Stability of superconductors cooled by supercritical helium in rapidly changing magnetic fields

The stability behavior of superconductors with respect to disturbances extended over a large magnet volume, e.g., by fast magnetic field changes, is discussed. Cooling by supercritical helium is considered, which is the usual cooling medium in cable-in-conduit conductors. On a time scale of a few milliseconds the heat transfer is mainly determined by heat diffusion. The solution of the one-dimensional heat diffusion equation allows the calculation of the stability limit as a function of the conductor parameters and of the external field change. Calculations for exponential and sinusoidal field variations were performed and compared with available experimental data. An easy-to-use stability criterion is given for exponential heat load