I held off on machining a cube-like fusor in the hopes that simulations will give insights on electron/ion behavior and general plasma dynamics. Much of my effort these past several months has been spent on writing a fully collisional, GPU-accelerated, particle-in-cell plasma simulation from scratch. I'm happy to say that after much debugging, the code is almost complete. I'll go much more in depth in the future when everything's done, but here's a very basic outline of how the code works:
- Import CAD model, generate initial electric field, prepare cross-section data
- Initialize all arrays for particle position, velocity, etc... included species: D+, D2+, D3+, D2, D, e
- Move relevant data to the GPU
- In a loop:
- Find collisions of particles with background gas using previous timestep's particle velocities
- Delete particles that reacted, add products
- Move particles using Boris algorithm (will be adding magnetic fields soon)
- Delete particles that impact the cathode and chamber
- Add secondary electrons from ions that impact the cathode
- Find particle densities, charge densities on the simulation grid
- Compute space charge and new electric field
- Compute the fusion rate using energy-binned particle densities
- Repeat indefinitely, or until some criterion is met
The results are in good agreement with other simulations and measurements. Central ion densities are on the order of 1e15/m^3 and computed fusion rates are ~1e6/s - 1e7/s. As expected, the vast majority of fusion reactions are beam-background and fast neutral-background, with the total contribution of beam-beam being a negligible ~0.0001% of the total. Further crushing hopes of recirculation in standard fusors, in the 10 - 50mtorr range the mean free path of D+, D2+, and D3+ ions is abysmal at a few cm.