Subsection 2.3.4 - The Setup Tab
Beamline 4.2.2 is unique at the ALS in that we use a sagittally focused 2nd crystal in our monochromator. This provides a spot shape that can be focused on a large range of detector distances with the entire beam hitting the focal point (usually the sample). A challenge during an energy change is keeping everything optimized for spot shape and maximum flux. Specifically, the beam focus and roll is subject to anticlastic bend and their values must be honed by staff on a somewhat regular basis. Once these values are entered, they tend to remain stable during the normal course of a user’s beamtime.
In order to provide the maximum flexibility for the experimenter, we have devised a simple lookup table which allows the user to choose specific energies for collection. Any energy from 5,500eV to 15,500eV can be made available. Users that wish to change energies are encouraged to let staff know prior to beamtime so that the lookup table and energies may be optimized during startup and tune.