Advanced control and manipulation of neutron beam intensity and polarisation in precsion neutron experiments

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Controlling the incident neutron spectrum is essential for almost every neutron experiment. We propose the development of a neutron optical component which allows not only to control the neutron spectrum but to produce polarised neutron pulses of nearly arbitrary time structure. The concept is based on the Drabkin neutron resonator combined with travelling magnetic fields. This device should allow an almost instantaneous variation of key instrumental parameters by electronic means only. This development is motivated by the upcoming PERC project which requires time definition and spectral control of the incident polarised neutron beam. The experimental test of polarisation preserving neutron guides, which define the neutron decay volume in the PERC instrument, is essential for its ultimate performance. The neutron resonator will enable to define the time structure of the pulsed PERC beam with regard to optimum relation of data taking and background periods which is particularly essential in high precision experiments. Assessment and minimisation of background events is an important aspect of this work. We plan the development of advanced shielding concepts by Monte Carlo simulations and experimental tests with general impact in neutron instrumentation. Another key component of the PERC instrument is the magnetic field which guides the charged neutron particles towards the detector, and the instrument performance will rely on its optimised design. Experiments will utilise the Triga Reactor in Vienna in continuous and pulsed mode.