The protection of a superconducting magnet system is imperative, even for well-stabilized designs that are not expected to undergo a quench. The possibility of some unforeseen failure in the system (e.g., breakdown of the vacuum or refrigerator) cannot be completely excluded. The magnet designer is faced with a trade-off between current level and dump voltage. The dump voltage for a particular system is chosen after performing calculations to determine the hot-spot temperature that would occur in the event of a quench. An acceptable hot-spot temperature depends on the stress that can be permitted as the result of a thermal differential. Usually, 150–200 K is taken as the maximum acceptable hot-spot temperature. An experiment on the LCT coils permitted a comparison of calculations and experiments to determine if the adiabatic calculations are conservative.A concern of FF coils is flow interruption. Does the coil have to be dumped, or can it be discharged in a controlled manner?To obtain important experimental data for large magnets, hot-spot and loss-of-flow tests were incorporated into the LCT test program. After assessment of coil instrumentation and their benefits, the GE/OR, EU, and WH coils were selected for hot-spot measurements, and the CH and EU coils were chosen for loss-of-flow investigations.The final experiment planned for the LCT array was the energizing of all coils to their critical current in the high-field zone (corner region) at a field level of 9 T or slightly higher. Since the critical current of the conductor in this region was not precisely known, the chance of a quench occurring was almost certain. This would constitute a dump from 50% more energy than the coils were designed for. It would be a conclusive test of the earlier hot-spot temperature measurements, the voltage withstand capability, and the whole cryogenic system and its ability to handle the discharge of the helium all at once.All of the fault experiments were successfully conducted with gratifying results.
5. Single-coil tests