Protection heater performance of Nb3Sn epoxy impregnated superconducting solenoids

The response time of Nb₃Sn coils with an active protection system is measured to quantify their performance during low current quenches. Tests are conducted on coils with bronze processed Nb ₃Sn conductors of 0.23 and 0.41 copper fractions and placed in a background field up to 7 T. Stainless steel heaters imbedded within the epoxy at the outer diameter of the coils are employed to normalize the magnets uniformly along their axes. The heater circuit consists of up to four heater strips connected in series in which a square wave pulse is applied for a duration of one second. The quench reaction time is studied as a function of heater input power, number of active heaters, and fraction of critical current density