Determination of stress-strain state of porous rubber buffer in a nonlinear deformation conditions

Розроблено підхід до чисельного аналізу напружено-деформованого стану пористого гумового буфера в умовах нелінійного деформування на основі моментної схеми скінченного елемента з використанням різних методів визначення ізотропних модулів пружності пористої гуми. Проведено розрахунок пористого гумового буфера в умовах в’язкопружного деформування з використанням ядра релаксації, що включає миттєвий і тривалий модуль пружності пористої гуми та в умовах геометрично нелінійного деформування.Approach for the numerical analysis of stress-strain state of the porous rubber buffer in non-linear strained conditions has been depeloped. There were examined the methods of isotropic elastic modulus of porous materials such as self-consistence method for the spherical, needle shaped and disk shaped pores as well as the Khashin-Shtrikman variation method for the free shaped pores. Geometric non-linear strain model that includes sequential solution of the linear problems including the recalculation on each step of matrix stiffness of the whole construction has been built, the finite strain tensor of porous body in this case being shown as a sum of linear and non-linear constituents. Porous body stress tensor is based on the general Hooke’s law and includes the dependence from the porous material elasticity, metric tensor components, approximation of the first, second and the third strain tensor invariants. For viscoelastic deformation modeling integral relations based on Boltzmann - Volterra genetic theory were used. In this case porous body stress tensor includes the tensors of instant and continuous porous materials elastic modules, metric tensor components and the linear part of the first strain tensor invariant. To solve the resulting integral equations in three dimensional statement there time discretization for viscoelastic deformation and load discretization for geometric non-linear deformation, was used with the further use of the modified Newton - Kantorovich method. To solve the problem finite element momentum scheme on each step was used. Geometric nonlinearity and viscoelasticity of the material was formed by entering the additional load vector based on variational principle. Calculation of porous rubber buffer allowing the relaxation only of the porous rubber shift module in terms of viscoelastic deformation using the relaxation core has been carried out. It includes instant and continuous porous materials shift modules. As a result, the components of deformation stress state i.e. time distribution of normal stresses and motion dependence on both time and stress has been obtained

Non-transversality of the gluon polarization tensor in a chromomagnetic background

We investigate the question about the transversality of the gluon polarization tensor in a homogeneous chromomagnetic background field. We re-derive the non transversality known from a pure one loop calculation using the Slavnov-Taylor identities. In addition we generalize the procedure to arbitrary gauge fixing parameter $\xi$ and calculate the $\xi$-dependent part of the polarization tensor.Comment: subm. to TM

Measurement of air and nitrogen fluorescence light yields induced by electron beam for UHECR experiments

Most of the Ultra High Energy Cosmic Ray (UHECR) experiments and projects (HiRes, AUGER, TA, EUSO, TUS,...) use air fluorescence to detect and measure extensive air showers (EAS). The precise knowledge of the Fluorescence Light Yield (FLY) is of paramount importance for the reconstruction of UHECR. The MACFLY - Measurement of Air Cherenkov and Fluorescence Light Yield - experiment has been designed to perform such FLY measurements. In this paper we will present the results of FLY in the 290-440 nm wavelength range for dry air and pure nitrogen, both excited by electrons with energy of 1.5 MeV, 20 GeV and 50 GeV. The experiment uses a 90Sr radioactive source for low energy measurement and a CERN SPS electron beam for high energy. We find that the FLY is proportional to the deposited energy (E_d) in the gas and we show that the air fluorescence properties remain constant independently of the electron energy. At the reference point: atmospheric dry air at 1013 hPa and 23C, the ratio FLY/E_d=17.6 photon/MeV with a systematic error of 13.2%.Comment: 19 pages, 8 figures. Accepted for publication in Astroparticle Physic

Chirp mitigation of plasma-accelerated beams using a modulated plasma density

Plasma-based accelerators offer the possibility to drive future compact light sources and high-energy physics applications. Achieving good beam quality, especially a small beam energy spread, is still one of the major challenges. For stable transport, the beam is located in the focusing region of the wakefield which covers only the slope of the accelerating field. This, however, imprints a longitudinal energy correlation (chirp) along the bunch. Here, we propose an alternating focusing scheme in the plasma to mitigate the development of this chirp and thus maintain a small energy spread

The CCFM Monte Carlo generator CASCADE 2.2.0

CASCADE is a full hadron level Monte Carlo event generator for ep, \gamma p and p\bar{p} and pp processes, which uses the CCFM evolution equation for the initial state cascade in a backward evolution approach supplemented with off - shell matrix elements for the hard scattering. A detailed program description is given, with emphasis on parameters the user wants to change and variables which completely specify the generated events

Measurement of air fluorescence light yield induced by an electromagnetic shower

For most of the Ultra High Energy Cosmic Ray (UHECR) experiments and projects (HiRes, AUGER, TA, JEM-EUSO, TUS,...), the detection technique of Extensive Air Showers (EAS) is based, at least, on the measurement of the air fluorescence induced signal. The knowledge of the Fluorescence Light Yield (FLY) is of paramount importance for the UHECR energy reconstruction. The MACFLY experiment was designed to perform such FLY measurements. In this paper we will present the results of dry air FLY induced by 50 GeV electromagnetic showers as a function of shower age and as a function of the pressure. The experiment was performed at CERN using an SPS electron test beam line. It is shown that the FLY is proportional to deposited energy in air (E_d) and that the ratio FLY/E_d and its pressure dependence remain constant independently of shower age and more generally independently of the excitation source used (single electron track or air shower).For most of the Ultra High Energy Cosmic Ray (UHECR) experiments and projects (HiRes, AUGER, TA, JEM-EUSO, TUS,...), the detection technique of Extensive Air Showers (EAS) is based, at least, on the measurement of the air fluorescence induced signal. The knowledge of the Fluorescence Light Yield (FLY) is of paramount importance for the UHECR energy reconstruction. The MACFLY experiment was designed to perform such FLY measurements. In this paper we will present the results of dry air FLY induced by 50 GeV electromagnetic showers as a function of shower age and as a function of the pressure. The experiment was performed at CERN using an SPS electron test beam line. It is shown that the FLY is proportional to deposited energy in air (E_d) and that the ratio FLY/E_d and its pressure dependence remain constant independently of shower age and more generally independently of the excitation source used (single electron track or air shower)

The FLASHForward Facility at DESY

The FLASHForward project at DESY is a pioneering plasma-wakefield acceleration experiment that aims to produce, in a few centimetres of ionised hydrogen, beams with energy of order GeV that are of quality sufficient to be used in a free-electron laser. The plasma wave will be driven by high-current density electron beams from the FLASH linear accelerator and will explore both external and internal witness-beam injection techniques. The plasma is created by ionising a gas in a gas cell with a multi-TW laser system, which can also be used to provide optical diagnostics of the plasma and electron beams due to the <30 fs synchronisation between the laser and the driving electron beam. The operation parameters of the experiment are discussed, as well as the scientific program.Comment: 19 pages, 9 figure