Deuterium high-confinement (H-mode) plasmas, lasting up to 3.45 s, have been generated in the EAST by ion cyclotron range of frequency (ICRF) heating. H-mode access was achieved by coating the molybdenum-tiled first wall with lithium to reduce the hydrogen recycling from the wall. H-mode plasmas with plasma currents between 0.4 and 0.6 MA and axial toroidal magnetic fields between 1.85 and 1.95 T were generated by 27 MHz ICRF heating of deuterium plasma with hydrogen minority. The ICRF input power required to access the H-mode was 1.6–1.8 MW. The line-averaged density was in the range (1.83–2.3) × 1019 m−3. 200–500 Hz type-III edge localized mode activity was observed during the H-mode phase. The H-mode confinement factor, H98IPB(y, 2), was ∼0.7.
A compact bandstop frequency selective surface (FSS) using fractal structure is proposed. This flexuous design elongates the cell perimeter of the ring-shaped FSS, which means the cell size gets smaller at the same resonance frequency. Furthermore, the unit cells adopt regular hexagon and the array employs equilateral triangle form. Because of its symmetric configuration, good frequency stability has been achieved for both horizontal and vertical polarizations at different oblique angles. For the stable bandstop character, this FSS can be used for protecting the staff of S-band radars against electromagnetic radiation, while the 900/1800/1900 MHz mobile bands and the 5.2/5.8 GHz wireless local area network signals are not affected. Minimal size FSS for long wavelength, Electron Lett 44 (2008), 394 -395. 9. K.Q. da Costa and V. Dmitriev, Theoretical analysis of a modified Koch monopole with reduced dimensions, IEE Proc-Microw Antennas Propag 5 (2006), 475-479. ABSTRACT: A 15-by-20-mm 2 dual-broadband printed monopole antenna fed by a coplanar waveguide is presented. With a numeral-7 slit etched from the rectangular radiating element, the antenna can excite for its lower and upper impedance bands two and one resonant modes, respectively. With a back-patch appropriately printed on the other side of the substrate, a lower (upper) impedance band with a bandwidth of 39.3% (19.5%) can be obtained. These two impedance bands can cover the frequency bands required by UMTS/IMT-2000/IEEE802.11a/b/g/ WiMAX.
Since the last IAEA Fusion Energy Conference in 2018, significant progress of the experimental program of HL-2A has been achieved on developing advanced plasma physics, edge localized mode (ELM) control physics and technology. Optimization of plasma confinement has been performed. In particular, high-N H-mode plasmas exhibiting an internal transport barrier have been obtained (normalized plasma pressure N reached up to 3). Injection of impurity improved the plasma confinement. ELM control using resonance magnetic perturbation (RMP) or impurity injection has been achieved in a wide parameter regime, including Types I and III. In addition, the impurity seeding with supersonic molecular beam injection (SMBI) or laser blow-off (LBO) techniques has been successfully applied to actively control the plasma confinement and instabilities, as well as the plasma disruption with the aid of disruption prediction. Disruption prediction algorithms based on deep learning are developed. A prediction accuracy of 96.8% can be reached by assembling convolutional neural network (CNN). Furthermore, transport resulted from a wide variety of phenomena such as energetic particles and magnetic islands have been investigated. In parallel with the HL-2A experiments, the HL-2M mega-ampere class tokamak was commissioned in 2020 with its first plasma. Key features and capabilities of HL-2M are briefly presented.
Three identical new WEST Ion Cyclotron Resonance Heating (ICRH) antennas have been designed, assembled then commissioned on plasma from 2013 to 2019. The WEST ICRH system is both load-resilient and compatible with long-pulse operations. The three antennas have been successfully operated together on plasma in 2019 and 2020. The load resilience capability has been demonstrated and the antenna feedback controls for phase and matching have been developed. The breakdown detection systems have been validated and successfully protected the antennas. The use of ICRH in combination with Lower Hybrid has triggered the first high confinement mode transitions identified on WEST.
ITER and to the advanced tokamak operation (e.g. the operation of future HL-2M), such as the access of H-mode, energetic particle physics, edge-localized mode (ELM) mitigation/suppression and disruption mitigation. Since the 2016 Fusion Energy Conference, the HL-2A team has focused on the investigations on the following areas: (i) pedestal dynamics and L-H transition, (ii) techniques of ELM control, (iii) the turbulence and transport, (iv) energetic particle physics. The HL-2A results demonstrated that the increase of mean E × B shear flow plays a key role in triggering L-I and I-H transitions. While the change of E × B flow is mainly induced by the ion pressure gradient. Both mitigation and suppression of ELMs were realized by laser blow-off (LBO) seeded impurity (Al, F e, W). The 30% N e mixture supersonic molecular beam injection (SMBI) seeding also robustly induced ELM mitigation. The ELMs were mitigated by low-hybrid current drive (LHCD). The stabilization of m/n=1/1 ion fishbone activities by electron cyclotron resonance heating (ECRH) was found on the HL-2A. A new m/n=2/1 ion fishbone activity was observed recently, and the modelling indicated that passing fast ions dominantly contribute to the driving of 2/1 fishbone. The non-linear coupling between toroidal Alfven eigenmode (TAE) and tearing mode (TM) leads to the generation of a high frequency mode with the toroidal mode number n=0. The turbulence is modulated by tearing mode when the island width exceeds a threshold and the modulation is localized merely in the inner area of the islands. Meanwhile, turbulence radially spreading takes place across the island region.
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