Preliminary R&amp;D on flat-type W/Cu plasma-facing materials and components for Experimental Advanced Superconducting Tokamak

Xu, Yujie; Xie, Chunyi; Qin, Sigui; Song, Jiupeng; Li, Q.; Zhao, Sixiang; Liu, G. H.; Wang, T. J.; Yu, Yang; Luo, Guang-Nan

doi:10.1088/0031-8949/2014/t159/014008

Cited by 17 publications

(8 citation statements)

References 17 publications

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“…We also designed a set of crossmachine experiments to find general guidelines for making disruption predictions about new devices using very limited disruption data from those devices. Moreover, unlike the machines used for previous studies [7,9,10], here, the three machines have very different features: EAST is a mediumsized (R = 1.85 m, a = 0.45 m) superconducting tokamak with a hybrid first wall: its lower divertor is carbon, the middle wall is molybdenum (Mo), while the upper divertor is made of tungsten [17]. DIII-D is a medium-sized (R = 1.67 m, a = 0.67 m) tokamak with a carbon wall and a relatively large error field: most of disruptive shots in our DIII-D database contain a locked mode as the last precursor in their event chain toward disruption [18,19].…”

Section: Introductionmentioning

confidence: 99%

Hybrid deep-learning architecture for general disruption prediction across multiple tokamaks

et al. 2020

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In this paper, we present a new deep-learning disruption-prediction algorithm based on important findings from explorative data analysis which effectively allows knowledge transfer from existing devices to new ones, thereby predicting disruptions using very limited disruption data from the new devices. The explorative data analysis, conducted via unsupervised clustering techniques confirms that time-sequence data are much better separators of disruptive and non-disruptive behavior than the instantaneous plasma-state data, with further advantageous implications for a sequence-based predictor. Based on such important findings, we have designed a new algorithm for multi-machine disruption prediction that achieves high predictive accuracy for the C-Mod (AUC = 0.801), DIII-D (AUC = 0.947) and EAST (AUC = 0.973) tokamaks with limited hyperparameter tuning. Through numerical experiments, we show that a boosted accuracy (AUC = 0.959) is achieved for the EAST predictions by including only 20 disruptive discharges with thousands of non-disruptive discharges from EAST in the training, combined with more than a thousand discharges from DIII-D and C-Mod. The improvement in the predictive ability obtained by combining disruption data from other devices is found to be true for all permutations of the three devices. Furthermore, by comparing the predictive performance of each individual numerical experiment, we find that non-disruption data are machine-specific, while disruption data from multiple devices contain device-independent knowledge that can be used to inform predictions for disruptions occurring in a new device.

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Section: Introductionmentioning

confidence: 99%

Hybrid deep-learning architecture for general disruption prediction across multiple tokamaks

et al. 2020

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“…Due to the mismatch of thermal and mechanical properties between W and Cu, large thermal stress is generated and concentrated at the interface. The cracking and debonding of the joint interface may be initially triggered during cyclic plasma discharges [47], and then the heat removal capability is deteriorated. Figure 10 shows the original joint interface without damage, and a typical cracking at the joint interface between the beveled W plate and Cu substrate on the W/Cu flat-type target without melting and exfoliation, which represents early cracking damage to the interface.…”

Section: Severe Melting On W/cu Flat-type Components At Horizontal Ta...mentioning

confidence: 99%

In situ melting phenomena on W plasma-facing components for lower divertor during long-pulse plasma operations in EAST

et al. 2023

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Tungsten (W) is one of the most promising plasma-facing materials (PFMs) for future fusion device. Although its melting point is the highest among all the metals, it still has great risk of melting under extremely high plasma heat fluxes, which is a big concern for the ITER and future reactors. Actively-cooled W plasma-facing components (PFCs) with both monoblocks and flat-type structure have been successfully installed in the lower divertor of the EAST tokamak since 2021, which provide a good opportunity for direct comparison of damage mechanism for the two types of PFCs. Various in-situ melting phenomena on the lower divertor have been observed by CCD cameras, which are further verified by Post-mortem inspections. Severe melting even exfoliation of the edge beveled W plates on some W/Cu flat-type components at horizontal outer targets were observed. A large number of droplets were ejected during long-pulse operations, which induced the significant increase of W impurity and total irradiation in the core plasma, and thus greatly deteriorated the plasma performance and even cause disruptions. Two different shaping structures of flat-type PFCs show different position of melting and corresponding mechanisms. Few slight melting has been found on the sharp leading edges of W/Cu monoblocks at the inter-cassette modules for horizontal targets with small droplets ejection, which is much improved compared to that occurred on the upper W divertor, illustrating that the application of large-sized bevel chamfer at inter-cassette modules was generally effective. In addition, an unexpected melting phenomenon on the dome plate was attributed to the extreme transient heat flux during disruption with runaway electrons. The application of both types of W/Cu PFCs for divertor provides important experiences and lessons for engineering design and optimization of divertor PFCs in future fusion devices.

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“…TEM and HR-TEM images of such a NW are presented in the bottom panel of Figure a,b, where the individual twin defects and WZ inclusions are clearly marked. We attribute the variation in crystal structure between NWs within the same growth run to (i) sensitive changes in temperature and V/III ratio over the two-inch wafer, ,, as well as (ii) a variation in density and interwire separation of the NW nucleation sites in the SiO 2 layer . Although accurate control of crystal layer stacking is not the main focus of the present study, it is important to note that deliberate tuning of crystal structure and of well-controlled WZ/ZB intermixing is, in general, feasible in the GaAs NW system. ,,, …”

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confidence: 98%

“…More recently, a large body of work has been reported on GaAs–AlGaAs based NW-QDs. − ,− However, in this material system QD-like emission has been reported from centers in the AlGaAs shell structure: for example, Ga-rich regions at the perimeter of {112}-oriented corner facets of radial AlGaAs/GaAs shell layers or from local AlGaAs alloy fluctuations distributed randomly within the AlGaAs shell . A different approach to deterministically create high brightness QD-like emitters directly in the GaAs NW core may exploit the intrinsic polytypical nature of GaAs-based NWs.…”

mentioning

confidence: 99%

Crystal Phase Quantum Dots in the Ultrathin Core of GaAs–AlGaAs Core–Shell Nanowires

et al. 2015

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Semiconductor quantum dots embedded in nanowires (NW-QDs) can be used as efficient sources of nonclassical light with ultrahigh brightness and indistinguishability, needed for photonic quantum information technologies. Although most NW-QDs studied so far focus on heterostructure-type QDs that provide an effective electronic confinement potential using chemically distinct regions with dissimilar electronic structure, homostructure NWs can localize excitons at crystal phase defects in leading to NW-QDs. Here, we optically investigate QD emitters embedded in GaAs-AlGaAs core-shell NWs, where the excitons are confined in an ultrathin-diameter NW core and localized along the axis of the NW core at wurtzite (WZ)/zincblende (ZB) crystal phase defects. Photoluminescence (PL)-excitation measurements performed on the QD-emission reveal sharp resonances arising from excited electronic states of the axial confinement potential. The QD-like nature of the emissive centers are suggested by the observation of a narrow PL line width, as low as ~300 μeV, and confirmed by the observation of clear photon antibunching in autocorrelation measurements. Most interestingly, time-resolved PL measurements reveal a very short radiative lifetime <1 ns, indicative of a transition from a type-II to type-I band alignment of the WZ/ZB crystal interface in GaAs due to the strong quantum confinement in the ultrathin NW core.

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Preliminary R&D on flat-type W/Cu plasma-facing materials and components for Experimental Advanced Superconducting Tokamak

Cited by 17 publications

References 17 publications

Hybrid deep-learning architecture for general disruption prediction across multiple tokamaks

Hybrid deep-learning architecture for general disruption prediction across multiple tokamaks

In situ melting phenomena on W plasma-facing components for lower divertor during long-pulse plasma operations in EAST

Crystal Phase Quantum Dots in the Ultrathin Core of GaAs–AlGaAs Core–Shell Nanowires

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