[ Identification | Description | Input parameters | Links ]

# The `Guide_multichannel` Component

Multichannel neutron guide with semi-transparent blades. Derived from Guide_channeled by Christian Nielsen. Allows to simulate bi-spectral extraction optics.

## Identification

- Site:
- Author: Jan Saroun (saroun@ujf.cas.cz)
- Origin: Nuclear Physics Institute, CAS, Rez
- Date: 17.3.2022

## Description

##

##

    Models a rectangular guide with equidistant vertical blades of finite thickness.
    The blades material can be either fully absorbing or semi-transparent. The absorption
    coefficient is wavelength dependent according to the semi-empirical model used
    e.g. in J. Baker et al., J. Appl. Cryst. 41 (2008) 1003 or
    A. Freund, Nucl. Instr. Meth. A 213 (1983) 495.
    Data are provided for Si and Al2O3.

    All walls are flat, curvature is not implemented (may be added as a future upgrade)
    Tapering is possible by setting different entry ad exit dimensions.
    Different guide coating can be set for vertical and horizontal mirrors.
    For transparent walls, neutrons are alloed to migrate between channels and to
    propagate through the blades.

    The model is almost equivalent to the GUIDE component in SIMRES (http://neutron.ujf.cas.cz/restrax)
    when used with zero curvature and type set to "guide or bender".
    The features from SIMRES not included in this McSas model are:
    - has a more conservative model for absorption in blades: events above r(m<mc) are automatically ABSORBED.
    - defines waviness
    - works with bent geometry
    - works with gravity
    - allows for 2D grid of blades

    bug fix 24/3/2017: incorrect handling of transition into blades = no transmission
    </PRE>

    Input parameters
    Parameters in boldface are required;
    the others are optional.

     NameUnitDescriptionDefault

     w1(m)    Width at the guide entry
     h1(m)    Height at the guide entry
     w2(m)    Width at the guide exit0
     h2(m)    Height at the guide exit0
     l(m)    Length of guide
     R0(1)    Low-angle reflectivity0.995
     Qc(AA-1) Critical scattering vector0
     alpha(AA)   Slope of reflectivity0
     m(1)    m-value of material. Zero means completely absorbing.0
     nslit(1)    Number of channels in the guide (>= 1)1
     dlam(m)    Thickness of lamellae0.0005
     Qcx(AA-1) Critical scattering vector for left and right vertical0.0218
     Qcy(AA-1) Critical scattering vector for top and bottom mirrors0.0218
     alphax(AA)   Slope of reflectivity for left and right vertical4.38
     alphay(AA)   Slope of reflectivity for top and bottom mirrors4.38
     W(AA-1) Width of supermirror cut-off for all mirrors0.003
     mx(1)    m-value of material for left and right vertical mirrors1
     my(1)    m-value of material for top and bottom mirrors. Zero1
     mater(string)   "Si", "Al2O3", or "absorb" (default)"absorb"

      AT (
      ,
      ,

      ) RELATIVE

      ROTATED (
      ,
      ,

      ) RELATIVE

    Links

       Source code for Guide_multichannel.comp.

     [ Identification
     | Description
     | Input parameters
     | Links ]