The compact linear accelerator for research and applications (CLARA) is an ultrabright electron beam test facility being developed at STFC Daresbury Laboratory. The ultimate aim of CLARA is to test advanced free electron laser (FEL) schemes that can later be implemented on existing and future short-wavelength FELs. In addition, CLARA is a unique facility to provide a high-quality electron beam to test novel concepts and ideas in a wide range of disciplines and to function as a technology demonstrator for a future United Kingdom x-ray FEL facility. CLARA is being built in three phases; the first phase, or front end (FE), comprises an S-band rf photoinjector, a linac, and an S-bend merging with the existing versatile electron linear accelerator beam line; the second phase will complete the acceleration to full beam energy of 250 MeV and also incorporate a separate beam line for use of electrons at 250 MeV; and the third phase will include the FEL section. The CLARA FE was commissioned during 2018, and the facility was later made available for user experiments. Significant advancements have been made in developing high-level software and a simulation framework for start-to-end simulations. The high-level software has been successfully used for unmanned rf conditioning and for characterization of the electron beam. This paper describes the design of the CLARA FE, performance of technical systems, high-level software developments, preliminary results of measured beam parameters, and plans for improvements and upgrades.

The transverse phase space of a beam in an accelerator can be characterized using well-established methods based on observation of changes in the beam profile between screens at different locations along the beamline, or on observation of changes on a single screen for different strengths of upstream quadrupoles. Studies on CLARA FE (the Compact Linear Accelerator for Research and Applications Front End, at Daresbury Laboratory, UK) show that where the beam has a complicated (nonelliptical) distribution in transverse phase space, conventional analysis techniques aimed at characterizing the beam in terms of the emittances and Courant–Snyder parameters fail to provide a good description of the beam behavior. Phase space tomography, however, allows the construction of a detailed representation of the phase space distribution that provides a better model for the beam. We compare the results from three measurement and analysis techniques applied on CLARA FE: emittance and optics measurements from observations on three screens; emittance and optics measurements from quadrupole scans on a single screen; and phase space tomography. The results show the advantages of phase space tomography in providing a detailed model of the beam distribution in phase space. We present the first experimental results from four-dimensional phase space tomography, which gives an insight into beam properties (such as the transverse coupling) that are of importance for optimizing machine performance.

Climate-change-induced hazards are negatively affecting the small islands across Indonesia. Sabang Island is one of the most vulnerable small islands due to the rising sea levels and increasing coastal inundation which threaten the low-lying coastal areas with and without coastal defences. However, there is still a lack of studies concerning the long-term trends in climatic variables and, consequently, sea level changes in the region. Accordingly, the current study attempts to comprehensively assess sea level changes and coastal inundation through satellite-derived datasets and model-based products around Sabang Island, Indonesia. The findings of the study show that the temperature (both minimum and maximum) and rainfall of the island are increasing by ~0.01 °C and ~11.5 mm per year, respectively. The trends of temperature and rainfall are closely associated with vegetative growth; an upward trend in the dense forest is noticed through the enhanced vegetation index (EVI). The trend analysis of satellite altimeter datasets shows that the sea level is increasing at a rate of 6.6 mm/year. The DEM-based modelling shows that sea level rise poses the greatest threat to coastal habitations and has significantly increased in recent years, accentuated by urbanisation. The GIS-based model results predict that about half of the coastal settlements (2.5 sq km) will be submerged completely within the next 30 years, provided the same sea level rise continues. The risk of coastal inundation is particularly severe in Sabang, the largest town on the island. The results allow regional, sub-regional, and local comparisons that can assess variations in climate change, sea level rise, coastal inundation, and associated vulnerabilities.