A cooling apparatus is described that has a first cooling structure, in thermal contact with a heat source having a temperature greater than a cool structure, including a channel through which a cooling fluid is passed, an isolator between the heat source and the cool structure, the isolator in thermal contact with the first cooling structure and including a material of low thermal conductivity, and a second cooling structure between the isolator and the cool structure, the second cooling structure including a channel through which cooling fluid is passed.