Forking Lines
A fork or photon_fork element marks the point where multiple lines can merge or branch off from. Forking elements can be used to describe X-ray lines branching from storage rings, injection or extraction lines, etc.
beginning[beta_a] = 10.0 ! m a-mode beta function
beginning[beta_b] = 10.0 ! m b-mode beta function
beginning[e_tot] = 10e6 ! eV
parameter[geometry] = open ! or closed
b: bend, l = 2, rho = pi/4
f: fork, to_line = extract_line, superimpose, offset = 0.4
d: drift, l = 2
extract_line: line = (d) ! The line forked to.
extract_line[geometry] = open
lat: line = (b)
use, lat ! Line used to construct the lattice
Copy this to a file fork.bmad and run Tao:
> tao -lat fork.bmad
Tao> place r11 floor
Gives:
The lattice is looks like:
Tao> show lat
Values at End of Element:
Index name key s l beta phi eta orbit beta phi eta orbit Track_State
a a a x [mm] b b b y [mm]
0 BEGINNING Beginning_Ele 0.000 --- 10.00 0.000 0.00 0.000 10.00 0.000 0.00 0.000 Alive
1 B#1 Sbend 0.400 0.400 9.77 0.040 0.03 0.000 10.02 0.040 0.00 0.000 Alive
2 F Fork 0.400 0.000 9.77 0.040 0.03 0.000 10.02 0.040 0.00 0.000 Alive
3 B#2 Sbend 2.000 1.600 5.32 0.249 0.75 0.000 10.40 0.197 0.00 0.000 Alive
4 END Marker 2.000 0.000 5.32 0.249 0.75 0.000 10.40 0.197 0.00 0.000 Alive
Lord Elements:
5 B Sbend 2.000 2.000 5.32 0.249 0.75 0.000 10.40 0.197 0.00 0.000 Alive
Index name key s l beta phi eta orbit beta phi eta orbit Track_State
a a a x [mm] b b b y [mm]
Values at End of Element:
Where is the line that was forked to? Bmad creates branches to hold the different lines. Branches are assigned an index starting from 0:
Tao> show branch
N_ele N_ele Default Live
Branch Track Max Ref_Particle Tracking_Species Geometry Branch From_Fork
0: LAT 4 5 Positron Ref_Particle Open T
1: EXTRACT_LINE 2 2 Positron Ref_Particle Open T 0>>2
Defines
Fork_Element Forking_To Direction To_Branch?
0>>2: LAT>>F 1>>0: EXTRACT_LINE>>BEGINNING 1 T
The show lat branch, by default, shows branch 0. To see other branches use the -branch option:
Tao> show lat -branch 1
Values at End of Element:
Index name key s l beta phi eta orbit beta phi eta orbit Track_State
a a a x [mm] b b b y [mm]
0 BEGINNING Beginning_Ele 0.000 --- 9.77 0.040 0.03 0.000 10.02 0.040 0.00 0.000 Alive
1 D Drift 2.000 2.000 8.04 0.268 0.34 0.000 10.58 0.236 0.00 0.000 Alive
2 END Marker 2.000 0.000 8.04 0.268 0.34 0.000 10.58 0.236 0.00 0.000 Alive
Index name key s l beta phi eta orbit beta phi eta orbit Track_State
a a a x [mm] b b b y [mm]
Values at End of Element:
Notes:
- The difference between fork and photon_fork is that the default species for fork is the same as the line forked from while for a photon_fork the default species are photons.
- A fork element is not restricted to forking to the beginning of a line. The place where a fork element connects can be set by the to_element attribute.