Context. Solar energetic particles observed in association with coronal mass ejections (CMEs) are produced by the CME-driven shock waves. The acceleration of particles is considered to be due to ...diffusive shock acceleration (DSA). Aims. We aim at a better understanding of DSA in the case of quasi-parallel shocks, in which self-generated turbulence in the shock vicinity plays a key role. Methods. We have developed and applied a new Monte Carlo simulation code for acceleration of protons in parallel coronal shocks. The code performs a self-consistent calculation of resonant interactions of particles with Alfvén waves based on the quasi-linear theory. In contrast to the existing Monte Carlo codes of DSA, the new code features the full quasi-linear resonance condition of particle pitch-angle scattering. This allows us to take anisotropy of particle pitch-angle scattering into account, while the older codes implement an approximate resonance condition leading to isotropic scattering. We performed simulations with the new code and with an old code, applying the same initial and boundary conditions, and have compared the results provided by both codes with each other, and with the predictions of the steady-state theory. Results. We have found that anisotropic pitch-angle scattering leads to less efficient acceleration of particles than isotropic. However, extrapolations to particle injection rates higher than those we were able to use suggest the capability of DSA to produce relativistic particles. The particle and wave distributions in the foreshock as well as their time evolution, provided by our new simulation code, are significantly different from the previous results and from the steady-state theory. Specifically, the mean free path in the simulations with the new code is increasing with energy, in contrast to the theoretical result.
Context. The source of high-energy protons (above ~500 MeV) responsible for ground level enhancements (GLEs) remains an open question in solar physics. One of the candidates is a shock wave driven by ...a coronal mass ejection, which is thought to accelerate particles via diffusive-shock acceleration. Aims. We perform physics-based simulations of proton acceleration using information on the shock and ambient plasma parameters derived from the observation of a real GLE event. We analyse the simulation results to find out which of the parameters are significant in controlling the acceleration efficiency and to get a better understanding of the conditions under which the shock can produce relativistic protons. Methods. We use the results of the recently developed technique to determine the shock and ambient plasma parameters, applied to the 17 May 2012 GLE event, and carry out proton acceleration simulations with the Coronal Shock Acceleration (CSA) model. Results. We performed proton acceleration simulations for nine individual magnetic field lines characterised by various plasma conditions. Analysis of the simulation results shows that the acceleration efficiency of the shock, i.e. its ability to accelerate particles to high energies, tends to be higher for those shock portions that are characterised by higher values of the scattering-centre compression ratio rc and/or the fast-mode Mach number MFM. At the same time, the acceleration efficiency can be strengthened by enhanced plasma density in the corresponding flux tube. The simulations show that protons can be accelerated to GLE energies in the shock portions characterised by the highest values of rc. Analysis of the delays between the flare onset and the production times of protons of 1 GV rigidity for different field lines in our simulations, and a subsequent comparison of those with the observed values indicate a possibility that quasi-perpendicular portions of the shock play the main role in producing relativistic protons.
We have measured the temperature-dependent thermal conductivity kappa(T) of individual multiwall boron nitride nanotubes using a microfabricated test fixture that allows direct transmission electron ...microscopy characterization of the tube being measured. kappa(T) is exceptionally sensitive to isotopic substitution, with a 50% enhancement in kappa(T) resulting for boron nitride nanotubes with 99.5% 11B. For isotopically pure boron nitride nanotubes, kappa rivals that of carbon nanotubes of similar diameter.
Aims.
We model the energetic storm particle (ESP) event of 14 July 2012 using the energetic particle acceleration and transport model named ‘PArticle Radiation Asset Directed at Interplanetary Space ...Exploration’ (PARADISE), together with the solar wind and coronal mass ejection (CME) model named ‘EUropean Heliospheric FORcasting Information Asset’ (EUHFORIA). The simulation results illustrate both the capabilities and limitations of the utilised models. We show that the models capture some essential structural features of the ESP event; however, for some aspects the simulations and observations diverge. We describe and, to some extent, assess the sources of errors in the modelling chain of EUHFORIA and PARADISE and discuss how they may be mitigated in the future.
Methods.
The PARADISE model computes energetic particle distributions in the heliosphere by solving the focused transport equation in a stochastic manner. This is done using a background solar wind configuration generated by the ideal magnetohydrodynamic module of EUHFORIA. The CME generating the ESP event is simulated by using the spheromak model of EUHFORIA, which approximates the CME’s flux rope as a linear force-free spheroidal magnetic field. In addition, a tool was developed to trace CME-driven shock waves in the EUHFORIA simulation domain. This tool is used in PARADISE to (i) inject 50 keV protons continuously at the CME-driven shock and (ii) include a foreshock and a sheath region, in which the energetic particle parallel mean free path,
λ
∥
, decreases towards the shock wave. The value of
λ
∥
at the shock wave is estimated from in situ observations of the ESP event.
Results.
For energies below ∼1 MeV, the simulation results agree well with both the upstream and downstream components of the ESP event observed by the Advanced Composition Explorer. This suggests that these low-energy protons are mainly the result of interplanetary particle acceleration. In the downstream region, the sharp drop in the energetic particle intensities is reproduced at the entry into the following magnetic cloud, illustrating the importance of a magnetised CME model.
A method based on measuring the shift of Ramsey spectral line in an atomic fountain in the gravitational field has been proposed to develop an atomic gravimeter involving the atomic fountain on ...ultracold atoms. The accuracy of the measurement of the gravitational acceleration with a fountain microwave frequency standard on Cs atoms is
. The achievable accuracy at the integration time τ
a
= 10 000 s is
μGal.
A two-dimensional analytical model of a brushless motor with permanent magnets is developed on the basis of the Fourier variable separation method. The general calculation area of this model includes ...ferromagnetic areas and permanent magnets with a real configuration. Permanent rotor magnets, stator winding currents, and induced magnetic inductions in the stator teeth are sources of the magnetic field. The calculated values of magnetic inductions in media are found with allowance for stator serration, winding harmonics of the magnetomotive force, and the geometric structure of the arrangement of permanent magnets. The calculated functional parameters of the motor (current, torque) obtained in the model are close to its passport values.
The focusing of an atomic beam with the use of a two-dimensional magneto-optical trap in order to increase the number of atoms in the region of their laser cooling and localization near an atom chip ...is discussed. Two regimes of the interaction of atoms with a focusing laser field are considered: (i) the Doppler interaction regime, which occurs at small detunings of the laser field from the atomic resonance, and (ii) the sub-Doppler interaction regime, which occurs at large detunings of the laser field from the atomic resonance. The efficiency of focusing in the first case is low because of the momentum diffusion. It has been shown that the momentum diffusion in the sub-Doppler cooling mechanism is insignificant and, as a result, the broadening of the transverse velocity distribution of atoms is small. The sharp focusing of the atomic beam is possible in this interaction regime.
Magnetic gears can be divided into two groups: uncontrollable reducers constructed on permanent magnets and controlled ones that contain, in addition to magnets, the stator winding with a frequency ...converter. The first group has a fixed coefficient of magnetic reduction, while, for the second group, it can be changed by means of a frequency converter. The suggested field analytical calculation method can be used to determine the functional properties of both types of these devices with a use of two Cartesian coordinates
x
and
y
. In each active region of the magnetic gear (air gaps, magnets, stator and rotor yokes, a rotor with through teeth and grooves (modulator)), the sought variables, i.e., magnetic potentials and magnetic inductions, are represented as a product of two functions, the first of which is affected by coordinate
x
and the other by coordinate
y
. These functions are also multiplied by some unknown constants, the values of which taken are from the boundary conditions of the magnetic field on the interface lines of active regions. The magnetic permeability of ferromagnetic regions (yoke, modulator rods) are assumed to be fixed, with their values being adjusted according to the calculations of magnetic circuit of the reducer. This approach makes it possible to implement the principle of superposition of magnetic fields formed by the rotor and stator sources, respectively. In this case, the calculations of the unknown constants are carried out twice for each source, since the latter have fundamentally different numbers of poles and, hence, have a different spectrum of harmonic components of the magnetomotive forces. The proposed method makes it possible to determine the magnetic inductions in working air gaps of the magnetic gear and the electromagnetic moments that act on the rotors and the stator. The results were confirmed by the experimental data. To implement the method, a set of functions available in the Mathcad mathematical program is enough.
Context.
It is thought that solar energetic ions associated with coronal and interplanetary shock waves are accelerated to high energies by the diffusive shock acceleration mechanism. For this ...mechanism to be efficient, intense magnetic turbulence is needed in the vicinity of the shock. The enhanced turbulence upstream of the shock can be produced self-consistently by the accelerated particles themselves via streaming instability. Comparisons of quasi-linear-theory-based particle acceleration models that include this process with observations have not been fully successful so far, which has motivated the development of acceleration models of a different nature.
Aims.
Our aim is to test how well our self-consistent quasi-linear SOLar Particle Acceleration in Coronal Shocks (SOLPACS) simulation code, developed earlier to simulate proton acceleration in coronal shocks, models the particle foreshock region.
Methods.
We applied SOLPACS to model the energetic storm particle (ESP) event observed by the STEREO A spacecraft on November 10, 2012.
Results.
All but one main input parameter of SOLPACS are fixed by the in situ plasma measurements from the spacecraft. By comparing a simulated proton energy spectrum at the shock with the observed one, we were able to fix the last simulation input parameter related to the efficiency of particle injection to the acceleration process. A subsequent comparison of simulated proton time-intensity profiles in a number of energy channels with the observed ones shows a very good correspondence throughout the upstream region.
Conclusions.
Our results strongly support the quasi-linear description of the foreshock region.
—During the operation of synchronous explicit-pole machines, the damper winding failures can occur due to electromechanical and thermal effects on the elements upon a sudden short circuit of a stator ...winding, at frequent launches in the motoring mode, and at three-phase voltage unbalance. These effects can lead to damage to the contacts of rods of the damper winding with its short-circuiting rings and to the destruction of elements of the rings themselves. The defects can appear in a noticeable form only in the transient, asynchronous, and asymmetric modes. Based on a 2D analytical model of a synchronous explicit-pole machine in
d
,
q
coordinates, the rod currents and electromagnetic torque are analyzed in the asynchronous machine mode upon breakage of rods and interpole bridges near one or two poles of a damper winding. It has been concluded that the most dangerous anomaly of a damper winding is the breakage of interpole bridges near one or two poles, upon which high currents occur in rods and the electromagnetic torque is ten times higher than the nominal value.
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