Beam optics and target conceptual designs for the NuMI project

Study of muon neutrino disappearance using the Fermilab Main Injector neutrino beam

“…The particles produced in the target are focused by two magnetic horns [17], shown schematically in Fig. 2.…”

“…Measurements of the horns show the expected 1=r falloff in the magnetic field to within a percent and the field at distances from the beam axis smaller than the inner conductors is observed to be less than 20 G. The absolute value of the current flowing through the horns was calibrated to within 0:5% and was observed to vary less than 0.2% over the course of the data collection period. The horns have parabolicshaped inner conductors [17], for which the focal length for point-to-parallel focusing of particles from the target is proportional to momentum [18,19]. The alignment of the target and horn system relative to the beam axis was checked using the proton beam itself [20].…”

Observation of Disappearance of Muon Neutrinos in the NuMI Beam

“…On the other hand it is relatively wide compared to the proton beams' transverse size. The size of the proton beam can not be arbitrarily small since that could damage the target [35].…”

“…Following the target are two magnetic horns [35] which are used to focus the positive particles down the decay volume (Figure 2.3). The horns bend π + and K + forward, in the direction of MINOS detectors, while bending away (defocusing) π − and K − .…”

Beam-based alignment of the NuMI target station components at FNAL

“…In such a technique, the charge ejected from the target when struck by the proton beam can be read by charge-sensitive electronics, the charge ejected being proportional to the fraction of the proton beam striking the target. Such a technique can provide a measurement of the target's position relative to the proton beam position, as was demonstrated in a beam test of a prototype target [14].…”