Ohmic Mode Research Articles

The effect of ohmic heating conditions and heating modes on gel properties of unwashed pre-rigor common carp (Cyprinus carpio) surimi.

Ohmic heating (OH) at different conditions (voltage: 15, 20, 25V; frequency: 1, 5, 10kHz) and one-step water bath (WB) were used to heat wash and unwash surimi prepared from fresh pre-rigor common carp. The optimal heating conditions were established through assessments of gel strength, Texture Profile Analysis (TPA), water-holding capacity (WHC), whiteness, and sensory evaluation. Then, the impact of heating modes on gelation properties of unwashed surimi based on the optimal heating conditions was investigated. The study findings indicated a significant enhancement in gel properties compared to WB. Unwashed surimi gel properties showed improvement when derived from freshly caught raw fish and subjected to OH treatment. Moreover, variations in frequencies and voltages were observed to influence the heating rate. Optimal gel quality was achieved at 10kHz 20V (10V/cm), facilitating swift progression through the gel deterioration stage, inhibition of protein hydrolyzing enzymes activity, and establishment of a stable gel network. Continuing to increase the heating rate would disrupt its network structure, resulting in diminished gel strength and WHC. The best quality of unwashed surimi gel was achieved by heating to 40°C for 30min, followed by heating to 90°C for another 30min (40°C 30min+90°C 30min) under 10kHz 20V. The gel strength increased when held for 1h at 40°C. For optimal heating efficiency, the heating mode of 40°C 30min+90°C 30min is recommended to prepare unwashed surimi gel. PRACTICAL APPLICATION: Ohmic heating, as a rapid food heat treatment method, can both increase the heating rate and improve the gelation properties of freshwater surimi. There is a wide range of potential applications for the heat treatment of the surimi.

Controlled commutation modes in a switch based on HTS composites

This paper presents the results of experimental studies of switching processes of high-temperature superconducting tapes under the action of a pulse current load of microsecond duration. The reversible, stable and irreversible switching of the superconductor to the normal state has been realized. To demonstrate the opportunity of controlled generation of transients in superconducting composites, the characteristics of a superconducting switch capable of cyclic switching between flux flow and ohmic modes with preservation of switching parameters were investigated. The characteristics of a superconducting switch have been calculated based on experimental results.

Low Ohmic Losses and Mode Selectivity Provided by a Distributed Bragg Reflector for Cavities of Terahertz Gyrotrons

Low Ohmic Losses and Mode Selectivity Provided by a Distributed Bragg Reflector for Cavities of Terahertz Gyrotrons

Overview of the first experiments at KTM tokamak to obtain plasma discharges

The article presents the results of experiments conducted in 2021 to obtain plasma discharge at the KTM tokamak. The experiments achieved a plasma current of ∼500 kA with a discharge time of ∼0.5 s. Plasma discharges were obtained in the ohmic heating mode, with a plasma column of quasi-circular cross-section (with a plasma elongation of k ≤ 1.25). The results achieved in 2021, described in the article, represent a significant step towards achieving the KTM design parameters.

A Critical Fault-Tolerant Inverter Based on Internal Evolutionary Short-Circuit Failure Mechanism of IGBT Module

Long-term and stable operation after failure is a challenge for high-reliability power converters. An extreme characteristic of IGBT is deeply explored, and a new cold-redundant inverter topology is proposed in this article. A quantity of epoxy-encapsulated IGBT modules is analyzed in short-circuit (SC) failure for critical energy. The evolution of the IGBT failure mechanism is crucial to the stability of this structure. An ohmic mode is discovered in dynamic characteristics analysis. Based on the robustness experimental test, the results revealed the characteristics of the internal structure reorganization and the evolution law of the electrical parameters under the rated current pulse stress. The epoxy-encapsulated IGBT module has a stable SC failure impedance characteristic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{{\text {sc}}}$ </tex-math></inline-formula> , with no more than 20% drift even after a 624-h continuous thermal cycle aging test. On this basis, the new cold-redundant inverter platform with this IGBT module is tested. There is only one paralleled safety leg connected in series with the faulty equipment without any additional complexity or extra cost. The full process like fault identification, isolation, structural reorganization, switching, and loading is verified and realized after the transient SC faults.

Exploiting elastic buckling of high-strength gold nanowire toward stable electrical probing

SummaryBuckling is a loss of structural stability. It occurs in long slender structures or thin plate structures which is subjected to compressive forces. For the structural materials, such a sudden change in shape has been considered to be avoided. In this study, we utilize the Au nanowire’s buckling instability for the electrical measurement. We confirmed that the high-strength single crystalline Au nanowire with an aspect ratio of 150 and 230-nm-diameter shows classical Euler buckling under constant compressive force without failure. The buckling instability enables stable contact between the Au nanowire and the substrate without any damage. Clearly, the in situ electrical measurement shows a transition of the contact resistance between the nanowire and the substrate from the Sharvin (ballistic limit) mode to the Holm (Ohmic) mode during deformation, enabling reliable electrical measurements. This study suggests Au nanowire probes exhibiting structural instability to ensure stable and precise electrical measurements at the nanoscale.

Design of a High-Q Diamond-Loaded Cavity for a Third-Harmonic Subterahertz Gyrotron Driven by a Low-Power Electron Beam

A continuous-wave (CW) high-harmonic gyrotron driven by a low-power electron beam is a compact radiation source demanded by terahertz applications. Its physical feasibility, however, is hampered by ohmic losses and mode competition in the gyrotron cavity. An ultralow-loss diamond loading of the cavity can give a clue to this problem. This article is concerned with theoretical aspects of mode selection and design for a gyrotron cavity loaded with coaxial rod made of chemical vapor deposition (CVD) diamond. As an example, the design of a high-Q diamond-loaded cavity for a third-harmonic 658-GHz gyrotron powered by a 0.1-A, 15-kV electron beam is presented. It is shown that the designed cavity enables the gyrotron to produce up to 116-W output power in a single oscillating mode.

Investigation on the Effect of Annealing Temperature on the Side Ohmic Contact Characteristics for Double Channel GaN/AlGaN Epitaxial Layer

A side ohmic contact mode for the double channel GaN/AlGaN epitaxial layer is proposed in this paper. Rectangle transmission line model (TLM) electrodes are prepared, and the specific contact resistance is tested at the annealing temperatures from 700 °C to 850 °C. The results show that the minimum specific contact resistance is 2.58 × 10−7 Ω·cm2 at the annealing temperature of 750 °C, which is three to four times lower than the surface contact mode. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and atomic force microscope (AFM) were carried out for the analysis of the morphology, element composition, and the height fluctuation at the contact edge. With the increase in the annealing temperature, the specific contact resistance decreases due to the alloying of electrodes and the raised number of N vacancies. However, when the annealing temperature exceeds 800 °C, the state of the stress in the electrode films transforms from compressive stress to tensile stress. Besides, the volume expansion of metal electrode film and the increase in the roughness at the contact edge leads to the degradation of the side ohmic contact characteristics.

The role of drifts on the isotope effect on divertor plasma detachment in JET Ohmic discharges

• The magnitude of the isotope effect is determined by the pressure in the sub-divertor. • Pumping of gas within the JET divertor is effective near the outer target only. • The re-distribution of the neutrals due to drifts decreases the throughput. • The total decrease of the throughput reduces the isotope effect. Experiments in JET-ILW Ohmic confinement mode plasmas show that the line-averaged detachment onset density in deuterium discharges is approx. 10% lower than in hydrogen discharges. The magnitude of the isotope effect on the detachment onset density depends on the divertor geometry, the magnetic configuration and the throughput of the sub-divertor/divertor cryopump system. Simulations with the edge fluid code EDGE2D-EIRENE revealed that the pumping of neutral gas within the JET divertor is effective near the outer divertor target only. The studies show that the magnitude of the isotope effect is determined by the molecular pressure in the sub-divertor pumping plenum. According to the simulations, operating in vertical configurations or closer proximity of the strike point increases the molecular pressure (and thus throughput) in front of the outer pumping plenum by up to 15% compared to the horizontal configuration, thus producing a stronger isotope effect on the detachment onset density. Similarly, EDGE2D-EIRENE predicts that plasma, hence neutral, redistribution due to E × B drifts in favourable B T configurations (ion B × grad(B) towards the divertor) decreases the throughput. The total decrease of the throughput reduces the isotope effect on the detachment onset density, and decreases the detachment onset density for both isotopes.

Comparative Experiments on Lower Hybrid Wave Heating of Ions in High-Density Hydrogen and Deuterium Plasmas at the FT-2 Tokamak

In the framework of the isotope effect studies at the FT-2 tokamak, the efficiencies were compared of the lower hybrid wave heating of the ion components of the hydrogen and deuterium plasmas with high densities (close to the Greenwald limit, 〈ne〉 ≤ 1020 m–3). It was experimentally ascertained that, in accordance with the theoretical concepts, the efficient axial heating of the deuterium plasma ions occurs, as opposed to the peripheral heating of the hydrogen plasma ions. Such an isotope effect occurs due to the different localization of the plasma-RF wave interaction regions. The distinctive feature of these experiments is the fact that, in deuterium plasma, during the preliminary ohmic heating, the dependence of the energy lifetime on density τЕ(n) is linear (LOC dependence), and, with increasing density, the transition to the improved ohmic confinement mode occurs. In hydrogen plasma, on the contrary, the transition to the saturation mode is observed. In this study, the considerable decrease in τЕ was revealed, observed during the additional lower hybrid wave heating in both hydrogen and deuterium plasmas.

Verification and modulation of multi-mode chiral hybrid metamaterial based on VO2 layer

In this paper, a high absorption performance metamaterial based on phase change material vanadium dioxide (VO2) is verified in experiments. Two absorption peaks (P1, P2) with 60% and 72% amplitudes are achieved based on bright-bright modes coupling or the Ohmic loss mode in 2–40.0 THz at room temperature. P1 and P2 are enhanced and shifted to lower frequency with the diameter D of metal disks increasing or the linear distance L reducing between two metal disks in experiments. When L = 0, a new metal array is achieved since two metal disks contacting with each other, which results in two new absorption peaks (P3, P4) based on new plasmon-resonance hybridization or Ohmic loss mode, respectively. In further experiments, a new absorption peak (P5) is found in heating process or cooling process based on the insulator-metal phase transition of the VO2 layer, while P1 and P2 are insensitive to temperature. The metamaterial exhibits the stability of the original absorption properties and the tunability of the temperature.

Study of the beam–wave interaction of a 220 GHz coaxial-cavity gyrotron with two electron beams

In this paper, the mode selection, ohmic loss quality factor, mode competition, and beam–wave interaction of a 220 GHz coaxial-cavity gyrotron with two electron beams are studied by using the linear and nonlinear theories of a gyrotron. Research shows that a coaxial-cavity gyrotron with two electron beams has more advantages than a coaxial-cavity gyrotron with one electron beam in mode selection, suppressing mode competition and increasing output power, and the eigenvalue and the ohmic loss quality factor of modes have similar monotonicity in the direction of the gyrotron axis. Results find that (1) the current ratio K of the gyrotron has a greater influence on the beam–wave interaction efficiency of the two electron beams, (2) under B = 8.90 T, I = 136 A, α = 1.40, and K = 0.45, the coaxial-cavity gyrotron with two electron beams can operate steadily in the TE51,32− mode, which has an efficiency of 37.67% and an output power of 4.53 MW at f = 220.04 GHz, and (3) the total ohmic loss power of the gyrotron accounts for 1.3% of the output power.

Influence of toroidal rotation from electron cyclotron resonance heating in KSTAR

Toroidal rotation behaviors from electron cyclotron resonance heating (ECH) injected Ohmic and high confinement mode (H-mode) plasmas are investigated in KSTAR. The on-axis ECH injection induces core toroidal rotation reversal by neoclassical toroidal viscosity (NTV) damping torque coincided with trapped electron mode (TEM)-driven co-current rotation torque in the countercurrent rotating Ohmic plasmas. In the ECH triggered H-mode plasmas with enhanced heating power, the toroidal rotation in the central region turns to the countercurrent direction and co-current direction in the outer region of the plasma.

Nonlinear Electron Transport and Effects of Resistive Switching in Iron Nanoparticle Metal Oxide/Metal Composites

Voltammetric methods are used to study longitudinal electron transport and the effects of resistive switching in films of nanoparticle metal oxide (Fe/FeOx)/metal composites grown by magnetron sputtering (in an argon atmosphere) and the ensuing iron oxidation. Formation of iron nanograins and intergrain oxide is controlled using the methods of electron microscopy, Raman spectroscopy, and X-ray diffraction. Analysis of voltammetric characteristics of the composite shows the linear ohmic mode of electron transport at low voltages and the nonlinear electron transport mode at high voltages. The resistive switching of the composite from the low conductivity state (LRS) into the high conductivity state (HRS) accompanied by formation of magnetite Fe3O4 regions in the intergrain FeOx oxide characteristic for memristor materials is registered at an increase in voltage. At a further increase in voltage, the reverse process is registered: the switching of the studied film from the high conductivity state in the low conductivity state due to oxidation of intergrain magnetite to maghemite. As the breakdown voltage is registered on the surface of such a composite, a system of oriented elongated ghematite nanoparticles with the average diameter of 45 nm and length of up to 2 μm is formed.

Nature of Electronic Conduction in "Pseudocapacitive" Films: Transition from the Insulator State to Band-Conduction.

The transition between the insulator state and the band-conducting state is investigated by means of cyclic voltammetry in cobalt oxide porous film electrodes in phosphate-buffered solutions. It is shown that a proton-coupled faradaic oxidative process starting in the insulator region eventually builds an ohmic conduction mode upon anodic polarization. This model allows one to understand the origin of the authentic capacitive behavior of conductive metal oxide films rather than the so-called "pseudocapacitive" behavior. The particular example of cobalt oxide serves to illustrate the way in which, more generally, the behavior of "pseudocapacitors", long ascribed to the superposition of faradaic reactions, is in fact that of true capacitors, once band-conduction has been established upon oxidation of the material.

Heat and Particle Transport in the Initial Phase of Ohmic Discharges in the Globus-M Spherical Tokamak

The results of experiments and simulations of the transport of heat and particles in the Globus-M spherical tokamak are presented. Investigations were carried out in the ohmic mode in hydrogen and deuterium plasma. It is shown that in the phase of current growth under the same initial conditions, as long as the condition is met at which the minimum of the safety factor exceeds unity, two scenarios of discharge development are possible: with an electron temperature dive or with an electron density peak. After the safety factor reaches the value of 1, the differences are no longer observed. Modeling of transport processes using the ASTRA code showed that the dive of the electron temperature and density is a consequence of the decrease in the transport of heat and particles in the plasma core (i.e., the presence of internal transport barriers).

Capacitively coupled radio frequency nitrogen plasma generated at two different exciting frequencies of 13.56 MHz and 40 MHz analyzed using Langmuir probe along with optical emission spectroscopy

Capacitively coupled nitrogen plasma discharges driven by two different exciting radio frequencies of 13.56 MHz, and 40 MHz are investigated. Langmuir probe diagnostics along with optical emission spectroscopy are used for interpreting the discharges. The results of these diagnostics are not shown sufficiently in the literature for 40 MHz even though there are some for 13.56 MHz. The electron density ne and the effective electron temperature Teff are calculated from the measurements of the current – voltage characteristics of the discharges. These calculated parameters are correlated with the vibrational temperatures of the N2 second positive system C3Πu−B3Πg and the N2+ first negative system B2Σu+−X2Σg+ measured via optical emission spectroscopy. The population of the vibrational excitation particles plays a crucial role in the determination of the vibrational temperature which strongly depends on ne and Teff. The transition from collisionless stochastic heating mode to collisional Ohmic heating mode into the bulk plasma appears at lower pressure value for 40 MHz as compared to 13.56 MHz. This effect is observed effectively with increasing the RF input power due to the high energy electrons. It is noted that the vibrational temperatures of N2 and N2+ decreases at high-pressure region (&amp;gt;0.3 Torr for 13.56 MHz and &amp;gt;0.2 Torr for 40 MHz) due to a reduction in the relative population of the vibrationally excited particle. The measurements of the Langmuir probe are very consistent with the results of the optical emission spectroscopy.

Experimental trends of reflectometry frequency spectra emerging from a systematic analysis of the Tore Supra database

One major goal of data science applications is to extract patterns from large datasets. Such a database approach has been applied, for the first time in fusion science, towards a systematic study of the frequency spectra computed from reflectometry signals in the Tore Supra database, which are related to density fluctuations. In particular, the decomposition of reflectometry frequency spectra has allowed us to discover and quantify general trends of spectral characteristics (fractional contribution and width) for different components in Ohmic and low-confinement mode (L-mode) plasmas. In Ohmic plasmas, the contribution of the broadband component (EBB) to the total spectrum power in the saturated Ohmic confinement (SOC) regime is observed to be systematically higher than in the linear Ohmic confinement (LOC) regime. A transition of the dominating instability from TEM to ITG could explain the observed spectral modifications, which are supported by the analysis of the dependence of density peaking on collisionality. The spectral characteristics of the broadband (BB) and low-frequency (LF) components were then investigated in L-mode plasmas with ICRH or LH heating. The similar trends of the BB components with collisionality observed in L-mode plasmas compared with the Ohmic cases suggest a similar explanation by linking the frequency spectra to the underlying instabilities. The database analysis motivates more detailed studies by full-wave and gyrokinetic simulations, in order to confirm this link for both Ohmic and L-mode plasmas.

Перенос тепла и частиц в начальной фазе омических разрядов сферического токамака Глобус-М

AbstractThe results of experiments and simulations of the transport of heat and particles in the Globus-M spherical tokamak are presented. Investigations were carried out in the ohmic mode in hydrogen and deuterium plasma. It is shown that in the phase of current growth under the same initial conditions, as long as the condition is met at which the minimum of the safety factor exceeds unity, two scenarios of discharge development are possible: with an electron temperature dive or with an electron density peak. After the safety factor reaches the value of 1, the differences are no longer observed. Modeling of transport processes using the ASTRA code showed that the dive of the electron temperature and density is a consequence of the decrease in the transport of heat and particles in the plasma core (i.e., the presence of internal transport barriers).

Numerical research on a 4 MW 170 GHz coaxial gyrotron with a double electron beam

In this paper, a coaxial gyrotron with a double electron beam is investigated on the ohmic loss, starting current, mode competition, and beam wave interaction. Its beam-wave interaction equation and dependence of the starting current on the static magnetic field and parameter K (the ratio of the current of an electron beam to the total current of a double electron beam) are given. On this basis, a 4 MW 170 GHz coaxial gyrotron with a double electron beam is studied. By the numerical calculation, the influence of K on the starting current is analyzed under a given static magnetic field and at different guiding center radii of the double electron beam. Studies show that the ability of the gyrotron to suppress the mode competition has a relation with the selection of the guiding center radii of the two electron beams. Then, the investigation of a time-dependent multi-mode competition of the gyrotron is performed, which shows that the gyrotron can stably operate in the TE38,18− mode. The results show that by considering the ohmic loss, the gyrotron can operate at 170.4 GHz with the output power of 4.04 MW and the beam-wave interaction efficiency of 35.47% when B = 6.82 T, U = 88 KV, I = 129 A, and K = 0.4. Each of the two electron beams in the gyrotron has different beam-wave interaction efficiencies. Compared to the coaxial gyrotron with one electron beam, the beam-wave interaction efficiency of each electron beam in the coaxial gyrotron with a double electron beam has a different increase.