12 Beam Lines
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The accelerator to be studied is known to OPAL as a sequence of physical elements called a beam line. A beam line is built from simpler beam lines whose definitions can be nested to any level. A LINE command provides the formal definition:
label: LINE = (member, ..., member);Each member may be:
- an element label,
- a beamline label,
- a sub-line enclosed in parentheses.
12.1 Simple Beam Lines
The simplest beam line is a list of elements:
label: LINE = (member, ..., member);Example:
L: LINE = (A, B, C, D, A, D);Line attributes:
ORIGIN-
position vector of the origin of the line. Elements placed using
ELEMEDGEuse this as reference. ORIENTATION- orientation vector of Tait-Bryan angles at the line origin.
12.2 Sub-lines
Instead of referring directly to an element, a beamline member can refer to another named beam line. This provides shorthand notation for repeated lattice segments. Lines and sub-lines can be entered in any order, but when a line is used, all of its sub-lines must already be known to the parser.
Example:
L: LINE = (A, B, S, B, A, S, A, B);
S: LINE = (C, D, E);The source manual expands this in two steps.
- Replace
Sby its definition:
(A, B, (C, D, E), B, A, (C, D, E), A, B)- Omit parentheses:
A, B, C, D, E, B, A, C, D, E, A, B