We report on measurements of the focusing of high-current, large-area beams of heavy metal ions using an electrostatic plasma lens. Tantalum ion beams were formed by a repetitively pulsed vacuum arc ion source, with energy in the 100 keV range, current up to 0.5 A, initial beam diameter 10 cm, and pulse length 250 μs. The plasma lens was of internal diameter 10 cm and length 20 cm, and had nine electrostatic ring electrodes with potential applied to the central electrode of up to 7 kV, in the presence of a pulsed magnetic field of up to 800 G. The current-density profile of the downstream, focused, ion beam was measured with a radially moveable, magnetically suppressed, Faraday cup. The tantalum ion-beam current density at the focus was compressed by a factor of up to 30. The results are important in that they provide a demonstration of a means of manipulating high-current ion beams without associated space-charge blowup.
Articles you may be interested inDevelopment of an all-permanent-magnet microwave ion source equipped with multicusp magnetic fields for high current proton beam productiona) Rev. Sci. Instrum. 79, 02B317 (2008); Development of a high-current plasma lens for focusing broad beams of heavy metal ions Rev.Characteristics of focused beam spots using negative ion beams from a compact surface plasma source and merits for new applications
The static and dynamic characteristics of a high-current plasma lens (PL) with the two-component quasineutral plasma medium formed by a wide-aperture pulse periodical ion beam and secondary ion–electron emission, with the features of focusing and control of a well-formed low-divergent multiaperture ion beam by this lens are investigated experimentally in a wide energy range. It is shown that a careful selection of magnetic field geometry, the fixing electrode number, and the external potential distribution on them, according to theoretical plasmaoptics principles, allow a radial electrical profile in a volume of PL to be modified in a given way. This enables the reduction of the spherical aberration of the beam which is being focused. Experimentally and theoretically it is shown that the controlled introduction of spherical aberrations makes it possible to control a radial beam profile on a target and, in particular, to make it homogeneous. The results of low-energy metal ion beams focused and controlled by PL are obtained. Lens collective processes caused by a principally unremovable magnetic field radial gradient in the ion beam focusing direction are investigated and it is shown that lens electron leakages are connected with these turbulent noises.
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