Dust Grain Growth Barriers 2D: Size-Velocity Phase Diagram

This is the 2D counterpart to the 3D protoplanetary-disk dust-coagulation simulation, built as an independent numerical model rather than a flattened version of the same particle box. Instead of watching aggregates drift and physically collide in a spatial patch, this model plots a population of dust tracers directly on the size-vs-collision-velocity phase diagram used throughout the real dust-growth literature to explain the bouncing and fragmentation barriers. Each tracer's radius climbs along the same turbulence-driven collision-velocity curve the 3D model uses, until that velocity crosses your fragmentation threshold (aggregate shatters back to a monomer) or the aggregate's size crosses your bounce-onset size (it stalls, rebounding instead of sticking). A live histogram tracks the population's size distribution piling up at whichever barrier bites first, while a separate pairwise sampling check reports real-time stick/bounce/fragment percentages computed from the exact same formulas. Adjust turbulence strength, the fragmentation threshold and the bounce-onset size to see the barrier lines move and watch which one wins.