Progress in Fusor Plasma Simulations

[Liam David]

Just a quick update as I work on a new and improved (read: much faster and with fewer bugs) iteration of the code. Some eye candy with ion optics:

https://youtu.be/XyJW5LpbuBE

[Nicolas Krause]

Lovely visualization Liam, are those level surfaces of ions in the video?

[Liam David]

It's the density of D2+ ions on the domain.

[Liam David]

I've rewritten much of the code and have fundamentally changed the data storage architecture to reduce memory operations, resulting in about an order of magnitude speedup especially at large particle counts. The precision has also been reduced from double to single.

I have also focused on maximizing the performance of collisionless particle tracking, meaning simulations of several million particles evolving for several milliseconds are possible with an overnight run (with a timestep of 40ps). A common performance metric for PIC codes is particle push/boundary check operations per second, and mine achieves ~10^10/s on an RTX 3080, or very roughly 600 GFLOPS. It's a memory-limited application, so the raw FLOP performance does not come close to the maximum of about 30 TFLOPS.

Other changes include:

• Implementing a 5-point stencil (instead of a 3-point) for the Laplacian in the electric field solver, and making it fully applicable to cylindrical coordinates by including the 1/r*df/dr term. It now accurately produces the logarithmic potentials found in cylindrical geometries.
• Adding magnetic fields, which is accomplished by providing a magnetization density vector field M and solving a Poisson equation much like the electrostatic case. Some preliminary simulations indicate that a moderate axial magnetic field can enhance ion lifetime, as well as the phase space of stable and quasi-stable orbits. The Boris algorithm is used to push the particles.
• Accounting for collision angle in the fusion rate calculation (work in progress).

5-point Laplacian

Magnetic field lines superimposed on electric potential

[Liam David]

As I hinted at before, the simulation reproduces the color bands seen on cylindrical cathodes, as well as the off-axis beams and circumferential ring bisecting the inside. Due to all the code changes, I can now simulate steady state, which constitutes ~8e6 total particles. I'm also getting hints of what may be ion acoustic waves (or transit time resonance) at ~13 MHz... I'm slowly building confidence in the simulation, although the calculated locations of fusion reactions are not where expected, as in not within the cathode due to anomalous electron trapping. More results to come.

High density beamline obscured to enhance contrast

[Javier Lopez]

Can you set external magnetic fields in your simulations?

[Dennis P Brown]

With all those posts and you still not using your full name either you are intentionally breaking the rules or feel you are above them. I'd suggest you follow the rules here if you want to continue posting.

[Richard Hull]

All of the posts by "fusion" will be deleted if he doesn't change his user name along with any responses to his posts.

Richard Hull

[Frank Sanns]

Negative. Do not delete Javier's posts.

He has been on here for over a decade but has just come back after the rule changes.

Give him a chance to respond. I have sent him an email but I do not want to change his login name as it will prevent him access.

Under no circumstances should we be nuking somebody with over 100 posts. It is not good form and it will screw up over 100 threads.

[Richard Hull]

Can we go back and un pink all those posts? I do not know how to do it.

Richard Hull