Welcome to the digital edition of the May/June 2020 issue of CERN Courier.

This month’s issue looks at the latest progress in niobium-tin (Nb₃Sn) accelerator magnets for high-energy exploration. Discovered to be a superconductor more than half a century ago, and already in widespread commercial use in MRI scanners and employed on a giant scale in the under-construction ITER fusion experiment, it is only recently that high-performance accelerator magnets made from Nb₃Sn have been mastered. The first use of Nb₃Sn conductor in particle physics will be the High-Luminosity LHC (HL-LHC), for which the first Nb₃Sn dipole and quadrupole magnets have recently been tested successfully at CERN and in the US. As our cover feature describes, the demonstration of Nb₃Sn in the HL-LHC also serves as a springboard to future hadron colliders, enabling physicists to reach significantly higher energies than are possible with present-generation niobium-titanium accelerator magnets. To this end, CERN and the US labs are achieving impressive results in driving up the performance of Nb₃Sn conductor in various demonstrator magnets.

Sticking with accelerators, this issue also lays out the possible paths towards a high-energy muon collider – long considered a dream machine for precision and discovery, but devilishly difficult in its details. We also describe the rapid progress being made at synchrotron X-ray sources, arguably the most significant application of accelerator science in recent decades, towards understanding the molecular structure of the SARS-CoV-2 virus. The importance of accelerators for neutron science is a theme of the Viewpoint article, and, in addition to the Courier’s regular coverage of the news, conferences and reviews, this issue includes reports on how high-energy physicists are responding to the COVID-19 pandemic.

j CERN Courier May/Jun 2020