Philips Achieva 3.0T: superconducting switch would not cool during field ramp
What happened
After a gradient coil replacement, during field ramp-up and switch cooling the frequency kept drifting down, as if the superconducting main switch had not cooled fully; repeated cooling attempts gave no result.
What was checked
- Repeated attempts to cool the superconducting switch, without success
- Consultation with the manufacturer's support engineers
Cause
The engineers concluded that the likely cause was that the field had not been fully ramped down: a small residual current or field was apparently enough to prevent the switch from cooling normally. The exact physics of the effect was not fully understood in this case.
What was done
The field was ramped fully down to zero and the magnet was left in that state overnight; the next morning the field was raised again using the standard manufacturer ramp procedure, performed by trained personnel, and this time the switch cooled normally and the ramp-up completed successfully.
Safety
A superconducting magnet stores a huge amount of energy and its strong static field is always present: treat ramp-down and ramp-up as high-risk work done strictly per the manufacturer's procedure, keep ferromagnetic objects out of the magnet room, and watch for helium venting and oxygen depletion.
Lesson: If a superconducting switch will not cool during ramp-up, first verify that the field was truly taken fully to zero — residual current can block proper switch cooling, and a complete ramp-down with an overnight settle may be the cure.
Covered in the course: MRI Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.