WFC design session v20: reasoning

Lab notebook — geometry fine-resolve around design #1, 2026-07-04

Held surface_factor (×0.25) and temp (3°C) fixed and swept annulus geometry finely. Result confirms what the coarse pass suggested: with Cdl and cell series R essentially pinned by the fixed Randles chemistry, tank Q tracks almost entirely with f_r, which tracks C_eff — smaller gap radii and higher C_eff push f_r down, which lowers Xl=Xc and lowers Q modestly (#1 at 9/13mm, 98.84kHz, Q 100.7 vs #5 at 10/13.6mm, 90.38kHz, Q 92.4). Series current is essentially flat across the whole cluster (982–986mA), all pinned near the 1A ceiling by the same Cdl/Rct branch — geometry has almost no leverage on current once chemistry is fixed. So the real trade-off this session isn't Q-vs-current, it's Q-vs-frequency-band: tighter annulus buys Q and cell voltage but pushes f_r toward the top of my usable drive band, and I'm not seeing breakdown margin move much (104–120×, no clear geometry trend, still chemistry-dominated).

Adopting #1: tightest gap, highest Q (100.7), best coil Q (1086.8), same choke/wire BOM as the rest, current 982.3mA still under ceiling, breakdown margin ×111 comfortable. The frequency (98.84kHz) is the only caution — near the top of my target band, worth confirming choke saturation headroom there.

Next session: hold this geometry, revisit surface_factor and temperature jointly (chemistry axis) now that geometry is resolved, and check choke core losses at f_r near 100kHz before pushing gap tighter still.