Cosmic Ray Simulation Research Articles

ACCELERATION OF COSMIC RAYS AT LARGE SCALE COSMIC SHOCKS IN THE UNIVERSE

Cosmological hydrodynamic simulations of large scale structure in the universe have shown that accretion shocks and merger shocks form due to flow motions associated with the gravitational collapse of nonlinear structures. Estimated speed and curvature radius of these shocks could be as large as a few 1000 km/s and several Mpc, respectively. According to the diffusive shock acceleration theory, populations of cosmic-ray particles can be injected and accelerated to very high energy by astrophysical shocks in tenuous plasmas. In order to explore the cosmic ray acceleration at the cosmic shocks, we have performed nonlinear numerical simulations of cosmic ray (CR) modified shocks with the newly developed CRASH (Cosmic Ray Amr SHock) numerical code. We adopted the Bohm diffusion model for CRs, based on the hypothesis that strong Alfven waves are self-generated by streaming CRs. The shock formation simulation includes a plasma-physics-based 'injection' model that transfers a small proportion of the thermal proton flux through the shock into low energy CRs for acceleration there. We found that, for strong accretion shocks, CRs can absorb most of shock kinetic energy and the accretion shock speed is reduced up to <TEX>$20\%$</TEX>, compared to pure gas dynamic shocks. For merger shocks with small Mach numbers, however, the energy transfer to CRs is only about <TEX>$10-20\%$</TEX> with an associated CR particle fraction of <TEX>$10^{-3}$</TEX>. Nonlinear feedback due to the CR pressure is insignificant in the latter shocks. Although detailed results depend on models for the particle diffusion and injection, these calculations show that cosmic shocks in large scale structure could provide acceleration sites of extragalactic cosmic rays of the highest energy.

Comparison of AGASA data with CORSIKA simulation

An interpretation of Akeno giant air shower array (AGASA) data by comparing the experimental results with the simulated ones by cosmic ray simulation for KASCADE (CORSIKA) has been made. General features of the electromagnetic component and low energy muons observed by AGASA can be well reproduced by CORSIKA. The form of the lateral distribution of charged particles agrees well with the experimental one between a few hundred metres and 2000 m from the core, irrespective of the hadronic interaction model studied and the primary composition (proton or iron). It does not depend on the primary energy between 10 17.5 and 10 20 eV as the experiment shows. If we evaluate the particle density measured by scintillators of 5 cm thickness at 600 m from the core S 0(600), suffix 0 denotes the vertically incident shower) by taking into account the similar conditions as in the experiment, the conversion relation from S 0(600) to the primary energy is expressed as E ( eV)=2.15×10 17S 0(600) 1.015 within 10% uncertainty among the models and composition used, which suggests the present AGASA conversion factor is the lower limit. Although the form of the muon lateral distribution fits well to the experiment within 1000 m from the core, the absolute values change with hadronic interaction model and primary composition. The slope of the ρ μ(600) (muon density above 1 GeV at 600 m from the core) vs. S 0(600) relation in experiment is flatter than that in simulation of any hadronic model and primary composition. As the experimental slope is constant from 10 15 to 10 19 eV, we need to study this relation in a wide primary energy range to infer the rate of change of chemical composition with energy.

What we can infer about the nuclear cosmic ray composition from the EAS longitudinal development

Abstract Results from a detailed Monte Carlo simulation for electromagnetic and hadronic cascades in the atmosphere, generated by primary γ-rays, p, O and Fe are provided in the primary energy range 10 12 –10 16 eV for vertical incident showers. In the simulation of the Extensive Air Showers (EAS) development, the CORSIKA (COsmic Ray SImulator for KAscade) code has been used to perform a full simulation of the electromagnetic and hadronic interactions. The main aims of this simulation are to obtain accurate information on the longitudinal development of the electromagnetic component, for both pure electromagnetic and hadronic cascades, for different primary cosmic rays. Results on the depencdence of the shower size and the photon number with primary energy are obtained. Ratios between the maximum development depth parameter and primary particle energy or the shower size have been studied and predicted values for the electron and photon content and fluctuations on these parameters have been determined at the maximum development depth of the EAS and at mountain altitude ( X = 800 g cm −2 ). We also seek to provide relations to interpret the experimental data, for those who do not have detailed simulation calculations available and also to provide material for a full and deep comparison of air shower Monte Carlo codes.

Method to infer about the nuclear UHE cosmic-ray composition from the EAS lateral development

Results from a detailed Monte-Carlo simulation for electromagnetic and hadronic cascades in the atmosphere, generated by primary γ-rays, p, O and Fe are provided in the primary energy range 10 12–10 16 eV for vertical incident showers. In the simulation of the Extensive Air Showers (EAS) development, the CORSIKA (COsmic Ray SImulator for KAscade) code has been used to perform a full simulation of the electromagnetic and hadronic interactions. The lateral development of the electromagnetic component, for both, pure electromagnetic and hadronic cascades have been deeply investigated and the NKG-type functions have been fitted to the lateral developments, to determine the lateral age parameters. Results on the variation of the shower size with the lateral age parameter and primary energy are obtained, as well as fluctuations on shower size at maximum development depth of the EAS and at mountain altitude ( X = 800 g cm −2). The main aim of this work is to obtain an accurate procedure to discriminate the nuclear composition of the UHE cosmic rays from the gamma rays background. We also seek to provide relations to interpret the experimental data, for those who do not have detailed simulation calculations available and also to provide material for a full and deep comparison of air shower Monte-Carlo codes.

Straight tracks reconstruction in all stereo drift chambers

We describe a track-finding algorithm for reconstructing straight tracks in drift chambers with cylindrical symmetry and with single sense wire cells arranged in an “all stereo” configuration. The algorithm starts from a short track segment and extends it by adding measured points one by one. It has been tested on Monte-Carlo simulations of cosmic rays and can be generalized to the case of bent trajectories. Results are presented and discussed.

3D heliospheric simulations of cosmic rays in the light of Ulysses

Recent Ulysses observations in the polar regions of the heliosphere have provided fundamental new insights into the modes of cosmic-ray transport in the heliosphere. Ulysses discovered variations in the magnetic field which are large enough to produce significant cosmic-ray effects, and which are consistent with a previous prediction. In addition to impeding the inward, radial diffusive and drift access of cosmic rays over the poles as discussed previously, the magnetic fluctuations imply a significantly larger latitudinal diffusion. These effects directly lead to both a much reduced latitudinal gradient and significant 27-day time variations near the pole. We conclude that the general picture of cosmic-ray transport and modulation developed over the past decade, with reasonable parameters, can account for most of the observed global, large-scale phenomena.

Muon content of UHE air showers: discrimination method between electromagnetic and hadronic cascades

Results from a detailed Monte Carlo simulation for the muon component of EAS, at mountain altitude (800 g cm-2), generated by vertical gamma -rays, protons, oxygen and iron primary cosmic rays, in the energy range 1012-1016 eV, are provided for muon threshold energies from 0.1 to 100 GeV. In the simulation of the different components of the shower ( mu +or-, e+or-, gamma ...), the CORSIKA (cosmic ray simulator for cascade) code has been used to allow for both, electromagnetic and hadronic interactions. Results on the variation and fluctuation of the total muon number with shower size and primary energy are obtained, as well as longitudinal developments, lateral distributions of low-energy muons in air showers and muon energy spectra. Moreover, analytical expressions are fitted to the muon lateral developments, and muon energy spectra have been parametrized to a log-normal distribution. Apart from their value as new results, they may be used for the design of current studies at mountain altitudes. We also seek to provide relations to interpret the experimental data, for those who do not have detailed simulation calculations available.

Cosmic ray simulator: A versatile apparatus for quantitative studies on the interaction of cosmic rays with frozen solids by on line and in situ quadrupole mass spectrometry and Fourier transform infrared spectroscopy

The cosmic ray simulator consists of a 50 ℓ cylindrical stainless steel chamber. A rotable cold finger milled of a silver (111) monocrystal optimizes heat conductivity and is connected to a programmable, closed cycle helium refrigerator allowing temperature control of an attached silver wafer between 10 and 340 K (±0.5 K). Oil-free ultrahigh vacuum (UHV) conditions of ≊10−10 mbar are provided by a membrane, drag, and cryopump, hence guaranteeing a vacuum system free of any contamination. Ice layers of defined crystal structures and reproducible thickness of (5±1) μm are achieved by depositing gases, e.g., CH4, CD4, CD4/O2, and CH4/O2, with a computer-assisted thermovalve on the cooled wafer. These frosts are irradiated at 10 and 50 K with 7.3 MeV protons and 9 MeV α particles of the compact cyclotron CV28 in Forschungszentrum Jülich up to doses of 150 eV per molecule, i.e., simulating the distribution maximum of galactic cosmic ray particles interacting with primordial matter in space during 0.7×109 yr. During the experiments, gas phase and solid state are monitored for the first time quantitatively on line and in situ by a quadrupole mass spectrometer (QMS) via matrix interval arithmetic and a Fourier transform infrared spectrometer (FTIR) in an absorption-reflection mode at 62.5°. For the first time, a cosmic ray simulator allows detailed and reproducible mechanistic studies on the interaction of cosmic ray particles with frozen gases in space based on pressure conditions (hydrocarbon free UHV conditions, the limitation of condensations of residual gases during an experiment to less than one monolayer), temperature regime (the use of silver monocrystals, FTIR in reflection, optimized ion currents, and target thicknesses &amp;lt;5 μm restrict temperature increasing to 14 K), and defined target systems. In combination with two on line and in situ analyses techniques, i.e., FTIR and QMS, the machine yields unprecedented options such as computing the heating of the ice surfaces directly exposed to the ion beam by a calibrated QMS and a complete quantification of product distribution. Preliminary results indicate a strong temperature-dependent component of the reaction mechanisms in the frosts: surface layers are heated by impinging ions to (14±1) K and yield (70%–100%) of higher molecular weight species, such as C11D24, whereas 10 K regions produce majority of simpler hydrocarbons, e.g., C3D8. Second, O2 contaminations influence the experiments dramatically by trapping of diffusive H atoms as O2H and, thus, yield oxygen-containing yellow to brown residues after heating to 293 K. Irradiation of pure methane targets, however, produce no residues. But an increasing concentration of H atoms exceeding (6%±3%) leads to ejection of up to 90% of the frosts into vacuum.

Cherenkov light shape of gamma and hadronic VHE air showers: Fit to analytical formulae

A detailed Monte Carlo simulation of Cherenkov light (300–480 nm) from electromagnetic and hadronic cascades in the atmosphere has been performed in the energy range 10 12–10 14 eV of γ, proton, oxygen, and iron primary cosmic rays for vertically incident showers. In the calculations of both cascade development and Cherenkov light production, the CORSIKA (COsmic Ray SImulator for KAscade) code [J.N. Capdevielle et al., Kerforschungszentrum Karlsruhe GmbH, Repr. KfK 4998 (1992)] has been used to allow for all, electromagnetic and hadronic, interactions. The main aim of our simulation is to obtain possibly accurate information on the lateral spread, longitudinal development, and temporal profile of Cherenkov light, from both pure electromagnetic and hadronic cascades, in order to obtain information to separate both. Time profile Cherenkov light pulse and primary cosmic ray dependence have been obtained. Parametrization of Cherenkov light pulses has been performed making use of gamma distributions. Apart from their value as new results, they may be used for the design, of current studies at mountain altitude. We also seek to provide relations to interpret the experimental data, for those who do not have detailed simulation calculations available.

Application of high energy implantation in semiconductors

A short survey of MeV ion implantation (I/I) is given. In the first part, we present measurements of ion ranges and profiles, the damage induced by high energy deposition, material modifications, and the annealing behavior. The second section presents device improvements or fabrication by high energy I/I: waveguides, cosmic ray simulation, SOI isolation, thyristors, magnetic bubbles, latch up and SEU prevention, ion lithography, retrograde p-wells and collectors, gridistors and PROM customization. The last part deals with technical problems: availability, costs, and handling.

An Experimental Study of the Effect of Absorbers on the Let of the Fission Particles Emitted by CF-252

The present work continues the developments of the 252Cf fission particle source for use in cosmic ray simulation. An experimental study has been made of the LET of 252Cf fission particles in thin aluminium foils, and of the variation of the mean LET with decreasing fission particle energy. Calculated LET values have been compared with the experimental results, and tabulation of LETs and ranges in aluminium and silicon included.

Use of a 252Cf source in cosmic ray simulation studies on CMOS memories

A laboratory 252Cf source has been found to provide a convenient and satisfactory technique for evaluating the susceptibility of VLSI static RAMs to cosmic-ray-induced single-event upsets. The calibration and use of the system are described, and results for some commercial CMOS RAMs are presented.

Cosmic Ray Simulation Experiments for the Study of Single Event Upsets and Latch-Up in CMOS Memories

Heavy ion induced single event upsets and latch-up in 4K CMOS RAMs and PROMs have been demonstrated using both the Harwell Variable Energy Cyclotron and a laboratory Californium-252 source. The latter provides a novel and convenient alternative which complements heavy ion accelerator techniques. A number of memories have been examined by both techniques, enabling appropriate cross sections to be measured.

Cosmic-Ray-Induced Errors in MOS Devices

The results are reported for a comprehensive analytical and experimental study of galactic cosmic-ray-induced errors in MOS devices. An error rate model is described which utilizes exact expressions for a path-length distribution function and a Linear Energy Transfer (LET) spectrum for the cosmic ray environment to calculate the expected cosmic-ray-induced error rate in space for a given parallel-piped-shaped sensitive volume. The model validity is confirmed by comparison of predictions to bit-error data from devices in orbiting satellites, and to cosmic ray simulation measurements on the same device types at a cyclotron. The experimental results and model predictions are described for a wide variety of device types, including NMOS, PMOS, CMOS/bulk, CMOS/SOS, and ANOS.