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All the particles (photons, electrons, positrons) carry the following
variables.
- TXYS(i)
- (i=0,1,2,3) Particle coordinates in meter.
Note that,
in contrast to ABEL, the time and the s-coordinates are
also defined for each particle. During tracking
by PUSH-ENDPUSH command all the particles have basically
the same time coordinate (an exception is the particles
just created), whereas in some cases
(e.g., after defined by BEAM command, after DRIFT S=
command, etc.) they have different t but same s.
Also note that, in contrast to ABEL, s-coordinate
does not simply change as but changes according
to the instantaneous longitudinal velocity so that longitudinal
mixing may occur for low energy or large angle particles.
- EP(i)
- (i=0,1,2,3) Energy-momentum in units of
(eV,eV/c).
- SPIN(i)
- (i=1,2,3)
The polarization component
for electrons/positrons, and the Stokes parameter
for photons.
is defined, as usual, in particle's rest frame.
Therefore, it aquires the
Thomas precession under
Lorentz transformation by LORENTZ command.
to 2em For defining the Stokes parameter, one needs a set of
orthonormal basis vectors
with the third
vector parallel to the momentum. In CAIN,
the first vector is taken to be the unit vector
along
and . This
is ill-defined when the momentum is exactly parallel to the
x-axis but this possibility is simply ignored. Except for
large angle photons,
is almost equal to for
right-going photons, and
for left-going photons.
to 2em See the next subsection for more detail on the
polarization.
- GEN
- Generation.
When a particle is generated by BEAM
command by Twiss parameters, etc, GEN=1. Created particles
such as beamstrahlung photons have GEN larger by one than that
of the parent particle. (This is also true for the `spent' parents.)
GEN of the secondary particles due to particle-particle
interaction (such as incoherent pairs) is the sum of GENs
of the parents. In this case GENs of the parents do not
change.
- WGT
- Weight. Number of real particles represented by the
macro-particle.
- NAME
- 4-byte character string. Normally blanks. The test particles have
Tnnn where nnn is a three-digit number. NAME of the particles
created by incoherent (particle-particle) interactions starts with `I'.
For example, `IBW ', `IBH ', `ILL ' for the pairs created
by incoherent Breit-Wheeler, Bethe-Heitler, Landau-Lifshitz processes,
respectively.
Next: Description of Polarization
Up: Particle Variables
Previous: Particle Variables
Toshiaki Tauchi
Thu Dec 3 17:27:26 JST 1998