With a powerful relativistic algorithm the three-dimensional trajectories o
f 10(4) ECR-heated and confined electrons are calculated in a standard ECRI
S with a deep minimum of \B\ and a new ECRIS with a very flat minimum of \B
\ The spatial electron (plasma) densities and electron energy densities ded
uced from these trajectories yield new and surprising insight in the perfor
mance of ECRIS.