SINQ and UCN – two high-power spallation sources operating at PSI

This paper presents an overview on most recent developments at and around SINQ, addressing accelerator and target performance, and the control system refurbishment. New instrument developments focus on EIGER, the new thermal triple axes spectrometer now at the start-up of operation, the strain scanner POLDI in a phase of major refurbishment and upgrades, and BOA, a new universal beamline. The status of MEGAPIE is briefly reported, after successful dismantling now having entered the PIE phase. One of the highlights at PSI in 2011 was the successful commissioning of UCN, the new spallation source for ultracold neutrons, which started operation in August 2011. First operation experience is briefly addressed. Details on this endeavour are reported in separate paper of this volume [1]. 1. SINQ operation and developments At the end of 2011, the Swiss spallation neutron source SINQ celebrated its 15th year of successful operation. The year 2011 was outstanding for SINQ with respect to both target and user operation. The target received a total charge of 6370 mAh, which exceeds clearly even the previous record of 6220 mAh from 2009. This is especially remarkable, since the operation period was shorter than usual (no accelerator operation in December). The gain was caused by three reasons: (i) an outstanding performance of the proton accelerator with an availability of 91% (ii) the further increase of the proton current with many highly stable periods of 2.2 mA (of which SINQ receives ~1.6 mA) and (iii) the again outstanding availability of SINQ itself (97%) with respect to the proton accelerator. The facility meanwhile hosts 17 instruments for neutron diffraction, spectroscopy and imaging, 12 of them in the user program. The excellent technical boundary conditions allowed almost 440 scheduled experiments on the 12 SINQ instruments. The presently operated spallation target (target 8) is a second edition of the compact Zr-canned lead ‘cannelloni’ target, in detail described in [2]. The first version (target 7, see Figure 1), having been in service in 2009/2010, is now awaiting inspection, dismantling and disposal. Target 7 had shown a problem, probably caused by some very fast abnormal deflection of the beam out-of-centre, hitting the 1 To whom any correspondence should be addressed. edge of the collimator and most likely also the Al-canned lead blanket. The failure was detected by lead-spallation products, in the first place 127Xe, in the water of the target cooling circuit. The inspection planned for early summer 2012 is expected to give information about the cause and location of the failure in order to allow future improvements. Figure 1: The compact Zr-canned lead-‘cannelloni’ target, of circular shape surrounded by a lead blanket/reflector canned in Aluminium In the presently operated target 8 such improvements could not yet be implemented, but so far it operates well. This target again (after a break with target 7) carries several tubes with STIP (SINQ Target Irradiation Program) samples, continuing this very important materials research program [3,4]. In spite of these STIP tubes, which were expected to reduce the neutron yield by up to 5%, our routine flux measurements by gold foil activation, within the scatter band of such measurements, did not reveal a flux decrease compared to target 7. Figure 2 shows the updated version of proton charge and related neutron production history. The year 2011 set the record in terms of highest proton charge accumulated and neutrons produced since the start-up of SINQ Figure 2: History of yearly accumulated proton charge on the SINQ target and related neutron