MD 2167: Effect of a resonant excitation on the evolution of the beam emittance and halo population

Abstract

Collimation with hollow electron beams or lenses (HEL) is currently one of the most promising concepts for active halo control in HL-LHC. In previous studies it has been shown that the halo can be efficiently removed with a hollow electron lens. Equally important as an efficient removal of the halo, is to demonstrate that the core stays unperturbed. In the case of an ideal hollow electron lens without bends, the field at the location of the beam core vanishes and the core remains unperturbed. In reality, the field at the beam core does not vanish entirely due to imperfections in the electron beam profile and the electron lens bends necessary to guide the electron in and out of the proton aperture. In particular, in the case of a pulsed operation of the electron lens the non-vanishing residual field induces noise on the proton beam. To identify the most sensitive pulsing patterns for the resonant mode and derive tolerances on the profile imperfections, a first MD was carried out of which the first results are presented in this note.

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.…”

“…Following the conceptual design of hollow electron lenses for beam halo control in the LHC, the preliminary mechanical design and simulation study of hollow electron beam collimation in the HL-LHC has been finished. Meanwhile, the effect of the pulsed hollow beam on the proton beam core (emittance), the halo population, and the halo removal rate in the LHC were simulated in detail [24,25]. In the above study, in order to obtain a higher halo removal rate, two different pulsing patterns instead of the dc mode are considered: a random mode and a resonant mode.…”

Analysis of BSRT Profiles in the LHC at Injection

“…8, which shows the difference between the right and left bin: with the bins indexed between [− n bins 2 , n bins 2 ]. This asymmetry is present in all profiles taken during MD1217 [2] and MD1415 [3]. The asymmetry can be either explained by and a constant closed orbit offset of the beam.…”

“…https://github.com/mfittere/pytimbertools Documentation is done in this note and in the docstrings. The analysis was developed based on the profiles taken at injection with E beam = 450 GeV in MD1217 [2] and MD1415 [3]. For simplicity but without loss of generality, we will only show plots for the reference bunches during these two MDs, meaning bunches without excitation.…”

“…Table I. Beam parameters for references bunches during MD1217 [2] and MD1415 [3]. A different analysis approach might have to be taken at top energy with E beam = 6.5 TeV or 7.0 TeV as the profiles then are limited mainly by diffraction.…”