Compression of large area, high-current ion beams by an electrostatic plasma lens Yu.M. Chekh a , A.M. Dobrovolsky a , A.A. Goncharov a, * , I.M. Protsenko a , I.G. Brown b,1 a Institute of Physics NASU, 46 pr. Nauky, Kiev 03028, Ukraine b Lawrence Berkeley National Laboratory, AFRD, 1 Cyclotron Road, Bldg. 4-230, Berkeley, CA 94720, USA Received 14 May 2005; received in revised form 24 June 2005 Available online 25 August 2005 Abstract We describe the results of experimental investigations of factors restricting the maximum compression of multi-aperture heavy-ion beams focused by a high-current electrostatic plasma lens. We show that, under optimal conditions of the lens operation for which all negative factors are removed or suppressed, the compression of the ion beam is determined only by its initial emittance. Ó 2005 Elsevier B.V. All rights reserved. PACS: 41.75.Ak; 41.85.Lc; 52.75.Rx; 52.90.+z Keywords: Electrostatic plasma lens; Plasma-optics; High-current ion beam; Emittance; Vacuum arc ion source; Ion beam focussing 1. Introduction 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 pos- sible 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 elec- trostatic plasma lens [1–5]. The electrostatic plasma lens is an axially-symmetric plasma-optics system consisting of a set of cylindrical ring electrodes located within an exter- nally-driven magnetic field, with field lines connecting ring electrode pairs symmetrically about the lens midplane. A simplified schematic of a plasma lens is shown in Fig. 1. The basic concept of this kind of lens was first described by Morozov and co-workers [1,2], and is 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. Elec- trons within the lens volume, formed for example by sec- ondary emission following collision of beam ions with lens electrodes, are able to stream freely along the field 0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.07.189 * Corresponding author. Tel./fax: +38 044 525 2329. E-mail addresses: gonchar@iop.kiev.ua (A.A. Goncharov), igbrown@ LBL.gov (I.G. Brown). 1 Tel.: +1 5106441272; fax: +1 5106442854. www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 243 (2006) 227–231 NIM B Beam Interactions with Materials & Atoms