The `Monochromator_pol` Component

Flat polarizaing monochromator crystal.

Identification

Author: Peter Christiansen
Origin: RISOE
Date: 2006
Version: 1.3

Description

Based on Monochromator_flat.
Flat, infinitely thin mosaic crystal, useful as a monochromator or analyzer.
For an unrotated monochromator component, the crystal surface lies in the Y-Z
plane (ie. parallel to the beam).
The mosaic and d-spread distributions are both Gaussian.
Neutrons are just reflected (billard ball like). No correction is done for 
mosaicity of reflecting crystal.
The crystal is assumed to be a ferromagnet with spin pointing up 
eta-tilde = (0, 1, 0) (along y-axis), so that the magnetic field is 
pointing opposite (0, -|B|, 0).

The polarisation is done by defining the reflectivity for spin up
(Rup) and spin down (Rdown) (which can be negative, see now!) and
based on this the nuclear and magnetic structure factors are
calculated:
FM = sign(Rup)*sqrt(|Rup|) + sign(Rdown)*sqrt(|Rdown|)
FN = sign(Rup)*sqrt(|Rup|) - sign(Rdown)*sqrt(|Rdown|)
and the physics is calculated as 
Pol in = (sx_in, sy_in, sz_in) 
Reflectivity R0 = FN*FN + 2*FN*FM*sy_in + FM*FM 
               (= |Rup| + |Rdown| (for sy_in=0))
Pol out:
	sx = (FN*FN - FM*FM)*sx_in/R0;
	sy = ((FN*FN - FM*FM)*sy_in + 2*FN*FM + FM*FM*sy_in)/R0;
	sz = (FN*FN - FM*FM)*sz_in/R0;

These equations are taken from: 
Lovesey: "Theory of neutron scattering from condensed matter, Volume
2", Eq. 10.96 and Eq. 10.110

This component works with gravity (uses PROP_X0).

Example: Monochromator_pol(zw=0.2, yh=0.2, mosaic=30.0, dspread=0.0025,
                           Rup=1.0, Rdown=0.0, Q=1.8734)

Input parameters

Parameters in boldface are required; the others are optional.

Name	Unit	Description	Default
zw	m	Width of crystal
yh	m	Height of crystal
mosaic	arc minutes	Mosaicity (FWHM)	30.0
dspread	1	Relative d-spread (FWHM)	0
Q	AA-1	Magnitude of scattering vector	1.8734
DM	Angstrom	monochromator d-spacing instead of Q = 2*pi/DM	0
pThreshold	-	if probability>pThreshold then accept and weight else random	0
Rup	1	Reflectivity of neutrons with polarization up	1
Rdown	1	Reflectivity of neutrons with polarization down	1
debug	-	if debug > 0 print out some info about the calculations	0

Output parameters

Name	Unit	Description	Default
mos_rms
d_rms
mono_Q
FN
FM

The Monochromator_pol Component

Identification

Description

Input parameters

Output parameters

Links

The `Monochromator_pol` Component