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Arrays for Particles

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=tex2html_wrap_inline8106 command, etc.) they have different t but same s.
Also note that, in contrast to ABEL, s-coordinate does not simply change as tex2html_wrap_inline9232 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 tex2html_wrap_inline9242   for electrons/positrons, and the Stokes parameter   tex2html_wrap_inline7622 for photons.
tex2html_wrap_inline9242 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 tex2html_wrap_inline7624 with the third vector tex2html_wrap_inline7626 parallel to the momentum. In CAIN, the first vector tex2html_wrap_inline7628 is taken to be the unit vector along tex2html_wrap_inline9254 and tex2html_wrap_inline7632. 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, tex2html_wrap_inline7624 is almost equal to tex2html_wrap_inline9262 for right-going photons, and tex2html_wrap_inline9264 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 up previous contents index
Next: Description of Polarization Up: Particle Variables Previous: Particle Variables

Toshiaki Tauchi
Thu Dec 3 17:27:26 JST 1998