Enhancement of the Stabilization of Superconducting Magnets by Hydro-statically Pressurized He II

He II under pressures from 1atm to saturated vapor pressure and constant bath temperature was investigated as a possible coolant for superconducting magnets. The cooling strength is described in terms of a critical frequency fc at which the peak transport currents corresponding to successive constant voltage pulses decrease abruptly due to a breakdown of superfluidity. Maximum fc was found under the pressure at the lower λ-point (He IIλ) i.e. with a hydrostatic pressure head of about 2m. This allows the use of ordinary cryostats while retaining the efficiency of saturated He II systems. He IIλ does not give full stabilization in the classical sense, but is a promising coolant for pulse magnets or meta-stabilized DC magnets.