The finite orbit widths of fusion products in tokamaks
cause their distribution function to become anisotropic in velocity
space. This anisotropy is closely related to the topology of fast ion
orbit motion.
For the study of orbit topology
the {\sl equatorial surface} is introduced which is a generalisation
of the horizontal mid plane for tokamaks with broken top--bottom
symmetry. By use of simple graphical methods the topology of guiding centre
orbits are obtained and displayed by parameters characterising
the particles at their intersections with this surface.
On the basis of the results of the orbit topology study the
anisotropic features of the distribution of fusion born
$\alpha$--particles are examined.
For routine analysis of $\alpha$--particles in JET plasmas
a code is developed which integrates the Fokker--Planck equation
describing classical slowdown of $\alpha$--particles
including finite orbit width effects.
The code applies a new Green's
function approach which considerably
reduces the computational
demands.
The possibilities for the
reconstruction of anisotropic distribution functions from CTS
measurements are investigated.
Results of tests and theoretical considerations for
components in the CTS receiver are outlined, and
a procedure, developed
for the calibration of the CTS detection system, is described.
Examples of data measured by the CTS diagnostic are presented
together with inferred fast ion distribution functions.