The development of precise and stable X-ray optics for beamlines is vital for a full utilization of the highly coherent and intense light from the MAX IV sources. Optical components, such as mirrors and gratings, must be manufactured with nanometer accuracy while at the same time be positioned with extreme precision. In addition they need to be supported such that vibrations and drift are minimized. Activities relating to X-ray optics are therefore undertaken by many different groups and teams at MAX IV, from the initial optical design of beamlines to the installation and alignment of beamline components.
The optical layouts of beamlines at MAX IV are typically designed by the individual beamline project manager in close collaboration with in-house experts on optics simulations. There are currently two optics simulation packages being developed at MAX IV:
- MASH – ray tracing and heat load calculations. Responsible:
- XRT – ray tracing and wavefront propagation. Responsible:
Optical components & systems
One output from the optics simulations is the desired properties of the mirrors, crystals and gratings that form the backbone of a beamline. These components must be manufactured with very high demands on surface roughness and slope errors and are purchased from specialist vendors or other synchrotron facilities around the world. The mechanical properties of the systems that hold and define the position and travel range of the optical components must in addition be defined according to e.g. the intended energy range of the beamline. Procurement of components and mechanical systems are generally handled by the individual beamline teams with support from the Beamline Office (BO). BO coordinates the process whereby requirements on the optics and optical systems are established and is also coordinating the manufacturing of blazed gratings.
Metrology of optical components may be carried out in-house using a white-light interferometer, a Fizeau interferometer or an AFM.
The first part of the beamline after the insertion device, but inside the ring (behind the ratchet wall) is defined as the front end. It has several functions, e.g. initial definition of the beam size and thereby removing the vast majority of the heat load from the X-ray beam, monitor the position of the X-ray beam, allow safe access into the optics hutch when required and protect the machine in case of vacuum failures at the beamline. The front ends are handled by BO.
Vibrations of beamline optics can severely affect the path of light from source to sample. In some cases, beamlines with samples positioned more than 50 meters from the source demand spatial stability on the order of micrometers. Mitigation of vibrations are therefore vital for beamline design and development. Several in-house projects at MAX IV have resulted in novel methods for creating stable optics. For example, most soft X-ray beamlines employ a parallel kinematic design for the mirror chambers which minimize the size and weight of the mirror vessel thus resulting in high Eigen frequencies. Vibration and stability issues at MAX IV is handled by the Stability Task Force.
Upon installation all optical components in a beamline are positioned according to the beamline design with micrometer precision. This alignment work is carried out by the SAM (Survey, Alignment and Mechanical Stability) team.