CRITICAL PHASE-TRANSITIONS MADE SELF-ORGANIZED - PROPOSED EXPERIMENTS

In Sornette, J. Phys. I France 2 (1992) 2065, a scenario for self-orga nized critically (SOC) has been proposed according to which SOC relies on a non-linear feedback of the order parameter on the control parame ter(s), the amplitude of this feedback being tuned by the spatial corr elation length xi. Implementing such a feedback mechanism, it is possi ble in principle to convert standard << unstable >> critical phase tra nsitions into self-organized critical dynamics. Here, we analyze this idea in more detail and suggest to couple a standard experiment on cri tical phenomena with some probing radiation or some electronic feedbac k using a microprocessor or analog device which pushed the temperature or analog control parameter to that value where the susceptibility, t he correlation length or the inverse of the decay rate is maximal. The practical realization of the feedback thus corresponds to an optimiza tion of the response of the system under the action of a probe or a di sturbance. We discuss liquid-vapor and binary demixion critical points , and briefly the He4 superfluid transition, magnetic systems, and sup erfluid transitions.