How do I disable relativistic effects?

Normally, SIMION applies any necessary relativistic corrections to the particle trajectory calculation (as described in the Computational Methods and User Programming accel_adjust sections of the SIMION manual). On occasion, however, it is useful to measure the significance of relativistic effects by comparing relativistic trajectories with classical trajectories–i.e. with relativistic effects omitted.

As of SIMION 8.1.0, the option “View > Particles > more… > Omit relativistic effects” will disable relativistic effects during the fly’m. This is also available via the sim_relativity reserved variable.

Earlier versions of SIMION lack the option to explicitly disable relativistic effects. However, there is a workaround that can be used in the case of static electric fields, though it doesn’t necessarily work otherwise. Just increase the particle mass by a sufficiently large factor of N such that further increase in N has little effect on the particle splat positions–i.e. trajectories become nonrelativisitic. For static electric fields, TOF’s will increase by a factor of \sqrt{N}, but trajectory shapes will remain the same. N=10000 and \sqrt{N} = 100 can be a convenient choice so that Data Recording results remain easy to interpret.

Although results with and without relativistic effects can be compared by examining the Data Recording output, it can also be helpful to visually compare the two on the screen using the “Keep” feature:

  • Enable relativistic effects.
  • Click Fly’m.
  • Click Particles > Keep.
  • Disable relativistic effects.
  • Click Fly’m. Trajectories from both runs will now display on the screen.
  • When done click Particles > Del and re-enable relativistic effects.