Speaker
Description
The Oak Ridge National Laboratory (ORNL) currently operates the High Flux Isotope Reactor (HFIR) and the Spallation Neutron Source (SNS), two of the world’s most advanced neutron scattering research facilities. The long-planned fourth-generation neutron source, the Second Target Station (STS), obtained the United States Department of Energy Critical Decision 1 approval in November 2020 and subsequently started preliminary design. The goal of the STS project is to construct an additional target station optimized for cold neutrons which will be able to accommodate 18 to 20 neutron scattering instruments. In 2021 a committee of 22 national and international experts selected the eight instruments to be built within the scope of the STS project: PIONEER, a single-crystal diffractometer; QIKR, a kinetics reflectometer; CHESS, a cold neutron spectrometer; CENTAUR, a SANS/WANS instrument; BWAVES, a broadband spectrometer; CUPI2D, a neutron imaging instrument; EXPANSE, a wide-angle neutron spin echo instrument; and VERDI, a polarized diffractometer. The first three of those instruments are expected to deliver early science at around 2034. The STS will operate as pulsed neutron source with 700 kW of proton beam power delivered in short, less than 1 µs long pulses, with 15 Hz repetition rate. The STS will receive one out-of-four pulses from the existing linear accelerator, which is currently undergoing an upgrade that will double the capability of the accelerator to a proton beam power of 2.8 MW. The core of the STS will be a rotating water-cooled tungsten target which will feed neutrons into two coupled cryogenic moderators filled with liquid hydrogen, surrounded with water pre-moderators and a beryllium reflector. The STS will be designed to provide exceptionally bright beams of cold neutrons and will be equipped with new-generation instruments optimized for the exploration of small samples of complex materials. It will complement the capabilities of the SNS First Target Station for high-resolution measurements and the strength of HFIR in producing intense continuous neutron beams. The high neutron beam brightness will be obtained by specifically optimizing the moderators for operation with pure parahydrogen, tight coupling of target and moderators, and small size neutron beams. The cylindrical moderator, which will serve 12 beamlines, will have four rectangular extraction ports with the viewed areas of 30 mm × 30 mm size, while the novel one-dimensional ”tube” moderator will have three circular viewed areas with 30 mm diameter and will serve six beamlines. This presentation will describe the status of the STS design.
