Experimental and Numerical Studies on the Proposed Application of Hollow Electron Beam Collimation for the LHC at CERN

Abstract

This thesis work was carried out in the framework of the U.S. LHC Accelerator Research Program (US-LARP), a collaboration between the European Organization for Nuclear Research (CERN) and the U.S. Department of Energy. The first half of the work was completed at Fermilab (USA), the location of the Tevatron, a proton-antiproton collider and the second largest particle collider in the world. The second half was completed at CERN (Switzerland), the location of the largest proton collider in the world (Large Hadron Collider (LHC)).This thesis characterizes a Hollow Electron Beam (HEB) for possible usage at the LHC to enhance its collimation through Hollow Electron Beam Lenses (HEBLs). Collimation is a long established principle in high energy particle accelerators. Hollow Electron Beam Collimation (HEBC) aims to enhance current collimation systems by controlling diffusion of primary halo particles into the limiting aperture. It works on the principle of a transverse radial electric field that kicks the primary halo particles outwards upon each pass in a multi-pass system. The transverse field is produced by a HEB that is coaxially aligned with the accelerator beam, producing a negligible electric field in the center and a strong transverse electric field at amplitudes higher than the inner radius of the electron beam. Ideally, halo particles are affected without perturbation of the beam core. One of the main advantages of this system is to decrease the dependence on instantaneous loss spikes and beam jitter. A solid experimental basis of HEBC was accumulated at the Tevatron. The application of this technique at the LHC is now under investigation.The aim of this thesis is to present a preliminary report to support a future optimal conceptual design report. It characterizes the available hardware in order to facilitate the design of a Hollow Electron Gun (HEG) for the LHC, characterizes the effect on beam diffusion by determining the transverse electric fields of the electron beam and initiates 3D simulations in order to determine the effect of the HEBL on the beam core.

Halo removal experiments with hollow electron lens in the BNL Relativistic Heavy Ion Collider

“…During these experiments, the same electron-lens current was seen by the antiprotons at each turn (the so-called "dc mode" of operation). More studies have followed, such as the calculation of the transverse kicks from the hollow electron-lens bends [20], the beam diocotron instability control [21], and the hollow electron gun characterization [22], as well as experimental and numerical studies for a hollow electron-lens system [23][24][25][26][27][28]. The above studies, as well as the existing electron-lens experience from Tevatron and RHIC [29][30][31][32][33][34], provide information for the design of a hollow electron-lens system that meets the halo removal requirements for the HL-LHC, as well as the future applications of beam collimation in the FCC-hh [35] at CERN or Super Proton-Proton Collider (SPPC) [36] in China.…”

Electron lenses: historical overview and outlook

“…Such richness and flexibility of the electron lenses have attracted researchers, leading to many inventive proposals, studies and theses, such as, e.g., [7][8][9][10][11][12][13][14][15]. The use of focusing space-charge forces of magnetically confined electron cloud in beam transport lines was first proposed by D.Gabor in 1947 [16] -see Fig.…”

“…Electron lenses in pulsed operation, enabled by the availability of high voltage modulators with fast rise times, can be synchronized with individual proton bunches or subsets of bunches and provide highly selective effects for each subset; electron beam stability: in a typical electron lens configuration, electrons are produced at the cathode of an electron gun and right after passing the interaction area get damped in a collector; thus, fresh electrons interact with the high-energy particles on each turn, leaving no possibility for coherent instabilities, similar to those that are driven by the electron clouds or other insufficiently controlled charge formations. Such richness and flexibility of the electron lenses have attracted researchers, leading to many inventive proposals, studies and theses, such as, e.g., [7][8][9][10][11][12][13][14][15]. The use of focusing space-charge forces of magnetically confined electron cloud in beam transport lines was first proposed by Gabor in 1947 [16] -see figure 3a.…”