  A discovery of a permanent electric dipole moment (EDM) of the neutron would
provide one of the most important low energy tests of the discrete symmetries
beyond the Standard Model of particle physics. A new search of neutron EDM, to
be conducted at the spallation neutron source (SNS) at ORNL, is designed to
improve the present experimental limit of ~10^-26 e-cm by two orders of
magnitude. The experiment is based on the magnetic-resonance technique in which
polarized neutrons precess at the Larmor frequency when placed in a static
magnetic field; a non-zero EDM would be evident as a difference in precession
frequency when a strong external electric field is applied parallel vs.
anti-parallel to the magnetic field. In addition to its role as neutron
spin-analyzer via the spin-dependent n+3He nuclear capture reaction, polarized
helium-3 (which has negligible EDM) will serve as co-magnetometer to correct
for drifts in the magnetic field. In one of the two methods that will be built
into the apparatus, the helium-3 precession signal is read out by SQUID-based
gradiometers. We present a design study of a SQUID system suitable for the
neutron EDM apparatus, and discuss using very long leads between the pickup
loop and the SQUID.
