The monitor modules are needed to obtain information about the wavelength, time, divergence or position (y-z-plane) dependent intensity or polarization distribution of the neutron beam at the position where it is placed. They write the intensity or average polarization as a function of the chosen parameter(s) as ASCII data into the monitor file. So the data of these file can either be visualised by the tool implemented in VITESS or by any graphics tool. The monitor modules do not influence the neutron beam, unless the option 'exclusive counts' is activated (see below).
There are different kinds of monitors:
- The generic module monitor1D allows to plot intensity (n/s) or polarisation as a function of any parameter, including color, in a 1D plot.
- The modules mon1_a allow to plot intensity (n/s) as a function of the parameter 'a' in a 1D plot
they exist for time, wavelength, energy, hor. position (y), vert. position (z), hor. diverg. (div-y), vert. diverg. (div-z) and radial diverg. (div-y-z)
- The modules monpol_a allow to plot polarization as a function of the parameter 'a' in a 1D plot
they exist for time, wavelength, hor. position (y), vert. position (z), hor. diverg. (div-y) and vert. diverg. (div-z)
- The generic module monitor2D allows to plot intensity or polarisation as a function of any combination of 2 parameters, including color, in a 2D plot
- The modules mon2_ab allow to plot intensity (n/s) as a function of the parameters 'a' and 'b' in a 2D plot
they exist for the combinations (y - z), (div-y - div-z), (ky - kz), (TOF - wavelength), (wavelength - div-y/div-z), (y - div-y), (z - div-z), (radius - div-y-z)
- The modules monitorpol_pos allows to plot polarization as a function of hor. and vert. pos (x - y) in a 2D plot
- The module mon_brilliance plots the brilliance (in n/(cm2sÅ sterad)) in a given time, position, wavelength and divergenz range in a 1D plot
The variable parameter can be: time, wavelength, y- or z-position, diy-y, div-z or div_rad (=div-y-z) or energy.
- Additionally, the intensity distribution on a banana shaped (or rectangular) detector can be shown by the module screen, which is described in the detector help file.
In contrast to the monitors, it propagates the neutrons to the defined area first before monitoring the distribution,
while all monitors take all neutron parameters as they are obtained by the previous module.
As practically all monitor functions are available using the generic monitors monitor1D or monitor2D or the brilliance monitor, all other monitors are practically obsolete. However, as many users will probably like to go on using some of the old monitor modules, mon1, mon2_pos and mon2_div will be kept in the future. The others are not supported anymore and will not be ported to VITESS 4.
These modules allow using any parameter ('monitor1D') or any combination of parameters ('monitor2D') to determine the distribution of either intensity or polarization. This includes the so-called 'color'. Using 'horizontal color' and 'vertical color' it can even be separated if reflection occur on horizontal or vertical guide walls.
Moreover, two of these parameters, in addition to the neutron wavelength, can be used as filters in order to restrict the parameter space shown in the plot. If desired, polarisation analysis can be applied, in which the average neutron spin component parallel to the analysis direction will be plotted in each bin of the diagram.
pos_x [cm] x component of the position pos_y [cm] y component of the position pos_z [cm] z component of the position div_y [deg] horizontal deviation of the flight direction from the beamline div_z [deg] vertical deviation of the flight direction from the beamline lambda [Ang] neutron wavelength energy [µeV] neutron energy time [ms] time of flight k_y [1/Ang] y component of the k-vector (k_y = 2 pi div_y / lambda) k_z [1/Ang] z component of the k-vector (k_z = 2 pi div_z / lambda) pos_r [cm] radius of the projection of the position vector on the y-z plane (in a cylindrical coordinate system) pos_phi [deg] orientation of pos_r in the y-z plane (0° in y-direction) pos_theta [deg] orientation of pos_r in the x-y plane (= horizontal component of the scattering angle, -180° - 180°) dir_phi [deg] orientation of the flight direction in the y-z plane (0° in y-direction) dir_theta [deg] deviation of the flight direction from beamline (= scattering angle, 0° - 180°) col_vert [] color of the trajectory by reflections in the vertical plane (i.e. on top or bottom plane) col_hor [] color of the trajectory by reflections in the horizontal plane (i.e. on left or right plane) color [] color of the trajectory (=col_hor+col_vert)
| Parameter Unit |
Description |
Range or Values |
Command Option |
| monitor file | The monitor output file contains intensity, its variation and the number of trajectories as a function of the chosen parameter | -O | |
| parameter on x-axis | the intensity or polarisation is shown as a function of this parameter | see parameter list | -X |
| minimal, maximal x-value | values defining the parameter range to be monitored on the 1st x-axis. | -w, -W | |
| number of x-bins | Number of the monitor channels on the x-axis | >0 default 100 |
-x |
| probability weight | if one deactivates the probability weight each neutron is considered with the weight 1, otherwise (default) the attributed probabilities. | 'yes' (default), 'no' | -p |
| exclusive counts | if activated, only those neutrons which have been monitored successfully are transferred to the subsequent module | 'no' (default), 'yes' | -e |
| filter lambda min, max |
minimal and maximal wavelength to be taken into account only neutrons with wavelengths in that range are considered in the evaluation |
-l, -L | |
| filter parameter 1, 2 |
1st and 2nd parameter so select trajectories to be considered for the monitor (But all are transferred to the successive modules, if 'exclusive counts'='no' is chosen.) |
see parameter list | -I, -J |
| filter combination | logical combination of the 2 filter parameters | 'AND', 'OR' | -C |
| filter 1 min, max | minimal and maximal value of filter parameter 1 | -u, -U | |
| filter 2 min, max | minimal and maximal value of filter parameter 2 | -v, -V | |
| Polarisation analysis | if activated, polarisation instead of intensity is monitored | 'no' (default), 'yes' | -e |
| analysis direction X, Y, Z |
only for monitoring polarization: the quantization direction is represented by a vector in cartesian coordinates |
default: (1, 0, 0) | -r, -s, -t |
| Parameter Unit |
Description |
Range or Values |
Command Option |
| monitor file | The monitor output file contains intensity, its variation and the number of trajectories as a function of the chosen parameter | -O | |
| parameter on x-axis, y-axis | parameter to be shown on the horizontal and vertical axis (see list above this table) | see parameter list | -X, -Y |
| minimal, maximal x-value | values defining the parameter range to be monitored on the horizontal axis. | -w, -W | |
| minimal, maximal y-value | values defining the parameter range to be monitored on the vertical axis. | -h, -H | |
| number of x-bins, y-bins | Number of the monitor channels on x- and y-axis resp. | >0 default 100 |
-x, -y |
| probability weight | if one deactivates the probability weight each neutron is considered with the weight 1, otherwise (default) the attributed probabilities. | 'yes' (default), 'no' | -p |
| exclusive counts | if activated, only those neutrons which have been monitored successfully are transferred to the subsequent module | 'no' (default), 'yes' | -e |
| file format |
Choose between matrix style and the 'xyz' representation (readable by gnuplot and other analysis software). 'compact' means a shorter header and fewer digits in the written float numbers of the simulated count rate values 'integer' means that detector counts are written to the matrix, they are obtained by multiplying the count rate and the measurement time given in the source module. If no value is given, 60 s are assumed. Note that the g2 program cannot handle integer values properly. |
'matrix', 'xyz', 'matrix_compact', 'xyz_compact' | -F | /td>
| filter lambda min, max |
minimal and maximal wavelength to be taken into account only neutrons with wavelengths in that range are considered in the evaluation |
-l, -L | |
| filter parameter 1, 2 |
1st and 2nd parameter so select trajectories to be considered for the monitor (But all are transferred to the successive modules, if 'exclusive counts'='no' is chosen.) |
see parameter list | -I, -J |
| filter combination | logical combination of the 2 filter parameters | 'AND', 'OR' | -C |
| filter 1 min, max | minimal and maximal value of filter parameter 1 | -u, -U | |
| filter 2 min, max | minimal and maximal value of filter parameter 2 | -v, -V | |
| Polarisation analysis | if activated, polarisation instead of intensity is monitored | 'no' (default), 'yes' | -e |
| analysis direction X, Y, Z |
only for monitoring polarization: the quantization direction is represented by a vector in cartesian coordinates |
default: (1, 0, 0) | -r, -s, -t |
| Parameter Unit |
Description |
Range or Values |
Command Option |
| monitor file | The monitor output file contains intensity, its variation and the number of trajectories as a function of the chosen parameter | -O | |
| number of bins | Number of the monitor channels | >= 0 default 100 |
-n |
| colour | if 'all files'='no', all neutrons witha color different than this are excluded from monitoring, if 'colour' >= 0\nif 'all files'='yes', this is the max. color to which additional monitor files are generated | default: -1 | -C |
| reference file | The monitor output file contains intensity, its variation and the number of trajectories as a function of the chosen parameter | -R | |
| minimal value maximal value |
the values defining the parameter range to be monitored. | ≥0 | -m, -M |
| time interval begin, end |
minimal and maximal TOF to be taken into account only neutrons arriving in that time interval are considered in the evaluation |
-t, -T | |
| normalise with binsize | 'no': intensities of the neutron trajctories are only distributed into channels 'yes': intensities are normalized to the channel width 'reference file': intensities are divided by those in the reference file | 'no' (default), 'yes', 'reference file' | -f |
| all files | if "yes" the intensity of all trajectories is displayed in the given monitor file and additionally files containing intensities of colour 0, 1, 2, ... 'colour' are written.'no' (default), 'yes' | -c | |
| probability weight | if one deactivates the probability weight ('no'), each trajectory is considered with the weight 1, otherwise ('yes') with the attributed intensity weight. Note: for a 1D intensity monitor, deactivation is not useful, as the number of contributing trajectories is anyway written to the output file so that one gets 2 identical columns in the monitor file |
'yes' (default), 'no' | -p |
| exclusive counts | if activated, only those neutrons which have been monitored successfully are transferred to the subsequent module | 'no' (default), 'yes' | -e |
| filter lambda min, max |
minimal and maximal wavelength to be taken into account only neutrons with wavelengths in that range are considered in the evaluation |
-l, -L | |
| filter Y pos min, max |
minimal and maximal wavelength to be taken into account only neutrons arriving in that range are considered in the evaluation |
-y, -Y | |
| filter Z pos min, max |
minimal and maximal wavelength to be taken into account only neutrons arriving in that range are considered in the evaluation |
-z, -Z |
| Parameter Unit |
Description |
Range or Values |
Command Option |
| monitor file | The monitor output file contains intensity, its variation and the number of trajectories as a function of the chosen parameter | -O | |
| number of bins | Number of the monitor channels | >= 0 default 100 |
-n |
| minimal value maximal value |
the values defining the parameter range to be monitored. | ≥0 | -m, -M |
| time interval begin, end |
minimal and maximal TOF to be taken into account only neutrons arriving in that time interval are considered in the evaluation |
-t, -T | |
| probability weight | if one deactivates the probability weight each neutron is considered with the weight 1, otherwise (default) the attributed probabilities (due to the operations of the modules before) are considered. |
'yes' (default), 'no' | -p |
| exclusive counts | if activated, only those neutrons which have been monitored successfully are transferred to the subsequent module (e.g. the wavelength of the neutron lies in the monitored wavelength interval and it is not taken our because of filters - see below) |
'no' (default), 'yes' | -e |
| analysis direction X, Y, Z | the quantization direction is represented by a vector in cartesian coordinates | default: (1, 0, 0) | -a, -b, -c |
| Parameter Unit |
Description |
Range or Values |
Command Option |
| monitor file | The monitor output file contains intensity, its variation and the number of trajectories as a function of the chosen parameter | -O | |
| number of y-, z-bins | Number of the monitor channels in horizontal and vertical direction resp. | ≥0 default 100 |
-y, -z |
| minimal, maximal y-value | values defining the parameter range to be monitored on the horizontal axis. | -w, -W | |
| minimal, maximal z-value | values defining the parameter range to be monitored on the vertical axis. | -h, -H | |
| probability weight | if one deactivates the probability weight ('no'), each trajectory is considered with the weight 1, otherwise ('yes') with the attributed intensity weight. | 'yes' (default), 'no' | -p |
| exclusive counts | if activated, only those neutrons which have been monitored successfully are transferred to the subsequent module | 'no' (default), 'yes' | -e |
| file format |
Choose between matrix style and the 'xyz' representation (readable by gnuplot and other analysis software). 'compact' means a shorter header and fewer digits in the written float numbers of the simulated count rate values 'integer' means that detector counts are written to the matrix, they are obtained by multiplying the count rate and the measurement time given in the source module. If no value is given, 60 s are assumed. Note that the g2 program cannot handle integer values properly. |
-F | |
| filter lambda min, max |
minimal and maximal wavelength to be taken into account only neutrons with wavelengths in that range are considered in the evaluation |
-l, -L | |
| filter Y pos min, max |
minimal and maximal wavelength to be taken into account only neutrons arriving in that range are considered in the evaluation |
-u, -U | |
| filter Z pos min, max |
minimal and maximal wavelength to be taken into account only neutrons arriving in that range are considered in the evaluation |
-v, -V |
These modules allow using any parameter ('monitor1D') or any combination of parameters ('monitor2D') to determine the distribution of either intensity or polarization. This includes the so-called 'color'. Using 'horizontal color' and 'vertical color' it can even be separated if reflection occur on horizontal or vertical guide walls.
For continuous sources the brilliance calculated is always a time averaged brilliance.
Therefore, time interval and frequency have to be left blank.
If the time averaged brilliance shall be calculated for pulsed sources, they have to be left blank as well.
Otherwise, the brilliance is calculated as the brilliance in the given time range and needs to be normalized by the frequency.
Depending on the existence of a reference file, the monitor file contains either the brilliance [n/(cm2 s sterad Å]
or the brilliance transfer, i.e. the fraction of the brilliance that is transferred from source (or another reference point)
to the position of the actual brilliance monitor. To get correct result, the brilliance monitors should be identical.
Average and peak brilliance - the maximal value found in the brilliance monitor file and the average value, i.e. the sum divided by the number
of bins - are written to the log file.
The following parameters define the phase space considered for the brilliance calculation. Neutrons are only considered if their properties are within all given ranges. A range has to be given for position, time, lambda or energy, divergence (either in cartesian or radial co-ordinates). A missing value is regarded as +∞ (max.) or -∞ (min.), or 0 for minimal radius. One of them has to be chosen as the 'variable parameter'. If 'time' is the variable parameter or a frequency > 0 is given, a pulsed source is assumed. If 'time' is the variable parameter and no frequency is given, the frequency is taken from 'simulation.inf'.
time [ms] time of flight lambda [Ang] neutron wavelength energy [meV] neutron energy pos_y [cm] y component of the position (horizontal) pos_z [cm] z component of the position (vertical) pos_rad [cm] distance from the beam axis div_y [deg] horizontal deviation of the flight direction from the beam axis div_z [deg] vertical deviation of the flight direction from the beam axis div_rad [deg] radial deviation of the flight direction from beam axis
| Parameter Unit |
Description |
Range or Values |
Command Option |
| monitor file | Name of the file containing the brilliance or the brilliance transfer (see below) as a function of the variable parameter | -O | |
| reference file | Name of the file containing the brilliance relative to which the brilliance transfer is calculated. 'Monitor file' contains the brilliance transfer in this case. | -S | |
| flux file | If a file name is given here, one line is written or added to this file, which contains the following numbers: mean wavelength (=center of the wavelength range), mean y-position and z-position, mean horizontal, vertical and radial divergence and average and peak brilliance (see above). This can be used calculate the brilliance as a function of a second parameter in running a series of simulation. | -F | |
| number of bins | the interval of the 'variable parameter' (e.g. 'lambda') will be partitioned into 'number of bins' segments of equal size. | ≥ 1 default 100 |
-n |
| colour | if colour = -1, the intensity of all trajectories is displayed if colour ≥ 0 only the trajectories of that colour are considered | ≥ -1 | -C |
| variable parameter | The brilliance is monitored as a function of this parameter (see list above this table). It will be the x-axis of the monitor file. | -k | |
| norm. type |
'absolute': absolute brilliance [n/(cm² s Å sr)] 'transfer': brilliance transfer '1% lambda': brilliance within 1% Δλ/λ [n/(cm² s Å sr)] |
'absolute', 'transfer', '1% lambda' | -N |
| logarithmic binning |
'no' : fixed channel width 'yes': constant ratio of upper to lower bound value of each channel, i.e. exponential increase in channel width |
'no' (default), 'yes' | -B |
| min., max. time [ms] |
minimal and maximal time of flight Only necessary for time dependent brilliance of pulsed sources. Leave the time range empty for time averaged brilliance on pulsed sources. |
-t, -T | |
| min., max. lambda [Å] |
minimal and maximal neutron wavelength | ≥ 0 | -l, -L |
| min., max. energy [meV] |
minimal and maximal neutron energy | ≥ 0 | -m, -M |
| low, up bound y-pos [cm] |
minimal and maximal horizontal position | -y, -Y | |
| low, up bound z-pos [cm] |
minimal and maximal vertical position | -z, -Z | |
| low, up bound radius [cm] |
minimal and maximal distance from the beam axis | ≥ 0 | -d, -D |
| low, up bound hor div [deg] |
minimal and maximal horizontal divergence | -h, -H | |
| low, up bound vert div [deg] |
minimal and maximal vertical divergence | -v, -V | |
| low, up bound radial div [deg] |
minimal and maximal radial divergence | ≥ 0 | -r, -R |
| frequency |
source frequency in case of a pulsed source It is necessary to calculate from time averaged to actual brilliance). If the frequency is given, a pulsed source is assumed. If it is not given and a frequency is needed, it is taken from 'simulation.inf'. |
-f |
Last modified: Mon Jun 30 17:24:23 MEST 2003 G. Zs.