Influence Of Source Parameters Research Articles

First operations with caesium of the negative ion source SPIDER

The negative-ion based neutral beam injector for heating and current drive of the ITER plasma (ITER HNB) is under development, at present focusing on the optimization of the full-scale plasma source in the SPIDER test stand. The production of H− or D− ions in the ion source is based on the low work function surfaces obtained by caesium evaporation. This paper describes the caesium conditioning procedure and the corresponding beam performances during the first operation of SPIDER with caesium. Technical solutions to overcome present limitations of the test stand are described. The influence of source parameters on the caesium effectiveness was investigated in short beam pulse operation; with total radio-frequency (RF) power of 400 kW and filling pressure below 0.4 Pa, and a limited number of extraction apertures, a negative ion current density of about 200 A m−2 was extracted in hydrogen, with beam energy lower than 60 keV. Beam optics and beam uniformity were assessed thanks to the acceleration of isolated ion beamlets. A possible procedure to accelerate a uniform beam was demonstrated at low RF power. The results obtained in this first investigation provided key indications on the operation of one of the largest existing sources of accelerated negative hydrogen-like ions.

Influence of Source Parameters and Non-Kolmogorov Turbulence on Evolution Properties of Radial Phased-Locked Partially Coherent Vortex Beam Array

Partially coherent optical vortices have been applicated widely to reduce the influence of atmospheric turbulence, especially for free-space optical (FSO) communication. Furthermore, the beam array is an effective way to increase the power of the light source, and can increase the propagation distance of the FSO communication system. Herein, we innovatively report evolution properties of the radial phased-locked partially coherent vortex (RPLPCV) beam array in non-Kolmogorov turbulence. The analytical expressions for the cross-spectral density and the average intensity of an RPLPCV beam array propagated through non-Kolmogorov turbulence are obtained. The numerical results reveal that the intensity distribution of the RPLPCV array propagated in the non-Kolmogorov turbulence is gradually converted to a standard Gaussian distribution. In addition, the larger the radial radius, radial number and waist radius are, the smaller the coherence length is. Moreover, the longer the wavelength is, the shorter the propagation distance required for the intensity distribution of the RPLPCV beam array to be converted into a Gaussian distribution in the non-Kolmogorov turbulence. The research in this paper provides a theoretical reference for the selection of light sources and the suppression of turbulence effects in wireless optical communication.

Influence of Source Parameters on the Polarization Properties of Beams for Practical Free-Space Quantum Key Distribution.

Polarization encoding has been extensively used in quantum key distribution (QKD) implementations along free-space links. However, the calculation model to characterize channel transmittance and quantum bit error rate (QBER) for free-space QKD has not been systematically studied. As a result, it is often assumed that misalignment error is equal to a fixed value, which is not theoretically rigorous. In this paper, we investigate the depolarization and rotation of the signal beams resulting from spatially-dependent polarization effects of the use of curved optics in an off-axis configuration, where decoherence can be characterized by the Huygens–Fresnel principle and the cross-spectral density matrix (CSDM). The transmittance and misalignment error in a practical free-space QKD can thus be estimated using the method. Furthermore, the numerical simulations clearly show that the polarization effect caused by turbulence can be effectively mitigated when maintaining good beam coherence properties.

Influence of source parameters on the growth of metal nanoparticles by sputter-gas-aggregation

We describe the production of size-selected manganese nanoclusters using a magnetron sputtering/aggregation source. Since nanoparticle production is sensitive to a range of overlapping operating parameters (in particular, the sputtering discharge power, the inert gas flow rates, and the aggregation length), we focus on a detailed map of the influence of each parameter on the average nanocluster size. In this way, it is possible to identify the main contribution of each parameter to the physical processes taking place within the source. The discharge power and argon flow supply the metal vapor, and argon also plays a crucial role in the formation of condensation nuclei via three-body collisions. However, the argon flow and the discharge power have a relatively weak effect on the average nanocluster size in the exiting beam. Here the defining role is played by the source residence time, governed by the helium supply (which raises the pressure and density of the gas column inside the source, resulting in more efficient transport of nanoparticles to the exit) and by the aggregation path length.

Effect of aberration correction on beam wander of electromagnetic multi-Gaussian shell-model beams in anisotropic turbulence

The influences of source parameters, non-Kolmogorov and anisotropic turbulence on the beam spreading and beam wander of electromagnetic Multi-Gaussian Shell-model (EMGSM) beams in the atmosphere with aberration correction were analyzed. Zernike tilt aberration correction method had more effect on beam spreading compared to beam wander. Increasing the anisotropic property of turbulence could degrade both beam spreading and beam wander. EMGSM beams with larger beam order, wavelength could better mitigate the turbulence effects than GSM beams, which could be adopted as a better light source with several adjustable parameters to lower scintillation and beam wander in free-space optical communication.

Far field of beams generated by quasi-homogeneous sources passing through polarization gratings

We analyze the polarization features of the beam, generated by a class of partially polarized quasi-homogeneous sources, which propagates through a polarization grating. Analytical expressions in the far zone for the beam coherence polarization matrix, the degree of polarization and the Stokes parameters are given. In particular, it is shown that, under some hypotheses, it is possible to completely and uniformly depolarize the beam in the far field. The influence of source parameters, such as the state of polarization, intensity and degree of coherence, on the degree of polarization and the Stokes parameters is also investigated.

Source influence parameters on elastic guided waves in an orthotropic plate

An exact analytical solution for a three-dimensional case of the vibration of an infinite orthotropic plate loaded on its upper boundary is considered. The influence of source parameters on the characteristics of wave propagation in an orthotropic elastic infinite plate are analyzed. An asymptotic approximation for evaluating displacement in the far field is developed. Sample numerical calculation results are presented for various source parameters.

Influence of Source Parameters on the Properties of an Ion Beam

Beam profile measurements have been carried out to study the influence of the length of the ion source outlet, the source pressure, and the source magnetic field on the properties of an ion beam. From a variation of the outlet length conditions can be deduced for optimum design with respect to gas efficiency and profile shape. The profile width is found to decrease with increasing source pressure and decreasing magnetic field. This effect is attributed to a corresponding change in the energy distribution of the ions. Profile distortions occurring at high source pressure are likely to be due to ion scattering in the extraction region.