[ Identification | Description | Input parameters | Links ]

# The `Test_Sqw_monitor` Instrument

A simple ToF with cylindrical/spherical sample, and furnace/cryostat/container. The sample can be hollow.

## Identification

- Site: Tests_samples
- Author: E. Farhi
- Origin: ILL
- Date: Feb 2014

## Description

    This instrument models a generic, tunable, neutron time-of-flight spectrometer.

    The incoming flux at the sample brings neutrons with 'beam_wavelength_Angs' wavelength.
    The energy resolution at the sample is given as 'beam_resolution_meV'.
    The beam size at the sample is set to the sample cross section (e.g. ~2 x 5 cm).

    The sample geometry is either cylindrical ('sample_radius_m' and 'sample_height_m')
    or spherical ('sample_height_m=0'). The sample can be hollow when given a thickness
    'sample_thickness_m', or filled ('sample_thickness_m=0'). When in cylindrical geometry,
    it is surrounded by a container with thickness 'container_thickness_m'. The container
    material is specified as a powder file name 'container' in the McStas Sqw or PowderN format,
    e.g. 'Al.laz' or 'Nb.laz'. Setting 'container=0' removes the container.

    The sample scattering is characterised by its coherent and incoherent contributions
    given as 'sample_coh' and 'sample_inc' file names in McStas Sqw or PowderN format.
    Setting the 'sample_coh=sample_inc=0' removes the sample, e.g. to study the container or
    environment only contribution.

    The sample and its container are located inside a cylindrical shield with radius
    'environment_radius_m' and thickness 'environment_thickness_m'. The material is set from
    the 'environment' file name in the McStas Sqw or PowderN format (e.g. 'Al.laz').
    This way, it is possible to estimate the contribution of a cryostat or furnace.
    Setting 'environment=0' removes the environment.

    The detector has a cylindrical geometry, with a radius 'sample_detector_distance_m'
    and tubes with height 'detector_height_m'. The detector covers a -30 to 140 deg angular range
    with 2.54 cm diameter tubes (the number of tubes is computed from the distance).
    The direct beam (non scattered neutrons) is discarded.

    The detector produces both (angle,tof) and (q,w) data sets, for:
    total scattering
    coherent single scattering from sample
    incoherent single scattering from sample
    multiple scattering from sample
    scattering from the container and sample environment
    The (angle,tof) results are corrected for the parallax effect from the detector height.

    Known configurations:
    ILL_IN4:
    beam_wavelength_Angs=2, beam_resolution_meV=0.5,
    sample_detector_distance_m=2.0, detector_height_m=0.3
    ILL_IN5:
    beam_wavelength_Angs=5, beam_resolution_meV=0.1,
    sample_detector_distance_m=4.0, detector_height_m=3.0
    ILL_IN6:
    beam_wavelength_Angs=4.1, beam_resolution_meV=0.1,
    sample_detector_distance_m=2.48, detector_height_m=1.2
    PSI_Focus:
    beam_wavelength_Angs=4.1, beam_resolution_meV=0.1,
    sample_detector_distance_m=2.5, detector_height_m=1.2
    FRM2_TOFTOF:
    beam_wavelength_Angs=3.0, beam_resolution_meV=0.3,
    sample_detector_distance_m=4.0, detector_height_m=2.0
    SNS_SEQUOIA:
    beam_wavelength_Angs=1.0, beam_resolution_meV=3.0,
    sample_detector_distance_m=5.5, detector_height_m=1.2
    SNS_ARCS:
    beam_wavelength_Angs=0.3, beam_resolution_meV=20.0,
    sample_detector_distance_m=3.0, detector_height_m=1.46
    NIST_DCS:
    beam_wavelength_Angs=3.0, beam_resolution_meV=0.2,
    sample_detector_distance_m=4.0, detector_height_m=1.2
    ISIS_MERLIN:
    beam_wavelength_Angs=1.0, beam_resolution_meV=2.4,
    sample_detector_distance_m=2.5, detector_height_m=3.0
    ISIS_LET:
    beam_wavelength_Angs=4.0, beam_resolution_meV=0.1,
    sample_detector_distance_m=3.5, detector_height_m=4.0

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default
beam_wavelength_Angs | Angs | incident neutron beam wavelength | 2
beam_resolution_meV | meV | incident energy range full width | 0.1
sample_coh | str | sample coherent Sqw data file or NULL | "Rb_liq_coh.sqw"
sample_inc | str | sample incoherent Sqw data file or NULL | "Rb_liq_inc.sqw"
sample_thickness_m | m | thickness of sample. 0=filled | 1e-3
sample_height_m | m | height of sample. 0=sphere | 0.03
sample_radius_m | m | radius of sample (outer) | 0.005
container | str | container material or NULL | "Al.laz"
container_thickness_m | m | container thickness | 50e-6
environment | str | sample environment material or NULL | "Al.laz"
environment_radius_m | m | sample environment outer radius | 0.025
environment_thickness_m | m | sample environment thickness | 2e-3
detector_height_m | m | detector tubes height | 3
sample_detector_distance_m | m | distance from sample to detector | 4.0

## Links

- Source code for `Test_Sqw_monitor.instr`.
- The Isotropic_Sqw sample
- The PowderN sample
- The Samples_Isotropic_Sqw example instrument
- The nMoldyn package to create Sqw data sets from MD trajectories

[ Identification | Description | Input parameters | Links ]