Neutron spallation sources at PSI and their applications

Full text: The Paul Scherrer Institute (PSI) is a multi-disciplinary research centre for natural sciences and technology. PSI collaborates with national and international universities, other research institutions and industry in the areas of solid-state research and materials sciences, particle physics, life sciences, energy research and environmental research. PSI concentrates on basic and applied research, but also contributes to the training of the next generation and to pave the way towards sustainable development of society and economy. The Institute is actively involved in the transfer of new discoveries into industry, and offers its services to external organisations. PSI employs 1300 members of staff, making it the largest of the national research institutions - and the only one of its kind within Switzerland. It develops, builds and operates complex large-scale research facilities that impose particularly high requirements in terms of knowledge, experience and professionalism, in particular a large continuous Spallation Neutron Source (SINQ) and a Synchrotron Light Source (SLS). PSI plays a special role as a user lab. Since the start of PSI, 15,000 - 20,000 external researchers have performed experiments in the fields of physics, chemistry, biology, material sciences, energy technology, environmental science and medical technology. SINQ has been designed as a neutron source mainly for research with extracted beams of thermal and cold neutrons, but also hosts facilities for isotope production and neutron activation analysis. Except for its different process of releasing the neutrons from matter, it resembles closely a medium flux research reactor for most of its users. The spallation neutron source SINQ is a continuous source - the first and still strongest of its kind in the world - with a total flux of about 1014 n/cm2/s. A cold moderator of liquid deuterium (cold source) slows a part of the neutrons down and shifts their spectrum to lower energies. At SINQ, main research activities center on the study of solid, liquid or soft condensed matter, using various state of the art instruments. Aside from scattering techniques, non-diffractive methods like imaging techniques are also being applied with increasing relevance for industrial applications. Besides the main goal of safe and reliable operation of SINQ, several development projects aim for an optimized neutron yield boosting sustainable facility performance. Among others, target development for proton accelerator driven systems and liquid metal target technology are fields of high priority, linked with the investigation of materials under high-dose radiation loads. The most prominent project in this context is MEGAPIE, a liquid metal target pilot experiment for megawatt beam application. During 2006, the MEGAPIE lead bismuth liquid metal target has been installed and operated successfully. It has been irradiated with a total of 3 mAhours of 600 MeV protons. Preparations for post irradiation examinations are in progress. Currently, a new type of ultracold neutron (UCN) source based on the spallation process is under construction at PSI. The key features are a very intense (Ip > 2mA) pulsed proton beam with a low duty cycle (1%), a lead/Zircaloy spallation target, a 3.6 m3 heavy water moderator and a 30 liter solid Deuterium (sD2) converter system. Spallation neutrons are thermalized in the D2O, further cooled and partially downscattered into the ultracold energy regime (E < 300 neV) in the sD2. The source is expected to deliver densities of more than 1000 UCN/cm3 into two experimental areas. Commissioning of the facility will start in late 2009, user operation in 2010. As the first main user of the UCN source, the international nEDM collaboration, aims at an improved measurement of the neutron electric dipole moment (nEDM). The approach is in steps: The apparatus of the former Sussex-RAL-ILL collaboration is transferred to the new PSI UCN source and installed during 2009. Data taking is planned for 2010 and 2011 with the goal to improve the sensi tivity to 5 x 10-27 e cm (95% CL). In parallel, a new n2EDM apparatus is being developed and constructed. It will again be a room temperature experiment with UCN in vacuum, applying the Ramsey method of separated oscillatory fields, but using a double neutron chamber and much improved magnetometry to control the systematics. The statistical sensitivity will be improved due to a much better adaption to the UCN source and an increase in electric field strength. After data taking 2012-2015 the sensitivity should reach 5 x 10-28 e cm (95% CL). (author)