George R. Tynan: physicist

[Banana]

@Dr.Razor

The “Easy Target” Fallacy: Your claim that bubbles are “free… just puff the fuel into FLiBe and—poof—instant target” ignores bubble stability, uniformity, and dynamics under compression. Have you accounted for the pollution of the fuel ? Injecting DT into a hot liquid like FLiBe (which has a non-zero vapor pressure) means your “pristine” fuel bubble is immediately contaminated by beryllium and lithium vapors. These high-Z impurities will quench your “volume ignition” via radiation losses before you even fire the laser.

Bubble Stability Analysis

Because both LiF and BeF₂ have extremely low vapor pressures, less than 1 \mu Bar at 850 K, a bubble of pure D–T fuel injected into molten FLiBe would acquire almost no evaporated contaminents (Li, F, and Be).

And even if some contamination did occur, the physics is surprisingly forgiving. In a 2024 study by Gatu Johnson, Impact of mid‑Z gas fill on dynamics and performance of shock‑driven implosions at the OMEGA laser, capsules filled with a 50:50 nitrogen–deuterium (N₂/D₂) mixture reached higher temperatures and suffered only a 7.2× reduction in yield relative to pure D₂. In other words, modest mid‑Z admixtures don’t catastrophically degrade performance.

@Dr.Razor

The Optical Nightmare: You describe hitting a target in a liquid as “easy, like a funnel.” In reality, you are trying to shoot a laser through a turbulent, refracting, and likely opaque liquid medium. The index of refraction fluctuations in a circulating, heated coolant make your “Archimedean Spiral Detector” a mathematical fantasy. What is the real signal-to-noise amidst molten salt emissions, shock waves, and thermal background? Nothing in the post quantifies detection precision or error budgets.

You’re painting an “optical nightmare” that just doesn’t match the actual physics inside a molten‑salt reactor. Here are some corrections:

• the FLiBe isn’t turbulent. The flow regime in this geometry is laminar, not chaotic, so the refractive‑index field isn’t being shredded by eddies or vortices.
• the salt isn’t opaque. High‑purity molten FLiBe is a clear liquid in the visible band, not a murky coolant. The “shooting a laser through soup” analogy simply doesn’t apply.
• the refractive index is unusually well‑behaved at 850 K. FLiBe has a minimum in n(T) near that temperature, which means dn/dT≈0. With the thermo‑optic coefficient suppressed, temperature fluctuations don’t produce the kind of optical distortions you’re imagining. Rays stay straight to within a degree or so over meter‑scale paths.
• there are no shock waves during bubble tracking. Nothing is exploding or generating acoustic fronts that would scramble the signal.
• thermal background isn’t a problem. At 850 K, the blackbody spectrum peaks deep in the infrared. The visible band is essentially dark, so optical beams and detectors operate with very high signal‑to‑noise.

So the “Archimedean Spiral Detector” isn’t fighting turbulence, opacity, shock fronts, or thermal glare. It’s operating in a clear, laminar, optically stable medium with a suppressed thermo‑optic coefficient. Under those conditions, multi‑occultation triangulation of a centimeter‑scale bubble is not a mathematical fantasy—it’s straightforward geometry.

@Dr.Razor

Tritium Over-Production: A TBR of >1.2 is scientifically absurd without massive neutron multipliers that you haven’t mentioned.

Here are OpenMC results, from simulations based on natural lithium isotopic ratios and no multiplier:
FLiBe sphere → TBR > 1.2 @ >1 meter radius
Lithium sphere → TBR = 1.8 @ 2.2 meter radius