Amplifier Specifications

The present amplifier is the NISUS undulator. The Near Infra-Red Scalable Undulator System (NISUS) was built by STI Optronics for the Boeing FEL program. It was originally built for the Army Space and Strategic Defense Comand’s High Average Power FEL Program. NISUS was loaned to BNL and moved to the SDL in late 1994. Ownership was ultimately transferred to BNL by the Army in 1999. As if to prove it is a scaleable design, the first 5 meters were completed in1988, and the second 5 meters added to it by the end of 1990. It takes an informed eye to spot this fact in the finished device.

This unique undulator was built in 16 segments with flexible joints between them that allows an energy taper of up to 20% overall. Since there are no gaps in the device, novel 4 wire steering stations were built into the vacuum chamber to allow focusing and steering corrections along the whole length of the device. NISUS was built on top of a 40 foot long optical table which has proven to be very useful as we complete our work to ready it for our experiments.

Near Infra-Red Scalable Undulator System (NISUS) Design Parameters

Parameter Unites Value Notes
Period   mm 38.9
Number of Periods 256 divided into 16 segments
Peak Field T 0.56 max
aw (rms) 1.44 max  
dBy/dx G/cm 100 average from canted poles
Four Wire Steering G/A 1.3 integrated steering field
Minimum Gap mm 14.4  
Overall Length m 10
Clear Aperature mm 11.4  

NISUS is a Rare Earth Permanent Magnet Hybrid Undulator using SmCo5 magnet material and Vanadium Permadur Poles. The structure uses wedged poles to increase available peak field. Each group of 16 periods (32 poles) has 6 alternately canted pole tips (10.8 mrad) to provide a transverse field gradient located at the center of each subset of poles. The full length of the device is comprised of 16 of these smaller units joined by tuning fork flexures to allow tapered gap from one section to the next.

STI Optronics has recently remapped the magnetic field of the NISUS undulator at a working gap of 20.6 mm and a peak field of 0.31T, followed by reshimming to reduce trajectory and phase errors. By powering the built-in bias coils and making fine, local gap adjustments, the initially large trajectory wander has been reduced to less than one wiggle amplitude, and the phase error has been reduced to only 4° rms. Transverse (skew) fields have also been measured and an initial set of vertical steering corrections with the four-wire system has been determined. The magnetic field quality is now such that we can expect near-ideal performance from the undulator.