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

Abstract

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.

High-Current Heavy Ion Beams in the Electrostatic Plasma Lens

“…For the case of tantalum beam with diameter 10 cm, the maximum beam compression at the lens focus was approximately a factor of 30, with current density up to 32 mA/cm 2 . Similar results were obtained for a copper ion beam on the Kiev set-up, where the compression was a factor 15 -25 depending on the total ion beam current passing through the lens and the current density was up to 170 mA/cm 2 (see [6][7][8] for details).…”

“…The experiments were carried out at Kiev using the set-up described in detail in [6] and at Berkeley described in [7,8]. For ion beam formation we use a two-chamber MEVVA ion source with grid anode and a three-electrode, multi-aperture, accel-decel ion extraction system.…”

“…Moderate energy, large area, high current, heavy ion beams can be focused in this way, as has been well demonstrated in a number of experiments carried out at Kiev and at Berkeley in recent years [7][8]. The lens used in these experiments employed a magnetic field that was established by conventional current-driven electromagnetic coils.…”

Effect of the electrostatic plasma lens on the emittance of a high-current heavy ion beam

“…Thus there is a need for new high current ion beam manipulation devices that preserve space-charge neutralization, thereby providing a tool that can allow the high current beams to be presented to accelerator LEBTs and transported through them without severe beam loss. One such device is the electrostatic plasma lens [1][2][3][4][5]. The electrostatic plasma lens is an axially-symmetric plasmaoptics system consisting of a set of cylindrical ring electrodes located within an externally-driven magnetic field, with field lines connecting ring electrode pairs symmetrically about the lens midplane.…”

“…Electrons within the lens volume, formed for example by secondary emission following collision of beam ions with lens electrodes, are able to stream freely along the field lines, thereby tying the potential to that of the electrostatic ring electrode to which the field line is attached. Electrostatic plasma lenses have been investigated for half a century; the status of experimental investigation has been summarized in references [1][2][3][4][5].…”