TC3 Quench Performance Michael Tartaglia Fermilab TD Magnet Systems - - PowerPoint PPT Presentation
MuCool_01 TC3 Quench Performance Michael Tartaglia Fermilab TD Magnet Systems 3/21/14 TC3 Temperature Profile 5 months to review, then implement improvements 1) Thermal shield (He boiloff gas return pipe & rib cage) 2) Careful MLI
NOTE: Cooling tube “bypass” (due to leak) is located at RTD2 location – worst cooling condition Temperatures are very stable, Eddy current heating is small: at 1.8 A/min dT=90mK at RTD2 (5.80K) 5 months to review, then implement improvements 1) Thermal shield (He boiloff gas return pipe & rib cage) 2) Careful MLI installation Good steady vacuum, P=4 ∙10-6 Torr
LHe Cooling Tube welded to outer Aluminum Ring Coil 1 Coil 8 Voltage Taps, protection diodes across each coil 12 layers per coil, stycast “wet layup” Cu/Nb-Ti Single Strand (L=600 H) Slip planes to reduce shear stress (?) There is no MICE Note or Publication
(There are for prototype test coils)
Coil 1 inner R Coil 8
Forces on Coils Axial Field at Coils 4,5 is near zero 765 N/m 450 N/m 630 N/m
Main concerns: frictional energy release caused by 1) stick-slip motion of coil wrt structure, 2) epoxy cracking from stress; 3) conductor motion
Voltage Spike disturbance profiles are the same in all events; only the amplitude changes. Note coil 4 disturbance is always flat (suggesting radial coil motion?) Diodes turn on in the range
increase somewhat with quench current ~ B First “triggered” event is at about twice the current previously reached in Sept. 2013 (64A). The very first event seen in Sept. at 62A was a similar voltage spike.
After this event, steps were taken to desensitize the quench protection half- coil difference signal. Quench Characterization system real time 8th coil voltage traces clearly show a lot of voltage spike activity (not just in coils 1,2,3), especially at higher
solenoid field. Clearly, not all disturbances result in a quench.
All quench development plots shown on the same {V,t} scale 10ms Hcoil filter and raised threshold (4.5V) It is clear now that voltage spike disturbances can lead to a real quench at this low current.
10 ms filter and 4.5 V threshold is still susceptible to tripping on spikes… From here on a 15ms validation delay for half coil above threshold is required.
Coil 5 is different here!
Coil 5 is noisy hereafter
A look at LTS Leads:
Hall Probe (current)
(relationship to hot spot temperature is not known!
Previous calcs predicted 130K at 210 A, but under different assumptions; here we are forcing all diodes to conduct.
Coil 2 also quenches
Quench Developments are all VERY SIMILAR Variable delay between time of disturbance and start of quench propagation depends upon: 1) Energy deposited >MQE 2) Distance from high field region Need T> critical surface (r,z) Expect Coil 1 diode to conduct Sometime soon! (14.6V)
PS turning
t( 5 ) = -.285 dV/dt(3V)=61 V/s t( 4 ) = -.235 dV/dt(3V)=65 t( 3 ) = -.130 dV/dt(3V)=93 t( 6 ) = -.130 dV/dt(3V)=35 Coils 3, 4, 5 motion at t=-.027 t( 2 ) = -.027 Quench starting in coils 5,4 must be at the coil end (axial field is small, radial field is maximal)
Quench Characterization plots show that all quenches in a given coil, at very similar currents, develop in essentially the same way. Quench velocity appears to scale with the peak axial field on the quenching coil, as might be expected. Coil4/5 quench velocity is consistent with being at the coil end.
Heng Pan at LBNL intends to model this.
Superconducting Magnet Group
3/21/2014
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Superconducting Magnet Group
3/21/2014
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(No Lorentz Forces in this picture)
Superconducting Magnet Group
3/21/2014
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Superconducting Magnet Group
3/21/2014
43
Gauges show “racheting”, due to mechanical stress changes.
… possibly unloading of coil pre-load with Lorentz force ~ I2