Speaker
Description
The Boris algorithm has become the standard for
particle trajectory integration in a magnetic field. The
high frequency electron cyclotron motion (GHz)
constrains the time-step below 10 ps. A guiding
centre approach neglects the detailed particle
cyclotron motion, describing its trajectory through
free motion of the orbit's centre along the field lines
and corresponding drifts. It works on the assumption
that the magnetic field strength varies in a much
larger length scale than the cyclotron orbit. This
approach is more computationally expensive per step
than direct orbit integration, but a shorter overall
computation time may be expected by using a larger
time-step (~100 ps). This work presents a study on
implementing the guiding centre approach in ECR ion
sources. It is shown to reproduce accurately the
trajectory drifts and confinement of electrons in a
minimum-B field, but the use of long time-steps
exacerbates a non-physical kinetic energy loss.
Following, non-confined electron trajectories in a
flatter field are analysed, as in a microwave discharge
ion source, where this method's drawbacks are
avoided due to a smaller magnetic field gradient and
a shorter electron lifetime.