Magnetic field component.
Author: Erik B Knudsen, Peter Christiansen and Peter Willendrup
Origin: RISOE
Date: July 2011
Region with a definable magnetic field.
The component is nestable if the concentric flag is set (the default). This means that it may have a construction like the following: // START MAGNETIC FIELD COMPONENT msf = Pol_Bfield(xwidth=0.08, yheight=0.08, zdepth=0.2, Bx=0, By=-0.678332e-4, Bz=0) AT (0, 0, 0) RELATIVE armMSF
// OTHER COMPONENTS INSIDE THE MAGNETIC FIELD CAN BE PLACED HERE
// STOP MAGNETIC FIELD COMPONENT msf_stop = Pol_simpleBfield_stop(magnet_comp_stop=msf) AT (0, 0, 0) RELATIVE armMSF
Note that if you have objects within the magnetic field that extend outside it you may get wrong results, because propagation within the field will then possibly extend outside, e.g. when using a tabled field. The evaluated field will then use the nearest defined field point _also_ outside the defintion area. If these outside-points have a non-zero field precession will continue - even after the neutron has left the field region.
In between the two component instances the propagation routine PROP_DT also handles spin propagation. The current algorithm used for spin propagation is: SimpleNumMagnetPrecession in pol-lib.
Example: Pol_Bfield(xwidth=0.1, yheight=0.1, zdepth=0.2, Bx=0, By=1, Bz=0) Pol_Bfield(xwidth=0.1, yheight=0.1, zdepth=0.2, field_type=1)
Functions supplied by the system are (the number is the ID of the function to be given as the field_type parameter: 1. Constant magnetic field: Constant field (Bx,By,Bz) within the region 2. Rotating magnetic_field: Field is initially (0,By,0) but after a length of zdepth has rotated to (By,0,0) 3. Majorana magnetic_field: Field is initially (Bx,By,0) with By<<Bx, then linearly transforms to (-Bx,By,0) at z=zdepth. 4. MSF field: 5. RF field: A radio frequency field is modeled by an implcit use of a roating frame. 6. Gradient field: Similar to Majorana by without an x-component to the field. I.e. it (0,By,0) at z=0, and becomes (0,-By,0) AT z=zdepth.
If the concentric parameter is set to 1 the magnetic field is turned on by an instance of this component, and turned off by an instance of Pol_simpleBfield_stop. Anything in between is considered inside the field. If concentric is zero the field is considered a closed component - neutrons are propagated through the field region, and no other components are permitted inside the field.
Parameters in boldface are required; the others are optional.
|
Name |
Unit |
Description |
Default |
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field_type |
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ID of function describing the magnetic field. 1:constant field, 2: rotating fiel, 3: majorana type field, 4: MSF, 5: RF-field, 6: gradient field. |
0 |
|
xwidth |
m |
Width of opening. |
0 |
|
yheight |
m |
Height of opening. |
0 |
|
zdepth |
m |
Length of field. |
0 |
|
radius |
m |
Radius of field if it is cylindrical or spherical. |
0 |
|
Bx |
T |
Parameter used for x composant of field. |
0 |
|
By |
T |
Parameter used for y composant of field. |
0 |
|
Bz |
T |
Parameter used for z composant of field. |
0 |
|
concentric |
|
Allow components and/or other fields inside field. Requires a subsequent Pol_simpleBfield_stop component. |
1 |
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Component source code found in file Pol_Bfield.comp.