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Viscous Drag

When the viscous drag option is selected, each ion is subjected to a drag force directed opposite to its motion. This drag force is proportional to the velocity of the ion:

where b is the damping coefficient.

The viscous drag option is especially useful for two objectives:

  1. forming crystals
  2. achieving dynamic equilibrium in the heating cloud regime (recall that stable equilibria in the heating regime are only attainable in region ) by attaining a configuration for which the heating rate equals the rate of energy loss due to viscous damping (see file cloud9A.trp).
In ion-trapping experiments, laser cooling is typically used when extensive cooling is required. Although velocity-selective laser-cooling is clearly a more complicated process, several computational research groups, use the simple frictional drag force employed by TrapApp as a suitable ``first approximation'' to laser cooling.[21,12]

Wolfgang Christian
Fri May 12 10:36:01 EDT 1995