Description

The electrostatic plasma lens is an axially-symmetric plasmaoptical 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. The basic concept of this kind of lens was first described by A.I. Morozov and coworkers, and was based on the use of magnetically insulated cold electrons to provide space-charge neutralization of the focused ion beam and maintain the magnetic field lines at equipotentials. Electrons within the lens volume, generated for example by secondary emission due to the bombardment of lens electrodes by beam ions, 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.

1 - permanent magnets,

2 - cylindrical electrodes,

3 - equipotentials,

4 - magnetic field lines.

Compression efficiency: Plasma Lenses provide increasing the ion beam current density up to 20-40 times, depending on the initial ion beam emittance

Stability: Plasma Lenses practically do not increase the ion beam noise modulation

Emittance effect: Plasma Lenses practically do not increase the value of the focused ion beam emittance

Current application status

The permanent magnet plasma lenses were successfully tested in a high doze ion implanter at Lawrence Berkley National Laboratory (USA) to decrease the time of exposure.

Prospects

There is a need in modern accelerator technology for new approaches to injecting high current ion beams into the low energy beam lines of particle accelerators. Even though ion source technologies have developed greatly in recent years, and heavy ion beams can be formed relatively straightforwardly with current much greater than was possible just a decade or two ago, there is a problem in the accelerator application of the new high current ion sources in that low energy (<100 keV), high current (~10-1000 mA) ion beams, frequently of high mass ion species (e.g., titanium, uranium), are subject to severe space-charge blowup when not fully space-charge compensated. There is a substantial beam loss whenever the beam is passed through any of the traditional beam focusing or steering devices because of the loss of space-charge neutralization of the beam within these optical elements. Thus new high-current ion beam manipulation devices are needed that preserve space-charge neutralization, providing a tool that can allow the high current beams to be presented to accelerator injector beam lines and transported through them without severe beam loss. One such device is the electrostatic plasma lens.