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In this paper, we study the horizon properties and scalar invariants of the spacetime around a regular black hole (BH) in 4D Einstein Gauss-Bonnet (4D EGB) gravity. It is observed that the presence of both Gauss-Bonnet (GB) coupling and magnetic charge parameters causes the shrinking of the outer horizon. We find that the range of the GB parameter α / M 2 ∈ (− 0.15869 , 1) , and the extreme value of magnetic charge reaches up to g extr = 0.886 M , which allows for the existence of a BH horizon, while it is g extr = 0.7698 M for pure Bardeen BH. We also investigate the dynamics of magnetized particles around the magnetically charged Bardeen BH, assuming the particle's motion occurs in the equatorial plane in the proper observation frame, and the direction of the magnetic dipole moment of the particles is always kept radially and its magnitude is constant. Moreover, the dynamics of magnetically charged particles are also studied, and it is shown that both the energy and angular momentum of the particles corresponding to circular orbits increases with the increase of their magnetic charge. Finally, we also study collisions of magnetized, electrically neutral, and magnetically charged particles around the Bardeen BHs, where we provide analyses of critical angular momentum that may allow collision of the particles near-horizon radius, producing enormous values of center of mass energy of the collisions. [ABSTRACT FROM AUTHOR]

In this paper, we study dynamics of massless (photon and neutrino-like) particles in the spacetime of regular Bardeen black hole (BH) in novel four-dimensional Einstein–Gauss–Bonnet (4D EGB) theory. First, we have analyzed the hor properties of the spacetime of the Bardeen BH with respect to the Gauss–Bonnet (GB) coupling parameter α. Our detailed analysis has shown that the GB coupling parameter is limited by maximum and minimum values at, α ∈ (− 0. 1 5 ÷ 1) and the extreme value of magnetic charge of the BH depends on the parameter α. We have explored motion of neutrino-like particles and photons around the Bardeen BH. We have also explored the possibility of mimicking cases of the spin of Kerr BH and charge of Reissner–Nordström BH by the Bardeen charge, providing the same values of impact parameter for photons corresponding to the BH shadow size. Finally, we have investigated spherically infalling accretion and shadow of the Bardeen BHs in 4D EGB theory. [ABSTRACT FROM AUTHOR]

In this paper, we study the horizon properties and scalar invariants of the spacetime around a regular black hole (BH) in 4D Einstein Gauss-Bonnet (4D EGB) gravity. It is observed that the presence of both Gauss-Bonnet (GB) coupling and magnetic charge parameters causes the shrinking of the outer horizon. We find that the range of the GB parameter α/M2∈(−0.15869,1), and the extreme value of magnetic charge reaches up to gextr=0.886M, which allows for the existence of a BH horizon, while it is gextr=0.7698M for pure Bardeen BH. We also investigate the dynamics of magnetized particles around the magnetically charged Bardeen BH, assuming the particle’s motion occurs in the equatorial plane in the proper observation frame, and the direction of the magnetic dipole moment of the particles is always kept radially and its magnitude is constant. Moreover, the dynamics of magnetically charged particles are also studied, and it is shown that both the energy and angular momentum of the particles corresponding to circular orbits increases with the increase of their magnetic charge. Finally, we also study collisions of magnetized, electrically neutral, and magnetically charged particles around the Bardeen BHs, where we provide analyses of critical angular momentum that may allow collision of the particles near-horizon radius, producing enormous values of center of mass energy of the collisions.

The contribution of low-energy particles down to ~200 eV to the dose deposited on the very near surface of materials subject to the space environment is investigated by means of GEANT4 Monte Carlo simulations. The contribution to the dose, of the low-energy parts of Global Radiation Earth ENvironment (GREEN) spectra (200 eV–40 keV for electrons, 200 eV–100 keV for protons), is compared with calculations performed with AE8/AP8. Both geostationary earth orbit (GEO) and low earth orbit (LEO) SPOT like orbits are studied. The dose depth profiles are estimated for silicon material. The impact on the dose calculation of different transport models is also investigated. Below 1 keV, the relevance of continuous processes is analyzed for electrons by comparison with a discrete model [GEANT4/microelectronic (MICROELEC)]. This analysis is also performed for protons below 10 keV. [ABSTRACT FROM AUTHOR]

The motion and acceleration of an electrically charged and magnetized particle around a cylindrical black hole in the presence of an external asymptotically uniform magnetic field parallel to the z -axis are investigated. We look at circular orbits around a central object and study the dependence of the most internal stable circular orbits (ISCO) on the so-called magnetic coupling parameters, which are responsible for the interaction between the external magnetic field and magnetized and charged particles. It is shown that the ISCO radius decreases with increasing magnetized interaction parameter. Therefore, we also studied collisions of magnetized particles around a cylindrical black hole immersed in an external magnetic field, and showed that the magnetic field can act as a particle accelerator near nonrotating cylindrical black holes. [ABSTRACT FROM AUTHOR]

In this work, we derive analytical relations for all projections of the orbital energy flow and spin flow in the focal plane of a strongly focused left-hand circularly polarized Gaussian beam, also calculating a torque exerted upon a dielectric ellipsoidal microparticle in the focus of the beam and discussing results of an experiment on rotating the microparticle around its center of mass. The on-axis projection of the torque exerted upon the microparticle is found to be negative, i.e., directed oppositely to the beam propagation axis. Such a torque is supposed to induce a clockwise rotation of a non-absorbing dielectric particle around its center of mass. We have been demonstrated that a reverse energy flow occurs in the light field regions where the longitudinal projection of the spin flow is negative and larger in magnitude than the longitudinal projection of the orbital energy flow, which is always positive. [ABSTRACT FROM AUTHOR]

We propose a robust way of advancement of the gyrotrons into the region of terahertz frequencies and MW-level power of radiation while retaining high efficiency and high stability of the frequency. These gyrotrons may be used for electron cyclotron resonance heating and current drive systems (ECRH&CD) in future fusion setups, in large complexes of coherently radiating gyrotrons for THz data and energy transmission, for THz particles acceleration. We at first demonstrate the advantages of this way at the example of the gyrotron with very-high-order operating mode TE56.24, driven by a relatively weak external monochromatic signal, and show that in the phase- and frequency-locking mode a significant enhancement of radiation parameters – frequency, power and efficiency – can be achieved. [ABSTRACT FROM AUTHOR]

This paper deals with the design, realization, and testing of an earth magnetic field simulator, which allows us to validate hardware-in-the-loop algorithms, as well as to test new actuators. The design is driven by typical small satellites functional requirements. The subsystems that compose the simulator are described in detail. The validation of the simulator is performed by assessing its functioning, the uniformity of the recreated magnetic field, and the functionality of a magnetorquer. [ABSTRACT FROM AUTHOR]

As the magnetic field used in nuclear magnetic resonance (NMR) research increases (up to 23 T), the irradiation frequency of the electromagnetic field used for dynamic nuclear polarization (DNP) needs to be in the terahertz band (140–600 GHz). This article analyzed and compared the influence of different external magnetic field profiles on start current and beam–wave interaction of a 394-GHz gyrotron. As the simulation results show, the minimum start current corresponding to the linear and parabolic external magnetic field profile is lower than that corresponding to the uniform magnetic field. The minimum start current in the case of parabolic magnetic field profile is a little lower than that in the case of a linear magnetic field profile. Based on the nonlinear self-consistent calculation, it is observed that the optimum output powers in both linear and parabolic magnetic field profile cases are nearly equal when the beam current is 0.25 A and both of them are larger than the optimum output power when the magnetic field is uniform. In the calculation of orbital efficiency $\eta _{\bot } $ , the maximum orbital efficiency in the soft-excitation region in the inhomogeneous magnetic field profile cases is larger than that in the case of uniform magnetic field profile. After comprehensive consideration of beam voltage, beam current, and efficiency, the final operation point is located in the place where the beam current is 0.25 A and the beam voltage is 15 kV. The output power is more than 300 W and meets the requirements of DNP-NMR experiment. [ABSTRACT FROM AUTHOR]

We compare magnetohydrodynamics (MHD) simulation results with observations from the Michibiki satellite, which is on the quasi-zenith orbit (QZO), to estimate the risk of surface charging. Surface charging results from plasma injection related to substorms. We simulated some charging events and compared the magnetic field variations causing the plasma injection. However, the magnetic field variations of simulation results tend to deviate from observations on QZO under a disturbed geomagnetic condition. We consider that the deviation under a disturbed geomagnetic condition is due to ring current enhancement in the inner magnetosphere. To produce the magnetic field variation due to ring current, we added an inner magnetospheric pressure model to the MHD simulation, which produces the ring current by artificially increasing the pressure in the inner magnetosphere. Then, we investigated the magnetic field variation causing the plasma injection. As a result, we found that the magnetic field variation causing plasma injection is reproduced in the simulation when we add the inner pressure model to the MHD simulation. This result suggests that the change in the magnetic field due to ring current in the inner magnetosphere affects the magnetic field variation of the plasma injection caused by nightside reconnection. [ABSTRACT FROM AUTHOR]

The Influence sur les Composants Avancés des Radiations de l’Espace-Nouvelle Génération (ICARE-NG) instrument onboard the Argentinian satellite Satelite de Aplicaciones Cientificas-D (SAC-D) detected much more protons during descending orbits (when latitude decreases) than for ascending orbits (increasing latitudes). In this paper, we will investigate the anisotropy seen by ICARE-NG Head-A for protons in the coincidence mode from Monte Carlo simulations performed with GEANT4. Our simulations show that the difference in the fluxes observed during ascending and descending orbits comes from the fact that the instrument observed trapped protons or not on each point of the orbits as a result of the instrument and satellite orientations. In addition, we show in this paper that the measurements performed by ICARE-NG can be used in conjunction with our GEANT4 simulations to study the anisotropy of trapped protons, i.e., their distribution relative to their equatorial pitch angle. [ABSTRACT FROM AUTHOR]

The Buneman–Hartree relation is a condition that determines the excitation of oscillations in magnetrons. However, experiments of different years indicate that for a whole class of similar generators, it is not accurate enough. In particular, this is observed for the so-called spatial-harmonic magnetrons, which have significant advantages over conventional ones in millimeter and subterahertz ranges. The operating parameters of these generators are close to the Hull cutoff parabola, i.e., they have substantially larger transverse dimensions of the interaction space for the same values of the operating voltage and magnetic field, and accordingly, a larger-sized slow-wave system is possible. The results obtained in the development of spatial-harmonic magnetrons for radars can serve to estimate the limits of applicability of the Buneman–Hartree condition. Experiments show that the initial voltage at which generation occurs is significantly higher than the value calculated from the conventional formula. Probable causes are a change in the pattern of motion of an electron near the Hull cutoff parabola and the possibility of exciting gyroresonances. The analysis of the experiments fully confirms that even for millimeter-band magnetrons operating under purely drift (conventional) resonance, an analytical model that takes into account the orbital motion of electrons more accurately describes the physical processes near the cutoff parabola and significantly improves the accuracy of the choice of generator parameters and operating modes. [ABSTRACT FROM AUTHOR]