Multiresolution analysis of the two-dimensional free decaying turbulence in a pure electron plasma

The two-dimensional (2D) freely decaying turbulence is investigated experimentally in an electron plasma confined in a Malmberg\u2013Penning trap and studied using a wavelet-based multiresolution analysis. The coherent and incoherent parts of the flow are extracted using a recursive denoising algorithm with an adaptive self-consistent threshold. Only a small number of wavelet coefficients (but corresponding to the greatest part of the enstrophy or energy contents) turns out to be necessary to represent the coherent component. The remaining small amplitude coefficients represent the incoherent component, which is characterized by a near Gaussian vorticity PDF. Scale contributions to the measured enstrophy and energy distributions are inferred, and the results are compared with recent experiments and theoretical pictures of the 2D turbulence. The results suggest that the computational complexity of 2D turbulent flows may be reduced in simulations by considering only coherent structures interacting with a statistically modeled background

Excitation of the l=3 diocotron mode in a pure electron plasma by means of a rotating electric field

The l=3 diocotron mode in an electron plasma confined in a Malmberg–Penning trap has been resonantly excited by means of a rotating electric field applied on an azimuthally four-sectored electrode. The experimental observations are interpreted with a theory based on the linearization of the drift-Poisson equations and by means of two-dimensional particle-in-cell simulations. The experimental technique presented in this paper is able to selectively excite different diocotron perturbations and can be efficiently used for electron or positron plasma control and manipulation

Applications of the Schwinger Multichannel method with pseudopotentials to electron scattering from polyatomic molecules II: rotational excitation cross sections

This paper reports results for rotational excitation of H2O and H2S molecules by electron impact. It is also a databasis including tables of previously published rotationally resolved cross sections for CH4, SiH4, GeH4, SnH4, PbH4, NH3, PH3, AsH3, SbH3, CF4, CCl4, SiCl4 SiBr4, and SiI4. Our scattering amplitudes were calculated using the Schwinger multichannel method with norm-conserving pseudopotentials and the rotational resolved cross sections were obtained with the help of the adiabatic nuclei rotation approximation. Our results are in good agreement with other theoretical data and experimental results when available.2129Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Excitation of the l=2 diocotron mode with a resistive load

The resistive wall instability of the l=2 diocotron mode in a pure electron plasma has been investigated with a systematic variation of the parameters of the external impedance connected to a pair of sectored electrodes. The measured growth rate is well described by a linear perturbation theory of the two-dimensional drift-Poisson system

Experimental and theoretical elastic cross sections for electron collisions with the C₃H₆ isomers

In the present work we report cross sections for electron collisions with the isomers propene (C₃H₆) and cyclopropane (c-C₃H₆). Electron-scattering differential cross sections (DCS) are reported for measurements carried out for energies 1.5-100 eV and the angular range of 20 degrees-120 degrees. Elastic integral cross sections (ECS), DCS, and momentum-transfer cross sections (MTCS) are reported for calculations carried out using the Schwinger multichannel method with pseudopotentials for the energy range of 2.0-40 eV and angular range of 0 degrees-180 degrees. The resemblance of the pi* shape resonance in the cross sections, observed at 1.5-2.0 eV for propene, to those in C₂F₄ and C₂F₄ clearly points to the effect of the double bond in the molecular structures for these molecules. Below 60 eV, we observed clear differences in peak positions and magnitudes between the DCS, ECS, and MTCS for C₃H₆ and c-C₃H₆, which we view as the isomer effect.This work was supported in part by a Grant-in-Aid from the Ministry of Education, Science, Technology, Sport, and Culture, Japan; the Japan Society for the Promotion of Science JSPS; and the Japan Atomic Energy Research Institute JAERI. One of the authors C.M. is also grateful to the JSPS for financial support under Grant No. P04064

Experimental and theoretical electron-scattering cross- section data for dichloromethane

We report on a combination of experimental and theoretical investigations into the elastic differential cross sections (DCSs) and integral cross sections for electron interactions with dichloromethane, CH₂Cl₂, in the incident electron energy over the 7.0-30 eV range. Elastic electron-scattering cross-section calculations have been performed within the framework of the Schwinger multichannel method implemented with pseudopotentials (SMCPP), and the independent-atom model with screening-corrected additivity rule including interference-effects correction (IAM-SCAR+I). The present elastic DCSs have been found to agree reasonably well with the results of IAM-SCAR+I calculations above 20 eV and also with the SMC calculations below 30 eV. Although some discrepancies were found for 7 eV, the agreement between the two theoretical methodologies is remarkable as the electron-impact energy increases. Calculated elastic DCSs are also reported up to 10000 eV for scattering angles from 0⁰ to 180⁰ together with total cross section within the IAM-SCAR+I framework

Electrostatic diagnostics of nanosecond pulsed electron beams in a Malmberg\u2013Penning trap

A fast electrostatic diagnostic and analysis scheme on nanosecond pulsed beams in the keV energy range has been developed in the Malmberg\u2013Penning trap ELTRAP. Low-noise electronics has been used for the detection of small induced current signals on the trap electrodes. A discrete wavelet-based procedure has been implemented for data postprocessing. The development of an effective electrostatic diagnostics together with proper data analysis techniques is of general interest in view of deducing the beam properties through comparison of the postprocessed data with the theoretically computed signal shape, which contains beam radius, length, and average density as fit parameters

Time-resolved diffuse optical tomography for non-invasive flap viability assessment: Pre-clinical tests on rats

We present a new setup for time-resolved diffuse optical tomography based on multiple source-detector acquisitions analysed by means of the Mellin-Laplace transform. The proposed setup has been used to perform pre-clinical measurements on rats in order to show its suitability for non-invasive assessment of flap viability

BNCT dosimetry: peculiarities and methods

Dosimetry in tissue exposed to the epithermal neutron beams utilized for BNCT is complex, due to the multiplicity of the possible neutron reactions and consequently of the secondary radiation that contains photons, charged particles and recoil nuclei. Owing to the different radiobiological effectiveness of the various components of the absorbed dose, it is necessary to attain the evaluation of each of them. In addition, the spatial distributions of these dose components changes considerably with size and shape of the irradiated volume. Therefore, BNCT dosimetry requires suitably developed calculations and experimental methods. In this work, Monte Carlo simulations in phantoms of different sizes and shapes have been developed. Experimental methods for separating the dose components, mainly based on gel dosimeters and thermoluminescence detectors, have been applied. Moreover, the change in the absorbed dose resulting from the addition of 157Gd was investigated. Both measurements and calculations have been done with the BNCT epithermal beam of the LVR-15 reactor