A beamline for macromolecular crystallography at the Advanced Light Source

Abstract

A beamline for macromolecular crystallography has been designed for the ALS. The source will be a 37-pole wiggler with a 2-T on-axis peak field. The wiggler will illuminate three beamlines, each accepting 3 mrad of horizontal aperture. The central beamline will primarily be used for multiple-wavelength anomalous dispersion measurements in the wavelength range from 4 to 0.9 Å. The beamline optics will comprise a double-crystal monochromator with a collimating premirror and a double-focusing mirror after the monochromator. The two side stations will be used for fixed-wavelength experiments within the wavelength range from 1.5 to 0.95 Å. The optics will consist of a conventional vertically focusing cylindrical mirror followed by an asymmetrically cut curved-crystal monochromator. This paper presents details of the optimization of the wiggler source for crystallography, gives a description of the beamline configuration, and discusses the reasons for the choices made.

The macromolecular crystallography facility at the advanced light source

“…The high field magnetic structure of this device can produce substantial flux and brightness down to 0.9 A wavelengths. To optimize the parameters of the wiggler we maximized the horizontal phase space density as the number of poles was varied using a fixed length of three meters [2]. The phase space is defined by the crystal size and maximum angular divergence (related to the unit cell dimensions).…”

Depth-of-field effects in wiggler radiation sources: Geometrical versus wave optics

“…Further studies of depth of field effects in wigglers, using the same geometrical optics approach, were reported in Refs. [4][5][6][7][8]. The effects are well known, namely the increase in horizontal source size as a function of off-axis viewing angle, or angular acceptance, as well as the decrease in brightness resulting in a less than linear dependence on device length.…”