Each piece is described by 5 planes: left, right, top , bottom and exit. Each plane is described by an equation of first order:
ax + by + cz + d = 0
The coefficients a,b,c,d are calculated from guide length as well as width
and height of entrance and exit. The trajectory is calculated until the
exit plane is reached, taking into account the intensity loss for each reflection.
A warning is given, if a trajectory is found out of the exit area.
In case of a polygon section, a radius of curvature (not equal zero) must be given. The co-ordinate system is rotated by an angle
beta = 2.0*arcsin(length/(2*radius))
between two succeeding pieces. The first piece is aligned to the preceding module, the last piece is aligned to the following module. The algorithm used here works properly only for guides with constant width. Therefore the combination of curvature and horizontal converging/diverging is not supported!
If the real guide does not consist of straight pieces, a large number
of pieces must be used for a good simulation. Alternatively, the module 'bender'
can be used. The module 'bender' uses arcs instead of planes for the surface
of the guide.
mirr0.dat: absorbing coating (reflectivity = 0.0)The reflectivity file contains the probability of reflection in dependence of the incident angle for neutrons with a wavelength of 1 Å. Each row contains 10 data points and covers 0.01 deg, i.e. each point gives the probability average over an angular interval of 0.001 deg (the second row covers 0.01-0.02 deg a.s.o.). The number of data points may vary between 1 and 1000. If end of file is reached (e.g. only 52 values are given) the probability to reflect 1 Å neutrons for higher angles is set to 0. If no reflectivity file is given as an input, the guide operates in total absorption mode, i.e. each neutron hitting a guide wall is lost.
mirr1a.dat: Ni coating (theta_Ni = 0.099138 deg/Å*lambda)
mirr1b.dat: Ni-58 coating (theta_Ni-58 = 0.11456 deg/Å*lambda)
mirr2linear.dat: supermirror coating,
reflectivity 0.99 -> 0.9 from theta_Ni to 2 theta_Ni; cutoff at 2 theta_Ni;
mirr30opt.dat: supermirror coating,
reflectivity 0.99 -> 0.8 from theta_Ni to 3 theta_Ni; cutoff at 3 theta_Ni;
mirr30std.dat: supermirror coating,
reflectivity 0.99 -> 0.75 from theta_Ni to 3 theta_Ni; cutoff at 3 theta_Ni;
mirr3+.dat: super-mirror coating (3.5 theta_Ni)
mirr23FeCo.dat: supermirror coating of FeCo-Si,
reflectivity 0.99 -> 0.77 from theta_Ni to 2.3 theta_Ni; cutoff at 2.3 theta_Ni;
| Parameter Unit |
Description | Command option |
| Horizontal / vertical shape |
shape of the guide: constant: same cross-section on the whole length (usually 1 piece) linear : linearly converging or diverging between entrance and exit (usually 1 piece) curved (only in horizontal plane): several pieces form part of a regular polygon . The first piece is aligned to the preceding, the last to the succeeding module. The radius of the circle through the polygon corners and the number or pieces need to be given. parabolic: the guide consists of several straight pieces that approach a parabola, which is defined by entrance and exit width. The number or pieces need to be given. elliptic: the guide consists of several straight pieces that approach an ellipse, which is defined by entrance and exit width, and an angle describing the position of the ellipse. This angle and the number or pieces need to be given (see below). |
-Y, -Z |
| entrance width, height [cm] |
size of the guide entrance (in y- and z-direction) | -w, -h |
| exit width, height [cm] |
size of the guide exit (in y- and z-direction) | -W, -H |
| piece length [cm] |
length of one piece of the guide | -p |
| number of pieces | number of pieces that build the polygon section | -n |
| curvature (radius) [m] |
radius of a circle through the polygon; for a straight guide: radius = 0 or nothing | -R |
| left, right, top/bottom plane | reflectivity file for the coating of the guide on the inner side
(left), on the outer side (right), on the top and on the bottom plane. If no file for the bottom plane is given, the file of the top plane is used for the bottom. |
-i, -I, -j, -J |
| number of channels | number of vertical channels, into which the guide is divided | -b |
| substrate width [cm] |
thickness of the material that separates two neighbouring channels | -s |
| surface waviness [deg] |
waviness of the inner guide surface, i.e. deviations from a perfectly
plane surface |
-r |
| angle defin. pos. of ellipse [deg] |
only needed for elliptic shape: This angle describes the position of the ellipse. 90 deg means that the guide entrance is the position of max. width/height of the ellipse, i.e. its center. An angle > 90 deg shifts the center towards the guide exit, i.e. the max. width / height is larger than the guide entrance and will be reached somewhere in the guide (or lies behind the guide exit.) An angle < 90 deg sets the center before the beginning of the guide. Thus the guide is converging on the whole length and the exit must be smaller than the entrance. |
-y, -z |
| abutment loss | yes: neutrons that hit the surface close to one of the ends of
the guide (or a guide segment) are rejected. no: neutrons are treated with the given reflectivity in the whole guide |
-a |
Last modified: Tuesday, 03-Jul-2007 16:14:09 CEST