Synchrotrons require precise knowledge of the instantaneous field for longitudinal and transversal beam control. In iron-dominated, fast-cycled magnets, saturation, hysteresis, and eddy currents are challenging to predict with the required accuracy using established modeling approaches. B-train systems provide a sufficiently accurate field based on real-time measurements of a witness magnet.
At CERN, we operate B-train systems in the injector chain (PSB, PS, SPS), as well as LEIR, AD, and ELENA. The systems were recently updated and are now fully operational since Run 3. In this seminar, we provide an introduction to how they work, their operation, limitations, and an outlook on possible future extensions.