves driven by energetic ions
Get PDFORCID 0000-0001-8894-3430By means of one-dimensional, electromagnetic, particle-in-cell simulations considering the effects of energetic-ion injection, we study the harmonic structure of lower hybrid waves (LHWs) driven by energetic ions under the condition where the electron plasma frequency (ωpe) is smaller than the electron cyclotron frequency (Ωe). It is found that after the LHWs are excited with the wave number and frequency of (k1,ω1), many harmonic LHWs are generated at (mk1,nω1) where m and n are integers, up to far beyond the lower hybrid resonance frequency, m and n∼10. We show that the harmonic LHWs are generated by nonlinear wave-wave coupling between the LHWs directly excited by the energetic ions and the energetic-ion cyclotron waves above the lower hybrid resonance frequency. We also find that the harmonic LHWs can exist even after the energetic ions are artificially removed because they can be coupled with ion Bernstein waves due to bulk ions. The effect of the energetic-ion injection and the dependence of ωpe/Ωe on the development of the harmonic LHWs are investigated to compare the simulation results with an observation in Earth's magnetosphere.journal articl
Cellular responses to compound stress induced by atmospheric-pressure plasma in fission yeast
Get PDFORCID 0000-0002-2401-4808The stress response is one of the most fundamental cellular processes. Although the molecular mechanisms underlying responses to a single stressor have been extensively studied, cellular responses to multiple stresses remain largely unknown. Here, we characterized fission yeast cellular responses to a novel stress inducer, non-thermal atmospheric-pressure plasma. Plasma irradiation generates ultraviolet radiation, electromagnetic fields and a variety of chemically reactive species simultaneously, and thus can impose multiple stresses on cells. We applied direct plasma irradiation to fission yeast and showed that strong plasma irradiation inhibited fission yeast growth. We demonstrated that mutants lacking sep1 and ace2, both of which encode transcription factors required for proper cell separation, were resistant to plasma irradiation. Sep1-target transcripts were downregulated by mild plasma irradiation. We also demonstrated that plasma irradiation inhibited the target of rapamycin kinase complex 1 (TORC1). These observations indicate that two pathways, namely the Sep1-Ace2 cell separation pathway and TORC1 pathway, operate when fission yeast cope with multiple stresses induced by plasma irradiation.journal articl
Measurement of 6Li burn-up reaction rate using a single crystal CVD diamond detector under fast neutron irradiation environment
Get PDFORCID 0000-0003-0920-2154The study aimed to develop a technique for measuring the 6Li burn-up rate using a single crystal diamond (SCD) detector (SDD) made by chemical vapor deposition (CVD) with a thin lithium fluoride foil. The method relied on pulse shape discrimination (PSD) to separate pulses by nuclear reaction products of 6Li from pulses due to fast neutrons and gamma-rays.
By applying the PSD method, the rectangular shape pulses induced by events occurred at the specific depth positions of the SCD, i.e., the incident surface, the ballistic center region (BCR), and the rear surface, were extracted. Thereafter, pulses occurred each specific depth position of the SCD were discriminated according to the pulse width.
Due to a short range of nuclear reaction products in the SCD, pulses at the incident surface should be induced by both fast neutrons and nuclear reaction products, although pulses at the BCR are caused by fast neutron only. The study demonstrated that quantitative measurements of nuclear reaction products in the 6Li burn-up reaction under fast neutron irradiation can be achieved using only one SDD by analyzing event rates at the incident surface and in the BCR region.journal articl
Prompt core confinement improvement across the L–H transition in DIII-D: Profile stiffness, turbulence dynamics, and isotope effect
Get PDF0000-0001-5669-1937We elaborate on the nature of the prompt core confinement improvement observed at the L–H transition in DIII-D, which is a long-standing issue unsolved for more than two decades and can impact future fusion reactor performance. Dynamic transport analysis suggests the essential role of the profile stiffness for understanding the mechanism of the prompt core confinement improvement. Beam emission spectroscopy shows that transport reduction at the core cannot be explained only by the ion scale turbulence density fluctuation suppression. Properties of nonlocal confinement improvement across the L–H transition are experimentally assessed in hydrogen (H) and deuterium (D) plasmas. Prompt core confinement improvement is found to be more rapid in the lighter hydrogen isotope.journal articl
ICRF Plasma Production with Hydrogen Minority Heating in Uragan-2M and Large Helical Device
Get PDFORCID 0000-0003-4948-0896This report compares results ion-cyclotron range of frequencies (ICRF) plasma production at hydrogen minority regime in Uragan-2M (U-2M) and Large Helical Device (LHD). The condition of the presence of the fundamental harmonic ion cyclotron resonance zone for the hydrogen inside the plasma column should be fulfilled for this method. The scenario is successful at both machines and weakly sensitive to the variation of the hydrogen concentration in the H2+He gas mixture. It should be noted that at LHD the start up is slower than at U-2M. The comparison of plasma production in ICRF with hydrogen minority at U-2M and LHD indicate that this scenario can be scaled to larger stellarator devices. The experiments made are the base for the proposal for usage this scenario for plasma production in ICRF at Wendelstein 7-X at magnetic field reduced to 1.7 T.journal articl
An extended Hasegawa–Mima equation for nonlinear drift wave turbulence in general magnetic configurations
Get PDFWe propose an extended Hasegawa–Mima equation describing the evolution of nonlinear drift wave turbulence in general magnetic configurations. Such HMGM equation can be derived within the kinetic framework of guiding center motion or from a two-fluid model of an ion-electron plasma by application of a drift wave turbulence ordering that does not involve conditions on spatial derivatives of magnetic field and plasma density. The HMGM equation is therefore appropriate to describe the evolution of drift wave turbulence in strongly inhomogeneous magnetized plasmas, such as magnetospheric and stellarator plasmas, involving complex magnetic field geometries and non-uniform plasma density distributions. We find conservation laws (mass, energy, and generalized enstrophy) of the HMGM equation, study its algebraic (Hamiltonian) structure, and prove a nonlinear stability criterion for steady solutions through the energy-Casimir method. We then apply these results to describe drift waves and infer the existence of stable toroidal zonal flows with radial shear in dipole magnetic fields.journal articl
Formation of corrugated nano-fuzz tungsten thin film on silicon via helium plasma irradiation
Get PDFORCID 0000-0001-8616-6041Tungsten thin films were deposited onto silicon substrates using sputtering techniques, and helium plasma irradiation was performed in a linear plasma device. Observations of the surface and cross-sectional morphology revealed the presence of a corrugated fiberform nanostructure, referred to as corrugated nano-fuzz, on the irradiated silicon samples. This structure has a distinct pattern of ridges and valleys with nanofibers on the surface. In addition to its unique morphology, the corrugated nano-fuzz demonstrates remarkable optical absorptivity, as revealed by optical absorptivity measurements, even after being exposed to helium plasma even for a short duration. The utilization of silicon-substrate thin film holds the potential to not only accelerate the processing for nanostructure growth but also yield uniformly corrugated structures and high optical absorptivity. These findings offer valuable insights for advancing the development of efficient fabrication methods within the field of nanotechnology.journal articl