Design of a Tapered Final Focusing Magnet for eRHIC

Presently, the electron-ion collider electron relativistic heavy ion collider (eRHIC) is under design. It aims to provide a facility with a peak luminosity of 10
³⁴
cm
^-2
sec
^-1
. In terms of magnet design, the IR magnets are particularly challenging due to the close proximity of the electron and hadron beams. This paper outlines the design for the so-called Q1 rear side magnet, which is a double aperture quadrupole magnet, 7.2 m from the interaction region. Due to space restrictions, both magnets are housed in the same iron yoke. The aperture of the hadron quadrupole is relatively small, but requires high gradients. While the required gradient for the electron quadrupole is relatively small, the aperture of this magnet needs to accommodate the beam and allow the synchrotron radiation fan to pass through. To accomplish this, both quadrupole magnets have a tapered aperture. To keep the gradients constant along the length of the magnets, a special winding pattern has been identified, which is described in this paper.