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We ask for R'EQUIP support to acquire a mobile Raman spectrometer, at a price of about CHF 182’000,-- , allowing to accurately determine and monitor the para-deuterium content of the deuterium (D2) which we use for the production of ultracold neutrons at the Paul Scherrer Institute (PSI). We have successfully tested such an instrument. Maintaining a minimal para-D2 content in the UCN production moderator is of paramount importance in order to achieve high ultracold neutron (UCN) intensities. Any improvement in UCN intensity will directly contribute to a higher sensitivity of experiments performed at the source, e.g. the search for the neutron electric dipole moment (nEDM). Also, any improvement in efficiency for producing and maintaining high ortho-D2 concentrations will gain running time for experiments using UCN. At times, when monitoring of the source is not needed, the Raman spectrometer will allow studying relevant para-to-ortho conversion processes offline in the laboratory of the group at ETH Zurich.The new high-intensity UCN source at PSI has started regular operation in August 2011 and has delivered UCN already for several months in 2011 and 2012. The production of high UCN densities is important for several experiments to test the Standard Model (SM) of particle physics and its possible extensions. A major driving force comes from the search for the electric dipole moment of the neutron in which we are playing a leading role.UCN production at PSI is based on the down-scattering of neutrons in solid deuterium at a temperature of ~5K. Several UCN loss mechanisms in solid D2 must be considered, most prominently phonon up-scattering, spin-flip up-scattering and nuclear capture. Deuterium molecules exist either as para-deuterium (J-odd states) or as ortho-deuterium (J-even states). Loss cross sections strongly depend on the D2 spin state. Around 5K UCN thermal up-scattering on para-D2 has a factor 10 larger cross-section than on ortho-D2. UCN up-scattering via spin-flip on para-D2 is a factor of ~200 larger than any other loss mechanism in D2. Consequently, para-D2 in the converter strongly reduces the UCN intensity and one aims at para-D2 contents below 1%. Then, the up-scattering losses are on the same level as nuclear capture, the latter being a deuterium property which cannot be modified.Part of the D2 system of the UCN source is a para-to-ortho converter applying a paramagnetic catalyst material at low temperatures. D2 gas samples can be extracted from the system in order to measure the para-ortho fraction. Determination of the para-content in this D2 is necessary to optimize the conversion and UCN output. Raman spectroscopy - mostly of rotational states - has been established as the method of choice for the determination of the para-D2 content. We have in the recent past contributed considerably to establishing the methods for para-to-ortho conversion and Raman spectroscopy for D2 based UCN sources.The mobile Raman spectrometer, subject of this proposal, will allow us to directly determine the para-D2 content in D2 gas samples taken at the UCN source’s sample port. It will allow optimizing the D2 para-ortho conversion and monitoring the temporal behavior and stability. It will also allow studying radiation induced conversion in solid D2, an important topic at PSI and reactor and spallation UCN sources worldwide. This can be done in-situ at the PSI UCN source but also offline in our laboratory at ETH Zurich. There we can also study other catalysts that may allow for more efficient conversion in the long term. This mobile, easy-to-use Raman system will replace a stationary and complex system, requiring considerable attention, and will thus be a major step forward.We ask for R'EQUIP support for a Raman spectrometer for D2 gas samples. It will directly contribute to an improved understanding of UCN source physics and possibly an improved UCN intensity at the ultracold neutron source at PSI. It will allow important offline studies aiming at understanding, e.g., radiation induced conversion and better conversion mechanisms.