Particle Transport
The simulation considered carbon molecules that are sputtered off of the
divertor plate surface due to incident deuterium or tritium ions. In the
simulation it was assumed that all of the ejected carbon molecules were neutral
methane (CH4), and they initiated at a point (0,0,0). All molecules were
assumed to have the same magnitude of initial velocity, which was calculated from the
surface temperature, and the angle of the initial velocity was chosen randomly. Since the particles emitted were
initally assumed neutral, the electromagnetic fields in the region did not
influence their transport. The particles progressed in straight lines until a
collision occurred, with probability
where the denominator of the second equation is the rate coefficients, which
are specific to the molecule under consideration,
multiplied by the plasma density.
Motion of charged particles obeys the Lorentz force equation.
The strong magnetic field confining the fuel also curves the trajectories of
the ions under consideration. Also, since electrons are lighter than positive
ions, they move faster due to the magnetic field. The resulting separation of
charges sets up an electric field due to the space charge. This electric field
also contributes to the force as described in the Lorentz equation. The trajectories of the carbon molecule was
followed and its ionization state tracked until either the the particle returnedto the divertor wall or the particle exited the simulation box, in which case it was assumed that the
particle did not redeposit and instead contributed to impurities in the plasma.