[ Identification | Description | Input parameters | Output parameters | Links ]

# The `Collimator_radial` Component

A radial Soller collimator.

## Identification

- Author: Emmanuel Farhi <farhi@ill.fr>
- Origin: ILL
- Date: July 2005
- Version: 1.8

## Description

    Radial Soller collimator with rectangular opening and specified length.
    The collimator is made of many rectangular channels stacked radially.
    Each channel is a set of transmitting layers, separated by an absorbing
    material, the whole stuff is inside an absorbing housing.
    The component should be positioned at the radius center.
    When specifying the divergence parameter, the transmission function is an
    average (triangular approximation) and does not utilize knowledge of
    the actual neutron trajectory.
    On the other hand, when specifying the number of blades, model is exact,
    but statistics is lowered by a factor 2.
    A zero divergence disables collimation (then the component works as a double
    slit). If the input/output (w1, w2) width are 0, then a perfect collimator
    is assumed (no slit check except for the total angular range and height).
    The component can be made oscillating (usual on diffractometers and TOF
    machines) with the 'roc' parameter.
    The neutron beam outside the collimator area is transmitted unaffected.

    Example: Contains shadow parts due to radial geometry
           Collimator_radial(w1=0.015, h1=.3, w2=0.015, h2=.3, len=.35,
                      divergence=40,transmission=1,
                      theta_min=5, theta_max=165, nchan=128, radius=0.9)

    Ideal: Collimator_radial(w1=0, h1=.3, w2=0, h2=.3, len=.35,
                      divergence=40,transmission=1,
                      theta_min=5, theta_max=165, radius=0.9)

## Input parameters

Parameters in boldface are required; the others are optional.

Name | Unit | Description | Default
--- | --- | --- | ---
w1 | m | Input window width | 0.015
h1 | m | Input window height | .3
w2 | m | Output window width | 0.015
h2 | m | Output window height | .3
len | m | Length/Distance between slits | .35
divergence | min of arc | Divergence angle. May also be specified with the nblades parameter | 40
transmission | 1 | Transmission of Soller (0<=t<=1) | 1
theta_min | deg | Minimum Theta angle for the radial setting | 5
theta_max | deg | Maximum Theta angle for the radial setting | 165
nchan | 1 | Number of channels in the theta range | 128
radius | m | Radius of the collimator (to entry window) | 0
nblades | 1 | Number of blades composing each Soller. Overrides the divergence parameter | 0
roc | 1 | Enable oscillation of collimator with an amplitude of 'roc' times a single soller size (w1). | 0
verbose | 0/1 | Gives additional information | 0

## Output parameters

Name | Unit | Description | Default
--- | --- | --- | ---
soller_theta1 |  |  |
soller_theta2 |  |  |
window_theta |  |  |
use_approx |  |  |
ideal |  |  |

## Links

- Source code for `Collimator_radial.comp`.

[ Identification | Description | Input parameters | Output parameters | Links ]