An Elliptical Polarized Wiggler (EPW) has been installed in the X13 straight section of the X-Ray Ring at the National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973. The device was designed and built jointly by Argonne National Laboratory (USA) and the Budker Institute of Nuclear Physics, (Novosibirsk, Russia). It implements a concept developed by Aharon Friedman at NSLS and is a prototype for future full-size devices that may be built and installed in the Advanced Photon Source at Argonne, as well as at the NSLS.
The EPW will produce variable polarized X-rays with right/left-handedness of polarization switchable at up to 100 Hz. The objectives of the initial testing program at NSLS will be (1) to study the electron orbit stability of the X-Ray Ring with an AC-driven, polarized insertion device, (2) to optimize the static and dynamic trim compensation of the EPW, and (3) to measure the characteristics of the emitted radiation. Eventually the light output may be made available to users on a limited basis.
The magnetic design of the EPW employs a vertically oriented, permanent-magnet (PM) "hybrid" structure, together with a horizontally oriented electromagnet (EM) wiggler. The poles of the EM are interleaved axially with the poles of the PM structure. The PM wiggler has 5 full-strength poles and 2 half-strength end poles which have been adjusted to minimize the first field integral (net steering). The EM structure consists of 6 full-strength poles, with a 2-pole, binomially-tapered end section at each end to minimize both first and second field integrals (steering and orbit displacement). The EM also has end trim electromagnets which have provision for linear control (for fine tuning of steering and displacement), feed-forward from an arbitrary function generator (for compensation of switching transients), and feedback from beam position monitors.
The amplitude of the vertical field is fixed at 0.8 Tesla (Ky =12) due to the fixed gap of the PM structure. The peak horizontal field can be varied from 0 to about 0.2 Tesla (Kx=3) by varying the current in the EM. With excitation off, the electron motion is planar and nearly sinusoidal, and the radiation has linear (horizontal) polarization in the midplane. With the EM current on, the electron trajectory through each PM pole is tilted alternately up and down, allowing the off-plane circularly polarized component of wiggler radiation to propagate down the beamline axis. The observed polarization is switched from right- to left-handed by reversing the EM current.
It is anticipated that a switchable, elliptically polarized wiggler will be more useful to users than a static polarized device because it will permit the use of lock-in amplifier techniques to detect the very weak signatures of circular dichroism and other effects associated with right- vs. left-handedness of some physical systems.
Commissioning of the EPW will begin in January 1995.Parameters of the Elliptical Polarized Wiggler
Contact: G. Rakowsky, firstname.lastname@example.org