The joint phase-space transformer up-scattering project

Full text: Neutrons from a moderating system have a certain phase space density corresponding to the moderator temperature. According to the Liouville Theorem, the phase-space density cannot be changed within a conservative system, but by means of advanced cooling methods. Nevertheless it is possible to change the shape and position of the phase-space element using conservative forces. Phase-space transformation has been used successfully in high-end backscattering instruments, such as the HFBS at NIST. Here the phase-space element is rotated in order to obtain more neutrons in the backscattering energy region, but with a higher beam divergence. Based on the original idea of Schelten and Alefeld, a new kind of phase-space transformation has been proposed: it is to change the position of the phase-space element in order to produce a well defined neutron beam by coherent up-scattering of an UCN gas. It has been shown that this principle could yield to gain factors of hundred and more compared to 'classical' beam generation. The Atominstitut and the Paul Scherrer Institut have joined to design and construct a 'proof of principle'-experiment. The aims of this experiment are to exploit the feasibility as well as the experimental limitations and to validate preceding MC-simulations. Its scalability makes it a solid starting point for future instruments. Employing a sophisticated mechanical system, Stage-2 Potassium intercalated HOPG crystals (d = 8.74 AA) will be moved with velocities up to 250 m/s. The experiment is planned to take place at the PF-2 UCN source at the ILL in the second half of 2007. (author)