FAFNER2. 3-D ''flux coordinate'' neutral beam injection code using Monte Carlo methods

The FAFNER2 ''Monte Carlo'' code is described which simulates the injection of fast neutral particles into a 3-dimensional toroidal plasma and the paths of the resulting fast ions until they are either lost to the system or fully thermalised. A comprehensive model for the neutral beam injection system is included. The ''guiding center'' equations for the fast ions are solved in ''Boozer'' flux coordinates. This is the main difference to the originally FAFNER1 version. The program is written especially for use on CRAY computers: in particular, the numerical treatment of the fast ion interaction with the background plasma, which uses the majority of the computer time, has been vectorised. Additionally to the standard W7-AS version used at the IPP also some test utilities are documented. Results obtained with the FAFNER2 code are compared with those from FAFNER1. (orig.)