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Decay Solenoid Report– 2nd June 2009
Decay Solenoid Status
MJD CourtholdMJ Hills
JH Rochford
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Decay Solenoid Report– 2nd June 2009
Important Fact
The Decay Solenoid now works !!
And has been tested to 5 Tesla
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Decay Solenoid Report– 2nd June 2009
Main Decay Solenoid Parameters
Parameters:
• Central field 5T
• Open inner Radius 60mm
• Coil inner Radius 65mm
• Coil length 8m
• Stored Energy 1.5MJ
• Max. Current 1000A
• Cu:NbTi ratio 3.5
• Current density 220 Amm-2
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Decay Solenoid Report– 2nd June 2009
Initial Decay Solenoid Powering Tests and Review -1
• Initial powering tests showed that the Decay Solenoid could not be powered beyond ~290 Amps, whereas 870 Amps is required for normal running at 5 Tesla.
• Investigations showed that coil #10 was always slightly ohmic, and caused the magnet to go normal at currents in excess of ~290 Amps
• Discussions with PSI revealed that essential MLI was missing from the 4.5K and 77K apertures at each end of the DS, allowing 300K radiation shine directly into the bore of the DS, which then had to pass through the coil windings before it could be removed by the cooling circuit
• Further analysis of the data and modelling confirmed the importance of the missing MLI
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Decay Solenoid Report– 2nd June 2009
Initial Decay Solenoid Powering Tests and Review -2
• Five layers of MLI were fitted over the 4.5K & 77K apertures at the DS exit-end, after which the DS was cooled-down and powering tests repeated.
• NB: The entry-end could not be treated at the same time, due to lack of access to the synchrotron vault until the ISIS shutdown in April.
• Test results confirmed that the additional MLI had fixed the problem at the exit-end, shifting the problem to the entry-end (coil #1 was still ohmic, although initial results were ambiguous, due to a data-logging error).
• The DS was reviewed on 3Mar09. The review board accepted that 300K radiation shine was the most likely cause of powering problems, and accepted the DS team’s repair plans & schedule, but remained concerned that other problems might be revealed once the identified problem had been fixed.
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Decay Solenoid Report– 2nd June 2009
Additional MLI
Additional Multi-Layer Insulation (MLI) was fitted in two locations at the exit end of the solenoid:
– Over the cold mass bore aperture (5 layers)
– Over the radiation shield aperture (5 layers)
Rad Shield MLI
Cold Mass MLI
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Decay Solenoid Report– 2nd June 2009
Additional Temperature Measurement
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Decay Solenoid Report– 2nd June 2009
Conclusions from January Tests
Quench always originated in coil 10The problem appeared to be thermal rather than an inherent
fault in the coil(s)– Measured temperatures of coil 10 (~7K), the iron tube (8-9K)
and the iron endplate (11-12K) were high – even before powering.
– Raising the temperature of the iron reduced the current needed to cause a quench - i.e the temperature margin of the superconductor had been reduced.
– The exit temperature of the coil cooling circuits was higher than seen at PSI for the same flow, suggesting a greater than expected heat load on the coils.
No evidence of a thermal stability problem– Temperatures all remained stable until after onset of quench– There was no indication of a blockage – the measured flow was
consistent with that measured at PSI
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Decay Solenoid Report– 2nd June 2009
Measured heat loads
•From the enthalpy of the fluid and the flow we calculated the measured heats loads on the system. •Flow is only measured into the magnet. Flow out is assumed to be the same as flow in, but this might not be true if the liquid level in the cryostat is fluctuating. Filling the cryostat may also contribute to the unaccounted for heat loads.•The flow meter measurement is limited to mass flows below 5g/s.
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Decay Solenoid Report– 2nd June 2009
Comparison of Measured Heat Loads
T (K) P(b) Ent' In J/g T (K) P(b) Ent out j/g Flow g/s watts
Iron yoke TI2=4.39 PI2=7.95 3.4 TI3=4.67 PI3=7.82 4.4 5.0 5.0
Coils 1-5 TI2=4.39 PI4=7.49 3.2 TI5=4.68 PI5=7.07 4.1 5.0 4.5
Coils 6-10 TI2=4.39 PI3=7.82 3.3 TI4=4.78 PI4=7.49 4.6 5.0 6.5
Heater 23.0
Unaccounted for loads 2.2
complete system TI1=6.42 PI1=7.69 12.9 TI0=4.4 PI0=1.17 21.2 5.0 41.2
Before MLI
After MLI T (K) P(b) Ent' In J/g T (K) P(b) Ent' out J/g Flow g/s watts
Iron yoke TI2=4.40 PI2=6.11 2.5 TI3=4.68 PI3=5.97 3.5 4.3 4.3
Coils 1-5 TI2=4.40 PI4=5.61 2.3 TI5=4.69 PI5=5.21 3.3 4.3 4.2
Coils 6-10 TI2=4.40 PI3=5.97 2.4 TI4=4.68 PI4=5.61 3.4 4.3 4.0
Heater 9.5
Unaccounted for loads 9.7
complete system TI1=6.36 PI1=6.04 13.5 TI0=4.42 PI0=1.18 20.9 4.3 31.7
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Decay Solenoid Report– 2nd June 2009
Radiative Load on CoilsSimplified Comsol model• Radiative exchange between
surfaces• Correct geometry exit and entry
ends• Assume simple cylindrical vessel• 3 cases
• No MLI windows• MLI windows at exit end• MLI windows at both ends
iron
Oxidised aluminium E~0.1Multi Layer Insulation (n>20)
E~0.001Glass Fibre E~0.2Conductivity of Coils worst case
assume conductivity of resin ~0.05W/mK
Vac ves, 300K, E=0.1 Rad shld, 77K, E=0.001
Coil K=0.05W/mK outer surface 4.4K heat sink Inner surface GRP tube E=0.2
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Decay Solenoid Report– 2nd June 2009
Coil peak 8.74KCoil peak 10.31K
Coil inner surface ~0.2m2
~1.1W coil 10~0.8W coil 1
Power crossing coil surfaces
No MLI windows present
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Decay Solenoid Report– 2nd June 2009
Coil peak 8.74KCoil peak 4.5K
Coil inner surface ~0.2m2
<0.1W coil 10
~0.8W coil 1
Power crossing coil surfaces
MLI windows at exit end only
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Decay Solenoid Report– 2nd June 2009
Coil peak 4.43KCoil peak 4.5K
Coil inner surface ~0.2m2
<0.014W coil 10
~0.004W coil 5
Power crossing coil surfaces
MLI windows at both ends
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Decay Solenoid Report– 2nd June 2009
Summary of Radiative Analysis
•Heat deposition in the coils due to lack of intermediate MLI windows on the 77K radiation shield would be significant.•This heat would be dissipated in the outer coils.•The predicted temperatures indicate that a significant portion of the coils would not be superconducting, or sitting very close to the critical surface.
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Decay Solenoid Report– 2nd June 2009
•Using quench data from solenoid runs• VF model of magnet can estimate Ic and Bp during runs
Superconductor margins
VF model;Peak field in conductor at nominal current - 870A is 5.1T(Consistent with PSI data)
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Decay Solenoid Report– 2nd June 2009
Margins
Jden Temp margin Temp
current Scon' winding Bp margin w.r.t 4.4K quench origin
A A/mm2 A/mm3 T % K K
300 234 47 2.3 66 ~3.4 7.8
870 680 136 5.1 17 ~1.1 5.5
1000 781 156 5.9 0 0 4.4
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Decay Solenoid Report– 2nd June 2009
Conclusions of thermal modelling•The predicted radiation loads gave temperatures that were consistent with those estimated for the temperature of the quenching conductor.
•Bit of hand waving here •for emissivities•and fitted a curve to the observed critical current in the conductor to estimate the margin
•Actual conductor data would have improved on these estimates •Strong evidence that radiative load on the coils was the culprit
Tq=Quench
estimate
1st coil to quench
Tq= Radiation
model
1st coil to quench
No windows ~8 Num 10 10.3 Num 10
One window ~8 Num 1 8.7 Num 1
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Decay Solenoid Report– 2nd June 2009
ConclusionsI. Before fitting additional MLI, source of magnet quench was clearly
coil#10.II. After fitting additional MLI, source of quench moved to coil #1 (although
an error in data-logging gave ambiguous results at the time).III. Enthalpy calculations showed that extra MLI had reduced heat load on
cold mass, particularly coils 6-10.IV. Additional MLI had also changed temperature distribution at exit end - iron
tube was colder and heating appeared to come from within magnet bore.V. Modelling of radiative heat loads predicted a significant heat load due to
direct shine from 300K window surface.VI. Coil temperatures predicted from thermal modelling were broadly
consistent with observed currents at quench.VII. Results suggested that the magnet was not cold enough to operate at full
current, due to radiation from 300K thin windows, but other unknown heat loads could not be ruled out.
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Decay Solenoid Report– 2nd June 2009
Repairs to Decay SolenoidDuring ISIS April Shutdown
•The entry-end window was removed, and 10 layers of MLI were fitted over the 4.5K and 77K apertures.•The exit-end window was also removed, and a further 10 layers of MLI added to the 5 layers of MLI previously fitted to the 77K aperture, as 10+ layers were now considered more prudent.•The vacuum system was purged continually with dry N2 whilst the system was open, to prevent the ingress of moisture, as this had previously created significant problems when pumping down the insulating vacuum.
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Decay Solenoid Report– 2nd June 2009
Additional Task Performed Whilst Decay Solenoid Open
•Two turbo-pump stacks fitted to Decay Solenoid vacuum system via electro-pneumatically operated gate-valves
• Water-vapour had been difficult to remove with previous pumping system via long DN40 hoses
• The two identical pumping systems, with short DN100 pipe-work, are now very efficient, and can individually pump down the system in less than 24 hours
• Access to the restricted DSA is an issue• The twin systems are now remotely controlled, and provide full
redundancy in the event of malfunction
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Decay Solenoid Report– 2nd June 2009
Rerun of Powering Testsand Analysis
•Rerun of powering tests• It was necessary to perform these tests initially with Quench Detector
active, but its action disabled, as in previous tests, up to ~300 Amps.•Investigation of Quench Detector issues
• Quench Detector is a modular design, so it was possible to check the individual comparator and relay boards by substitution.
• By elimination, it was discovered that all QD problems (during closure of PSU circuit-breakers, and during ramping) were due to a broken wire in the internal cable loom, which was repaired.
• During testing it was found that the QD PSU and Battery Backup PSU create significant quantities of noise, suggesting that the PSUs are in need of refurbishment.
•Rerun of powering tests following QD repairs• Powering tests were repeated without an further issues, and with the
QD fully active.• The Decay Solenoid was powered to 870 Amps for one hour, and
briefly to 900 Amps.
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Decay Solenoid Report– 2nd June 2009
Issues: open / in hand / closed
Mechanical
•Significant leak in transfer line at turret.•Fit strain-relieving collar around transfer line, with load taken by neighbouring support column (following slide).•A strengthening collar may also be necessary.•If leak persists it will be necessary to replace existing vacuum flange with a more substantial one.
•Smaller leaks in Decay Solenoid insulating vacuum.•Live with these.
•Vacuum system upgrade.•Complete
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Decay Solenoid Report– 2nd June 2009
Issues: open / in hand / closed
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Decay Solenoid Report– 2nd June 2009
Issues: open / in hand / closedOperational
•Refrigerator transition at 60K still an issue•Some work required on control system. Linde to attend and analyse next cool-down in July, and complete the implementation of a fully automatic & reliable control program, including recovery from interruptions. Linde requested this visit, and I would anticipate them bearing the cost
•Quench system now functioning normally, but refurbishment or replacement is required to ensure future reliability.
•DL staff are addressing this issue.•Aim is to make system almost turnkey and increase the number of experienced operators. Reconsider the consequences of having separated the DS control from the refrigerator control
•Need to produce comprehensive documentation, and identify operators.
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Decay Solenoid Report– 2nd June 2009
Typical cool-down - with interventionstill some issues around 60K, when refrigerator goes into
normal operation, that require addressing
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Decay Solenoid Report– 2nd June 2009Typical cool-down - without intervention
improved control required for radiation shields – presently very sensitive to mass flow variations into cold mass
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Decay Solenoid Report– 2nd June 2009
Issues: open / in hand / closedFinal testing phase
•The Decay Solenoid will be cooled down in the presence of Linde•This is aniticipated to take longer than usual, due to potential interruptions by Linde.
•Linde will consider modifications to the control programme whilst powering tests are under way.•The DS will be powered to 5 Tesla, and soak-tested for at least 24 hours.•The DS must be signed off by 7/8/09, in order to allow the TB to make the final decision to remove the synchrotron-hall beam-stop.•The DS will be warmed up, to allow Linde to implement final modifications to the control programme, and then retest the cool-down process.