14.58  The Pol_bender_tapering McStas Component

Polarising bender.

Identification

• Author: Erik Bergbaeck Knudsen (erkn@fysik.dtu.dk)

• Origin: DTU Physics

• Date: June 2012

Description

A component modelling a set of identical blades bent to form a multcihannel (nslits) bender. The bender has a cylindrically curved entry plane (Will be extended to also allow a flat entry plane).

The bender may also be tapered such that it can have focusing or defocusing porperties. This may be specified through the "channel_file"-parameter, which points to a data file in which the individual channels are defined by an entry- and an exit-width.

The file format for channel file columns: > #d-spacing1 d-spacing2 l_spacer d-coating1 d-coating2

> 1e-3  0.8e-3 1e-5  1e-9 1e-9

Each blades is considered coated with a reflecting coating, whose thickness is defined in the latter two columsn of the channel data file.

Coating reflectivities are read from another data file with separate reflectivities for up and down spin. When a neutron ray hits a blade the polarization vector associated with the ray is decomposed into spin-up and down probablities, which in turn determines the overall reflectivity for this ray on the mirror. Furthermore the probabilities are used to also reconstruct the polarization vector of the reflected ray.

File format for the reflectivity file: > #parameter = m > q/m R(up) R(down)

The effect of spacers inside the channels is modelled by absorption only. The depth of the spacers in a channel is considered constant for one channel (set in the channel data file), the number of them is constant across all channels and is an input parameter to the component.

Input parameters

Parameters in boldface are required; the others are optional.

Links

• Component source code found in file Pol_bender_tapering.comp.