Tearing Mode Instability — Magnetic Island Formation in a Tokamak

Tokamak plasmas are confined by nested toroidal magnetic surfaces, but wherever the safety factor q(r) crosses a low-order rational number m/n, a resistive tearing mode can reconnect field lines and rip open a chain of m magnetic islands. This simulator renders the poloidal cross-section of a tokamak as a real Poincaré-style point cloud, integrates a simplified Rutherford equation to grow (or decay) the island width from your chosen tearing stability index Δ′, and lets you retune the mode numbers and the edge safety factor to move the resonant surface and watch the island chain reshape in real time — the same 2/1 island structure that is a well-known precursor to major tokamak disruptions.