Damping ring kickers for the Next Linear Collider

The Next Linear Collider (NLC) uses a damping ring for the electron beam, a pre-damping ring and a main damping ring for the positron beam to reduce the beam emittances. The requirements of the main damping ring kickers are to bend a 2 GeV beam by an angle of 2 mrad over a length of 1.2 m. This results in a required field of 139 G. The magnet aperture is 30×30 mm. The pre-damping ring kicker requirements are based on a 2 GeV beam with a bend angle of 8 mrad in 1.2 m, or a field of 308 G. The magnet aperture is 62×45 mm (H×V). A pulse width is 130 ns with rise and fall times of less than 60 ns is the same for both the pre-damping ring and main damping ring kickers. The three rings operate at a 180 Hz repetition rate. The kicker magnets being developed to meet these requirements consist of two strip line conductors in the vacuum chamber, for the pre-damping ring kickers they may be loaded with ferrite, to give a matching impedance of 25 Ω. The buses are separated from magnetic flux linkage by a grounded flux excluder, which also serves as a low impedance return for the beam current. Both busses of the magnet are driven in parallel from the same modulator and are grounded at the end opposite the feed. The modulator uses two IGBT stacks which both act as opening switches in order to meet the rise time requirements