Decay Solenoid Status

1. Decay Solenoid Status MJD Courthold MJ Hills JH Rochford

2. Important Fact The Decay Solenoid now works !! And has been tested to 5 Tesla

3. 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

4. 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

5. 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.

6. 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) Cold Mass MLI Rad Shield MLI

7. Additional Temperature Measurement

8. Conclusions from January Tests • Quench always originated in coil 10 • The 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

9. 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.

10. Comparison of Measured Heat Loads Before MLI After MLI

11. 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 Oxidised aluminium E~0.1 Multi Layer Insulation (n>20) E~0.001 Glass Fibre E~0.2 Conductivity of Coils worst case assume conductivity of resin ~0.05W/mK iron Vac ves, 300K, E=0.1 Radshld, 77K, E=0.001 Coil K=0.05W/mK outer surface 4.4K heat sink Inner surface GRP tube E=0.2

12. No MLI windows present Coil peak 10.31K Coil peak 8.74K Coil inner surface ~0.2m2 Power crossing coil surfaces ~1.1W coil 10 ~0.8W coil 1

13. MLI windows at exit end only Coil peak 8.74K Coil peak 4.5K Coil inner surface ~0.2m2 Power crossing coil surfaces <0.1W coil 10 ~0.8W coil 1

14. MLI windows at both ends Coil peak 4.43K Coil peak 4.5K Coil inner surface ~0.2m2 Power crossing coil surfaces <0.014W coil 10 ~0.004W coil 5

15. 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.

16. Superconductor margins • Using quench data from solenoid runs • VF model of magnet can estimate Ic and Bp during runs VF model; Peak field in conductor at nominal current - 870A is 5.1T (Consistent with PSI data)

17. Margins

18. 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

19. Conclusions Before fitting additional MLI, source of magnet quench was clearly coil#10. After fitting additional MLI, source of quench moved to coil #1 (although an error in data-logging gave ambiguous results at the time). Enthalpy calculations showed that extra MLI had reduced heat load on cold mass, particularly coils 6-10. Additional MLI had also changed temperature distribution at exit end - iron tube was colder and heating appeared to come from within magnet bore. Modelling of radiative heat loads predicted a significant heat load due to direct shine from 300K window surface. Coil temperatures predicted from thermal modelling were broadly consistent with observed currents at quench. 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.

20. 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.

21. 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

22. 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.

23. 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

24. Issues: open / in hand / closed

25. Issues: open / in hand / closed • Operational • 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.

26. Typical cool-down - with interventionstill some issues around 60K, when refrigerator goes into normal operation, that require addressing

27. Typical cool-down - without interventionimproved control required for radiation shields – presently very sensitive to mass flow variations into cold mass

28. Issues: open / in hand / closed • Final 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.