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182 results on '"Hu, Q. M."'

3. Wide operational windows of edge-localized mode suppression by resonant magnetic perturbations in the DIII-D tokamak

Author

Hu, Q. M., Nazikian, R., Grierson, B. A., Logan, N. C., Orlov, D. M., Paz-Soldan, C., and Yu, Q.

Subjects
Physics - Plasma Physics
Abstract

Edge-Localized-Mode (ELM) suppression by resonant magnetic perturbations (RMPs) generally occurs over very narrow ranges of the plasma current (or magnetic safety factor q95) in the DIII-D tokamak. However, wide q95 ranges of ELM suppression are needed for the safety and operational flexibility of ITER and future reactors. In DIII-D ITER Similar Shape (ISS) plasmas with n=3 RMPs, the range of q95 for ELM suppression is found to increase with decreasing electron density. Nonlinear two-fluid MHD simulations reproduce the observed q95 windows of ELM suppression and the dependence on plasma density, based on the conditions for resonant field penetration at the top of the pedestal. When the RMP amplitude is close to the threshold for resonant field penetration, only narrow isolated magnetic islands form near the top of the pedestal, leading to narrow q95 windows of ELM suppression. However, as the threshold for field penetration decreases with decreasing density, resonant field penetration can take place over a wider range of q95. For sufficiently low density (penetration threshold) multiple magnetic islands form near the top of the pedestal giving rise to continuous q95 windows of ELM suppression. The model predicts that wide q95 windows of ELM suppression can be achieved at substantially higher pedestal pressure in DIII-D by shifting to higher toroidal mode number (n=4) RMPs.

Published
2019
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4. The Density Dependence of Edge-Localized-Mode Suppression and Pump-out by Resonant Magnetic Perturbations in the DIII-D Tokamak

Author

Hu, Q. M., Nazikian, R., Grierson, B., Logan, N. C., Park, J-K., Paz-Soldan, C., and Yu, Q.

Subjects
Physics - Plasma Physics
Abstract

The density dependence of edge-localized-mode (ELM) suppression and density pump-out (density reduction) by n = 2 resonant magnetic perturbations (RMPs) is consistent with the effects of narrow well-separated magnetic islands at the top and bottom of the H-mode pedestal in DIII-D low-collisionality plasmas. Nonlinear two-fluid MHD simulations for DIII-D ITER Similar Shape (ISS) discharges show that, at low collisionality, low pedestal density is required for resonant field penetration at the pedestal top, consistent with the ubiquitous low density requirement for ELM suppression in these DIII-D plasmas. The simulations predict a drop in the pedestal pressure due to parallel transport across these narrow width (0.02) magnetic islands at the top of the pedestal that is stabilizing to Peeling-Ballooning-Modes (PBMs), and comparable to the pedestal pressure reduction observed in experiment at the onset of ELM suppression. The simulations predict density pump-out at experimentally relevant levels (-20%) at low pedestal collisionality due to very narrow (~0.01-0.02) RMP driven magnetic islands at the pedestal foot at ~0.99. The simulations show decreasing pump-out with increasing density, consistent with experiment, resulting from the inverse dependence of parallel particle transport on resistivity at the foot of the pedestal. The robust screening of resonant fields is predicted between the top and bottom of the pedestal during density pump-out and ELM suppression, consistent with the preservation of strong temperature gradients in the edge transport barrier as seen in experiment.

Published
2019
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5. Thermal vacancy formation energies of random solid solutions

Author

Luo, H. B., Hu, Q. M., Du, J., Yan, A. R., and Liu, J. P.

Subjects
Condensed Matter - Materials Science
Abstract

Vacancy mechanism plays a dominant role in the atomic migration when a close-packed disordered alloy undergoes ordering transition. However, the calculation of thermal vacancy formation energies (VFEs) of random solid solutions is usually cumbersome due to the difficulty in considering various local atomic environments. Here, we propose a transparent way that combines coherent potential approximation and supercell-local cluster expansion to investigate VFEs of random solid solutions. This method is used to study the effects of temperature, strain and magnetism on the VFEs of random A1-FePt alloy. The results show that the mean VFE increases with increasing temperature, decreases under (001) in-plane tensile and compressive strains, and can be further reduced by the magnetic excitation. These effects are explained by discussing the dependence of VFE on local atomic environments and the overall bond strength within., Comment: 9 pages, 5 figures and 1 table. This work was mainly finished in the end of 2015, with some modification of the definition of VFE later. Since then, all authors, including Prof. Ruban in KTH, have got the original manuscript and commented the method and the results

Published
2017

13. The distributivity characterization of idempotent null-uninorms over two special aggregation operators.

Author

Zhang, T. H., Qin, F., Wan, J., and Hu, Q. M.

Subjects
AGGREGATION operators, TRIANGULAR norms, LEGAL education
Abstract

Recently, Zhao et al. [55] characterized the distributivity equations of null-uninorms with continuous and Archimedean underlying operators over overlap or grouping functions. Moreover, Liu et al. [34] studied the distributive laws of continuous t-norms over overlap functions. In this paper, we proceed with the distributivity characterization of idempotent null-uninorms over overlap or grouping functions. In order to do that, we introduce a class of weak overlap and grouping functions with weak coefficients, and obtain the full characterizations of overlap and grouping functions by considering the different values of underlying uninorms’ associated functions of idempotent null-uninorms on the interval endpoints and comparing them with the weak coefficients. Obviously, idempotent null-uninorms generalize idempotent uninorms. Thus, the obtained results also generalize the distributivity of idempotent uninorms proposed as future work in [34]. [ABSTRACT FROM AUTHOR]

Published
2023

16. Predicting operational windows of ELMs suppression by resonant magnetic perturbations in the DIII-D and KSTAR tokamaks

Author

Hu, Q. M., primary, Nazikian, R., additional, Logan, N. C., additional, Park, J.-K., additional, Paz-Soldan, C., additional, Yang, S. M., additional, Grierson, B. A., additional, In, Y., additional, Jeon, Y. M., additional, Kim, M., additional, Kim, S. K., additional, Orlov, D. M., additional, Park, G. Y., additional, and Yu, Q., additional

Published
2021
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26. Point defects in TiNi from ab-initio calculations

Author

Kulkova, Svetlana E., Hu, Q. M., Yang, Rui, Bakulin, Alexander V., Томский государственный университет Физический факультет Научные подразделения ФФ, and Томский государственный университет Физический факультет Кафедра теоретической физики

Subjects
Condensed Matter::Materials Science, сплавы, Physics::Atomic and Molecular Clusters, точечные дефекты, никелид титана
Abstract

Ab initio calculations of the electronic structure and elastic properties of TiNi-based alloys were performed within density functional theory. The influence of impurities (transition, noble and simple metals) substituted both Ti or Ni atoms on the electronic structure of alloys near the Fermi level are analyzed. The formation energies of defects (antisites, vacancies, atomic swaps) are estimated. It is shown that Ni-antisites and swap defects have the lowest formation energies in TiNi-based alloys. The elastic constants of ternary TiNi-based alloys are calculated.

Published
2015

50. Dependence of plasma responses to an externally applied perturbation field on MHD oscillation frequency on the J-TEXT tokamak.

Author

Jin, W., Ding, Y. H., Rao, B., Hu, Q. M., Jin, X. S., Wang, N. C., Zhang, X. Q., Wang, Z. J., Chen, Z. Y., and Zhuang, G.

Subjects
MAGNETOHYDRODYNAMICS, FLUID dynamics, OSCILLATIONS, PERTURBATION theory, APPROXIMATION theory, FUNCTIONAL analysis, MATHEMATICAL models
Abstract

The plasma response to externally applied perturbation fields is investigated on the J-TEXT tokamak using a set of static resonant magnetic perturbation (SRMP) coils. Several different experimental results are obtained including partial or complete suppression of the existing m/n = 2/1 tearing mode, mode locking or non-uniform magnetohydrodynamic (MHD) oscillations. These results depend sensitively on the tearing mode frequency and the amplitude of the perturbation field. It is found that mode locking is most likely to happen at a lower rotation frequency (< ∼ 5 kHz) and the threshold for mode locking has a linear relation with MHD frequency. However, complete suppression of the tearing mode happens in a region where the MHD frequencies are higher (∼6 kHz). The experimental observations are explained by numerical simulations based on reduced MHD equations. The error field contributes to an offset between the mode-locking thresholds for the two opposite spatial phases of the SRMP, through which the intrinsic error field of J-TEXT can be estimated. [ABSTRACT FROM AUTHOR]

Published
2013
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