four original Cavities, a smaller fifth cavity was added in 1979. It is operated at 150 megahertz as a flat-top cavity, and has enabled a significant increase in the number of extracted particles. Since 2008 all the old aluminium cavities of the Ring Cyclotron have been replaced with new copper cavities. These allow higher voltage amplitudes and thus a greater acceleration of the protons per revolution. The number of revolutions of the protons in the cyclotron could thus be reduced from approx. 200 to 186, and the distance travelled by the protons in the cyclotron decreased from 6 km to 4 km. With a beam current of 2.2 mA, this proton facility at PSI is currently the most powerful continuous particle accelerator in the world. The 1.3 MW strong proton beam is directed towards the muon source (SμS) and the spallation neutron source (SINQ). Swiss Muon Source (SμS) In the middle of the large experimental hall, the proton beam of the Ring Cyclotron collides with two targets – rings of carbon. During the collisions of the protons with the atomic carbon nuclei, pions are first formed and then decay into muons after about 26 billionths of a second. Magnets then direct these muons to instruments used in materials science and particle physics. Thanks to the Ring Cyclotron's enormously high proton current, the muon source is able to generate the world's most intense muon beams. These enable researchers to conduct experiments in particle physics and materials science that cannot be carried out anywhere else. The Swiss Muon Source (SμS) has seven beamlines that scientists can use to investigate various aspects of modern physics. Some materials scientists use them for muon spin spectroscopy experiments. PSI is the only place in the world where a muon beam of sufficient intensity is available at a very low energy of only a few kiloelectron volts – thanks to the Muon Source's high muon intensity and a special process. The resulting muons are slow enough to be used to analyse thin layers of material and surfaces. Six measuring stations (FLAME (from 2021), DOLLY, GPD, GPS, HAL-9500, and LEM) with instruments for a wide range of applications are available for such investigations. Particle physicists are using some of the beamlines to perform high-precision measurements to test the limits of the Standard Model. Swiss Spallation Neutron Source (SINQ) The neutron source SINQ, which has been in operation since