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Domain-Specific Naming Conventions for Neutron raytracing codes

openPMD extension name: NRAYTRACING

Introduction

This extention is designed for neutron raytracing data that can be transfered between neutron raytracing simulation codes. The neutrons are saved in rays with a given weight corresponding to expected intensity of the ray.

For most records, the information is stored per neutron and so they must have the same length, which is the case for position, velocity, polarization, weight and time. The largest deviation from the base openPMD standard is that neutron raytracing packages keeps independent time for each particle, as they are non-interacting.

If positionOffset only contain a single set of coordinates, it is assumed to be constant for all neutrons, but it is allowed to have individual for each ray, in which case the length should match the remaining vectors. timeOffset however is only allowed to be a scalar, as no situations with independent timeOffset for each neutron is foreseen.

The neutron polarization is optional as it is only relevant for a minority of experiments/simulations. The positionOffset and timeOffset are optional as a value of zero for both is

Coordinates are defined with z in the beam direction and if possible y in the direction opposite gravity.

Particle Records

  • position/

    • type: Required
    • description: particle Position relative to the positionOffset. That is, true position relative to the coordinate origin is position + positionOffset.
    • x
      • type: Required (real)
      • description: x coordinate
      • unitDimension: [m] (1., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0
    • y
      • type: Required (real)
      • description: y coordinate
      • unitDimension: [m] (1., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0
    • z
      • type: Required (real)
      • description: z coordinate
      • unitDimension: [m] (1., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0

  • positionOffset/

    • type: Optional
    • description: Offset for each particle position component relative to the coordinate origin. Assumed zero if not present. If only one present, assumed the same for each particle.
    • x
      • type: Optional (real)
      • description: x coordinate offset
      • unitDimension: [m] (1., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0
    • y
      • type: Optional (real)
      • description: y coordinate offset
      • unitDimension: [m] (1., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0
    • z
      • type: Optional (real)
      • description: z coordinate offset
      • unitDimension: [m] (1., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0

  • velocity/

    • type: Required
    • description: (x, y, z) velocity vector. Used over momentum due to direct relevance for ray-tracing.
    • x
      • type: Required (real)
      • description: x velocity
      • unitDimension: [m/s] (1., 0., -1.0, 0., 0., 0., 0.)
      • unitSI: 1.0
    • y
      • type: Required (real)
      • description: y velocity
      • unitDimension: [m/s] (1., 0., -1.0, 0., 0., 0., 0.)
      • unitSI: 1.0
    • z
      • type: Required (real)
      • description: z velocity
      • unitDimension: [m/s] (1., 0., -1.0, 0., 0., 0., 0.)
      • unitSI: 1.0

  • spin/

    • type: Optional
    • description: Particle polarisation direction, no unit. The entire record is optional, but if it is given all components are required.
    • x
      • type: Required (real)
      • description: x component of polarisation
      • unitDimension: [unitless] (0., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0
    • y
      • type: Required (real)
      • description: y component of polarisation
      • unitDimension: [unitless] (0., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0
    • z
      • type: Required (real)
      • description: z component of polarisation
      • unitDimension: [unitless] (0., 0., 0., 0., 0., 0., 0.)
      • unitSI: 1.0

  • weight/

    • type: Required (real)
    • description: Weight of the neutron ray with the physical unit of intensity, neutrons per second. When simulating a source with a given intensity, this intensity is split up into weights of the neutron rays that will be simulated.
    • unitDimension: [neutrons/s] (0., 0., 0., 0., 0., 0., 0.)
    • unitSI: 1.0

  • time/

    • type: Required (real)
    • description: Time relative to timeOffset. That is, absolute time = time + timeOffset.
    • unitDimension: [s] (0., 0., 1., 0., 0., 0., 0.)
    • unitSI: 1.0

  • timeOffset/

    • type: Optional (real)
    • description: Base time from which time is measured. That is, absolute time = time + timeOffset. Assumed zero if not present. Some programs will use the timeOffset to store the reference time in which case time will then be the deviation from the reference.
    • unitDimension: [s] (0., 0., 1., 0., 0., 0., 0.)
    • unitSI: 1.0