VIC design session v98: reasoning

Lab notebook — VIC resonant sweep, film-Td tuning attempt.

The headline result is a negative one, and I'll record it plainly: this sweep did NOT hit its target. I set out to pull V_cell down from the 321-Td townsend regime into the 80-250 Td / 3-6 eV cold-chemistry window by pairing a finer choke grid near 581µH with a lower-voltage, lower-duty drive. Instead every surviving candidate lands at 842V across the 0.1mm film = 336 Td, still in townsend-avalanche, ABOVE the window. Score pinned flat at 0.413 across all five — the film diagnostic can't tell them apart because none of them lit inside the target band. The duty sweep (2/5/10/20%) only moves average input current (12→118mA); it does nothing to Td, because Td is set by cell voltage, not duty. That's the real lesson: duty is a throughput/thermal lever, not a plasma-regime lever.

The tank tells the same story. At f_r = 94.28kHz the ×8.4 magnification is fixed by tank Q = 8.4 (Xl = Xc = 1422Ω), and coil Q ~8000+ means my losses are almost entirely the water branch, not the copper — nudging turns (20 vs 24) barely perturbs it. To drop Td I must drop V_cell (~500V would put me near 200 Td), which means either lower Q or lower drive, and I chose the wrong knob.

I'm adopting #1 provisionally — lowest duty, lowest circulating-current exposure (0.59A CW), simplest to instrument — but only as a baseline, not a winner.

Next session: attack V_cell directly. Cut drive to ~60V and/or detune off resonance to bleed Q toward ~5, widen the film-gap assumption, and re-sweep purity so breakdown margin (×341, plenty) buys me room to lower voltage.