That violet halo spinning off the blade tips isn’t fire and it isn’t fuel. It’s air being torn into plasma by one of the most elegant high-voltage machines ever built: the Tesla coil. A Tesla coil is a resonant air-core transformer. Mains power feeds a primary circuit tuned to oscillate at a specific frequency (here, around 450 kHz). The secondary coil is tuned to that same frequency, so energy sloshes back and forth between the two in resonance, stacking voltage with every cycle. A modest wall input becomes hundreds of thousands of volts at radio frequency. At those potentials, air stops behaving like an insulator. Around sharp points and edges the electric field gets strong enough to strip electrons off nitrogen and oxygen molecules. That ionized air is plasma, and the violet glow is its fingerprint: excited nitrogen emits mostly in the blue-violet band, which is why corona discharge in air trends purple rather than the orange of a chemical flame. So why does the rotor spin on its...