(Science: radiobiology) Outer layer of a plasma which is affected (scraped off) by a divertor or limiter. That is, the outer layer of a magnetically confined plasma (ca. 2 cm thick) where the field lines penetrate a material surface (limiter or divertor plate) rather than close upon themselves. This region defines the outer limit of the plasma because any plasma crossing into the sOL is rapidly lost since transport along the field is much faster than that across the field. That is, particles follow these field lines into the material surface and are lost from the plasma.