NXbeam¶
Status:
base class, extends NXobject
Description:
Properties of the neutron or X-ray beam at a given location.
It will be referenced by beamline component groups within the NXinstrument group or by the NXsample group. Note that variables such as the incident energy could be scalar values or arrays. This group is especially valuable in storing the results of instrument simulations in which it is useful to specify the beam profile, time distribution etc. at each beamline component. Otherwise, its most likely use is in the NXsample group in which it defines the results of the neutron scattering by the sample, e.g., energy transfer, polarizations.
Symbols:
No symbol table
- Groups cited:
Structure:
@default: (optional) NX_CHAR
Declares which child group contains a path leading to a NXdata group.
It is recommended (as of NIAC2014) to use this attribute to help define the path to the default dataset to be plotted. See https://www.nexusformat.org/2014_How_to_find_default_data.html for a summary of the discussion.
distance: (optional) NX_FLOAT {units=NX_LENGTH}
Distance from sample. Note, it is recommended to use NXtransformations instead.
incident_energy: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_ENERGY}
Energy on entering beamline component
final_energy: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_ENERGY}
Energy on leaving beamline component
energy_transfer: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_ENERGY}
Energy change caused by beamline component
incident_wavelength: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_WAVELENGTH}
Wavelength on entering beamline component
incident_wavelength_spread: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_WAVELENGTH}
Wavelength spread FWHM on entering component
incident_beam_divergence: (optional) NX_FLOAT (Rank: 2, Dimensions: [2, j]) {units=NX_ANGLE}
Divergence of beam entering this component
extent: (optional) NX_FLOAT (Rank: 2, Dimensions: [2, j]) {units=NX_LENGTH}
Size of the beam entering this component
final_wavelength: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_WAVELENGTH}
Wavelength on leaving beamline component
incident_polarization: (optional) NX_FLOAT (Rank: 2, Dimensions: [2, j]) {units=NX_ANY}
Polarization vector on entering beamline component
final_polarization: (optional) NX_FLOAT (Rank: 2, Dimensions: [2, j]) {units=NX_ANY}
Polarization vector on leaving beamline component
final_wavelength_spread: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_WAVELENGTH}
Wavelength spread FWHM of beam leaving this component
final_beam_divergence: (optional) NX_FLOAT (Rank: 2, Dimensions: [2, j]) {units=NX_ANGLE}
Divergence FWHM of beam leaving this component
flux: (optional) NX_FLOAT (Rank: 1, Dimensions: [i]) {units=NX_FLUX}
flux incident on beam plane area
depends_on: (optional) NX_CHAR
The NeXus coordinate system defines the Z axis to be along the nominal beam direction. This is the same as the McStas coordinate system (see :ref:Design-CoordinateSystem). However, the additional transformations needed to represent an altered beam direction can be provided using this depends_on field that contains the path to a NXtransformations group. This could represent redirection of the beam, or a refined beam direction.
DATA: (optional) NXdata
Distribution of beam with respect to relevant variable e.g. wavelength. This is mainly useful for simulations which need to store plottable information at each beamline component.
TRANSFORMATIONS: (optional) NXtransformations
Direction (and location) for the beam. The location of the beam can be given by any point which it passes through as its offset attribute.
DIRECTION: (optional) NX_NUMBER {units=NX_TRANSFORMATION}
Direction of beam vector, its value is ignored. If missing, then the beam direction is defined as [0,0,1] and passes through the origin
@transformation_type: (optional) NX_CHAR
Obligatory value:
translation@vector: (optional) NX_NUMBER
Three values that define the direction of beam vector
@offset: (optional) NX_NUMBER
Three values that define the location of a point through which the beam passes
@depends_on: (optional) NX_CHAR
Points to the path to a field defining the location on which this depends or the string “.” for origin.
reference_plane: (optional) NX_NUMBER {units=NX_TRANSFORMATION}
Direction of normal to reference plane used to measure azimuth relative to the beam, its value is ignored. This also defines the parallel and perpendicular components of the beam’s polarization. If missing, then the reference plane normal is defined as [0,1,0] and passes through the origin
@transformation_type: (optional) NX_CHAR
Obligatory value:
translation@vector: (optional) NX_NUMBER
Three values that define the direction of reference plane normal
@offset: (optional) NX_NUMBER
Not required as beam direction offset locates the plane
@depends_on: (optional) NX_CHAR
Points to the path to a field defining the location on which this depends or the string “.” for origin.
Hypertext Anchors¶
List of hypertext anchors for all groups, fields, attributes, and links defined in this class.
