tof.Chopper

class tof.Chopper(*, frequency, distance, name, phase=None, open=None, close=None, centers=None, widths=None, direction=Direction.CLOCKWISE)

A chopper is a rotating device with cutouts that blocks the beam at certain times.

Parameters:

• frequency (Variable) – The frequency of the chopper. Must be positive.

• distance (Variable) – The distance from the source to the chopper.

• name (str) – The name of the chopper.

• phase (Variable | None, default: None) – The phase of the chopper. Because the phase offset implemented as a time delay on real beamline choppers, it is applied in the opposite direction to the chopper rotation direction. For example, if the chopper rotates clockwise, a phase of 10 degrees will shift all window angles by 10 degrees in the anticlockwise direction, which will result in the windows opening later.

• open (Variable | None, default: None) – The opening angles of the chopper cutouts.

• close (Variable | None, default: None) – The closing angles of the chopper cutouts.

• centers (Variable | None, default: None) – The centers of the chopper cutouts.

• widths (Variable | None, default: None) – The widths of the chopper cutouts.

Notes

Either open and close or centers and widths must be provided, but not both.

__init__(*, frequency, distance, name, phase=None, open=None, close=None, centers=None, widths=None, direction=Direction.CLOCKWISE)

Methods

__init__(*, frequency, distance, name[, ...])
as_dict()	Return the chopper as a dictionary.
as_json()	Return the chopper as a JSON-serializable dictionary.
from_diskchopper(disk_chopper[, name])	Create a Chopper from a scippneutron DiskChopper.
from_nexus(nexus_chopper[, name])	Create a Chopper from a NeXus chopper group.
open_close_times([time_limit, unit])	The times at which the chopper opens and closes.
to_diskchopper()	Export the chopper as a scippneutron DiskChopper.

Attributes

omega

The angular velocity of the chopper.

as_dict()

Return the chopper as a dictionary.

Return type:

dict

as_json()

Return the chopper as a JSON-serializable dictionary.

Return type:

dict

classmethod from_diskchopper(disk_chopper, name=None)

Create a Chopper from a scippneutron DiskChopper.

Return type:

Chopper

Example

>>> import scipp as sc
>>> import tof
>>> from scippneutron.chopper import DiskChopper
>>> disk_chopper = DiskChopper(
...     frequency=sc.scalar(28.0, unit='Hz'),
...     beam_position=sc.scalar(30.0, unit='deg'),
...     slit_begin=sc.array(
...         dims=['slit'], values=[0.0, 90.0, 150.0], unit='deg'
...     ),
...     slit_end=sc.array(
...         dims=['slit'], values=[60.0, 120.0, 210.0], unit='deg'
...     ),
...     phase=sc.scalar(15.0, unit='deg'),
...     axle_position=sc.vector(value=[0.0, 0.0, 13.0], unit='m'),
... )
>>> chopper = tof.Chopper.from_diskchopper(disk_chopper)

classmethod from_nexus(nexus_chopper, name=None)

Create a Chopper from a NeXus chopper group.

Return type:

Chopper

Example

>>> # Assuming a chopper NeXus structure
>>> import scipp as sc
>>> import tof
>>> nexus_chopper = {
...     'position': sc.vector([0.0, 0.0, 2.0], unit='m'),
...     'rotation_speed': sc.scalar(12.0, unit='Hz'),
...     'beam_position': sc.scalar(45.0, unit='deg'),
...     'phase': sc.scalar(20.0, unit='deg'),
...     'slit_edges': sc.array(
...         dims=['slit'],
...         values=[0.0, 60.0, 124.0, 126.0],
...         unit='deg',
...     ),
...     'slit_height': sc.scalar(0.4, unit='m'),
...     'radius': sc.scalar(0.5, unit='m'),
... }
>>> chopper = tof.Chopper.from_nexus(nexus_chopper)

property omega: Variable

The angular velocity of the chopper.

open_close_times(time_limit=None, unit=None)

The times at which the chopper opens and closes.

Parameters:

• time_limit (Variable | None, default: None) – Determines how many rotations the chopper needs to perform to reach the time limit. If not specified, the chopper will perform a single rotation.

• unit (str | None, default: None) – The unit of the returned times. If not specified, the unit of time_limit is used.

Return type:

tuple[Variable, Variable]

to_diskchopper()

Export the chopper as a scippneutron DiskChopper.

Return type:

DiskChopper