clinics and the pharmaceutical industry. PSI also supplies local hospitals with radiopharmaceuticals if required. Since the opening of the Synchrotron Light Source Switzerland (SLS), structural biology has been a further focus of research in the field of human health. Here, the structure and function of biomolecules are being investigated – preferably at atomic resolution. The PSI researchers are primarily concerned with proteins. Every living cell needs a myriad of these molecules in order, for example, to be able to metabolise, receive and transmit signals or to divide. The aim is to understand these life processes better and thus to be able to treat or prevent diseases more effectively. For example, PSI is investigating the structure of filamentous structures, the so-called microtubules, which, among other things, pull apart chromosomes during cell division. They consist of long protein chains. When chemotherapy is used to treat cancer, it disturbs the assembly or breakdown of these chains so that the cancer cells can no longer divide. Researchers are closely observing the structure of these proteins and how they change to find out exactly where cancer drugs have to attack the microtubules. With the help of PSI's SwissFEL free-electron X-ray laser, which was inaugurated in 2016, researchers have been able to analyse dynamic processes in biomolecules with extremely high time resolution – less than a trillionth of a second (picosecond). For example, they have detected how certain proteins in the photoreceptors of the retina of our eyes are activated by light. Accelerators and large research facilities at PSI Proton accelerator facility While PSI's proton accelerator, which went into service in 1974, was primarily used in the early days for elementary particle physics, today the focus is on applications for solid-state physics, radiopharmaceuticals and cancer therapy. Since it started operating, it has been constantly developed further, and its performance today is as much as 2.4 mA, which is 24 times higher than the initial 100 µA. This is why the facility is now considered a high-performance proton accelerator, or HIPA (High Intensity Proton Accelerator) for short. Basically, it consists of three accelerators in series: the Cockcroft-Walton, the injector-2 cyclotron, and the ring-cyclotron. They accelerate the protons to around 80 percent of the speed of light. Proton source and Cockcroft-Walton In a proton source based on cyclotron resonance, microwaves are used to strip electrons from hydrogen atoms. What remains are the hydrogen atomic nuclei, each consisting of