Background: The twist of bent crystal is a common problem of sagittal focusing monochromators.In Shanghai Synchrotron Radiation Facility(SSRF)

one of monochromators has an unfocused beam profile because of crystal twist.Purpose: In order to amend the twist problem and get theoretical understanding for further design optimization

a study on the mechanism of crystal twist has been developed.Methods: Finite Element Analysis(FEA) models considering anisotropic effect of crystal were constructed to study some common factors

i.e.crystal orientation

clamping method

stiffening ribs and asymmetric clamping on the bent crystal profile.Results: The simulation result shows that among those factors

asymmetric clamping is the main reason causing the crystal twist while crystal orientation is also important.Clamping method is a factor that restricts the asymmetric clamping to a certain scale.Conclusions: For optimizing the system

asymmetric clamping should be controlled and crystal should be cut in a particular orientation.