  A neutrino horn based on a solenoid lens offers several potential advantages
over a conventionl toroidal horn when used with a multimegawatt proton source
to pursue studies of CP violation in neutrino oscillations. 1) A solenoid horn
can produce a neutrino spectrum with a sequence of peaks at momenta P = P_0 /
(2 n + 1), which has the same form as the sequence of momenta at which the
neutrino oscillation probability is maximal for a fixed distance from source to
detector. 2) The neutrino flux is a roughly equal mixture of neutrinos and
antineutrinos. 3) Rates of electron neutrinos from muon decay are suppressed
relative to those in a broad-band neutrino beam. 4) A solenoid magnet has its
coils far from the axis where the target is located, and hence the coils are
more readily protected from radiation damage. 5) A solenoid magnet is readily
compatible with a liquid metal target, as will be needed for use with very
intense proton sources. 6) A solenoid magnet is a DC device, and hence not
subject to pulse fatigue as for a conventional toroidal horn.
