• Book : 4(1)
• Pub. Date : 2025
• Page : pp.100141
• Keyword :

Abstract

Al-doped Ga2O3 microbelts with widths ranging from 20 to 154 μm and lengths up to 2 mm were grown using carbothermal reduction. Based on these ultra-wide microbelts, single-microbelt (37 μm wide) and double-microbelts(38 μm/42 μm wide) metal-semiconductor-metal photoconductive ultraviolet (UV) detectors PDs were fabricated and their optoelectronic performances were investigated at Vacuum-UV (VUV) wavelengths of 185 nm. Under irradiation of 185 nm, the Al-doped Ga2O3 PD has a very-high photocurrent (Iph) of 192.07 μA and extremely low dark current (Id) of 156 fA at 10 V, and presents a ultra-high light-to-dark current ratio of 1.23 × 10⁹. The responsivity (R), external quantum efficiency (EQE), and detectivity (D*) of the double-microbelts detector device were 1920 A W⁻¹, 9.36 × 10⁵%, and 8.6 × 10¹⁶ Jones, respectively. Since the bandgap of the Al-doped microbelts becomes wider, and the fabricated detector has weaker sensitivity to radiation in the 254/365 nm wavelengths. Compared with the 254 nm and 365 nm UV cases, the devices under 185 nm VUV show the excellent high selectivity ratios of 1.47 × 10⁶ and 1.7× 10⁷, respectively. This paper should provide a new insight on the VUV photodetectors utilizing Ga2O3 microbelts.

• Book : 36(2)
• Pub. Date : 2025
• Page : pp.025202
• Keyword :

• Book : 20(1)
• Pub. Date : 2025
• Page : pp.560-565
• Keyword :

• Book : 227()
• Pub. Date : 2025
• Page : pp.112367
• Keyword :

• Book : 227()
• Pub. Date : 2025
• Page : pp.112351
• Keyword :

• Book : 227()
• Pub. Date : 2025
• Page : pp.112426
• Keyword :

• Book : 227()
• Pub. Date : 2025
• Page : pp.112354
• Keyword :

• Book : 559()
• Pub. Date : 2025
• Page : pp.165581
• Keyword :

Abstract

We developed a redundant logic for predicting Vertical Displacement Events (VDEs) using only magnetic diagnostics with a Support Vector Machine (Inoue et al 2022 Nucl. Fusion62 086007). This logic was experimentally validated in the integrated commissioning of JT-60SA. Triggering of VDEs results in significant asymmetric heat loads on first walls and electromagnetic loads on conducting materials. These concerns are mitigated by a newly proposed direction control for VDEs. We successfully detected VDEs in experiments and controlled their direction by setting the control voltage to zero upon detection, thus guiding VDEs in an intended direction and reducing the risk to the device from unmitigated VDEs in either direction, although completely avoiding VDEs remains the ideal. In the developed predictor, VDEs are predicted using proxies to monitor the controller’s performance with an adaptive voltage allocation scheme (Inoue et al 2021 Nucl. Fusion61 096009). For future experiments, we plan to extend our approach to monitor more detailed information from the equilibrium controller, including control values of each PID component, which has been shown to enhance the prediction accuracy of VDEs.

• Book : 65(1)
• Pub. Date : 2025
• Page : pp.016013
• Keyword :

Abstract

Magnetic fluctuations affecting turbulence and transport, which are manifest at finite normalized plasma pressure β, pose a significant challenge to magnetic confinement fusion devices aiming to achieve high performance. Such regimes are not yet comprehensively understood in stellarator geometry. This work presents simulations of electromagnetic instabilities and high-β turbulence in the Wendelstein 7-X (W7-X) stellarator, showing how ion-temperature-gradient-driven (ITG) turbulence is enhanced by unconventional kinetic ballooning modes well below the ideal MHD threshold. These sub-threshold KBMs (stKBMs) become strongly excited in the turbulent state and enable higher fluxes via zonal-flow erosion. The threshold of stKBM impact on turbulent fluxes is heavily dependent on the pressure gradient, evidenced here by the enhanced destabilization and fluxes resulting from the inclusion of an electron temperature gradient. Understanding and controlling these stKBMs will be paramount for W7-X and potentially other stellarators to achieve optimal performance.

• Book : 65(1)
• Pub. Date : 2025
• Page : pp.016022
• Keyword :