Why Grapes Make Plasma: The Dielectric Dimer Resonance Window at 2.45 GHz, and Which Objects Fall Inside It

A touching pair of water-rich dielectric spheres forms a coupled Mie-type resonator at 2.45 GHz, following Khattak, Bianucci and Slepkov (PNAS 2019). With lambda0 = 12.236 cm and water permittivity 77, the isolated-sphere resonant diameter is 1.394 cm and, with a stated dimer factor of 1.45, the dimer resonant diameter is 2.022 cm, with a central window of 1.516 to 2.527 cm. Grapes (2.0-2.5 cm), soaked hydrogel beads (about 2.0 cm) and cherry tomatoes (about 2.5 cm) fall inside; blueberries, single isolated grapes, glass marbles (resonant diameter at permittivity 7 would be 6.706 cm), dry pairs and metal balls fall outside. The central bridge-field estimate is 0.89 million V/m without seeding and 3.55 million V/m with a stated alkali seeding factor, against an air breakdown field of about 3.0 million V/m; sodium (5.139 eV) and potassium (4.341 eV) ionisation energies are about one third of nitrogen (15.58 eV). All numbers are produced by the deposited compute.py. AI use is disclosed: drafting and computation assistance was provided by Dave, an AI system built and operated under the author's direction. The author, William Alexander Aldred, directed the work and is sole author of record.