Speaker
Description
For the Electron Ion Collider (EIC) at BNL, the interaction region (IR) magnet closest to the EIC experiment on the forward (outgoing hadron and incoming electron) side, denoted B0PF-Q0EF, must satisfy many conflicting machine detector interface (MDI) requirements. First it must provide sufficient transverse field in a large warm bore to provide spectrometer functionality for outgoing particles that would otherwise be missed in a forward angular region between the inner edge of the detector acceptance and the maximum acceptance in combined angle and momentum offset that can pass the rest of the forward hadron magnets to reach Roman Pots and the Zero Degree Calorimeter. For this function the experiment places several planes of silicon tracking and a compact calorimeter immediately surrounding a warm beam pipe though which the hadron beam circulates. However, even with a crossing angle of 25 mrad the electron beam must also pass through this warm B0PF-Q0EF main aperture, and the incoming electron beam would generate unacceptable levels of synchrotron radiation in the detector if it experienced this same, 1.56 T·m, integrated field. For this reason, the hadron spectrometer field is deliberately made combined function such that the combined dipole and local quadrupole field components cancel at the electron beam axis and the electron beam only sees a linear defocusing field with very close to zero net dipole component. This combined function field is achieved by powering large concentric quadrupole and dipole superconducting coils in series inside a magnetic yoke and we use an additional small aperture dipole superconducting corrector coil, just around the electron beam aperture, to null out any residual dipole field. Unlike the other dipoles in the hadron ring this B0PF magnet is run at the same field independent of the hadron beam energy with later IR dipoles adjusted to close the orbit bump initiated by B0PF. Note the residual B0PF defocusing field at the electron beam axis is very close in strength to what is required for the first electron quadrupole element, Q0EF, at the 10 GeV e-beam operating point. In order to provide correct operating gradients at the other e-beam energies of 18 and 5 GeV, we also provide a small aperture electron gradient tuning coil to add or subtract gradient as needed for the electron IR optics. Both the large hadron and smaller electron superconducting coils will be fabricated using the BNL Direct Wind technique. Since the main hadron B0PF coils have quite large combined inductance, special care is required for their quench protection. Also, with the B0PF-Q0EF nested warm and cold structures and very limited longitudinal allocated space, the cryostat design necessitates careful optimization. These and other B0PF-Q0EF design challenges are addressed in this paper.
Work supported by Brookhaven Science Associates, LLC under Contract No. DE-SC0012704 with the US Department of Energy.
*Presently based at MIT Bates Research & Engineering Center, Middleton, MA 01949, U.S.A.
