2015-06-Response2MagShldRev¶

The recommendations of the review of the partial return yoke (PRY) implemented to mitigate the effects of the stray field generated by the superconducting solenoids that form the MICE channel (28Apr15) may be found here. The response of the MICE project team to each of these recommendations is given below.

1. It was felt that the various quench scenarios were unclear, particularly over whether there are any safety implications of one magnet quenching without the others. It was felt that quench-back should not be relied on to quench the whole channel, and there were remaining questions over the reliability of the electronics in the quench detection system and its ability to avoid false quenching. This should be clarified.
   • The 3 superconducting magnets of the cooling channel, the upstream (SSU) and downstream (SSD) spectrometer solenoids and the focus coil (FC), represent 3 independent devices. The magnets have been shown to operate reliably with their quench protection (QP) systems as part of their acceptance tests. Thus there are no outstanding concerns about the reliability of the QP systems. Since the QP systems have each been re-deployed in conjunction with the installation of the magnets in the MICE Hall, their operation will be fully characterized as part of the magnet commissioning process in the hall.
   • Within each spectrometer solenoid, the quench-back effect ensures that all of the coils in a given spectrometer solenoid will quench when any single coil quenches. This is the only way in which quench-back is relied on and the magnet quench behavior was fully characterized during the spectrometer solenoid acceptance tests.
   • Between magnets, which have no individual iron return yokes, the strong inductive coupling is expected to induce a quench in the adjacent magnet(s) when a fully energized magnet quenches. Since each magnet is individually protected there are no operational concerns associated with this behavior to be addressed.
2. A cryogenic safety analysis including a loss of vacuum should be in place. This should be made available for the ISIS-MICE Safety Committee.
   • All four superconducting magnets in the MICE beamline use liquid cryogens, so are subject to typical risks associated with the handling and release of cryogenic fluids, as well as some hazards specific to the MICE experiment. Pre-cooling and bath filling represent the most commonly encountered operational risk to operators but are effectively mitigated by training and oxygen depletion measures. Magnet quenches and vacuum loss, leading to rapid release of cold gas, are unexpected and uncontrolled processes, so mitigation relies on reduced occupancy of the hazardous areas. The remainder of cryogen-related risks are associated with condensation and are managed to acceptable levels. Supporting material:
     • Cryogen Risk Assessment: 2015_07_15_MICE_RA_cryogens.pdf
     • Oxygen depletion hazard in the MICE Hall: 2015-07-15-MICE-ODH.pdf
     • Focus Coil filling procedures: 2015-07_Focus_Coil_LHe_Fill_Procedure_2.pdf
     • Spectrometer Solenoid filling procedures: MICE_Spectrometer_Solenoids_OPS.pdf
     • Decay Solenoid user manual: 2014_11_Decay_Solenoid_User_Manual.pdf
3. A plan for the stray field mapping around the PRY during commissioning should be completed and presented for review to the ISIS-MICE Safety Committee.
   • A three-stage process has been defined for mapping the field in the MICE Hall (see 2015-07-09Measurement-of-stray-magnetic-field.pdf). This process involves sampling the field using a hand-held Hall probe to determine whether the 5G line determined through FEA calculation is consistent with measurement; the recording of the magnetic field on fixed Hall probes mounted at three known locations on the north side of the experiment and, to validate the FEA, a full survey of the magnetic field in the Hall.
4. Training should be put in place to establish competence of anybody having controlled access to the hall with the magnets energized, for compliance with STFC safety code 39. A list of competent people should be kept and checked before granting entry.
   • There is a broad range of interventions that may be required in the MICE Hall when the magnets are energised. Examples include re-setting crates or boards that are in low field regions and measurement of the magnetic field itself. Appropriate training will be provided in the light of the planned intervention.
   • An initial list of competent persons has been generated (2015-07-22-MICE-magnet-competencies-I1.pdf). This list will be maintained by the Group Leader in Matters of Safety.
   • The training regime, criteria for being judged a competent person and record-keeping system will be documented. When documented it will be posted and circulated.
5. There were concerns that in the event of a full quench during a controlled entry, visibility in the hall would be low and that therefore consideration should be given to putting high visibility emergency exit signs on the floor.
   • Fluorescent tape has been placed on the Hall floor to guide people to the exit in the eventuality described.
6. There remained some concern over the effect of forces acting on the coils due to the presence of the shielding. It is recommended that MICE look at the simulation work that has been done in order to quantify the forces, and to ensure that the coil supports will be strong enough in the direction that the forces will be acting.
   • The forces on the magnets and the partial return yoke in the "as built" configuration were calculated using COMSOL (see Forces-on-coils-and-PRY.pdf). The calculations show that there are no significant differences between the as-built forces and the forces that would be experienced by the magnets in the reference configuration.

Status of sign-off of PPS actions:¶

• At 02Jul15: