The Fermi National Accelerator Laboratory (Fermilab) is building an Accumulator Ring to store antiprotons for high energy physics proton-antiproton collisions in the Tevatron accelerator. The Accumulator Ring approximately 474 m in circumference, consists of many quadrupole and dipole magnets connected with stainless steel vacuum chambers for beam circulation. The vacuum pressure required is in the low 10/sup -10/ Torr range. To reach this pressure, the vacuum chambers are bake to 300/sup 0/C each time they have been opened to atmospheric pressure. The critical problem is to bake the chambers in the magnets at high temperature without overheating the laminated magnets. Some of the magnets are 5 m long with very restrictive space for the heaters and insulation. An average space of only 7.5 mm around the chambers is available. In this space a heating system has been designed and tested to heat the chamber to 300/sup 0/C and allow a maximum temperature of 65/sup 0/C nest to the magnet components. This was accomplished by using a heating blanket completely covered with a water cooled copper heat sink jacket to protect the magnet from the high temperatures. The design of a final selected heating blanket is discussed. A prototype test results more » are given with comparison of calculated and measured temperature distribution. « less