Drift Direction Research Articles

Spatially resolved radio signatures of electron beams in a coronal shock

Context. Type II radio bursts are a type of solar radio bursts associated with coronal shocks. Type II bursts usually exhibit fine structures in dynamic spectra that represent signatures of accelerated electron beams. So far, the sources of individual fine structures in type II bursts have not been spatially resolved in high-resolution low-frequency radio imaging. Aims. The objective of this study is to resolve the radio sources of the herringbone bursts found in type II solar radio bursts and investigate the properties of the acceleration regions in coronal shocks. Methods. We used low-frequency interferometric imaging observations from the Low Frequency Array to provide a spatially resolved analysis for three herringbone groups (A, B, and C) in a type II radio burst that occurred on 16 October 2015. Results. The herringbones in groups A and C have a typical frequency drift direction and a propagation direction along the frequency. Their frequency drift rates correspond to those of type III bursts and previously studied herringbones. Group B has a more complex spatial distribution, with two distinct sources separated by 50 arcsec and no clear spatial propagation with frequency. One of the herringbones in group B was found to have an exceptionally large frequency drift rate. Conclusions. The characteristics derived from imaging spectroscopy suggest that the studied herringbones originate from different processes. Herringbone groups A and C most likely originate from single-direction beam electrons, while group B may be explained by counterstreaming beam electrons.

Impact-Aware Foot Motion Reconstruction and Ramp/Stair Detection Using One Foot-Mounted Inertial Measurement Unit.

Motion reconstruction using wearable sensors enables broad opportunities for gait analysis outside laboratory environments. Inertial Measurement Unit (IMU)-based foot trajectory reconstruction is an essential component of estimating the foot motion and user position required for any related biomechanics metrics. However, limitations remain in the reconstruction quality due to well-known sensor noise and drift issues, and in some cases, limited sensor bandwidth and range. In this work, to reduce drift in the height direction and handle the impulsive velocity error at heel strike, we enhanced the integration reconstruction with a novel kinematic model that partitions integration velocity errors into estimates of acceleration bias and heel strike vertical velocity error. Using this model, we achieve reduced height drift in reconstruction and simultaneously accomplish reliable terrain determination among level ground, ramps, and stairs. The reconstruction performance of the proposed method is compared against the widely used Error State Kalman Filter-based Pedestrian Dead Reckoning and integration-based foot-IMU motion reconstruction method with 15 trials from six subjects, including one prosthesis user. The mean height errors per stride are 0.03±0.08 cm on level ground, 0.95±0.37 cm on ramps, and 1.27±1.22 cm on stairs. The proposed method can determine the terrain types accurately by thresholding on the model output and demonstrates great reconstruction improvement in level-ground walking and moderate improvement on ramps and stairs.

Design and 3D Electrical Simulations for a Controllable Equal-Gap Large-Area Silicon Drift Detector.

In this study, a controllable equal-gap large-area silicon drift detector (L-SDD) is designed. The surface leakage current is reduced by reducing the SiO2-Si interface through the new controllable equal-gap design. The design of the equal gap also solves the problem whereby the gap widens due to the larger detector size in the previous SDD design, which leads to a large invalid area of the detector. In this paper, a spiral hexagonal equal-gap L-SDD of 1 cm radius is selected for design calculation, and we implement 3D modeling and simulation of the device. The simulation results show that the internal potential gradient distribution of the L-SDD is uniform and forms a drift electric field, with the direction of electron drift pointing towards the collecting anode. The L-SDD has an excellent electron drift channel inside, and this article also analyzes the electrical performance of the drift channel to verify the correctness of the design method of the L-SDD.

Isotope effects on transport characteristics of edge and core plasmas heated by neutral beam injection (NBI) in an inward shifted configuration at the Large Helical Device

Isotope effects have been investigated in Neutral Beam Injection (NBI) heated plasmas on the Large Helical Device with similar operational parameters between Hydrogen (H) and Deuterium (D) plasmas. Experimental results show that the global energy confinement has no significant dependence on the isotope mass under similar discharge conditions with nearly the same heating power, line-averaged density ( nˉe ) and magnetic field. For both electron and ion energy transport, the transport coefficients, which are obtained based on local power balance analysis, have analogous profiles between H and D dominant plasmas. For neoclassical χe and χi values, they are almost equal between H and D dominant plasmas in low nˉe discharges, whereas in high nˉe cases they are lower in H plasmas than those in D ones. At low nˉe , the electron and ion thermal transport in both H and D plasmas are dominated by neoclassical transport at a certain zone ( ρ≈0.6−0.85 ), while the anomalous transport process has primary effects in the remaining area, and the density fluctuations exhibit ion temperature gradient mode nature. With increase of nˉe , the anomalous transport becomes prevailing and the density fluctuations propagate along electron diamagnetic drift direction. Bispectral analysis reveals that the H plasma has stronger nonlinear coupling in edge density fluctuations in both low and high density discharges, which is probably due to that the D plasma has stronger damping rate for the nonlinear interaction of turbulence. For a comparative study, the present results have been compared with those observed in the ECRH discharges (Tanaka et al 2019 Nucl. Fusion 59 126040). The reasons for the similarities and dissimilarities between these two different heating manners are not clear yet. To unravel the underlying physics, essential inputs from theories and simulations are required.

Bursting core-localized ellipticity-induced Alfvén eigenmodes driven by energetic electrons during EAST ohmic discharges

A series of high-frequency ( 400∼1000 kHz ) bursting core-localized Alfvén instabilities have been observed during ohmic discharges in EAST tokamak. The instability trigger favours the discharge conditions of low toroidal magnetic field and low electron density. The toroidal mode numbers are mainly n=2∼3 and they propagate in the ion diamagnetic drift (co-current) direction. These modes are radially localized in the range of ρtor=0.2∼0.35 based on Doppler BackScatter measurement. They are identified as ellipticity-induced Alfvén eigenmodes (EAEs) occurring at q=1 rational surfaces by magnetohydrodynamics simulations using the realistic geometry and plasma profiles. The EAEs show regular bursts with ∼10 ms duration along with the mode frequency chirping downwards and upwards rapidly. It is also found that sawtooth events can interrupt the growth and evolution of the EAEs, causing the modes to disappear immediately. Passing energetic electrons (EEs) that move much faster than Alfvén velocity are responsible for the destabilization of these EAEs, which attribute to the fact that the large poloidal and toroidal frequencies mostly cancel each other and satisfy the EAE resonance condition with primary energy exchange. These novel experimental results of the wave-particle interaction between EAEs and EEs are helpful for extrapolating alpha particle physics that are characterized by small orbit width with respect to machine size in future fusion reactors.

Studying the nulling, subpulse drifting, and moding in PSR J1921+1948 with the FAST

ABSTRACT We reported the observations of nulling, subpulse drifting, and moding of radio radiation in pulsar (PSR) B1918+19 at 1250 MHz with the Five-hundred-meter Aperture Spherical radio Telescope. The nulling fraction is 2.6 ± 0.1 per cent and no periodicity of nulling can be seen. We confirmed the existence of three different drift modes (A, B, C) and a disordered mode (N) at 1250 MHz. Unlike the other three modes where the second component of the average pulse profile dominates, the first component of the average pulse profile in mode C is brighter than the other components, the second component shifts forward and the fourth component shifts backward. The bidrifting phenomenon is observed in PSR B1918+19, the drifting of the first and second components is positive, and the drift direction of the fourth component is negative. The drifting rate of the drift bands composed of the first and second components has an obvious evolutionary trend. Mode B has a short duration and no clear trend can be seen. But for mode A, the drift rate of each drift band starts relatively fast, then slows down to a steady state, and finally increases slowly until it enters either null or mode N. Further analysis shows that the emergence and significant variation in the drifting period of multidrifting subpulse emission modes for PSR B1918+19 may be due to the aliasing effect. The interesting subpulse emission phenomenon of PSR B1918+19 at different frequencies provides a unique opportunity to understand the switching mechanism of the multidrift mode of the pulsars.

Pushchino multibeams pulsar search – III. Drift periods of pulsars from summed power spectra method

ABSTRACT The drift periods P2 and P3 were searched for using the summed power spectra of 41 pulsars observed at declinations from −9° to +42°. The power spectra of pulses with a given period, pulse width, and drift behaviour have been simulated, the applicability of such a method for estimating drift parameters is shown. For most pulsars, the distribution of harmonic amplitudes in the power spectra corresponds to the expected distribution for these pulsars without drift. At the same time, it was found that for a number of sources, the summed power spectra accumulated over a long period of time give the same drift parameters as those determined by other methods. For 11 pulsars we have defined or redefined the drift period P2. For eight sources the drift period P3 has been determined or redefined. The drift direction of subpulses was redefined for them.

Reversal of drift direction during the Laschamp geomagnetic excursion

Earth's magnetic field changes in both space and time: the temporal changes are called geomagnetic and paleomagnetic secular variations. Westward drift has been noted as a feature of secular variation for several centuries, but eastward drift has received less attention. We use three global geomagnetic field models covering the past 100 kyr to extend temporal coverage for tracking the zonal (azimuthal) motion of the radial magnetic field. The models we use are GGF100k (100–0 ka), GGFSS70 (70–15 ka), LSMOD.2 (50–30 ka); the extent of the models enables the inclusion of the extreme secular variations found during excursions, particularly the Laschamp excursion (42–40 ka). GGFSS70 and LSMOD.2 have higher temporal resolution than GGF100k, but their underlying data have poorer spatial coverage. Spatial structure is greatly diminished in all models for spherical harmonic degrees l>4.We use two types of time-longitude plots, one of the full radial field to expose reverse and intense flux patches at the core-mantle boundary. The second time-longitude plot is processed to enhance zonal motion signatures and allows us to use Radon drift analyses to uncover characteristic time scales of both westward and eastward drift at mid to high latitudes in both the northern and southern hemispheres. Our results differ across the three models, which we attribute to varying degrees of resolution, accuracy, and data distribution. Nevertheless, recurrent episodes of both eastward and westward drift ranging from ±0.05o/yr to ±0.18o/yr occur in both the northern and southern hemispheres. Westward drift dominates. We also observe 8–20 kyr intervals between occurrences of high-latitude reverse flux patches correlated with strong drift signals. Focusing on the period 50–30 ka, we observe dominant eastward drift preceding the Laschamp excursion and westward drift subsequently. In a period not associated with an excursion, 90–80 ka, we see strong mid to high latitude drift signatures in the northern hemisphere.

Experimental study on up-down asymmetry of tungsten impurities in EAST tokamak

By using the high-performance extreme ultraviolet spatial resolution impurity spectrometer, the up-down asymmetric distribution of tungsten impurity radiation in EAST tokamak is studied experimentally for the first time. The results show that during the co-directional neutral beam injection, the central toroidal rotation velocity is large, the up-down asymmetry is strong, and the side with strong radiation deviates from ion <inline-formula><tex-math id="Z-20240121170250">\begin{document}$B\times \nabla B$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231448_Z-20240121170250.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231448_Z-20240121170250.png"/></alternatives></inline-formula> drift direction. However, after injecting deuterated methane CD<sub>4</sub> into plasma through the valve of the upper divertor outer plate, the central toroidal rotation velocity decreases rapidly, and the asymmetry of the original tungsten impurity radiation decreases soon and finally reverses. In this work, a further statistical study of the W<sup>32+</sup> impurity radiation asymmetry factor <i>I</i><sub>u</sub>/<i>I</i><sub>d</sub> depending on the central toroidal rotation velocity <i>V</i><sub>t0</sub> is performed. The results show that when <i>V</i><sub>t0</sub> is larger than 30 km/s, the side with strong radiation deviates from ion <inline-formula><tex-math id="Z-20240121170255">\begin{document}$B\times \nabla B$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231448_Z-20240121170255.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231448_Z-20240121170255.png"/></alternatives></inline-formula> drift direction, however, when <i>V</i><sub>t0</sub> decreases to below 20 km/s, the asymmetry can be reversed. The relation of toroidal rotation velocity with impurity radiation asymmetry validates the prediction from drift-kinetic theory, and demonstrates that the centrifugal force induced by the toroidal rotation directly causes the asymmetric distribution of tungsten impurities through affecting the momentum conservation parallel to the magnetic field. The experimental observation of the asymmetric distribution of tungsten impurities in this work lays a solid foundation for further studying the poloidal transport of high-<i>Z</i> impurities and provides some important references for controlling the high-<i>Z</i> impurities in future fusion reactors.

Temporal evolution and mechanism of secondary streamers in N2/O2 mixtures at atmospheric pressure under DC voltage

In this work, the temporal evolution of secondary streamers in N2/O2 mixtures at atmospheric pressure under DC voltage were investigated using a two-dimensional axisymmetric fluid model. The effects of voltage amplitude, polarity and oxygen concentration were analyzed. The propagation of secondary streamers is divided into two stages: fast propagation followed by slow propagation. The interior of secondary streamers is filled with positive space charges, while the exterior contains negative space charges. The reduced electric field in the secondary streamer is initially linearly proportional to the applied voltage and decreases linearly with the length of secondary streamers. The length of secondary streamers is primarily determined by the applied voltage, regardless of the oxygen concentration. A reversed propagation direction is simulated under negative applied voltage. We propose a different mechanism for secondary streamers. The high-density positive charge layer near the electrode initiates the propagation of secondary streamers, and the extension of positive charge region dominates the propagation. The distribution of electric field along the channel is mainly determined by the distribution of net space charge. The propagation direction is opposite to the direction of electron drift. The secondary streamer eventually stagnates due to the decrease in electron density in high oxygen concentration, while it is caused by the uniform current density at the front of the secondary streamer in low oxygen concentration.

High-sensitivity and directional-identification fiber magnetic field sensor via polarimetric fiber ring laser with a fiber Faraday rotator

A highly sensitive fiber magnetic field sensor with directional identification utilizing multi-longitudinal-mode fiber ring laser (FRL) based on polarization-mode beat frequency (PMBF) is experimentally demonstrated. A bismuth-doped iron garnet (BIG), as a kind of fiber Faraday rotator, is embedded in the FRL and serves as a fiber magnetic field probe, whose birefringence shows strong dependence on the external magnetic field due to magneto-optical Faraday effect, leading to the frequency drift of PMBF. Thus, the external magnetic field can be characterized by monitoring the change in a certain PMBF. Additionally, the drift direction of the tracked PMBF is closely related to the applied magnetic field direction, which is attributed to the non-reciprocity of Faraday magneto-optical rotation. Therefore, it shows the good ability to distinguish the applied forward (positive) and reverse (negative) magnetic field. The experimental results reveal that the tracked PMBF signal near 100 MHz has opposite frequency drift signs in the forward (positive) range of 0–20 mT and reverse (negative) range of 0 - −20 mT, which can be used to identify the axial orientation of the applied magnetic field. Additionally, it shows the maximum magnetic field sensitivities of −100.76 and −105.73 kHz/mT in the positive and negative magnetic field ranges, respectively. The designed device makes full use of the advantages of the fiber laser that rapidly demodulates the magnetic field with the help of high-speed digital processing technology, as well as fast response, high integration and low cost of fiber Faraday rotator, offering potentials in high-sensitivity magnetic field measurement in a confined space.

EARLY PARLIAMENTARY ELECTIONS IN SERBIA

The article is devoted to the early elections held in Serbia on December 17, 2023 – parliamentary, metropolitan and partly local. The main motive for their early holding: the desire to confirm the legitimacy of power after mass protests of the opposition, also to demonstrate its political impotence, and simultaneously buy time on the foreign policy stage to reduce pressure from Washington and Brussels. The outcome of the election was another victory for President A. Vučič and ruling Serbian Progressive Party. She was not a mystery to observers or participants beforehand. You could only argue about the account. But in the capital, the opposition had good chances, and this was confirmed. The voting results were considered and an assessment was given of the opposition demonstrations after the elections, as well as the degree and nature of involvement in these events of Brussels and Washington. The reasons for the persistent invincibility of the ruling «progressives», the partial strengthening of the pro-Western «democratic» opposition and the unexpected success of the new populist movement «We are a voice from the people» have been revealed. The logic of political behavior and the relationship between foreign and political balancing of the President of Serbia were analyzed. It was concluded that A. Vučič mainly achieved his goals and retained such a structure of power that provides him with a central role in Serbian politics, as well as free hands in further orientation in the international arena. It will not be unambiguous and straightforward in any case. But his room for maneuver has narrowed, and the direction of drift will be determined by the balance of power in the confrontation between West and East.

Fluctuation relation in continuous-time random walks driven by an external field

We study a fluctuation relation representing a non-equilibrium equality indicating that the ratio between the distribution of trajectories obtained by exchanging the initial and final positions is characterized by free energy differences for the duration of the trajectories. We examine the fluctuation relation for noninteracting charge carriers driven by an external electric field by using a continuous-time lattice random walk model with a general waiting-time distribution of transitions. The fluctuation relation is obtained regardless of the lattice structure factor or the form of the waiting-time distribution. However, the fluctuation relation is satisfied only after taking the continuum limit in the presence of a reflecting boundary. Moreover, in free space without boundary conditions, exchanging the initial and final positions is equivalent to exchanging the field (or drift) directions. However, we show that the exchanging field (or drift) directions is not relevant for studying the fluctuation relation under the reflecting boundary condition.

Chirality and curvature determine the meandering of spirals in multilayer excitable media

We study the emergence of meandering spiral waves in a multilayer structure where two spirals, originating independently, evolve in space–time. The FitzHugh-Nagumo model, enhanced with electromagnetic induction effects, defines the nodal dynamics. The layers are chemically coupled, and the drift of spirals is influenced by interlayer flux coupling. An external magnetic flux force is also necessary to destabilize and unpin spiral rotors. The effects of unique characteristics of spiral patterns, like chirality and tip curvature, are assessed. We find that spirals often drift within a bounded meandering area; however, determining the drift directions and overall meandering regions is complex. The forced spiral generally drifts a greater distance, except for identical co-rotating spirals, which drift synchronously. Spirals with opposite chirality exhibit asynchronous drift and wavefront asymmetry, even with identical tip curvature. Regardless of chirality, non-identical spirals are geometrically aligned and amplified before drifting. Stimulating the more loosely curved spiral ensures both spirals drift.

On the Creation, Depletion, and End of Life of Polar Cap Patches

AbstractIonospheric convection patterns from the Super Dual Auroral Radar Network are used to determine the trajectories, transit times, and decay rates of three polar cap patches from their creation in the dayside polar cap ionosphere to their end of life on the nightside. The first two polar cap patches were created within 12 min of each other and traveled through the dayside convection throat, before entering the nightside auroral oval after 104 and 92 min, respectively. When the patches approached the nightside auroral oval, an intensification in the poleward auroral boundary occurred close to their exit point, followed by a decrease in the transit velocity. The last patch (patch 3) decayed completely within the polar cap and had a lifetime of only 78 min. After a change in drift direction, patch 3 had a radar backscatter power half‐life of 4.23 min, which reduced to 1.80 min after a stagnation, indicating a variable decay rate. 28 minutes after the change in direction, and 16 min after coming to a halt within the Clyde River radar field‐of‐view, patch 3 appeared to reach its end of life. We relate this rapid decay to increased frictional heating, which speeds up the recombination rate. Therefore, we suggest that the slowed patch motion within the polar cap convection pattern is a major factor in determining whether the patch survives as a recognizable density enhancement by the time the flux tubes comprising the initial patch cross into the nightside auroral oval.

Synergizing a Large Ordinary Nernst Effect and Axis-Dependent Conduction Polarity in Flat Band KMgBi Crystals.

The exploration of quantum materials in which an applied thermo/electrical/magnetic field along one crystallographic direction produces an anisotropic response has led to unique functionalities. Along these lines, KMgBi is a layered, narrow gap semiconductor near a critical state between multiple Dirac phases due to the presence of a flat band near the Fermi level. The valence band is highly anisotropic with minimal cross-plane dispersion, which, in combination with an isotropic conduction band, enables axis-dependent conduction polarity. Thermopower and Hall measurements indicate dominant p-type conduction along the cross-plane direction, and n-type conduction along the in-plane direction, leading to a significant zero-field transverse thermoelectric response when the heat flux is at an angle to the principal crystallographic directions. Additionally, a large Ordinary Nernst effect (ONE) is observed with an applied field. It arises from the ambipolar term in the Nernst effect, whereby the Lorentz force on electrons and holes makes them drift in opposite directions so that the resulting Nernst voltage becomes a function of the difference between their partial thermopowers, greatly enhancing the ONE. It is proven that axis-dependent polaritycan synergistically enhance the ONE, in addition to leading to a zero-field transverse thermoelectric performance.

Quantifying dune migration patterns and influencing factors in the central Sahara Desert

Based on Landsat images and ERA5 climate data, here we analyzed geomorphic dune patterns and the spatial characteristics of dune migration in the central Sahara Desert region (SW Libya, SE Algeria), using the COSI-Corr technique. Our results revealed clear observable drift potential (DP) and resultant drift potential (RDP) gradients, these decreasing from a northerly to southerly direction. Moreover, the annual average RDP/DP in most areas was <0.3 (i.e., highly variable). The main dune types in the study area included complex transverse ridges (22.82 %), linear dunes (19.87 %), barchan and barchanoid chains (16.95 %), and star dunes (13.55 %). Of these, barchans and barchanoid chains, as well as complex transverse ridges, appeared in areas of relatively high DP, while complex longitudinal ridges and honeycomb dunes were found in those of low DP. Linear dunes had a simpler wind composition, being mainly distributed in areas with intermediate wind variability. Both the honeycomb dunes and complex longitudinal ridges had nearly always formed in complex multi-directional wind environments. Dune migration displacement in dune fields ranged widely, from 0.5 to 23.57 m (mean = 6.71 m), during the 30-year study period (1993–2022). Barchans and barchanoid chains migrated fastest, with a mean value > 10 m/yr; in contrast, complex longitudinal ridges and honeycomb dunes had the slowest migration rate, always at < 5 m/yr. Overall, the dune migration rate was mainly related to dune height and wind regime. Spatially, the dune migration trend was basically consistent with that of the resultant drift direction (RDD), mainly in a northwesterly direction (28.36 %). The accuracy testing results indicated that the COSI-Corr displacement measurement accuracy was generally higher than the dune migration direction accuracy. This study provides not only valuable reference data for regional aeolian activities, but also insight into the developmental environments and migration dynamics of differing dune types, which could be used for prospective regional aeolian geomorphology research in the Sahara Desert.

The effects of illumination on the current conduction mechanisms of the Au/C20H12/n-Si Schottky barrier diode (SBD)

Using the I-V characteristics both in the dark and under varied illumination-intensities (50–250 mW.cm−2) by 50 mW.cm−2 steps in the wide range bias-voltage (±5 V), specific fundamental electrical and photo effects parameters of the Au/C20H12/n-Si SBD were examined. Due to the creation of electron–hole pairs and their drift in opposite directions under the influence of an electric field, the value of photocurrent in the reverse bias (Iph) increases when illumination density is increased. The barrier height (ΦB0) tended to decrease due to the increase in photocurrent, while the diode’s ideality factor (n) increased with increasing illumination intensity. Also, the Schottky structure’s open-circuit voltage (Voc), short circuit current (Isc), filling factor (FF), and efficiency (η) were determined to be 0.358 V, 95.5 μA, 33%, and 0.028% under 50 mW.cm−2, respectively. The Rs and Rsh values found using Ohm’s law are a vital function of illumination and voltage which decrease with increasing illumination intensity. Additionally, using the forward bias I-V data and accounting for the bias dependent of the effective barrier height (Φe) and ideality factor n(V) for different illumination intensities, the energy density distribution profile of surface states (Nss) was obtained. According to these results, the organic interlayer consisting of C20H12 is light-sensitive and suitable for optoelectronic devices such as photodetectors and photodiodes.

Observation of pedestal quasi-coherent mode in Type-I ELMy H-mode of HL-2A tokamak

High confinement mode plasma experiments with Type-I edge localized modes (ELMs) have been carried out on HL-2A tokamak. With neutral beam injection and lower hybrid current drive heating, a quasi-coherent mode (QCM) located at pedestal region has been observed, which exists during the ELM-free stage till the first ELM burst. Analysis based on density and magnetic fluctuations has revealed that the QCM propagating radially outward is electrostatic in nature whose radial wavenumber is kr∼0.5 cm−1 as well as the poloidal wavenumber around kθ∼1.4 cm−1, rotating in electron diamagnetic drift direction. The central frequency of the mode gradually decreases from 50 to 20 kHz, which varies almost linearly with toroidal rotation. Experimental findings indicate that the QCM is excited above a critical electron density gradient in the ELM-free phase during which the latter gradually increases due to the confinement transition. The disappearance of QCM is closely associated with the onset of ELMy H-mode, suggesting that the presence of QCM could potentially delay the occurrence of ELM bursts, consequently supporting the maintenance of an ELM-free operational regime. Moreover, the pedestal region locates more radially outside where the density gradient shows a more spanned region with QCM. A quantitative comparison between experimental measurements and linear GENE gyrokinetic simulations suggests that the dissipative trapped electron mode might be the candidate interpretation of the QCM.

Blowup Analysis of a Hysteresis Model Based Upon Singular Perturbations

In this paper, we provide a geometric analysis of a new hysteresis model that is based upon singular perturbations. Here hysteresis refers to a type of regularization of piecewise smooth differential equations where the past of a trajectory, in a small neighborhood of the discontinuity set, determines the vector-field at present. In fact, in the limit where the neighborhood of the discontinuity vanishes, hysteresis converges in an appropriate sense to Filippov’s sliding vector-field. Recently (2022), however, Bonet and Seara showed that hysteresis, in contrast to regularization through smoothing, leads to chaos in the regularization of grazing bifurcations, even in two dimensions. The hysteresis model we analyze in the present paper—which was developed by Bonet et al in a paper from 2017 as an attempt to unify different regularizations of piecewise smooth systems—involves two singular perturbation parameters and includes a combination of slow–fast and nonsmooth effects. The description of this model is therefore—from the perspective of singular perturbation theory—challenging, even in two dimensions. Using blowup as our main technical tool, we prove existence of an invariant cylinder carrying fast dynamics in the azimuthal direction and a slow drift in the axial direction. We find that the slow drift is given by Filippov’s sliding vector-field to leading order. Moreover, in the case of grazing, we identify two important parameter regimes that relate the model to smoothing (through a saddle-node bifurcation of limit cycles) and hysteresis (through chaotic dynamics, due to a folded saddle and a novel return mechanism).