CAIN is a stand-alone FORTRAN Monte-Carlo code for the interaction involving
high energy electron, positron, and photons. Originally, it started
with the name ABEL[1] in 1984 for the beam-beam interaction
in 
linear colliders. At that time the main concern was the
beam deformation due to the Coulomb field and the synchrotron radiation
(beamstrahlung). Later, the pair creation by particle-particle collision
was added, and, it was renamed to CAIN when the interaction with laser beams
(radiation by electrons/positrons and pair creation by photons
in a strong laser field) was added for the 
- colliders.
The first version CAIN 1.1[2], which is a combined program of modified
ABEL and a laser QED code, is limited because it
cannot handle the laser interaction and the interaction
simultaneously and does not accept mixed beams.
To overcome these problems, CAIN 2.0 was written from scratch.
It now allows any mixture of e
, e
, and lasers, and
multiple-stage interactions.
The input data format has been refreshed completely.
The physical objects which appear in the present version CAIN are two particle beams, lasers, and external fields. Each of the two beams may consist of high-energy electrons, positrons and photons. One of the beams may be absent. A basic assumption is that each beam must be a `beam', i.e., most particles in each beam go almost parallel. (CAIN assumes the two beams go opposite direction. For the case they make a large angle, you can apply CAIN command for Lorentz transformation so that the collision looks head-on.) The lasers can go any direction. The present version accepts only constant external fields.
The interactions that can be treated by the present version CAIN2.1
are
e ).
pair creation by photons, electrons and
positrons.