abrat field-file [-3dFieldFile] [-interpolateField=parameterName,[,order=n][,extrapolate][,permissive]] [-scan=x | xp | y | yp | delta,lower,upper,number | -beamFiles=input,output ] -vertex=x-in-meters,z-in-meters -nominalEntrance=x,y -nominalExit=x,y -theta=targetInDegrees -rigidity=Tesla-meters [-output=filename] [-fsc=value] [-dxDipole=m] [-dzDipole=m] [-yawDipole=value] [-optimize[=verbose][fse,dx,dz,yaw]] -fseLimit=min,max -dxLimit=min,max -dzLimit=min,max -yawLimit=min,max [-fieldmapOutput=filename,zmin,zmax,nz,xmin,xmax,nx] [-tolerance=integration-tolerance] [-quiet]
- field-file — Field map file. Normally, needs to contain columns x, z, and B, giving the field in the midplane. In 3D mode, when the -3dFieldFile option is given, then the file should contain x, y, z, Bx, By, and Bz. In all cases, the beam is assumed to move from left (z < 0) to right (z > 0) with the field bending counter clockwise. Positive x is away from the center of curvature.
- -3dFieldFile — If given, then field-file is expected to contain a 3D field map. See above for details.
- -interpolate — If given, then field-file is expected to contain at least two 2D field
maps on separate pages of the file. These field maps could be, for example, from
measurements with different excitation currents, with the excitation current for each case
being stored in a named parameter; the pages must be arranged so that the parameter
values increase monotonically.
brat will then automatically interpolate among the field
maps to determine the required excitation current (for example); this overrides the fse
parameter of the -optimize option. By default, linear interpolation is used (order=1).
By default, the search will not go outside the range of the parameter values in the data;
if extrapolate is given, however, extrapolation outside this range is performed. By
default, the grid parameters of the several pages must match exactly; if permissive is
given, however, this requirement is not enforced.
- -scan — If given, then the value of the named accelerator coordinate is scanned to create a bundle of incoming rays. Output is provided for each ray.
- -beamFiles — If given, then an elegant-style beam is read and the particles therein are tracked through the dipole. A simular file is created for the output coordinates. Coordinates are defined at the nominal entrance and exit planes. Back-drifts are used to ensure that integration begins and ends outside the magnetic field region (i.e., all of the defined field is included).
- -output — If given, particle trajectories are written to the named file.
- -fsc — If given, the fractional strength change to apply to the field. Typically taken from a previous optimization run.
- -dxDipole — If given, the x positional change to apply to the field. A positive value moves the field away from the center of curvature. Typically taken from a previous optimization run.
- -dzDipole — If given, the z positional change to apply to the field. A positive value moves the field further from the incoming beam. Typically taken from a previous optimization run.
- -yawDipole — If given, the yaw to apply to the field. A positive value rotates the magnet in the direction of bending. Typically taken from a previous optimization run.
- -optimize, -fseLimit, dxLimit, dzLimit, yawLimit — Invokes optimization of the various strength and alignment parameters and specifies the allow range of variation.
- -fieldMapOutput — Requests output of a field map, allowing confirmation of the input data.
- -tolerance — Integration tolerance.
- N.B.: The usage message describes additional switches that have had limited testing. Use with caution.