The injection bumper system for LEIR

To satisfy the ion beam luminosity requirements for CERN´s future large hadron collider (LHC), a small accumulator, the low energy ion ring (LEIR), is being built in the injector chain of accelerators. LEIR will use a combined longitudinal and transverse multiturn injection scheme that requires a bumper system comprising four individually pulsed dipole magnets. The paper discusses the bumper system, in particular the power supplies that will produce a pulsed current linearly decreasing from 1.2 kA to zero in a time variable between 120 us and 300 us. Each power supply employs a primary discharge circuit, comprising a storage capacitor, an IGBT switch and the magnet load inductance, to establish the peak current, and a freewheel circuit in parallel with the magnet, comprising a diode and capacitor, to produce the linear current slope. A novel feature of the circuit is the use of a variable bias voltage on the freewheel capacitor, allowing continuous variation of the slope duration.