Particle conservation in numerical models of the tokamak plasma edge

The test particle Monte-Carlo models for neutral particles are often used in the tokamak edge modelling codes. The drawback of this approach is that the self-consistent solution suffers from random error introduced by the statistical method. A particular case where the onset of nonphysical solutions can be clearly identified is violation of the global particle balance due to non-converged residuals. There are techniques which can reduce the residuals - such as internal iterations in the code B2-EIRENE - but they may pose severe restrictions on the time-step and slow down the computations. Numerical diagnostics described in the paper can be used to unambiguously identify when the too large error in the global particle balance is due to finite-volume residuals, and their reduction is absolutely necessary. Algorithms which reduce the error while allowing large time-step are also discussed.Comment: Link to journal publication: http://aip.scitation.org/doi/full/10.1063/1.498085

ПРОГНОЗ ТЕМПЕРАТУРНОГО РЕЖИМА НАСЫПИ СЕВЕРНОЙ ЖЕЛЕЗНОЙ ДОРОГИ (В ТУНДРОВОЙ ЗОНЕ У СТАНЦИИ ХАНОВЕЙ)

ПРОГНОЗ ТЕМПЕРАТУРНОГО РЕЖИМА НАСЫПИ СЕВЕРНОЙ ЖЕЛЕЗНОЙ ДОРОГИ (В ТУНДРОВОЙ ЗОНЕ У СТАНЦИИ ХАНОВЕЙ)ПРОГНОЗ ТЕМПЕРАТУРНОГО РЕЖИМА НАСЫПИ СЕВЕРНОЙ ЖЕЛЕЗНОЙ ДОРОГИ (В ТУНДРОВОЙ ЗОНЕ У СТАНЦИИ ХАНОВЕЙ)The article presents the results of fi eld studies near Northern Railway embankment (Hanovey station) in fi eldwork area of Geocryology Department (Lomonosov Moscow State University), where performed: cone penetration test, measuring thickness of active layer of and soil temperatures, monitoring settlement of embankment, laboratory tests. Mathematical model was compiled in the Qfrost program based on these data taking into account the unevenness of the snow cover in the study area. Calculations of the temperature regime of the embankment until 2050, carried out taking into account climatic changes (according to the RCP 4.5 scenario), showed that the thickness of the talik at the embankment will increase 40% in 30 years and without taking this factor into account — 17%. The article also discusses the features of the position and structure of the embankment, the composition and properties of frozen soils, which signifi cantly aff ect the stability of the embankment.publishedVersio

The Possibilities of Fission Material Reproduction Increase in Thermal Reactor with the Assemblies with a Hard Neutron Spectrum

This paper addresses the problem of fission material reproduction increase in thermal reactors. Reproduction increase is achieved while decreasing the fission material content in the fuel. In that case, a decrease of neutron loss in construction materials and a neutron leakage decrease are required for obtaining reactor criticality. Effectiveness of the reactor functioning can be increased by the use of additional neutron sources, for example, n-2n reaction in beryllium framing. The possibility of additional neutron source development with the use of fast neutrons with an energy distribution close to the fission spectrum in the major part of thermal reactor core is researched in this paper

The Design Technique for Power Management Unit of the Tag IC for Radio Frequency Identification of Critical Infrastructure Objects

The ultra-high frequency (UHF) tag IC’s main part of the power management unit (PMU) design technique is presented. The technique is a step-by-step algorithm for designing a PMU and consists of five interrelated stages. At the first stage, the requirements for the parameters of the PMU (output voltage, output DC power, efficiency, output capacitor capacity) and the Q-factor of the tag analog front-end are determinates. At the second stage, the design of an electrical circuit of a voltage multiplier (VM) is carried out. VM is required to convert the voltage of the input radio frequency (RF) signal into an DC voltage. During the third stage, the design of the electrical circuit of the DC voltage limiter is carried out, which is necessary to reduce the output voltage of VM to a safe level. The result of stage 4 is an electrical circuit of surge protection designed to provide the required level of immunity of the tag IC to the effects of electrostatic discharge and a high-power RF signal. As part of the final stage, the evaluation and alignment with the required Q-factor value of the tag IC analog front-end is carried out. The proposed technique can be used for the development of domestic UHF tag ICs (ISO 18000-6C, GJB 7377.1, etc.) based on CMOS technological processes, including ICs designed for radio frequency identification of critical infrastructure objects. Using the presented technique, the design of a PMU with an estimated efficiency value of 70%, an estimated Q-factor of the analog front-end of less than 15 at an RF input signal power of -12.7 dBm was performed

ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider

This paper reviews and extends searches for the direct pair production of the scalar supersymmetric partners of the top and bottom quarks in proton-proton collisions collected by the ATLAS collaboration during the LHC Run 1. Most of the analyses use 20 fb$^{-1}$ of collisions at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV, although in some case an additional 4.7 fb$^{-1}$ of collision data at $\sqrt{s}$ = 7 TeV are used. New analyses are introduced to improve the sensitivity to specific regions of the model parameter space. Since no evidence of third-generation squarks is found, exclusion limits are derived by combining several analyses and are presented in both a simplified model framework, assuming simple decay chains, as well as within the context of more elaborate phenomenological supersymmetric models

B2-B2.5 Code Benchmarking, Part III: Convergence issues of the B2-EIRENE code

B2-EIRENE is a nite-volume Computational Fluid Dynamics (CFD) code which describes flow of magnetized charged particles combined self-consistently with kinetic Monte-Carlo (MC)model for neutral particles. The issue of the run-time and accuracy of the coupled package is addressed in the present report. Convergence of different iteration schemes is analyzed in termsof generalized residuals. Particular focus is on the global particle balance. The results and discussions may be of general interest for developers and users of tokamak edge codes based ona CFD-MC combination

Hydrogen Spectral Line Shape Formation in the SOL of Fusion Reactor Plasmas

The problems related to the spectral line-shape formation in the scrape of layer (SOL) in fusion reactor plasma for typical observation chords are considered. The SOL plasma is characterized by the relatively low electron density (1012–1013 cm−3) and high temperature (from 10 eV up to 1 keV). The main effects responsible for the line-shape formation in the SOL are Doppler and Zeeman effects. The main problem is a correct modeling of the neutral atom velocity distribution function (VDF). The VDF is determined by a number of atomic processes, namely: molecular dissociation, ionization and charge exchange of neutral atoms on plasma ions, electron excitation accompanied by the charge exchange from atomic excited states, and atom reflection from the wall. All the processes take place step by step during atom motion from the wall to the plasma core. In practice, the largest contribution to the neutral atom radiation emission comes from a thin layer near the wall with typical size 10–20 cm, which is small as compared with the minor radius of modern devices including international test experimental reactor ITER (radius 2 m). The important problem is a strongly non-uniform distribution of plasma parameters (electron and ion densities and temperatures). The distributions vary for different observation chords and ITER operation regimes. In the present report, most attention is paid to the problem of the VDF calculations. The most correct method for solving the problem is an application of the Monte Carlo method for atom motion near the wall. However, the method is sometimes too complicated to be combined with other numerical codes for plasma modeling for various regimes of fusion reactor operation. Thus, it is important to develop simpler methods for neutral atom VDF in space coordinates and velocities. The efficiency of such methods has to be tested via a comparison with the Monte Carlo codes for particular plasma conditions. Here a new simplified method for description of neutral atoms penetration into plasma is suggested. The method is based on the ballistic motion of neutrals along the line-of-sight (LoS) in the forward–back approximation. As a result, two-dimensional distribution functions, dependent on the LoS coordinate and the velocity projection on the LoS, and responsible for the Doppler broadening of the line shape, are calculated. A comparison of the method with Monte Carlo calculations allows the evaluation of the accuracy of the ballistic model. The Balmer spectral line shapes are calculated for specific LoS typical for ITER diagnostic