Foreword to the special issue on advanced neutron scattering instrumentation

Neutron scattering facilities are called to address an ever-expanding mission in the investigation, development and use of a broad range of materials: from investigating cultural heritage artifacts to advanced bio-materials, from studies of phase transitions and quantum matter to advanced engineering composites for aircraft.This breadth of applications, together with the complex problems they present for making scientific and technical progress, are key drivers for new advanced neutron sources and novel instrumentation that covers an enormously broad scale in both time and space.These challenges must be met by neutron user facilities within a rapidly changing landscape, and there are significant investments under way in both neutron sources and instrumentation.While it is not possible to include everything, a number of these developments are highlighted within a new virtual special issue of Journal of Applied Crystallography (https://journals.iucr.org/special_issues/2018/ansi/).Europe is constructing the European Spallation Source (ESS), an investment of over two billion USD that is rapidly rising from the ground in Lund, Sweden; the US Department of Energy is investing in the Spallation Neutron Source (SNS) to double its proton beam power on target from 1.4 to 2.8 MW.Both the spallation source at JPARC, Japan, and the SNS are advancing plans for additional target stations.The ISIS facility in the UK is also advancing to fully instrument its second target station.The Institut Laue-Langevin (ILL) is currently executing phase one of its Endurance instrument upgrade program.Both ANSTO's Australian Centre for Neutron Scattering (ACNS) in Sydney, Australia, and the Maier-Leibnitz Zentrum (MLZ) in Munich, Germany, are making significant investments in instrumentation technology and instruments to meet rising user demands.Within these exciting developments, this special issue on advanced neutron scattering instrumentation highlights some of the innovative advances in neutron scattering instrumentation at facilities around the world that address a broad scientific and industrial scope of applications.The special issue provides us with an opportunity to take a glimpse on a global scale at some of the exciting developments in source and instrument suite design, high-performance instrumentation, and software.These developments are enabling new opportunities for science discovery through technologies such as detectors, sample environments and data acquisition advances.Always, the design of a brand-new source offers the opportunity to do things differently.Borrowing ideas from the ISIS second target station approach to moderator design, the work described by Andersen et al. (2018) for the ESS takes a global optimization approach for moderator and instruments together.The ESS design makes use of recently developed high-brightness low-dimensional moderators, and highly integrated neutronics and Monte Carlo instrument simulations are used to optimize key moderator parameters in order to deliver maximal performance over a wide variety of instruments that will be built at the ESS.While this is a unique opportunity at a source under construction, Heller et al. (2018) describe the optimizations and synergies across the small-angle neutron scattering (SANS) suite at SNS, where integration of user-supplied sample environments with the data acquisition system is a significant challenge.Similar integration of SANS instruments at ACNS described by Rehm et al. (2018) purposefully enables the characterization of microstructure over four orders of magnitude in size (1 nm to 10 mm).While facilities and specific instrument-class suites aim to cover a large variety of scientific problems, instrument design efforts at facilities also aim to significantly boost performance by taking advantage of new instrument concepts and technologies.One of