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Polarized Cold Neutron Facility ``FUNSPIN'' at SINQ -

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 $ \approx$  450 layers, Ni/Ti supermirrors (reflection index m  $ \approx$  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:

Figure 5: Layout of the Polarized Cold Neutron Facility at PSI.
\includegraphics [height=9.5cm]{areal12.eps}

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 2 . 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 [18]. 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).

Figure 6: (a) Neutron wavelength spectrum measured using the TOF technique and a thin 3He transmission detector. (b) Wavelength dependence of the beam polarization.
\includegraphics [height=6.5cm]{npolar.eps}

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.

Figure 7: Beam profiles (right) and a representation of the beam intensity obtained by interpolation (left). Note different scales for ``z'' and ``x'' directions, which indicate the distance from the beam exit and the horizontal position across the beam, respectively.
\includegraphics [height=5.5cm]{beam_profx.eps}


next up previous contents
Next: Development of the Detecting Up: Status of the Experiment Previous: Status of the Experiment   Contents
Christian Hilbes
2001-03-02