Compensation of head-on beam-beam induced resonance driving terms and tune spread in the Relativistic Heavy Ion Collider

Abstract

A head-on beam-beam compensation scheme was implemented for operation in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory [Phys. Rev. Lett. 115, 264801 (2015)]. The compensation consists of electron lenses for the reduction of the beam-beam induced tune spread, and a lattice for the minimization of beam-beam generated resonance driving terms. We describe the implementations of the lattice and electron lenses, and report on measurements of lattice properties and the effect of the electron lenses on the hadron beam.

Electron lenses for head-on beam-beam compensation in RHIC

“…All the above electron beam characteristics as well as the e-lens lattice [18] ensure the success of the RHIC e-lenses for partial head-on beam-beam compensation leading to higher luminosities.…”

“…To satisfy a 1.0 A dc electron beam current requirement, an emission current density on the cathode surface of 10 A=cm 2 is needed [18]. The choice for this electron source is a hightemperature thermionic cathode electron gun.…”

“…For head-on beam-beam compensation with 250 GeV proton beams, IrCe (iridium-cerium alloy) is selected as the 4.1 mm radius cathode material [18]. IrCe offers a comfortable combination of a high-emission current density and a long lifetime.…”

“…A strong magnetic field in the interaction region is needed to stabilize the low-energy electron beam during the interaction with the proton beam [10]. The up to 6 T strong field is also used to magnetically compress the electron beam to the proton beam size [18]. Figure 8 shows the cross section of the superconducting magnet, which includes the main coil, trim coil, fringe coil, antifringe coil, and a total of 12 dipole correctors.…”

“…The lattice design and measurement, the head-on beambeam-induced resonance-driving terms, and tune spread compensation will be presented in another paper [18]. In this paper, the design considerations of the RHIC e-lenses needed to satisfy these requirements are presented as well as e-lens commissioning results.…”