MQXF state of work and analysis of HQ experimental current decays with the QLASA model used for MQXF . Vittorio Marinozzi 10/28/2013. 1.1 MQXF state of work. Current decay with dumping resistance are faster than expected, because of high dI / dt effects
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Current decay with dumping resistance are faster than expected, because of high dI/dt effects
Considering residual bronze in cables causes a drop of ~30 K in the hot spot temperature estimation
With 60 mΩ dumping resistance, dI/dt is very higher than MQXF one.
Question: do dynamic effects affect the decay with smaller dumping resistance? If yes, how much conservative have we been?
Considering bronze, at given MIITS we have ~30 K less in hot spot temperature
Impact of the material properties uncertainty on the MIITs-T curve
Analysis of HQ PH test with no dumping resistance
Analysis of HQ PH tests with 5 mΩ dumping resistance (dI/dt similar to MQXF one)
Coils resistance measurement during a discharge
MQXF protection with IL-HF block PH
Comparison between MIITs calculated by QMIITs (Tiinasalmi) with CRYCOMP/NIST and MATPRO database
Non negligible uncertainty!
Question: what are the right material properties?
Temperature measurement needed to answer
A good understanding of the quench heaters simulation is important
An analysis of HQ02 heaters test is in progress
Question to answer:
How much conservative are the MQXF simulations?
The average of the simulated delays in the HF/LF block is used as delay time in QLASA
Current starts to decay after few ms. Heaters do not induce quench so quickly (checked on voltage taps)
a “dark” resistance
Could it be that this is the reason of the similarity between the MIITs developed during 5 mΩ dumping resistance and no dumping resistance tests?
Simulation repeated with a 3 mΩdumping resistance, in order to simulate the “dark” resistance
Ideal for giving a more accurate MIITs estimation
Same analysis, on a 7kA test (0.4 of SSL)
Most significant case for MQXF
In MQXF, a MIITs overestimation of ~10% at 350 K corresponds to about 50 K less in hot spot temperature!
Same program and assumptions used for MQXF
Most significant case for MQXF
In order to answer, we’ve measured the coils resistance during the discharge. Then, experimental data have be compared to the simulated resistance growth. This measurement allows measuring theinductance.
Question: in the case of negligibledI/dt effects in MQXF, are we still conservative? Is the coils resistance growth simulation conservative?
After dumping resistance (80 ms), data are unusable
Heaters-induced quench start:
Quench induced in all the turns, except the bottom and the top of the OL
Unfortunately, the “dark” resistance makes this measure unreliable. Anyway, results seem consistent with the nominal inductance value (~6mΩ)
What’s the impact of protection heaters in the inner layer
(only high-field zone) on the hot spot temperature?
Only OL PH case
8.9 % less
11.1 % less
7.2 % less
8.7 % less
We could consider the idea of protection heaters on the inner layer, high-field block. It could be enough only on the high-field turn.
Question to answer: What’s the impact of the bubbles caused by helium evaporation?
Inconvenient: this measure can be done only at low current, for protection reasons, and for preventing development of quench in the coils not covered by heaters. For protection reason, a 60 mΩdumping resistance is used after 80 ms.
Because of acquisition problems, data are available only for two coils (unfortunately two opposite coils). Therefore the analysis is based on two tests, one with quenched coils, one with no quenched coils. The current decay is almost coincident, so the approximation is very good
Resistive voltage growth is not equal in the two coils . Quench heaters act differently (verified with voltage taps check)
Current of 8.2 kA at 4.6 K, 0.5 of SSL
In simulations, I’ve made some different assumptions on heaters delaytime and heaters-induced quench size at the start
About heaters delay time, I’ve used two values:
Experimental quench start (35-40 ms)
Time at which quench reaches a voltage of 1V (47-52 ms). This voltage corresponds to the simulated voltage between the coil ends after 2 ms. This is because, in the simulation, quench starts suddenly in several turns, instead in the actual case the quench start is distributed along the time.
About quench initial size, I’ve analyzed three cases:
Quench is induced in all the turns, except the top and the bottom turn of the OL (case similar to MQXF one).
Quench is induced in all the turns, except the three top and the three bottom turns of the OL
Quench is induced only in the high-field turn of the OL
Simulations have been done for the cases with no dumping resistance and with 3 mΩdumping resistance
Results with the 3 mΩdumping resistance are similar