A summary of issues arising during operation of the MICE target during the MICE data taking in the period 2-5th August 2013

Nebrensky, H

Overton, E

Rogers, CT

English

Brunel University Research Archive

MICE Target Issues During Run 2nd-5thAugust 2013H. Nebrensky, E. Overton, C. T. Rogers1 IntroductionBelow is a summary of issues arising during operation of the MICE target duringthe MICE data taking in the period 2-5th August 2013. Those involved in thedata taking are listed below.• MICE Operations Manager: Victoria Blackmore• Beam Line On-Call: Henry Nebrensky (HN)• Software On-Call: Chris Rogers, Durga Rajaram• Shifters: Ian Taylor, Yordan Karadzhov, Steve Boyd, Chris Hunt, Alexan-der Dick, Ray GametThree separate and apparently unrelated issues were observed. The targetcontrol crate had a hardware failure which was diagnosed and fixed duringpre-run testing; the target controller reported several ADC Quadrature failuresduring pre-run testing caused by a fibre readout error; and the target controllerreported a Quadrature Continuity failure during operation resulting in anISIS trip.2 Target Control CrateOn 30th July, prior to MICE running, HN observed some unexpected numbersbeing read back on the Target Drive panel, which were traced back to faultycards in the Control Crate in the Target Vac-Rack. This crate provides theinterface to the target drive and also to the target frame stepper controller. AnADC and a carrier card within the crate was replaced resolving the problem.The ISIS Gate valve was closed during the replacement as a precaution.3 Fibre Readout ErrorOn a number of occasions prior to the last MICE run the target has failed toactivate at the start of the day during pre-run tests with the frame raised. Thetarget control mechanism has reported an error14 BPS Error 2Status: Fatal Error 12: ADC quadrature.This occurred two during the shifter training on 22nd July and then on the30 and 31 July prior to the MICE run itself. This error indicates a too low signallevel from the optical quadrature system, and suggests a drop in the amount oflight returned.4 BPS ErrorHN received a phone call from MICE Local Control Room (MLCR) on Saturday3rd August. The target had stopped at 11:42 withStatus: Fatal Error 13: Quadrature ContinuityThe target controller had reacted as expected: that is, it tripped the BPSstopping ISIS, and started the frame jogging up. The frame reached the topsoon after HN got to the MLCR a few minutes later, and he then returned thebrass MICE Target Enable key to the ISIS crew so that ISIS operation couldcontinue.A 10-15 minute delay between the quadrature error/BPS trip and the MTENBLkey being returned to the ISIS MCR to allow running to resume was experiencedas expected. In these circumstances the stepper system raises the target framein ”jog” mode which is noticably slower than normal; this might give someoneunfamiliar with the system a false impression of a problem. The use of theslower ”jog” mode to withdraw the frame was communicated to ISIS during theBPS integration and approval process.At some point before HN arrived, ISIS crew had also come down to theMLCR to re-set a PPS crate that had stopped reading out, which is believed tobe an unrelated issue.5 Fibre Readout Error InvestigationIn the short term the reduced light yield from the fibre is being increased byincreasing the input laser power level and amplifier gains; we estimate there issufficient headroom to overcome the increasing losses and ensure reliable opera-tion until Christmas. As a precaution we also checked the reported signal levelsat the start and end of each day during the last MICE run, and experienced nofailures during the run itself.The cause of the increasing light loss is not yet known; the most obviouscandidate is radiation damage (darkening) of the optical fibres. We also notethat activation levels in the vicinity of the MICE target appear to be higher thisshutdown than previously - it was not therefore possible to remove and replaceany section of fibre, for testing.Plans for investigating the increasing light loss are in preparation; if damageis found to the main fibres then it would be necessary to pull new sets of fibresfrom the MLCR through to the MICE Target.6 BPS Error Investigation 36 BPS Error InvestigationThe most serious error was the BPS trip and this has prompted further inves-tigation by the MICE target team.The cause of the trip originated from a part of the control system responsiblefor monitoring the optical quadrature system used to track the target position.During operation the position tracking system is critical to selecting which coilsneed to be switched on to produce the correct trajectory; a malfunction herecan result in undefined behaviour of the mechanism, which in the past has ledto damage of the mechanism requiring replacement (namely T1).To reduce the risk of this occurring again, the control firmware monitors thetwo signals from the quadrature system during the first 1.25ms of an actuation.If a signal is not seen on both of these inputs within this time the controlsystem assumes a failure has occurred and terminates the actuation by cuttingthe power to the coils. This results in the target slowly falling onto the bottomstop. When the frame is in its lowered position this means the target will befully in beam before the next injection and therefore this error also trips off theBPS.As the optical quadrature system was operating normally it is suspectedthat the source of this error was a lack of instantaneous acceleration at thestart of the actuation. This may be caused by a reduced force on the shaftdue to an unfortunate position of the permanent magnets after the previouscapture, with respect to the driving coils of the motor while running withinspecification. Another possibility is the longer cable runs slowing the rise timeof the coil current compared with those used during calibration in R78.During running we have been monitoring the acceleration of the mechanismover the whole actuation (as this is one of the diagnostics). This has not differedfrom a typical test conducted in R78 before installation. This indicates thatthe 1.25ms limit used to check the quadrature system is a little too short andrequires revising. Increasing the limit to 1.40 ms will cause a negligible changeto how the quadrature check functions, but will be more robust to this kind ofmisinterpretation in the future.7 ConclusionsFurther actions and modifications to MICE procedures are:• MICE will add explicit training for all BLOCs in the upcoming trainingsession to ensure they understand the situation, and to ensure that if noton site they are able to guide by phone the MOM through the process ofreturning the MTENBL key to the ISIS MCR as soon as the frame is fullyraised, to allow ISIS to resume as quickly as possible (HN).• The time limit for the quadrature system check will be increased to 1.40ms (MICE Target Group).7 Conclusions 4• The cause of reduced light yield at the target controller is under investi-gation. Specific actions will be taken depending on the outcome of thatstudy (MICE Target Group).

MICE target issues during run 2nd-5th August 2013

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MICE target issues during run 2nd-5th August 2013

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