# VITESS Tool: Generate Extraction System

This tool generates an input file for the sm_ensemble module, describing a (e.g. bispectral) extraction system consisting of up to 50 mirrors. Each mirror can be either transparent, i.e. taking attenuation of the chosen material into account, or intransparent, i.e. non-reflected neutrons are absorbed (guide walls). Restrictions like the same shape for all mirrors do not reflect restrictions in the sm_ensemble module; if more complicated mirror setups than foreseen in this tool are desired, this tool can be used as starting point to understand the creation process of a sm_ensemle input file, in particular the geometry description. For the same reason, reflectivity and and attenuation are set to be equal for up- and down-type spins here.

## The following information has to be given as input:

File format old/new
Old file format means the default format before VITESS 3.2. The only change here is the interpretation of the first number in each row, which has been extended from 0 (turned off) and 1 (turned on) to the additional possibility 2: turned on only for reflection, i.e. intransparent wall. The new file format does not include thetac, thetacsm, Rcsm, μ*d and μincoh*d anymore. Instead, the thickness d and the supermirror coating m are listed. Intransparent walls are marked by setting the first number (on/off switch) to 2.
See also sm_ensemble help.
Number of mirrors
Number of super-mirror coated plates. (Note: Differently to VITESS 3.1, transparent and intransparent mirrors (guide walls) are not counted separately anymore.)
Mirror plane
refers to the orientation of the mirror plates: vertical (horizontal) means the mirror is (approximately) embedded in the x-z (x-y) plane.
Equidistant mirrors of same length and with same inclination?
Yes/No: if yes, a stack of identical mirror plates is assumed (either transparent or intransparent). Only a common length, angle to the x-axis, substrate thickness and coating has to be given. The smallest y or z coordinate (y1 in fig. 1) and the distance between mirrors define the position of each mirror in the system (see figure 1). In this case, x=0 is set at the beginning of the mirrors.
If no, a seperate angle, length and position (in x and y or z) has to be given for each mirror (see fig. 2), and transparent plates can be combined with intransparent (e.g. guide walls) with different mirror coatings.
Transparent mirror
Yes or no: if no, the mirror can only reflect or absorb neutrons.
Mirror inclination w.r.t. x-axis
Angle to x-axis, see examples in figures 1-3.
Mirror length
Length of the mirror's projection on x-axis, see fig. 1.
(Smallest) y/z-coordinate
Horizontal (vertical) position of the lowest mirror when viewed in x-y (x-z) plane (y1 in example of figure 1). Has to be given only for equidistant mirrors of same length and with same inclination. Otherwise, every yi (zi) has to be specified (as in figures 2,3).
Mirror coating m
m-value of supermirror coating between 1 and 7 [→ theta_csm=0.00173⋅m, R_csm(m) as given on http://www.swissneutronics.ch/products/coatings.html. For non-integer m, R_csm(m) is extrapolated.].
Are the mirrors rectangular? Mirror width
Yes/No: if yes, only one width (i.e. length in y or z direction) has to be given. If no, a trapezoidal shape is assumed and width1 and width2 have to be given seperately, where the former corresponds to the width at lower x position (i.e. at the entry of the extraction system) as shown in the lower part of figure 1. All mirrors have the same width1, width2. For guide walls, each wall has to be assigned a seperate width1, width 2.
Mirror substrate thickness d
Substrate thickness, determines attenuation: in old file format, silicon is assumed [→ μ*d=0.0048⋅d, μ_incoh*d=0.030⋅d]. If the new file format has been chosen, the thickness is directly written to the file and is used in the sm_ensemble module with the chosen substrate material to determine the attenuation.

Figure 1: Simple mirror system of 3 parallel mirrors with same length and angle, mirror plane is vertical.

Figure 2: Mirror system of 3 mirrors with different length and angles (α3>α2>α1>0, α1,wall<0), and one non-transparent guide wall. Mirror plane is vertical.

Figure 3: Bent mirror built by 3 seperate mirror plates.