Neutron Scattering

nel" coils) the required homogeneity may be achieved . The correction elements positioned
in the neutron beam have to realize radial current distributions around the magnetic axis .
Three radial elements per arm in principle allow for a full correction .
However the making
of such elements that are transparent for neutrons and are able to carry the required high
current densities with the required accuracy is difficult .
Currently the improvement by a
factor of 100, sufficient for operation with the above parameters, is barely achievable .
Figure 11 .7 : Correction element for the field integral homogenization, material : aluminum
.
Fig .
11 .7 shows the shape of the radial correction elements which are used in the Jülich
NSE . The uncorrected inhomogeneity is proportional to the main precession fields and
therefore proportional to the Fourier time t .
In the current setup the residual inhomogeneity
(after correction) sets the limit for the maximum Fourier time .
Figure 11 .8 illustrates
how the echo amplitude decreases due to resolution effects even
with correction elements .
Without correction the amplitude would drop to values below
0 .1 above Fourier times of a few us . The resolution functions as show in figure 11 .8 can
be determined using the scattering from a reference sample which is
known to exhibit
elastic scattering only (> 99.9%), here : microcrystalline MgO . The experimental results
(normalized echo amplitudes) of all samples have to be divided by the normalized echo