define particle data structure

[dtabell]

The obvious start is

mutable struct Particle
    string name
    PScoord orbit
    Quaternion spin
end

with

mutable struct PScoord
    x
    px
    y
    py
    z
    pz
end

and

mutable struct Quaternion
    w
    x
    y
    z
end

What's missing (besides comments)?

[DavidSagan]

Comments:

• For particle name I think better would be AbstractSpecies from AtomicAndPhysicalConstants.jl
• Since operations on phase space coordinates use a vector, my druthers would be to make orbit a vector.
• To promote interoperability, the spin quaternion should use the struct defined by ReferenceFrameRotations.jl.

[DavidSagan]

Missing is:

• ix_turn Turn index when doing long term tracking.
• state ALIVE, DEAD, PREBORN, etc.
• direction Longitudinal direction of travel (+1 or -1).
• time_dir Time direction (+1 forward in time or -1 backwards in time).
• location Location within an element: UPSTREAM_END, INSIDE, or DOWNSTREAM_END.
• user Dict for custom information.
• ele Pointer to element being tracked through.
• ID Particle identification (EG index of particle in the particle array of a bunch).
• weight Weight used in computing bunch statistics (like bunch sigma matrix).

[mattsignorelli]

This should this be in #23

[DavidSagan]

Actually this is needed independent of OpenPMD.