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/*******************************************************************************
*
* VITESS and McStas, neutron ray-tracing packages
* Copyright 1997-2005, All rights reserved
* Hahn-Meitner-Institut Berlin, Germany
* Risoe National Laboratory, Roskilde, Denmark
* Institut Laue Langevin, Grenoble, France
*
* Component: Vitess_ChopperFermi
*
* %I
* Written by: Geza Zsigmond
* Date: Sep 2004
* Origin: VITESS module 'chopper_fermi'
* Modified by: adapted for McStas by <a href="mailto:lieutena@ill.fr">K. Lieutenant</a>, Mar 2005;
*
* Fermi chopper with absorbing walls using the VITESS module 'chopper_fermi'
*
* %D
* This component simulates a Fermi chopper with absorbing walls. The rotation axis is
* vertical (y-axis), i.e. the path length through the channels is given by the length
* 'depth' along the z-axis.
* The shape of the channels can be straight, curved with circular, or curved with ideal
* (i.e. close to a parabolic) shape. This is determined by the parameter 'GeomOption'.
*
* Geometry for straight and circular channels:
* The geometry of the chopper consists of a rectangular shaped object with a channel
* system. In transmission position, there are 'Nchannels' slits along the x-axis,
* separated by absorbing walls of thickness 'wallwidth' giving a total width 'width'.
* The rectangular channel system is surrounded by a so-called shadowing cylinder
* (cf component manual).
*
* Geometry for parabolic channels:
* In this case, the Fermi chopper is supposed to be a full cylinder, i.e. the central
* channels are longer than those on the edges (cf. figure in the component manual).
* The other features are the same as for the other options.
*
* Apart from the frequency of rotation, the phase of the chopper at t=0 has to be given;
* phase = 0 means transmission orientation.
*
* The option 'zerotime' may be used to reset the time at the chopper position. The
* consequence is that only 1 pulse is generated instead of several.
*
* NOTE: This component must NOT be located at the same position as the previous one.
* This also stands for monitors and Arms. A non zero distance must be defined.
*
* Examples:
* straight Fermi chopper, 18000 rpm, 20 channels a 0.9 mm separated by 0.1 mm walls,
* 16 mm channel length, minimal shadowing cylinder, phased to be open at 1 ms,
* generation of only 1 pulse, normal precision (for short wavelength neutrons)
* Vitess_ChopperFermi(GeomOption=0, zerotime=1, Nchannels=20, Ngates=4,
* freq=300.0, height=0.06, width=0.0201,
* depth=0.016, r_curv=0.0, diameter=0.025691, Phase=-108.0,
* wallwidth=0.0001, sGeomFileName="FC_geom_str.dat")
*
* Fermi chopper with circular channels, 12000 rpm, optimized for 6 Ang, several pulses,
* highest accuracy (because of long wavelength neutrons used), rest as above
* Vitess_ChopperFermi(GeomOption=2, zerotime=0, Nchannels=20, Ngates=8,
* freq=200.0, height=0.06, width=0.0201,
* depth=0.016, r_curv=0.2623, diameter=0.025691, Phase=-72.0,
* wallwidth=0.0001, sGeomFileName="FC_geom_circ.dat")
*
* %VALIDATION
* Apr 2005: extensive external test, most problems solved (cf. 'Bugs' and source header)
* Validated by: K. Lieutenant
*
* limitations: slow (10 times slower than FermiChopper), especially for a high number of channels
*
* %BUGS
* reduction of transmission by a large shadowing cylinder underestimated
*
* %P
* GeomOption: [1] option: 0:straight 1:parabolic 2:circular
* zerotime: [1] option: 1:'set time to zero' 0: 'do not'
* Nchannels: [1] number of channels of the Fermi chopper
* Ngates: [1] number of gates defining the channel: 4=default, 6 or 8 for long wavelengths
* freq: [Hz] number of rotations per second
* height: [m] height of the Fermi chopper
* width: [m] total width of the Fermi chopper
* depth: [m] channel length of the Fermi chopper
* r_curv: [m] radius of curvature of the curved Fermi chopper
* diameter: [m] diameter of the shadowing cylinder
* Phase: [deg] dephasing angle at zero time
* wallwidth: [m] thickness of walls separating the channels
* sGeomFileName: [str] name of output file for geometry information
*
* CALCULATED PARAMETERS:
* Option: [-] 1: straight FC, 2: curved FC
* CurvGeomOption: [-] 1: ideal shape (nearly parabolic) 2: circular
* TOF: [ms] TOF of neutron under consideration
* WL: [Ang] wavelength of neutron
* radius_of_curv: [cm] radius of curvature (curved FC)
* main_depth: [cm] max. channel length due to diameter and total_width
* shift_y: [cm] shift to channel actually written to geometry file
* angle_channel: [rad] half of the curvature of a curved Fermi chopper
* phase0: [rad] chopper phase at TOF of neutron to chopper centre
* y_ch: [cm] position of gates perpendicular to flight direction
* x_ch: [cm] position of gates along flight direction
* coef_pi: [-] number of half-rotation to reach identical state
* GeomFilePtr: [-] pointer to geometry file name
* Pos: [cm] position of neutron
* Dir: [-] flight direction of neutron
* Neutrons: [-] neutron parameter set at end of chopper
* pos_ch: [cm] centre position of the Fermi chopper
* omega: [1/s] angular frequency of the chopper
* optimal_wl: [Ang] wavelength of highest transmission of curved FC
*
*
* %Link
* <a href="http://www.hmi.de/projects/ess/vitess/DOC/chopper_fermi_str.html">straight VITESS Fermi chopper</a>
* %Link
* <a href="http://www.hmi.de/projects/ess/vitess/DOC/chopper_fermi_cur.html">curved VITESS Fermi chopper</a>
*
* %E
*******************************************************************************/
DEFINE COMPONENT Vitess_ChopperFermi
SETTING PARAMETERS (string sGeomFileName=0, int GeomOption=0, int zerotime=0,
int Nchannels=20, int Ngates=4,
freq=300.0, height=0.05, width=0.04,
depth=0.03, r_curv=0.5, diameter=0.071, Phase=0.0,
wallwidth=0.0002)
/* Neutron parameters: (x,y,z,vx,vy,vz,t,sx,sy,sz,p) */
SHARE
%{
%include "general.c"
%include "intersection.c"
%include "vitess-lib"
%include "chopper_fermi"
%}
DECLARE
%{
double omega; /* rotation frequency */
double optimal_wl; /* optimal wavelength */
VectorType pos_ch; /* centre pos. of the FC in the frame of the exit of the prev. comp. [cm] */
%}
INITIALIZE
%{
omega = 0.0;
optimal_wl = 0.0;
double x,y,z;
coords_get(POS_R_COMP_INDEX(INDEX_CURRENT_COMP), &x, &y, &z);
pos_ch[0] = -100.0 * z;
pos_ch[1] = -100.0 * x;
pos_ch[2] = -100.0 * y;
McInitVt();
/* transformation of units */
height *= 100.0; /* m -> cm */
width *= 100.0;
depth *= 100.0;
diameter *= 100.0;
r_curv *= 100.0;
wallwidth *= 100.0;
omega = freq*2*PI/1000.0; /* 1/s -> 2pi/ms */
Phase *= DEG2RAD;
/* checks and completion of input data */
CurvGeomOption = (int) GeomOption;
if (GeomOption > 0 && omega*r_curv==0)
{
printf("Error: 'omega*r_curv' must not be zero for curved Fermi chopper"); exit(-1);
}
switch(GeomOption)
{
case 0: Option=1; optimal_wl=0.0; break;
case 1: Option=2; optimal_wl=LAMBDA_FROM_V(2.0*omega*r_curv); break;
case 2: Option=2; optimal_wl=LAMBDA_FROM_V(2.0*omega*r_curv); break;
default: printf("Wrong option! Good options: 0-straight, 1-parabolic, 2-circular");
}
ChopperFermiInit(0, NULL);
%}
TRACE
%{
int i=0;
InputNeutrons[i] = mcstas2vitess(x, y, z, vx, vy, vz, t, sx, sy, sz, p);
#define MCSTAS_TRACE
%include "chopper_fermi.c"
#undef MCSTAS_TRACE
vitess2mcstas(Neutrons, &x, &y, &z, &vx, &vy, &vz, &t, &sx, &sy, &sz, &p);
%}
FINALLY
%{
ChopperFermiCleanup();
McCleanupVt();
%}
MCDISPLAY
%{
double index=0;
double xpos, zpos, ymin, ymax, rad, w_ch;
Nchannels = (Nchannels > 11 ? 11 : Nchannels);
w_ch = (width - (Nchannels+1) * wallwidth) / Nchannels/100;
rad = diameter/2.0/100;
ymin = -height/2.0/100;
ymax = height/2.0/100;
/* cylinder top/center/bottom */
circle("xz", 0,ymax,0,rad);
circle("xz", 0,0 ,0,rad);
circle("xz", 0,ymin,0,rad);
/* vertical lines to make a kind of volume */
line( 0 ,ymin,-rad, 0 ,ymax,-rad);
line( 0 ,ymin, rad, 0 ,ymax, rad);
line(-rad,ymin, 0 ,-rad,ymax, 0 );
line( rad,ymin, 0 , rad,ymax, 0 );
/* slit package */
index = -Nchannels/2;
zpos = depth/2/100;
for (index = -Nchannels/2; index < Nchannels/2; index++) {
xpos = index*w_ch;
multiline(5, xpos, ymin, -zpos,
xpos, ymax, -zpos,
xpos, ymax, +zpos,
xpos, ymin, +zpos,
xpos, ymin, -zpos);
}
/* cylinder inner sides containing slit package */
xpos = Nchannels*w_ch/2;
zpos = sqrt(rad*rad - xpos*xpos);
multiline(5, xpos, ymin, -zpos,
xpos, ymax, -zpos,
xpos, ymax, +zpos,
xpos, ymin, +zpos,
xpos, ymin, -zpos);
xpos *= -1;
multiline(5, xpos, ymin, -zpos,
xpos, ymax, -zpos,
xpos, ymax, +zpos,
xpos, ymin, +zpos,
xpos, ymin, -zpos);
%}
END
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