Optimization of the soft X-ray transmission microscopy beamline at the ALBA light source

Mistral is the soft X-ray full field microscopy beamline at the ALBA light source. The beamline is designed to have large source acceptance and to provide constant magnification at the exit slit for photon energies between 270 and 2600 eV. The monochromator is a variation of the Petersen plane grating monochromator in which a variable line spacing grating is used to maintain the beam focused at the exit slit, independently of the fixed focus constant, and to cancel aberrations. We present the alignment strategy used to compensate errors of the optical elements, and report about the commissioning results.