Iowa State Undulator Installed
An electromagnetic undulator, the first of two new insertion devices intended for SRC,
was installed on the Aladdin storage ring on November 6, 1993. Initial tests of the
undulator after delivery by Maxwell- Brobeck Division have demonstrated that the device
can be run over its entire design magnetic field range without impact on the electron beam
The Iowa State Undulator, placed on Aladdin in the straight section LSS-4, was designed
for very high resolution over the specific energy range from 15 to 30 eV. Cost and
complexity were minimized, and efficiency was maximized, by limiting the long period,
low-K undulator to this very important energy region.
By optimizing the entire beamline, from undulator to detector, over a small energy
range, researchers will see an improvement of a factor of four over the best achievable
result on a bending magnet. Dr. Clifford Olson, who, with Dr. David Lynch, designed the
undulator, commented on this increase in resolution: "We've given up the versatility
and what we've gained is performance."
Dr. Olson anticipates that the majority of the work done with the undulator's beamline
will involve high temperature superconductors, although increased resolution is important
for study of more conventional materials as well, such as studies of epitaxial overlayers
with large unit cells.
The specifications of the undulator and beamline were handled by Olson and Lynch in
cooperation with SRC, which participated in the joint discussions with industry and
ISU/Ames Laboratory on the design and procurement of the device. The SRC team contributed
flux performance specifications, as well as input into the structuring, content, and
review of the bid document submitted to industry. The design phase culminated in a
proposal for a 16 period, 2.4 meter long undulator, with electromagnetic coils for ease of
change of photon energy. Funding was primarily provided by the National Science
Foundation, with a major contribution from Iowa State University.
Preparation for installation of the undulator upon delivery was handled by Bill Winter,
engineering group leader at SRC. About five months ahead of delivery, the engineering team
started their preparation for the undulator, including:
- fabrication of a new section of vacuum chamber for Aladdin
- completion of a cooling system as well as electrical and water hookups to the undulator
- construction of a kinematic translation plate, complete with retractable undercarriage
support to allow for unimpaired storage ring injection.
Greg Rogers of SRC was responsible for shielding the undulator, preventing radiation
problems, and aligning the undulator to the beam.
Walt Trzeciak, Ed Rowe and Mike Green, senior scientists in accelerator development at
SRC, have assisted from the beginning of the project in order to assure smooth adaptation
of the undulator into the ring environment. The main concern for the SRC with the
installation of a new insertion device was that Aladdin's performance, and therefore
users' beamlines, was disrupted as little as possible. According to Green, testing after
installation has revealed an almost negligible shift in tune, and, as expected, absence of
any coupling contribution which could affect either vertical beam size or
horizontal/vertical beam rotation.
SRC, Olson and Lynch specified magnetic parameters such that the device will not
interfere with operation and usage of Aladdin by other users, even when the undulator's
excitation is changed dynamically. The electromagnetic design of the ISU undulator also
allows the undulator to be "shut off" during Aladdin's injections to eliminate
Trzeciak explained that for initially, and for the near future, the SRC operators will
have complete control over all undulator parameters. Each user will have the undulator set
in a specific operation mode for the duration of their beam time. In the future, the
beamline user will be able to change the undulator wavelength from the beamline with no
impact on other users.