There are VITESS modules for two different spin flip components: Coil or Mezei flipper and Gradient flipper
This module simulates a rectangular coil flipper. Inside the coil the field component is homogeneous and in the walls increases/decreases from 0 Gauss to the value of the coil field component given as input. The guide field is added to the total field. This module only rotates the spin vectors belonging to trajectories which pass through the rectangular geometry. No attenuation is considered in the walls.
|
Parameter Unit |
Description | Command option |
| position main X, Y, Z [cm] | center position of the rectangular coil in the input frame | -k, -l, -m |
| coil axes shows | orientation of the coil axes (1: Y direction, default; else: Z direction) | -y |
|
offset horiz./vert. [deg] |
rotation angle of the coil axes in horizontal (first rotation) and vertical direction | -i, -j |
|
dimension X, Y, Z [cm] |
dimensions of the rectangular coil in X,Y and Z direction when coil axes shows in Y direction | -X, -Y, -V |
|
guide field [Gs] |
strength of the guide magnetic field which is considered parallel to the beam axes | -G |
|
coil field component [Gs] |
strength of the coil magnetic field which is considered parallel to the coil axes | -H |
|
wall thickness [cm] |
thickness of the coil wire (wall) | -t |
| field steps | number of 'boxes' in which the field is devided (max:100) | -N |
|
output X, Y, Z [cm] |
position of the output frame (in the input frame) | -p, -r, -s |
This module simulates spin precessions in the magnetic field of a special kind:
The first part of such a field is a rotating magnetic field. The amplitude of this field
has to have a sinus function with a semi-period corresponding to the dimensions of the rotating field volume.
The magnetic field can rotate about the axes X, Y or Z. (The X axis has the direction of the neutron beam).
The second part of the general field is a guide magnetic field.
A random magnetic field can be added also.
The spin precessions are treated classically i.e. this module only rotates the spin
vectors belonging to trajectories which pass through the rectangular geometry.
No attenuation is considered during the flight.
-----------FIRST-PART-----------ROTATING FIELD----------------------
FORMULAS OF ROTATION: AROUND X AXIS
B_x = B0_x
B_y = B0_y + B_rot*sin(Omega*(T + TOF) + BeginPhase)
B_z = B0_z + B_rot*cos(Omega*(T + TOF) + BeginPhase)
FORMULAS OF ROTATION: AROUND Y AXIS
B_x = B0_x + B_rot*sin(Omega*(T + TOF) + BeginPhase)
B_y = B0_y
B_z = B0_z + B_rot*cos(Omega*(T + TOF) + BeginPhase)
FORMULAS OF ROTATION: AROUND Z AXIS
B_x = B0_x + B_rot*cos(Omega*(T + TOF) + BeginPhase)
B_y = B0_y + B_rot*sin(Omega*(T + TOF) + BeginPhase)
B_z = B0_z
B0_x, B0_y, B0_z: components of permanent magnetic field [Gauss]
B_rot : strength amplitude) of rotating magnetic field in Gauss
TOF : time of flight of neutron from preceding modules for rotating field phase
Omega = 2*PI*omega/1000, omega = [Hz], Omega = [rad/ms]
BeginPhase in degree
So for T+TOF=0, the magnetic field is directed vertically upwards for rotation about the X axis. If the 'TOF from the previous module' is not used, TOF is set to zero. In that case, the rotation of magnetic field and the neutron time of flight are NOT SYNCHRONIZED, which is unsuitable e.g. for Spin Echo simulations.
The amplitude FieldValue can have a 3 types of distributions:
1. sinus law (with semi-period - appropriate dimensions of the magnetic field volume)
2. permanent law
3. solinoid formula (not yet active)
-----------SECOND-----PART: GUIDE-MAGNETIC-FIELD---
This part can have 3 types of distributions, too:
1. cosine law : with semi-period - appropriate dimensions of the magnetic field volume
2. linear law : with period - appropriate dimensions of the rotating field volume
3. pernanent law
We have simulated a gradient flipper with a sinus function for the rotating magnetic field and a linear function for the guide field
and have got a good results.
The frequency of the rotating magnetic field and components of the guide magnetic fields can be randomized.
| Parameter Unit |
Description | Range or Values | Command option |
| common field X,Y,Z [cm] |
Size of the cuboidel flipper in X, Y, Z direction | >0 | -X, -Y, -V |
| position center X,Y,Z [cm] |
Center position of the flipper. | any | -k, -l, -m |
| horizontal offset [deg] |
Horizontal (around vertical axis) rotation angle of the magnetic field volume. | -180° - 180° | -i |
| output frame X,Y,Z [cm] |
Position of the output frame (in the input frame). | any | -p, -r, -s |
| number domains in X, Y, Z direction | Number of domains in the X direction (flight direction), Y (left) and / (Upwards) direction | ≥1 | -C, -D, -E |
| magnetic field amplitude [Gs] |
Amplitude of the rotating magnetic field | ≥0 | -d |
| rotation frequency [Hz] |
frequency of the rotating magnetic field. | ≥0 | -w |
| begin phase [deg] |
Initial phase for the rotating field. | 0° - 360° | -z |
| rotating field axis | Choice of the axis about which the field is rotating, X, Y or Z | 0X, 0Y, 0Z | -M |
| amplitude changing by | The strength of the rotating magnetic field varies by sinus function (with semi-period - corresponding to the field size) or by solenoid formula (not yet active) or is constant | 'sinus', 'permanent', 'solenoid' | -h |
| amplitude changing along axis | Choice of the axis, along which the amplitude of the rotating field changes. Needed if the time dependence 'sinus' is chosen. | 0X, 0Y, 0Z | -y |
| Deviation of amplitude [%] |
Deviation of the amplitude of the rotating magnetic field in percent | ≥0.0 | -a |
| Deviation of frequency [%] | Deviation of Rotation frequency of the magnetic field in percent | ≥0.0 | -b |
| amplitude distribution | Distribution of the amplitude of the rotating magnetic field see text above |
'Normal', 'Uniform' | -e |
| frequency distribution | Distribution of the frequency of the rotating magnetic field see text above |
'Normal', 'Uniform' | -v |
| TOF from prec. module |
'yes': use the neutron TOF from the preceding modules for the calculation of the rotating field phase 'no' : set TOF = 0; |
'yes', 'no' | -n |
| perm. / initial component X, Y and Z [Gs] | Permanent(for cosine amd permanent laws) or initial(for linear law) value of the X, Y or Z components (projection in the axis X, Y, Z) of the guide magnetic field in Gauss | any | -I, -A, -K |
| Amplitude or final X, Y and Z [Gs] | Amplitude(for cosine law) or final(for linear law) value of the X,Y,Z component (projection in the axis X, Y, Z) of the guide magnetic field in Gauss | ≥0.0 | -P -Q -R |
| additional random\n magnetic field [Gs] |
Amplitude of an additional random magnetic field | ≥0.0 | -q |
| Law of changing | Laws of distribution of guide magnetic field: cosine law (with semi-period corresponding to the size of the rotating field), linearly and permanently | 'cosinus', 'linear', 'permanent' | -u |
| amplitude changing along axis | Axis along which the amplitude changes: X, Y or Z. Needed if cosinus law of changing was chosen. | 0X, 0Y, 0Z | -t |
| Output file: polarisation | Name of the file for output results: polarisation, spin components | -O | |
| Output file: magneticfield | Name of the file for output results: total magnetic field components | -N | |
| Output results | Output of intermediate results of the simulations(spin and total magnetic field during flight) in files | 'yes', 'no' | -S |
Last modified: Sep 30 19:07:01 MEST 2003