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Purpose The aim of this study was to prove that radio-frequency (RF) energy with 13.56 MHz can be used for heating building structures in a controlled manner exploiting the advantage that homogeneous heating with sufficient penetration depths can be achieved. Design/methodology/approach Because parallel electrodes on both sides of the heated structure cannot be used in many practical applications, two special electrode designs have been developed by modeling the field distribution and energy absorption and by carrying out test experiments to validate the simulation results. Findings One solution is based on a two-dimensional surface capacitor providing certain penetration depths and being especially suitable for treating thin structures such as wooden parquet floor. Such an arrangement can be particularly used for pest control even when sensitive surfaces have to be protected. The other solution uses a capacitive coupling between the grounded shielding and an electrode or an equivalent structure (e.g. moist soil) at the other side of the masonry to establish a sufficiently strong electrical field between a “hot” electrode on the side of the shielding and the coupled rear electrode. Originality/value Both solutions significantly enhance the application potential of RF heating.

The objectives of NSTX-U research are to reinforce the advantages of STs while addressing the challenges. To extend confinement physics of low-A, high beta plasmas to lower collisionality levels, understanding of the transport mechanisms that set confinement performance and pedestal profiles is being advanced through gyrokinetic simulations, reduced model development, and comparison to NSTX experiment, as well as improved simulation of RF heating. To develop stable non-inductive scenarios needed for steady-state operation, various performance-limiting modes of instability were studied, including MHD, tearing modes, and energetic particle instabilities. Predictive tools were developed, covering disruptions, runaway electrons, equilibrium reconstruction, and control tools. To develop power and particle handling techniques to optimize plasma exhaust in high performance scenarios, innovative lithium-based solutions are being developed to handle the very high heat flux levels that the increased heating power and compact geometry of NSTX-U will produce, and will be seen in future STs. Predictive capabilities accounting for plasma phenomena, like edge harmonic oscillations, ELMs, and blobs, are being tested and improved. In these ways, NSTX-U researchers are advancing the physics understanding of ST plasmas to maximize the benefit that will be gained from further NSTX-U experiments and to increase confidence in projections to future devices.

Foodborne illnesses occur due to contamination by pathogenic microorganisms. Therefore, decontaminating food is vital before marketing and circulation. Radio frequency (RF) heating stands out in several branches of industry, mainly food processing, as an alternative method to conventional pasteurization which takes long process times and overheating. RF heating functions without relying on heat conduction. It generates internal heat by inducing the rotation of polar molecules and the motion of ions. The advantages of dielectric heating with greater wave penetration include rapid, uniform and volumetric heating, presenting high energy efficiency. Furthermore, it is an effective, validated method for eliminating pathogens in agricultural products and is free from chemical residues. Although many reviews have discussed this technology, few reviews have covered the research trends in this field in the recent years, during which the number of studies discussing RF treatment of foods have increased. Therefore, this review focuses on the RF applications in the food industry for pest control, microbial and enzymatic inactivation of solid, liquid, and powdered foods in the last five years. Besides covering the fundamental aspects of RF technology, we also examine its benefits and drawbacks, address the challenges it presents, and explore future prospects Graphical Abstract

The results of the first experimental series to produce a plasma using the radio frequency discharge (RF) above the ion cyclotron frequency at relatively low magnetic fields (0.5–0.6 T) in the Large Helical Device (LHD) are presented 1.43 MW of RF power produced target plasma with density up to 6 × 1018 m−3 to deuterium. Tangential NBI application into such a plasma increases plasma parameters. Electron temperatures up to ≈0.9 keV and densities up to ≈2.4 × 1019 m−3 had been achieved, and the maximum value of <βdia> was 2.6%. These experiments open possibilities for new regimes of LHD operation which are also interested to W7-X.

We describe a new technique for the efficient generation of high-energy ions with electromagnetic ion cyclotron waves in multi-ion plasmas. The discussed ‘three-ion’ scenarios are especially suited for strong wave absorption by a very low number of resonant ions. To observe this effect, the plasma composition has to be properly adjusted, as prescribed by theory. We demonstrate the potential of the method on the world-largest plasma magnetic confinement device, JET (Joint European Torus, Culham, UK), and the high-magnetic-field tokamak Alcator C-Mod (Cambridge, USA). The obtained results demonstrate efficient acceleration of 3 He ions to high energies in dedicated hydrogen–deuterium mixtures. Simultaneously, effective plasma heating is observed, as a result of the slowing-down of the fast 3 He ions. The developed technique is not only limited to laboratory plasmas, but can also be applied to explain observations of energetic ions in space-plasma environments, in particular, 3 He-rich solar flares. Triggering and sustaining fusion reactions — with the goal of overall energy production — in a tokamak plasma requires efficient heating. Radio-frequency heating of a three-ion plasma is now experimentally shown to be a potentially viable technique.

W—for tungsten—Environment in Steady-state Tokamak (WEST) is a superconducting tokamak with a full-tungsten environment and an actively cooled ITER-grade divertor. It is a unique European facility, offering crucial insights for the operation of future magnetic fusion devices with metallic environments in steady-state conditions. The heating and current drive in WEST is provided exclusively by radio-frequency (RF) systems, featuring dominant electron heating with negligible torque input. Recent WEST experiments have resulted in a new record of 1337 s pulse length and 2.6 GJ injected energy, using 2–3 MW of lower-hybrid current drive (LHCD). This achievement was facilitated by the use of an advanced LHCD monitoring system. An ITER-relevant use of the ion-cyclotron resonant heating (ICRH) antenna, such as wall conditioning with ICRH, has been evaluated during the three last WEST campaigns. ECWC is not considered today on WEST due to water leak risk due to high heat fluxes on the vacuum vessel wall. A new concept of ICRH system, the travelling wave array (TWA) antenna, is currently under design for WEST. Finally, a new electron-cyclotron heating system, featuring three 1 MW gyrotrons is under commissioning.

The aim of this study was to optimize sequential ultrasound-radio frequency–assisted extraction (URAE) of pectin from pomelo peel. Effects of sonication power and time, radio frequency (RF) heating temperature, and time on the pectin yield (PY) were evaluated. Based upon optimized URAE parameters, the yield, physicochemical, and structure properties of pectin recovered from sequential radio frequency-ultrasound–assisted extraction (RUAE), ultrasound-assisted extraction (UAE), and RF-assisted extraction (RFAE) were also compared. A maximal PY of 28.36 ± 0.85% was attained at the optimized URAE conditions including solvent pH of 1.5 (citric acid), sonication at 183 W for 24 min, and RF heating at 87 °C for 23 min. Although all four samples had a high degree of esterification more than 50%, URAE was the lowest. No significant changes were observed in the types of monosaccharides among different samples. Furthermore, all four samples (6.6–10.3 mg GAE/g) showed significantly higher total phenolic content than those of commercial citrus pectin (1.2 mg GAE/g), and among them, RFAE was the highest with the best antioxidant capacity. The water and oil holding capacities of the four samples were between 3.5 to 4.0 and 2.6 to 3.0 g/g, respectively, but there was no significant difference ( p  > 0.05) between each other. Structure properties indicated that there were no significant differences in the main chemical structures among the four pectin samples. Morphology analysis of URAE showed a more compact, smoother, and flatter surface than that of RUAE and RFAE. The results observed in this paper suggest that sequential URAE is an efficient strategy for the recovery of high-quality pectins.

Non-uniform heating of RF energy is the main obstacle for its large-scale application in blanching. In this study, we proposed a new blanching method: steam (ST)-assisted radio frequency (RF) blanching of fresh-cut stem lettuce cuboids. The relative peroxidase (POD) activity, heating uniformity, and physicochemical properties of samples treated by steam-assisted RF blanching at different conditions (RF-50 °C + ST-2.5 min, RF-65 °C + ST-2 min, and RF-80 °C + ST-1 min) were evaluated in comparison with single RF heating and steam blanching. Both the temperature distribution images and the heating uniformity index indicated that steam-assisted RF blanching overcame the defect of local overheating of single blanching mode and achieved more uniform temperature distribution. Besides steam-assisted RF, blanched reduced the thermal damage to cells, which can be demonstrated by lower relative electrolyte leakage rate, thereby maintained better texture, color, and higher vitamin C retention at the same relative POD activity of 5%. Among the three steam-assisted RF blanching treatments, RF-80 °C + ST-1 min achieved optimum heating uniformity and quality of samples. This study suggested that steam-assisted RF blanching can be used as a potential blanching method to improve inactivation efficiency of enzyme and quality of fruits and vegetables.

Conventional thermal treatment in food processing relies on the transfer of heat by conduction and convection. One alternative to this conventional thermal treatment is radio-frequency (RF) heating in which electromagnetic energy is transferred directly to the heated product. The longer wavelengths of RF compared with microwaves are able to penetrate further into the food products resulting in more even heating. A review of RF heating for the food processing industry is presented here with an emphasis on scientific principles and the advantages and applications of RF. Applications of RF heating include blanching, thawing, drying, and processing of foods. RF heating represents considerable potential for additional research and the transfer of technology to the food processing industry. Computer simulation can be used to improve RF heating uniformity. Moreover, the heating uniformity in the rotated eggs is greater than in the static eggs. RF has also been used to blanch vegetables to increase ascorbic acid content to achieve the highest vitamin C levels. The use of the thawing technology has resulted in better quality of treated food. There has been increased interest in the RF-drying method due to the homogeneity of heating, greater penetration depth, and more stable control of the product temperature. RF-treated meat had improved quality and coagulation with acceptable taste and appearance. In addition, RF heating is used in pasteurization of yogurt and destruction of microorganisms in liquid and solid foods.

This work shows that radio‐frequency (RF) fields can simultaneously align carbon nanotubes (CNTs) dispersed in a resin and induce Joule heating to cure the resin. The timescales of alignment and curing using RF heating are numerically computed and compared at different field strengths in order to determine a temperature where alignment happens before the matrix crosslinks. Composites are experimentally fabricated at the desired target temperature and are optically analyzed and quantified; the CNT network is successfully aligned in the direction of the applied electric field. This methodology can be used to create composites where the local alignment can be varied across the sample. Composites fabricated using RF fields have higher electrical conductivity in the direction of the aligned CNTs than an oven‐cured, randomly aligned sample. Also, RF‐cured nanocomposites exhibit higher tensile strength and modulus in the direction of alignment compared to an oven‐cured sample. Finally, it is further demonstrated how this methodology can be coupled with a direct ink writing additive manufacturing process to induce alignment in any desired direction, even orthogonal to the shear forces in the extrusion direction. Radio‐frequency fields induce two competing effects in carbon nanotube (CNT)‐filled resins: alignment of CNTs due to electric field‐induced torque, and Joule heating which results in curing. This work addresses the potential to use these competing effects to rapidly heat and cure the CNT‐filled resin to fabricate nanocomposites with aligned CNT networks.