Compact Variable-Gap Undulator with Hydraulic-Assist Driver

Following successful proof-of-concept experiments, we constructed compact varying-gap undulator with Hydraulic-Assist Driver. The 1.5m long undulator features a pure permanent magnet structure, period of 28.4mm and a minimum gap of 6.75mm. The bench test of the device indicated excellent mechanical and magnetic performances. It demonstrated ≤3°RMS optical phase errors in a wide range of gap variation; ∼1.0×10−4 (or better) repeatability in normalized Kund (ΔK∕K) from one gap variation to another. In special mode, when the gap was varied in correlation with undulator temperature, undulator demonstrated ∼6.6×10−5RMS of ΔK∕K long-term (∼24hrs) stability while the undulator temperature change was ∼1.3°C.