Electron Lenses for Particle Collimation in Lhc

Electron Lenses built and installed in Tevatron have proven themselves as safe and very reliable instruments which can be effectively used in hadron collider operation for a number of applications, including compensation of beam-beam effects [1], DC beam removal from abort gaps [2], as a diagnostic tool. In this presentation we – following original proposal [3] – consider in more detail a possibility of using electron lenses with hollow electron beam for ion and proton collimation in LHC. Figure 1: (top – bottom) current distribution in the e-lens for collimation; electric field and diffusion speed; cartoon of the particle distribution during halo removal by hollow beam e-lens. HOLLOW ELECTRON BEAM FOR LHC COLLIMATION As depicted in Fig.1, an ideal round hollow electron beam has no electric or magnetic field inside and strongly nonlinear fields outside. The non-linear field components significantly enhance transverse diffusion of high-energy particles in a storage ring with betatron amplitudes larger than e-beam size, as experimentally demonstrated in the beam studies with Tevatron Electron Lenses (see Fig.6 in Ref.[4]). The speed of diffusion of the large amplitude particles can be greatly enhanced if the electron current varies in sync with betatron oscillations or at the nearest non-linear resonance line. The hollow e-beam can serve as primary collimator or as an enchancer – a device for faster delivery of halo particles to secondary collimators which can be then placed further from the primary one and the beam itself – see cartoon in Fig.1. Hollow eLens also offers a viable solution for a primary collimator of the LHC ion beam, because such an electromagnetic collimator does not break an ion into fragments (as any primary collimator made of usual material would do). In that case, the hollow e-beam systems would have to be installed to replace the current primary LHC collimators. Figure 2: (a) hollow electron beam [5]; (b) cylindrical electron gun tested in [6]. Hollow electron beams are widely used in electron cooling devices [5,6] and corresponding electron guns have been developed and extensively tested – see Fig. 2. Figure 3: Electron lens configuration for collimation