Component Manual for the Neutron Ray-Tracing Package McStas, version 3.8.6

14.52  The Monochromator_bent McStas Component

A bent crystal monochromator. Based on the model implemented by Jan Šaroun in NIMA 529 (2004) pp 162-165. An article describing the component has been written and can be seen in Quantum Beam Sci. 2026, 10, 6. https://doi.org/10.3390/qubs10010006 Mosacity and bending radius can be set.

Identification

Description

This monochromator is an array of crystals, that can be bent. The crystals are placed by the user in the x,y,z pos and rot parameters. The crystal is bent, so that it follows a curve on a cylinder of radius_x. The monochromator lies along the z plane, so when a diffraction angle of theta is desired, it should just be inserted in the ROTATED parameter around the y-axis. Instruments that showcase the use of this component is the "Test_monochromator_bent.instr", and the "ILL_SALSA.instr" under the examples folder. SALSA showcases its complex use in a real instrument, while Test_monochromator_bent makes a simple show of its capabilities.

Input parameters

Parameters in boldface are required; the others are optional.

Name

Unit

Description

Default

zwidth

m

Width of each crystal without bending.

0.2

yheight

m

Height of each crystal without bending.

0.1

xthickness

m

Thickness of each crystal without bending.

0.0005

radius_x

m

Radius of the circle the monochromator bends on in the plane. Can be negative.

2

radius_y

m

Radius of the (very large) circle the monochromator bends on as a side effect of the horizontal bending. The code assumes that it is so small that it does not affect the points of intersection appreciatively of the crystal.

0

plane_of_reflection

"Si\(^{400}\)"

The plane of reflection from the material. The list of possible reflections can be seen in the source code.

"Si400"

angle_to_cut_horizontal

degrees

Angle between cut and normal of crystal slab, horizontally

0

mosaicity

arcmin

Gaussian mosaicity of the crystal. Always the horizontal mosaicity

30

mosaic_anisotropy

1

Anisotropy of the mosaicity, changes vertical mosaicity to be mosaic_anisotropy*mosaicity

1

n_crystals

#

Number of crystals in your array.

1

domainthickness

μm

Thickness of the crystal domains.

10

temperature

K

Temperature of the monochromator in Kelvin.

300

optimize

Flag to tell if the component should optimize for reflections or not.

0

x_pos

vector

x-Position of each crystal

NULL

y_pos

vector

y-Position of each crystal

NULL

z_pos

vector

z-Position of each crystal

NULL

x_rot

vector

Rotation around x-axis for each crystal

NULL

y_rot

vector

Rotation around y-axis for each crystal

NULL

z_rot

vector

Rotation around z-axis for each crystal NOTE: Rotations happen around x, then y, then z.

NULL

n_reflections

The maximum number of reflections a neutron can undergo in the crystal array.

100

verbose

Verbosity of the monochromator. Used for debugging.

0

draw_as_rectangles

Draw the monochromators as boxes. DOES NOT WORK WHEN USING _rot parameters.

0

Links