a method for controlling electromagnetic flux concentration in a discharge guide tube for a metal refining apparatus is provided . the discharge guide tube comprises a base plate , an extension , a central orifice that extends through the extension from a source of liquid metal to an outlet in the discharge guide tube for directing a stream of metal therethrough , and an interior discharge guide tube flux concentration configuration ; an induction heater system that generates an electromagnetic field in the discharge guide tube , the induction heater system being disposed on the extension with a gap defined therebetween , the induction heater system and the discharge guide tube being capable of relative vertical movement and subsequent positions with respect to each other with the gap being essentially constant . the method for providing electromagnetic flux concentration comprises providing current to the induction heater system ; generating an electromagnetic field resulting from the step of providing current ; and directing an electromagnetic flux to the central orifice at locations defined by the interior discharge guide tube . the step of generating an electromagnetic flux also generates heat and the step of generating heat provides a control of the flow of the stream of metal in its liquidus condition . the electromagnetic field is applied at a substantially constant level regardless of the relative vertical movement and subsequent positions between the induction heater system and the discharge guide tube .