Control system for a variable period undulator prototype

The magnetic structure of the proposed variable period undulator consists of cylindrical magnets. Each magnet can be rotated by a small stepper motor, in order to adjust the magnetic field and form an arbitrarily shaped magnetic field profile on-axis. Meanwhile, a short prototype exists, equipped with a scalable control system to drive a large amount of stepper motors. This paper describes details of the control system implementation, results of the tests on different rotary encoder concepts for a magnet positioning feedback, and first magnetic measurements of the variable period undulator prototype.