Module Rotating_field

# VITESS Module Rotating_field

This module simulates spin precessions in a rotating magnetic field. The permanent magnetic field can be added to the rotating field. This is useful for simulations of RF-flippers and so NRSE instruments. Magnetic field is rotating around a axises OX or OY or OZ. The random magnetic field can be added also.
*IF*BOOTSTRAP*OPTION*IS*ACTIVATED**
Precession volume is devided for two(2) parts. For the first part the frequency of a rotating field and all permanent components are chosen as input datas. For the second part all these parameters are become negative (multiple by -1.0).
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.
------ROTATING FIELD-WITH-PERMANENT-MAGNETIC-FIELD--------
FORMULAS OF ROTATION: AROUND AXIS 0X
X = X0
Y = Y0 + FieldValue*sin(Omega*(T + TOF) + BeginPhase)
Z = Z0 + FieldValue*cos(Omega*(T + TOF) + BeginPhase)
FORMULAS OF ROTATION: AROUND AXIS 0Y
X = X0 + FieldValue*sin(Omega*(T + TOF) + BeginPhase)
Y = Y0
Z = Z0 + FieldValue*cos(Omega*(T + TOF) + BeginPhase)
FORMULAS OF ROTATION: AROUND AXIS 0Z
X = X0 + FieldValue*cos(Omega*(T + TOF) + BeginPhase)
Y = Y0 + FieldValue*sin(Omega*(T + TOF) + BeginPhase)
Z = Z0
X0, Y0, Z0 - components of permanent magnetic field [Oe=Gauss],
Omega = 2*PI*omega/1000, omega = [Hz], Omega = [rad/ms],
FieldValue - Strength (Amplitude) of rotating magnetic field in Oe=Gauss,
BeginPhase in degree
TOF - time of flight of neutron from preceding modules for rotating field phase.
So, if TOF=0 is used: The magnetic field is directed vertically upwards for rotating around of the axis 0X, when NEUTRON WAS LEFT THE MODERATOR SURFACE.
Also, if TOF is zero, the rotation of magnetic field and neutron time of flight are NOT SYNHRONIZED and so unsuatible for Spin Echo simulations!!!
The amplitude FieldValue can have a 5th types of distributions:
1. normal_ran: Normal randomization of amplitude during the domains changing
2. uniform_ran: Unifrom randomization of amplitude during the domains changing
3. normal: Normal distribution of FieldValue with amplitude=FieldValue
4. uniform: Permanent value with value=FieldValue
5. from_file: Distribution is reading from the file, which was created by user
This file must cotains the two rows with names:
Position Amplitude
and at least two columns.
Example:
-1.0 100.0
-0.5 120.0
0.0 150.0
0.5 170.0
1.0 200.0
The first row "Position" must have a increasing values. Minimal and maximal values must be equal the half of dimesions of common field X with sign "-" and sign "+". The values, which are describing amplitude must be positive always. During simulations the current value of amplitude is taking from interpolation of datas, which was given in the file. This possibility is very useful for simulating of realistic magnetic field, for example magnetic field from solenoid
The frequency of rotating and components of permanent magnetic fields can be randomized too.

Module parameters:

Parameter Unit | Description | Command option
dimensions of field volume X,Y,Z [cm] | Dimension of the common precession volume X,Y,Z | -X, -Y, -V
position main X,Y,Z [cm] | Center position of the field volume. | -k, -l, -m
offset horiz. [deg] | Horizontal (around vertical axis) rotation angle of the magnetic field volume. This is useful for the simulations of NRSE and/or SESANS instruments | -i
output X,Y,Z [cm] | Position of the output frame (in the input frame). | -p, -r, -s
Number of domains in the X direction | Number of domains in the X direction (flight direction) | -C
Number of domains in the Y direction | Number of domains in the Y direction | -D
Number of domains in the Z direction | Number of domains in the Z direction | -E
Rotating field around given axis | Choose rotating field around of a axis OX or OY or OZ , values 0, 1, 2 respective | -M
Strength of magnetic field [Oe=gauss] | Strength(Amplitude) of the rotating magnetic field. | -d
Frequency of rotating [Hz] | Rotation frequency of the magnetic field. | -w
Begin Phase [degree] | Initial phase. | -z
File with distribution | Name of file, which is describing the amplitude of the rotating field distribution | -t
Deviation of amplitude [%] | Deviation (or sigma for normal distribution) of amplitude of the rotating magnetic field in percent | -a
Amplitude distribution | Distribution of amplitude of the rotating magnetic field {Normal_ran Uniform_ran Normal Uniform From_file} {0 1 2 3 4} | -e
Deviation of frequency [%] | Deviation of Rotation frequency of the magnetic field in percent | -b
Frequency distribution | Distribution of random values: frequency of the rotating magnetic field {Normal Uniform} {0 1} | -v
TOF from preceding modules | Value 1 - use the neutron TOF from preceding modules for the rotating field phase; 0 - No -> TOF = 0; | -n
Permanent magnetic field components X, Y and Z [Oe] | Components X, Y, Z of permanent magnetic field, which can be added to the components of rotating magnetic field (projection on the axis). | -I, -A, -K
Additional random\n magnetic field [Oe] | Amplitude of additional random magnetic field | -q
Output results | Output intermediately results of simulations(spin and total magnetic field during flight) in the file {yes no} {1 0} | -S
Output file: polarisation | Name of file for: results - polarisation, spin components | -O
Output file: magneticfield | Name of file for output results - total magnetic field components | -N
Bootstrap option | Activate or not the bootstrap option | -T
Rotating field calculation | Calculate of amplitude of the rotating field according given wavelength (Calc. wavelength) and dimension of common field X (depth) values 0(no), 1(yes) | -x
Calc. wavelength | Wavelength for calculation of conditions for PI-flipping. This is working with option -x | -W

The calculated amplitude of the rotating field can be found in the "down" VITESS window called LOG and will be used as parameter "amplitude of the rotating magnetic field, option -d".

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Last modified: Sep 30 19:07:01 MEST 2003