Space charge compensation of low energy ion beam

Abstract

Simplified beam line for low energy Ion implantation is considered. Compensation of the space charge of high perveance, low energy ion beam in beam lines for ion implantation and isotope separation has been investigated. Different mechanisms of the compensating particle formation such as ionization by the beam, secondary emission of electrons and negative ions, electronegative gas admixture, and external plasma sources are discussed. Advanced space charge compensation increases an intensity of low energy ion beam after analyzer magnet up to 3-4 times. Space charge compensation of positive ion beam by admixture of electronegative gases and damping of the beam instability are discussed. Up to 6 mA of 11 B + ions with energy 3 keV, 11 mA with 5 keV, and 18 mA with 10 keV have been transported through an analyzer magnet of a high current implanter with space charge compensation by electronegative gases

Electrostatic energy analyzer measurements of low energy zirconium beam parameters in a plasma sputter-type negative ion source

“…Lower beam mean energies translate to blown up energy spreads and thus less focused beam caused by space charge forces. 23,24 The transverse ion current measurements using the semi-cylindrical FC are represented by the solid line shown in Figure 4 at -450V target potential. The beam widths were determined using Eq.…”

“…21 The relative decrease in current as the flow rate is increased is due to the space charge compensation within the path of the ion beam. 22,23 The ESA plot using the semi-cylindrical FC is shown in Figure 3(b) under the same experimental parameters except discharge voltage at 30 V to maintain the discharge current at 1 A. There is a reduction in the current reading to about an order of magnitude due to the lower discharge voltage and selective capability of the FC allowing only particles along the beam axis to pass.…”

Low energy beam transport system developments

“…Some designs of shortened MLEBT were proposed in [29], including one solenoid MLEBT, movable for Twiss parameter optimization. This problem is not of high priority for high energy positive ions but is more important for low energy positive [28] and negative ion beams.…”

“…However, for low energy positive ions for low emittance preservation, very high gas density is needed, which causes more significant beam attenuation because the ionization cross sections become very low [28] but electron capture cross sections are high. In this situation for more efficient compensating particle generation it is better to use secondary emission of electrons and negative ions or active plasma generation by a plasma gun or by electron beams [28].…”

“…Using the advanced test stand and the PIC code WARP it is possible to produce a better understanding of complex SCC processes and improve MLEBT performance. Active generation of compensating plasma can be useful to produce the highest beam performance [28]. Another possibility for a predictable LEBT is an electrostatic LEBT (ELEBT).…”