Extending an internally cooled superconducting magnet to higher fields

An internally cooled superconducting (ICS) magnet was built and tested earlier at Oak Ridge National Laboratory (ORNL), and its stability margin as a function of operating fields was measured at an ambient helium temperature of 4.2 K. In the experiment reported here, we retested this magnet with lower bulk helium temperatures. The stability margins of the magnet as a function of temperature were measured. The results demonstrate clearly the flexibility offered by an ICS magnet: The stability margin can be improved substantially or the field output can be extended without sacrificing the stability margin simply by feeding the magnet with lower temperature helium. The analysis made in a previous paper on extended field operation of an ICS magnet is thus confirmed.