Petschek reconnection

Petschek reconnection is a model of fast magnetic reconnection proposed by Harry Petschek in 1964, resolving the timescale crisis of the Sweet-Parker model by introducing standing slow-mode shocks that accelerate the outflow from the reconnection region. Unlike the long, narrow current sheet of Sweet-Parker, Petschek's configuration produces a compact diffusion region with shock-boundary layers that open like a pair of scissors, allowing reconnection rates approaching a significant fraction of the Alfvén speed. While Petschek reconnection is now understood to require specific conditions that are not always met in astrophysical plasmas, it established the conceptual framework that reconnection can be fast — and that the geometry of the current sheet matters as much as its resistivity.

Petschek showed that reconnection need not crawl; it can sprint. The shock geometry he introduced remains the conceptual template for every fast reconnection model that followed.