Module trajectory 

Opt-in recorder of ion paths: the collision points of chosen histories.

TrajectoryRecorder is a BcaTally like any other, so the engine pays nothing for it unless a run uses it: no field on Particle, no flag and no branch in the transport loop. Recorded forwards every hook to an ordinary tally as well, so the usual results come out of the same run and are identical with recording on or off (the recorder draws no random numbers and never touches the engine state).

Convention

A history is a list of tracks: the primary (generation 0) and every displaced atom (a recoil, generation = parent + 1). A track is an ordered list of points, positions in metres (x the depth) and energies in eV:

• a recoil starts with its state at creation;
• every collision partner adds the particle’s incoming state at the collision (the BcaTally::partner convention). A crystal step with several simultaneous partners adds one point. The primary’s own track therefore starts at its first collision, not at the surface;
• a track that stops or leaves the target ends with that state (for an escape, the state outside after refraction by the surface barrier), the same position the other tallies see. A recoil that is created below the recoil cutoff, or with cascades off, is stopped at creation and has that one point.

Each non-primary track names its parent track in the same history. The engine reports no track-start event; the recorder rebuilds the link by mirroring the engine’s last-in first-out queue of recoils: a recoil reported and then stopped with the identical state was never queued, any other is followed after its parent ends, the most recent first.

Bounds

Memory is bounded by two caps. Only histories with index below TrajectoryConfig::max_histories are recorded, so the lowest indices win whatever the thread count; the others are counted in TrajectoryRecorder::histories_skipped. A history keeps at most TrajectoryConfig::max_points points over all its tracks; further points (and the tracks of further recoils) are dropped and the history is flagged History::truncated. Histories are merged in chunk order, so the output is bit-identical at any thread count.

Structs

History

The recorded tracks of one primary history. tracks[0] is the primary; every parent index is smaller than the track’s own.

Recorded

An ordinary tally and a TrajectoryRecorder fed by the same events of one run. inner sees exactly what it would see alone.

Track

The path of one particle.

TrajectoryConfig

Caps on what a TrajectoryRecorder keeps.

TrajectoryPoint

One point of a track.

TrajectoryRecorder

A BcaTally that records ion and recoil paths. See the module documentation for the convention and the caps.

Enums

TrackEnd

How a track ended.