SmartCopy: Custom Default Initialization

[ax3l]

Problem Description

For scenarios such as HEP LWFA/PWFA ionization injection (and any injection that is non-external), QED beam collisions & radiation generation, etc. we often need to know where newly generated particles originated.

Generally, we add a runtime attribute orig_x/y/z to particles that stores position_x/y/z at t=0 of the simulation. When generating electrons and photons during the simulation (t>0) with ionization & qed, we cannot yet store their position at generation.

What Needs to be Done First

We need to implement a more general version of SmartCopy, which is used in ionization and QED physics.

• Smart Copy copies matching attributes, and default-initializes all other attributes in the destination particle.
• We would need a policy (runtime or compile-time) that allows us to do custom initialization in the destination particle.
• In particular, we need a method to init the dest runtime attributes orig_x/y/z with src position_x/y/z on particle creation.

Files that implement these routines:

• https://github.com/ECP-WarpX/WarpX/blob/development/Source/Particles/ParticleCreation/SmartCopy.H
• https://github.com/ECP-WarpX/WarpX/blob/development/Source/Particles/ParticleCreation/DefaultInitialization.H

What Will be Follow-Up Tasks

• Update ionization and QED generation logic to support this.