FTABLE—Tracks through a magnetic field which is expressed by a SDDS table.

10.37 FTABLE—Tracks through a magnetic field which is expressed by a SDDS table.

Tracks through a magnetic field which is expressed by a SDDS table.
Parallel capable? : yes
GPU capable? : no
Back-tracking capable? : no


Parameter Name	Units	Type	Default	Description

L	M	double	0.0	The effective field length measured along a straight line.

ANGLE	RAD	double	0.0	The designed bending angle

L1	M	double	0.0	The left fringe field length.

L2	M	double	0.0	The right fringe field length. L1+L+L2=Total z span in the input field table.

E1	RAD	double	0.0	The designed entrance edge angle

E2	RAD	double	0.0	The designed exit edge angle

TILT	RAD	double	0.0	rotation about incoming longitudinal axis

DX	M	double	0.0	misalignment

DY	M	double	0.0	misalignment

DZ	M	double	0.0	misalignment

FACTOR		double	1	Factor by which to multiply field data.

THRESHOLD		double	1e-08	Fields smaller than this are considered 0.

INPUT_FILE		STRING	NULL	Name of SDDS file which contains field data.

N_KICKS		long	1	Number of kicks into which to split the element.

VERBOSE		short	0	Used for debugging code. Not applicable to Pelegant

SIMPLE_INPUT		short	0	If non-zero, use simple input format.

GROUP		string	NULL	Optionally used to assign an element to a group, with a user-defined name. Group names will appear in the parameter output file in the column ElementGroup

This element is used for tracking through an arbitrary magnetic field when its values are known at regularly spaced grid points and it is hard to find a suitable model to describe it. The input magnet parameter and coordinate system definition are illustrated in Fig:1.

The THRESHOLD parameter sets the magnitude of magnetic field below which the field is considered zero. If this is too small, there may be numerical problems.

The field data is provided in an SDDS file, with two formats available. The recommended format can be used if the SIMPLE_INPUT parameter is non-zero.

Simple input format — This format is shared with the BMXYZ and BRAT elements and is more convenient than the original, default format. The field map file is an SDDS file with the following columns:

x, y, z — Transverse coordinates in meters (units should be “m”).
Bx, By, Bz — Field values in Tesla (units should be “T”).

The field map file must contain a rectangular grid of points, equispaced (separately) in x, y, and z. There should be no missing values in the grid (this is not checked by elegant). In addition, the x values must vary fastest as the values are accessed in row order, then the y values. To ensure that this is the case, use the following command on the field file:

sddssort fieldFile -column=z,incr -column=y,incr -column=x,incr

N.B.: Particles are injected into the field region with z=0. Hence, one would normally want the minimum value of z to be 0.

Original input format — This format is difficult to understand and set up. Although it is not recommended, it is the default at present for historical reasons.

The field data is saved in a 3 pages (B_x, B_y, B_z) 3D histogram SDDS table (see MHISTOGRAM for detail). An example is shown in Fig:2. This SDDS file must have one column Frequency to store the field data in Tesla, and following parameters:

ND — Type “long”; Value “3”.
Variable00Name, Variable01Name,Variable02Name — Type “string”; Value “x”, “y”, “z”.
Variable00Min, Variable01Min, Variable02Min — Type “double”; Value: the minimum boundary coordinates of “x”, “y”, “z” in meter. Variable02Min (z_min) must start from zero.
Variable00Max,Variable01Max, Variable02Max — Type “double”; Value: the maximum boundary coordinates of “x”, “y”, “z” in meter.
Variable00Interval, Variable01Interval,Variable02Interval — Type “double”; Value of the grid size of “x”, “y”, “z” in meter.
Variable00Dimension,Variable01Dimension, Variable02Dimension — Type “long”; Value of total number of grid points in “x”, “y”, “z”. For example: Variable00Dimension =(Variable00Max-Variable00Min)/Variable00Interval + 1.

N.B.: Particles are injected into the field region with z=0. Hence, one would normally want Variable02Min=0. If Variable02Min<0, data ahead of the injection point.

Figure 1: Illustration of coordinate system and magnet definition.

Figure 2: Example of SDDS input file. The column x_index, y_index, z_index is not the necessary part, it’s shown here just for clarifying how the data is arranged

FTRFMODE

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