1,451 research outputs found
Electromagnetic turbulence simulation of tokamak edge plasma dynamics and divertor heat load during thermal quench
The edge plasma turbulence and transport dynamics, as well as the divertor
power loads during the thermal quench phase of tokamak disruptions are
numerically investigated with BOUT++'s flux-driven, six-field electromagnetic
turbulence model. Here a transient yet intense particle and energy sources are
applied at the pedestal top to mimic the plasma power drive at the edge induced
by a core thermal collapse, which flattens core temperature profile.
Interesting features such as surging of divertor heat load (up to 50 times),
and broadening of heat flux width (up to 4 times) on the outer divertor target
plate, are observed in the simulation, in qualitative agreement with
experimental observations. The dramatic changes of divertor heat load and width
are due to the enhanced plasma turbulence activities inside the separatrix. Two
cross-field transport mechanisms, namely the turbulent convection
and the stochastic parallel advection/conduction, are identified to play
important roles in this process. Firstly, elevated edge pressure gradient
drives instabilities and subsequent turbulence in the entire pedestal region.
The enhanced turbulence not only transports particles and energy radially
across the separatrix via convection which causes the initial
divertor heat load burst, but also induces an amplified magnetic fluctuation
. Once the magnetic fluctuation is large enough to break the
magnetic flux surface, magnetic flutter effect provides an additional radial
transport channel. In the late stage of our simulation,
reaches to level that completely breaks magnetic flux surfaces such
that stochastic field-lines are directly connecting pedestal top plasma to the
divertor target plates or first wall, further contributing to the divertor heat
flux width broadening.Comment: 20 pages, 12 figure
Drift reduced Landau fluid model for magnetized plasma turbulence simulations in BOUT++ framework
Recently the drift-reduced Landau fluid six-field turbulence model within the
BOUT++ framework has been upgraded. In particular, this new model employs a new
normalization, adds a volumetric flux-driven source option, the Landau fluid
closure for parallel heat flux and a Laplacian inversion solver which is able
to capture n=0 axisymmetric mode evolution in realistic tokamak configurations.
These improvements substantially extended model's capability to study a wider
range of tokamak edge phenomena, and are essential to build a fully
self-consistent edge turbulence model capable of both transient (e.g., ELM,
disruption) and transport time-scale simulations.Comment: 26 pages, 14 figure
Deterministic Spin-Orbit Torque Switching of Mn3Sn with the Interplay between Spin Polarization and Kagome Plane
Previous studies have demonstrated spin-orbit torque (SOT) switching of Mn3Sn
where the spin polarization lies in the kagome plane (configuration I).
However, the critical current density () is unrealistically large (= A/) and independent on the external field (). The stabilized magnetic state also depends on the initial state.
These features conflict with the ferromagnet (FM) switching scheme as claimed
in those studies, and thus call for other explanations. Alternatively, the
system with the spin polarization perpendicular to the kagome plane
(configuration II) is more like the FM based system since the spin polarization
is orthogonal to all magnetic moments. In this work, we show SOT switching of
Mn3Sn in configuration II. Similar to the FM, Jcrit and Hext are in the order
of A/ and hundreds of Oersted, respectively. The switching
result is also independent of the initial state. Interestingly, the unique spin
structure of Mn3Sn also leads to distinct features from FM systems. We
demonstrate that Jcrit increases linearly with Hext, and extrapolation gives
ultralow for the field-free switching system. In addition, the
switching polarity is opposite to the FM. We also provide the switching phase
diagram as a guideline for experimental demonstration. Our work provides
comprehensive understanding for the switching mechanism in both configurations.
The switching protocol proposed in this work is more advantageous in realistic
spintronic applications. We also clearly reveal the fundamental difference
between FM and noncollinear antiferromagnetic switching
Study of Doubly Heavy Baryon Spectrum via QCD Sum Rules
In this work, we calculate the mass spectrum of doubly heavy baryons with the
diquark model in terms of the QCD sum rules. The interpolating currents are
composed of a heavy diquark field and a light quark field. Contributions of the
operators up to dimension six are taken into account in the operator product
expansion. Within a reasonable error tolerance, our numerical results are
compatible with other theoretical predictions. This indicates that the diquark
picture reflects the reality and is applicable to the study of doubly heavy
baryons.Comment: 23 pages, 9 figures, minor corrections in expression
Mechanical and Thermal Properties of All-Wood Biocomposites through Controllable Dissolution of Cellulose with Ionic Liquid.
All-wood biocomposites were prepared with an efficient method. The ionic liquid of 1-butyl-3-methylimidazolium chloride (BMIMCl) was used to impregnate manchurian ash (MA) before hot-pressing, and the all-wood biocomposites were prepared by controllable dissolving and regenerating the cellulose in MA. The Fourier transform infrared analysis suggested that all the components of MA remained unchanged during the preparation. X-ray diffraction, thermogravimetric and scanning electron microscope analysis were carried out to study the process parameters of hot-pressing pressure and time on the crystallinity, thermal properties and microstructure of the all-wood biocomposites. The tensile strength of the prepared all-wood biocomposites reached its highest at 212.6 MPa and was increased by 239% compared with that of the original MA sample. The thermogravimetric analysis indicated that as the thermo-stability of the all-wood biocomposites increased, the mass of the residual carbon increased from 19.7% to 22.7% under a hot-pressing pressure of 10 MPa. This work provides a simple and promising pathway for the industrial application of high-performance and environmentally friendly all-wood biocomposites
Particle Emission-dependent Timing Noise of Pulsars?
Though pulsars spin regularly, the differences between the observed and
predicted ToA (time of arrival), known as "timing noise", can still reach a few
milliseconds or more. We try to understand the noise in this paper. As proposed
by Xu & Qiao in 2001, both dipole radiation and particle emission would result
in pulsar braking. Accordingly, possible fluctuation of particle current flow
is suggested here to contribute significant ToA variation of pulsars. We find
that the particle emission fluctuation could lead to timing noise which can't
be eliminated in timing process, and that a longer period fluctuation would
arouse a stronger noise. The simulated timing noise profile and amplitude are
in accord with the observed timing behaviors on the timescale of years.Comment: 6 pages, 2 figures. (Accepted by Chin. Phys. Lett.
The Motivation-Based Promotion of Proactive Control: The Role of Salience Network
It has been shown that reward motivation can facilitate proactive control, a cognitive control mode that is characterized of prior preparation and sustained holding of the goal-relevant information in working memory. However, it remains to be established the neural networks that may be involved in this promotion effect. In this study, participants underwent the AX-Continuous Performance Task (AX-CPT) that measures relative proactive control during functional magnetic resonance imaging (fMRI) scanning. We employed independent component analysis to decompose multiple brain networks and identified the task related network. Results showed that the salience network (SN) was engaged in the AX-CPT protocol. Importantly, our data demonstrated that reward modulated the association between task engagement of SN and proactive control, whereby the positive correlation was particularly observed in the reward condition. Moreover, reward modulated task engagement of the SN in a proactive manner, which may contribute to the behavioral proactive performance. Overall, our data suggest the involvement of SN in the reward facilitation effect of proactive control
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