Focusing of high-current, large-area, heavy-ion beams with an electrostatic plasma lens

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 p ulse length 250 mu s. The plasma lens was of internal diameter 10 cm and le ngth 20 cm, and had nine electrostatic ring electrodes with potential appli ed to the central electrode of up to 7 kV, in the presence of a pulsed magn etic field of up to 800 G. The current-density profile of the downstream, f ocused, ion beam was measured with a radially moveable, magnetically suppre ssed, Faraday cup. The tantalum ion-beam current density at the focus was c ompressed by a factor of up to 30. The results are important in that they p rovide a demonstration of a means of manipulating high-current ion beams wi thout associated space-charge blowup. (C) 1999 American Institute of Physic s. [S0003-6951(99)01333-9].