7.43 obstruction_data

• type: setup command
• function: define obstructions in the global coordinate system (Z,X)
• sequence: must follow floor_coodinates and preceed track
• Command syntax, including use of equations and subcommands, is discussed in 7.2.

• input — Name of SDDS file containing obstruction data. The file must contain two columns, Z and X, giving the global coordinates of points on the obstruction contour in the Y = 0 plane, in units of meters. The file may contain more than one page, with each page giving a closed contour for a separate obstruction. By default, obstructions are considered to extend over Y : [-∞,∞]; however, different contours can be defined for different vertical planes, as described below. The file must also contain three parameters:
  • Superperiodicty —- integer parameter giving the number of repetitions of the defined obstructions in the full ring. For example, for the 40-sector APS ring, if the obstruction data covered a single sector, then the value would be 40.
  • XCenter, ZCenter — floating point parameters giving the position of center of the ring in meters. The obstructions are rotated about this center if periodic.

  The file may optionally contain two other parameters:

  • CanGo — This integer parameter can be used to distinguish between “no-go” and “can-go” regions. By default, all contours enclose “no-go” regions, so that particles inside are assumed to be lost. If this parameter is specified and the value is non-zero, the contour instead defines a region inside which particles can propagate. This is typically used to override part of a no-go region.
  • Y — This floating-point parameter can be used to specify the vertical plane occupied by the contour. The values must be equispaced with spacing giving by the y_spacing parameter, as discussed below.
• periods — Obstructions represented by the provided data are to be repeated in a periodic fashion the number of times given. It is assumed that the system is a storage ring.
• disable — If nonzero, then the command is ignored.
• y_spacing — If nonzero, then the input file is expected to have data for multiple vertical planes, instead of the default y = 0 midplane. The plane for each page is identified by the parameter Y in the input file. The data must be sorted in increasing order of Y, which can be accomplished using sddssort, e.g.,
  sddssort input.sdds -parameter=Y

• y_limit — Allows specifying maximum limits on the vertical coordinate, beyond which particles are lost.