Target Update – Mico Meeting Monday 21 st April 2008 General Expect to obtain new coils for stators anytime New Shafts at RAL for metrology. Will be back at Sheffield soon (This week?) Other?

Thermal Tests 24 coils in each stator – In the ‘current’ design there are 6 copper shims (25um) between each pair of coils to extract the heat from the coils. The heat flows from the shims into a copper water cooled Jacket where it is extracted. All of the heat extraction components have to be earthed. A metallic bore that runs through the centre of all the coils and separates the stator from the ISIS vacuum is also earthed Last two ‘demonstrator’ stators failed due to electrical breakdown between the coils and earth. Cause is due to insufficient insulation between live and earthed parts. We built a new test stator out of the coils we rescued from the two damaged stators.

New stator We built in two ‘parts’ to test two different materials. Bottom half of the stator we used a pair of Mica washers to separate the coils from the copper. shims – Mica 50um Thick, so we could only use 2 copper shims Top half of the stator we used Kapton to separate the coils from the copper shims – Kapton 25um Thick, so we could only use 4 copper shims. Centre Bore Insulated with several wraps of 25um Kapton. All coils Insulation Tested to > 1000 Volts. Put pairs of T/C in on both sides of insulation. Coils Copper Shims Kapton Mica Top half of Stator Bottom half of Stator

Coils and Coil Varnish are both rated to a maximum of 200 deg C. Kapton Rated to 400 deg C Exact Mica Rating is unknown but will be >>200 deg C T/C connected to: Between coils 6/7 (Kapton Insulation) Between coils 12/13 (Kapton/ Mica Interface) Between coils 18/19 (Mica Insulation) Water In Water Out Actuator has been run for about 45 minutes Old Actuator use to run at about deg C with water temp in of ~15 deg C

MICA T/C Coil / Insulation Temp Insulation / Shim Temp Cooling Water In ~0.5 Hz~1.0 Hz

Coil / Insulation Temp Insulation / Shim Temp Cooling Water In KAPTON T/C ~0.5 Hz~1.0 Hz

MICA & KAPTON Results Combined ~0.5 Hz~1.0 Hz

Conclusions Adding Insulation Increases the operating temperature of the stator (as expected!) but is within specification of the components The added Insulation also appears to provides adequate electrical protection. (Insulation tested to >1KV) Normal running is at ~200V with spikes up to ~600V expected. Only done a single short run! We would like to run the actuator for an extended period to show long term reliability. Water temperature at ISIS is ~30 deg C as opposed to the ~12 deg C we used. Expect operating temperature at ISIS to be even higher than illustrated here. Higher temperature may impact upon the life of the permanent magnets. This is currently unknown If running at a higher temperature does reduce the life of magnets then the target can be run at a slower rate – but clearly impacts upon MICE running. If this is the case then future development could reduce power consumption of actuator but would need significant development. (Not for now!)