Alignment of the VISA Undulator

Abstract

The Visible-Infrared SASE Amplifier (VISA) undulator [1] consists of four 99cm long segments. Each undulator segment is set up on a pulsed-wire bench, to characterize the magnetic properties and to locate the magnetic axis of the FODO array [2]. Subsequently, the location of the magnetic axis, as defined by the wire, is referenced to tooling balls on each magnet segment by means of a straightness interferometer. After installation in the vacuum chamber, the four magnet segments are aligned with respect to themselves and globally to the beam line reference laser. A specially designed alignment fixture is used to mount one straightness interferometer each in the horizontal and vertical plane of the beam. The goal of these procedures is to keep the combined rms trajectory error, due to magnetic and alignment errors, to 50µm.

Initial Gain Measurements of a 800nm SASE FEL, VISA

“…We have set the requirement on aligning the four 1m sections to be within 30µm. To do this, a laser interferometric alignment system [8] has been developed in which these strict alignment tolerances can be reached.…”