A forced-cooled superconducting coil has been studied for the next step fusion machines because of many merits. The coil can be cooled by supercritical helium below 4.5K, which improves the stability and other superconducting characteristics. To study the stability of the coil at lower temperature, a test coil wound in a one-layer solenoid with a CIC conductor was tested below 4.5K. It was proved that the stability at lower temperature would be able to predict from the relationship between the critical current below 4.5K and the stability characteristics at 4.5K. The limiting current at lower temperature is in good agreement with the Lottin's experimental results.
