NOVELTY - The apparatus has an inductor (1202) e.g. toroidal inductor, comprising an inner face, an outer face, two sides, an annular core, and an aperture, where the aperture is circumferentially surrounded by the annular core. A set of coolant containment parts comprises an outer surface and an inner surface, where the set of coolant containment parts hold a non-conductive coolant. The inductor is immersed in the coolant. Heat sink fins are connected to the outer surface of one of the coolant containment parts. A tapered inductor is mounted partially into the aperture of the inductor.    USE - Apparatus for cooling an inverter or converter system or power supply in an electrical system (claimed). Uses include but are not limited to rectification from alternating current (AC) to supply electrochemical processes with large controlled levels of direct current, rectification of AC to direct current (DC) followed by inversion to a controlled frequency of AC to supply variable-speed AC motors, interfacing DC power sources such as fuel cells and photoelectric devices, production of DC from AC power for underground railway and streetcar systems, production of controlled DC voltage for speed-control of DC motors in industrial application, and transmission of DC electric power between rectifier station and inverter station within AC generation and transmission network, in inverter system e.g. for a variable speed drive, an adjustable speed drive, for transferring power to and/or from an energy device such as an electrical transmission line, generator, turbine, battery, flywheel, fuel cell, wind turbine, biomass, or any other high frequency inverters or converters, and load.    ADVANTAGE - The apparatus allows selected components to comprise elements to be attenuated or eliminated from supply signal such as noise and/or harmonic components to reduce total harmonic distortion. The apparatus provides high resonant frequency construction to improve reliability of the inductor. The apparatus allows winding to utilize specialized magnet wire for use with particular applications, which include a secondary silicone or other high dielectric coating in addition to normal coatings to minimize corona potential. The apparatus provides housing to minimize interference with the winding and improve heat radiation characteristics. The apparatus allows toroid inductor of electrical system to use a combination of individual and separately mounted single phase toroids, which are mountable inside a system cabinet or enclosure to improve efficiency and reduce airflow restrictions. The apparatus reduces conductor size which reduces overall size and weight of the inductor.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method for controlling an operating temperature of an electrical system    (2) an electrical system comprising an inductor.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of a multi-core cooling system.    Cooling system (1200)    Cooling channel (1201)    Inductor (1202)    Closed box (1203)    Single phase assembly mounting plate (1204)