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Drift the particles to a certain time or to a certain
s coordinate.
DRIFT
T=DT=S=,
[RIGHT,] [LEFT,]
[KIND=k(,),]
[EXTERNALFIELD,]
;
-
- Drift until Time= (meter).
-
- Drift over time interval (meter).
-
- Drift to s coordinate (meter).
In any of the three cases T, DT, and S,
the particles may go backwards in time
depending on the parameters.
- RIGHT,LEFT
- Drift right- or left-going particles only.
- k
- Drift only particles of kind k.
- EXTERNALFILED
- Take into account the external field.
When there is only external field without beam interaction,
DRIFT EXTERNAL is much better (more accurate and faster)
than the PUSH command. The difference is that DRIFT EXTERNAL
uses an exact solution in a constant field whereas PUSH carries out
step-by-step integration, and that PUSH accepts only t as the
independent variable while DRIFT also allows s (as in most
accelerator program codes).
How to use DRIFT EXTERNAL may be understood by the following
example. Suppose that the region is shined by a laser.
An electron beam comes from the left and goes through the laser
region to created back-scattered photons, and subsequently goes
through a magnetic field region . If the interval
is shorter than the bunch length, the bunch head is already in the
field region when the tail gets out of the laser region.
If you use PUSH command, you have to track the beam till the end
of the magnetic field region. Instead, you can do more elegantly,
Toshiaki Tauchi
Thu Dec 3 17:27:26 JST 1998