MICE

MICE Target Mechanism

Paul SmithUniversity of Sheffield

8th June 2010(Based upon talk given by Chris

Booth at CM26)

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History & Overview• T1 – DLC bearings – running in ISIS (Installed Aug 2009)

– > 215k + 50 k actuations - DLC on DLC

• T2 – nominally identical to T1– Bearing failed rapidly - DLC on DLC

• T2.2 – like T1, improved QA– Failed after ~80k actuations - DLC on DLC

• T2.3 – same stator & shaft as T2.2– New Vespel (polyimide) bearings – Vespel on DLC– Tested for >2.1M pulses in R78 Jan/Feb 2010

Results of T1 running, T2.3 tests, and plans

08/06/2010

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Actuation

08/06/2010

Strike

Beam Centre Distance (BCD)

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• T2 distribution 3-4 times as broad

• Can be interpreted as a result of the target “sticking” due to adhesive pick-up of particulate DLC - wear. Confirmed when taking target apart – Mice note 269

• MICE use the BCD histograms as a diagnostic to spot changes in target performance

T1

T2

BCD (beam centre distance) DAQ Analysis

(analysis by Paul Hodgson)

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Overlay of T1 Calibration Plots

08/06/2010

Represents 71K to 142K Actuations

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Summary for Target 1

• Target continues to perform reliably (> 215k + 50 k actuations)

• No sign of significant change in BCD distributions

• No sign of dust production on view port – Latest photo 07/06/2010 – No Dust

• Target keeps running!

08/06/2010

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Status of Target 2.3• T2 Vespel installed in R78 Jan 25th 2010

• DLC coated shaft (from T2.2) – Vespel bearings

• Same stator body as previous T2

• Pulsed target continuously for 2.15×106 pulses

• Approx. one month of operation at ~1 Hz

• Two short interruptions, chiller failed 1/2/2010, UPS failed 8/2/2010(!)

• Neither problem associated with target mechanical performance

• Target was deliberately stopped for inspection

• Very little dust on view-port (~ daily photos)

08/06/2010

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T2 BCD over month

08/06/2010

720k s 1680k s

Changeover ~1 dayStart up period

DAQ gain changes

1×106 pulses

Early Mid Late

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T2 Acceleration over month

08/06/2010

Chiller failure

Test power off

UPS failure

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T2 Acceleration regions

08/06/2010

Steady decline 848 to 838 ms-2

Stable operation (838 ± 5) ms-2

Increasedvariability

Early Mid Late

720k s 1680k s

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Questions and Comments

• How would the target have performed if we had carried on pulsing ?

Remember we arbitrarily stopped at 2.15 × 106 pulses.

• Does the early period correspond to the target “bedding in” ?

The mid period lasted approx. 1 million pulses where the target showed stable operation.

There was a reasonably rapid (1 day) change in performance after which the target parameters were (slightly) more variable.

• None of the variation seen above would compromise the normal target operation.

• The typical beam centre varies more than the target BCD.

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Disassembly & Inspection of Target 2(Jason Tarrant)

08/06/2010

• Target stopped after 2.16M actuations• Optics block removed & upper bearing exposed• Bellows removed & lower bearing exposed• Significant amounts of Vespel dust, adhered to

surfaces

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Disassembly – View of upper Bearing

08/06/2010

First look

Little dust(polished flat)

Most dust(rough flat)

Polished flat

Rough flat

Amalgamateddust balls

DustOn shaft,On bearing,On lock ring

Survey point

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Disassembly – View of lower Bearing

08/06/2010

Dust around bearing,lock ring removed

Internal face

External face

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Observation – Dust• Amount

– Most at upper bearing – esp. anti-rotate rough flat side– (Only one flat on shaft polished)– Amalgamated at bearings – scraped off

• Location– Coated internal components, has escaped externally– How does it move / defy gravity?

• Thrown off?• Electrostatic attraction?• Vibration movement?• When let up to air?

• Attachment– Fixed – by what?

08/06/2010

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Stator QA

08/06/2010

• Is stator 2 different from stator 1?

Stator field mapped with assistance of group at Diamond

Indication of ~300um offset in magnetic axis. Note: This value is to be re-checked!

Stator will be run in R78 with bearings aligned with the offset. Will this improve wear rate?

An FE model of the stator has been built, the predicted forces match the observed forces very well.

The model predicts strong lateral forces if shaft is not aligned with magnetic axis (for 500m offset max lateral force = 10% thrust Force)

The modelling and field measurements suggest that we need to improve the coil design/manufacture to ensure magnetic axis aligns with the geometric axis.

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Next Steps

08/06/2010

• Reduce wear & dust production

- Polished flats, burnished bearing faces

- Continue using Vespel (but there are additional plastics that can be tried)

- Align bearings with known magnetic offset

• Trap dust in catcher

• Further tests to start in June

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Summary• Target 1 installed and operating well in ISIS

• Target 2 with plastic bearings performed reliably for >2M actuations– Stopped for inspection, not due to failure

• Test & measurement programme for reducing and trapping dust

• Stators have been magnetically mapped to improve QA – indication that there is a magnetic offset with stator 2.

08/06/2010