Directions in Future Particle Accelerators for Fundamental Science and Applications

Accelerators have been a major success story for science and society since the invention of the radio-frequency, resonant particle acceleration in the 1920's. The charged particle beams from accelerators enabled the discovery of new particles and nuclei, the measurement of fundamental forces and the development of numerous applications for industry, health and science. The footprints of modern particle accelerators range from a few meters all the way up to 27 km. Some of those devices are among the largest and most complex machines that mankind has built. Future goals aim at higher beam currents, new kinds of particles, increased beam energy or faster acceleration, amongst others. The colloquium talk discusses several important limitations, that are practically constraining new facilities. Future directions and expected gains are explained. Advances in hadron beams and the handling of their halos are discussed, including automatic algorithms. The potential with beams from plasma accelerators and their trade-offs are presented. An outlook for ion beam facilities is given.