WFC design session v9: reasoning

Lab notebook — resonant sweep, single-cell vs stacking, 540 candidates

All five top candidates cluster tightly around 76.2mm cell length with rod/tube annulus ratio near 0.77-0.78, C ≈ 1.29-1.32nF, and the same 2×1mH choke pair. That's telling me the geometry is fairly flat near the optimum — I moved rod diameter ±3mm and tube diameter tracked with it, and cost only dropped 0.3% in score. Multi-cell stacking (2-3 in parallel) never beat 1-cell in this run; adding cells raises total C, which pulls f_r down and demands either more L or accepts a lower Xc, and the resulting tank Q consistently came in below single-cell configs once I transformed water's parallel R to series equivalent — the water resistance dominates loss at these C values regardless of cell count. So for now, stacking isn't buying Q, just more surface area and more current draw risk.

The real trade-off I'm seeing: as C creeps up with larger annulus gap, f_r drops from ~99 to ~98kHz and tank Q drops with it (64.9 → 64.2), while series current stays pinned near 625mA across all five — comfortably under the 1A ceiling, so current isn't yet the binding constraint here, geometry/Q is.

Adopting #1: 22.8mm rod / 29.5mm tube × 76.2mm, single cell, 99.08kHz, Q=64.9, 779V output. Best voltage magnification of the set, still within all bounds.

Next session: sweep choke turns/wire gauge to see if raising coil Q (currently only 707 vs theoretical ceiling) pulls tank Q past 65 without touching cell geometry.