The facility with its new system of guides views the cold source of SINQ
on the opposite side from that feeding the main guide hall. The available
neutron channel has been equipped with a large aperture and large momentum
acceptance beam guide, which starts at the border of the D2O moderator
tank. This guide is coated with 450 layers, Ni/Ti supermirrors
m 3.3). The main neutron beam shutter is
integrated into the SINQ
shielding (Fig. 5). The external part of the beam line
is a compact (total length outside the SINQ shielding of around 7 m), high
efficiency neutron optic system. It consists of a multi-slit supermirror
polarizer and bender, a cold neutron beam stop, a focusing beam guide (tapering
from 8 x 15 cm2 down to 4 x 15 cm2), radio-frequency spin
flippers, a polarization analyzer system with a chopper for time-of-flight
measurements, and two further cold neutron beam dumps placed downstream.
A spin guide field is provided by permanent magnets. The external beam line
has its own independent vacuum system. Its front section, including polarizer
and bender, has been mounted inside the SINQ shielding to contain radiation
associated with the neutron capture reactions. The external part of the guide
is enclosed by a sandwich-type radiation shielding
(brass/polyethylene/iron/lead) against fast neutrons penetrating
the walls as well as secondary gamma rays. The whole facility is contained
in a massive, concrete shield.
The facility has been described in [16,17].
We repeat the most important features here:
The cold neutron flux density of
unpolarized neutrons, measured at the border of
the SINQ shielding is around 109 (cm2 . s . mA)-1; the
``thermal equivalent flux'' would be
3 . 109 (cm2 . s . mA)-1.
The total number of unpolarized neutrons with the characteristic cold spectrum
exceeds 1011 (s . mA)-1. The commissioning data measured at the
location of the experiment show a flux of polarized cold neutrons of
. 108 (cm2 . s . mA)-1.
The characteristic cold neutron spectrum and the wavelength dependence of the
beam polarization was then determined (Fig. 6) using the
time-of-flight technique, a polarization analyzer and a combination of high
efficiency spin flippers .
The total intensity of the polarized
neutron beam exceeds 1010 (s . mA)-1. At present the SINQ source
operates routinely at 1.2 mA proton beam. The average polarization in the
central part of the beam exceeds 97% (Fig. 6).
Detailed investigations of the beam properties, i.e. the flux and polarization distributions and divergence, are in progress. Fig. 7 presents the first results from the measurements of the horizontal beam profiles and the computer representation of the beam intensity for the polarized, compressed beam at the experimental station.