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 multi-turn injection scheme which requires a bumper system comprising four individually pulsed dipole magnets. The paper discusses the bumper system, in particular the power supplies which will produce a pulsed current linearly decreasing from 1.2kA to zero in a time variable between 120µs and 300µs. 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 free-wheel 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 free-wheel capacitor, allowing continuous variation of the slope duration.