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The ion sources play an important role in the framework of the nuclear fusion, as a fundamental part of the neutral beam injection systems needed for the auxiliary heating of the plasma magnetically confined in fusion devices. In the case of large experiments, such as ITER and beyond, the use of negative ions was found necessary to increase the neutralization efficiency of high-energy beams, calling for an additional effort in the research on the physical mechanisms regulating their formation and extraction as a beam from the source. This paper summarizes the analyses investigating the physical phenomena occurring in the source and their effect on the optics of the extracted beam. The results, carried out by means of advanced numerical tools, are particularly useful to yield a better evaluation of the real performances of the system, and particularly of the accelerator, whose modeling usually neglect some characteristics of the source. These analyses were performed for the specific case of the SPIDER experiment (Source for Production of Ion of Deuterium Extracted from an RF plasma), representing the major test bed for negative ion source worldwide. The choice of a specific device for the source modeling was found useful to support its operational phase and to help the experimental data interpretation and the identification of dangerous operating conditions. Nonetheless, the validity of the results here presented still holds in more general cases. [ABSTRACT FROM PUBLISHER]

The linear and nonlinear theory of a plasma-filled relativistic Cerenkov generator with coaxial slow-wave structure (SWS) is developed. Linear analysis includes the space-charge limiting current, dispersion relations, dispersion curves, and coupling impedance. In nonlinear theory, the electron beam space-charge effect, nonsynchronous interaction, and complex reflection coefficients of the electromagnetic wave at the boundaries of the SWS are taken into account. With the assumption of quasi steady state, the self-consistent equations are numerically calculated using the fourth-order Runga-Kutta method. The effects of the relative phase between inner and outer corrugations, phase and amplitude of the complex reflection coefficient at the boundaries of the SWS, and plasma density on device efficiency are discussed. Efficiencies of up to 37% without plasma and about 59% with plasma density of np = 3-7 × 1011 cm-3 are obtained. [ABSTRACT FROM AUTHOR]

Periodic structures in plasmas form unique dispersions of electromagnetic waves, which are examined in numerical calculation. Above electron plasma frequency, where waves equivalently propagate in dielectric media, plasma arrays with 2-D periodicity produce frequency regions of forbidden propagation, like band gaps in a photonic crystal. Below electron plasma frequency, where waves are usually forbidden to propagate due to cutoff phenomenon, bulk plasmas with periodic holes can become wave-propagating media in which localized surface modes play an important role. Such features give rise to concepts of dynamic wave controllers that change their inner electron density in time. [ABSTRACT FROM AUTHOR]

Transverse gaps are introduced in thin-wire conductors to extend the region of phase variations of currents that are induced on them by an incident electromagnetic wave. Periodically placed gaps lead to qualitative changes in the properties of reradiated waves, such as the appearance of resonances corresponding to total reflection and total transmission of the incident wave. It is shown that total reflection occurs in a narrow band and depends very weakly on the incident angle of the illuminating radiation. This idea leads to novel filters and switches, whose operation is practically independent of the structure of the incident wave. Total resonant reflection can occur for conductors with high optical transparency, a property that is useful for various microwave diagnostic devices. Because of the increased radiation resistance of such structures, the resonant effects under consideration depend weakly on conductivity. For gratings made using these conductors with gaps stacked above a metal ground plane, it is possible to controllably collimate the rays. Expansion of the scattered fields in terms of Rayleigh's series, together with Poisson's summation formula, are used for numerical simulations of such structures. [ABSTRACT FROM AUTHOR]