Protection heater performance of Nb3Sn epoxy impregnated superconducting solenoids

The response time of Nb3Sn coils with an active protection system is measur ed to quantify their performance during ion current quenches, Tests are con ducted on coils with bronze processed Nb3Sn conductors of 0.23 and 0.41 cop per fractions and placed in a background field up to 7 T, Stainless steel h eaters imbedded within the epoxy at the outer diameter of the coils are emp loyed to normalize the magnets uniformly along their axes. The heater circu it consists of up to four heater strips connected in series in which a squa re 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 heate rs, and fraction of critical current density.