The first measurement of plasma density in an ECRIS-like device by means of a frequency-sweep microwave interferometer

The note presents the first plasma density measurements collected by a novel microwave interferometer in a compact Electron Cyclotron Resonance Ion Sources (ECRIS). The developed K-band (18.5 ÷ 26.5 GHz) microwave interferometry, based on the Frequency-Modulated Continuous-Wave method, has been able to discriminate the plasma signal from the spurious components due to the reflections at the plasma chamber walls, when working in the extreme unfavorable condition λp≃ Lp≃ Lc(λp, Lp, and Lcbeing the probing signal wavelength, the plasma dimension and the plasma chamber length, respectively). The note describes the experimental procedure when probing a high density plasma (ne> 1 · 1018cm-3) produced by an ECRIS prototype operating at 3.75 GHz

Electron cyclotron resonance ion source plasma characterization by energy dispersive x-ray imaging

Pinhole and CCD based quasi-optical x-ray imaging technique was applied to investigate the plasma of an electron cyclotron resonance ion source (ECRIS). Spectrally integrated and energy resolved images were taken from an axial perspective. The comparison of integrated images taken of argon plasma highlights the structural changes affected by some ECRIS setting parameters, like strength of the axial magnetic confinement, RF frequency and microwave power. Photon counting analysis gives precise intensity distribution of the x-ray emitted by the argon plasma and by the plasma chamber walls. This advanced technique points out that the spatial positions of the electron losses are strongly determined by the kinetic energy of the electrons themselves to be lost and also shows evidences how strongly the plasma distribution is affected by slight changes in the RF frequency. © 2017 IOP Publishing Ltd

Information theory in the study of anisotropic radiation

Information theory is used to perform a thermodynamic study of non equilibrium anisotropic radiation. We limit our analysis to a second-order truncation of the moments, obtaining a distribution function which leads to a natural closure of the hierarchy of radiative transfer equations in the so-called variable Eddington factor scheme. Some Eddington factors appearing in the literature can be recovered as particular cases of our two-parameter Eddington factor. We focus our attention in the study of the thermodynamic properties of such systems and relate it to recent nonequilibrium thermodynamic theories. Finally we comment the possibility of introducing a nonequilibrium chemical potential for photons.Comment: 1 eps figure upon request by e-mail, to appear in Journal of Physics

Prompt electrons driving ion acceleration and formation of a two temperatures plasma in nanosecond laser-ablation domain

We present the results of an experiment on plasma generation via laser ablation at 10^12 W/cm^2 of power intensity and in a nanosecond domain. Prompt electrons emission and complex plasma plume fragmentation were simultaneously observed for the first time in this laser intensity regime, along with a double electron temperature inside the plasma bulk surviving for a long time to the plume expansion. 1D PIC simulations are in agreement with experimental data as long as the emission of initial prompt electrons is considered. This assumption results to be the key to explain all the other experimental evidences.Comment: 5 pages, 6 figures, Europhysics Letters in pres

Hemispheric functional segregation facilitates target detection during sustained visuospatial attention

Visuospatial attention is strongly lateralized, with the right hemisphere commonly exhibiting stronger activation and connectivity patterns than the left hemisphere during attentive processes. However, whether such asymmetry influences inter-hemispheric information transfer and behavioral performance is not known. Here we used a region of interest (ROI) and network-based approach to determine steady-state fMRI functional connectivity (FC) in the whole cerebral cortex during a leftward/rightward covert visuospatial attention task. We found that the global FC topology between either ROIs or networks was independent on the attended side. The side of attention significantly modulated FC strength between brain networks, with leftward attention primarily involving the connections of the right visual network with dorsal and ventral attention networks in both the left and right hemisphere. High hemispheric functional segregation significantly correlated with faster target detection response times (i.e., better performance). Our findings suggest that the dominance of the right hemisphere in visuospatial attention is associated with an hemispheric functional segregation that is beneficial for behavioral performance

Copropagating schemes for dielectric laser accelerators

f of principle electrons laser acceleration experiments, car- ried out by several groups, have demonstrated accelerating gradients larger than 200 MeV/m. However, the adopted configurations (free space coupled gratings, dual pillar, phase reset devices) cannot be easily scaled in length, because they require a transversely incident laser light, impinging laterally along the whole in- teraction dielectric structure. In this paper, extended interaction structures with collinear propagation of the accelerating electromagnetic field and the particles to be accelerated are described: both 2D and 3D photonic-crystals-based structures and slot hollow-core waveguides are compared in terms of accelerating gradient and characteristic interaction impedance, a fundamental quality parameter for Dielectric Laser Accelerators (DLAs)