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Frascati , 15 th November 2012 QXF session. ISSUES IN QXF PROTECTION. E. Todesco With contributions from H. Bajas , H. Felice , T. Salmi , M. Sorbi. QXF: DUMP RESISTOR. Short magnets have been always tested with extraction through dump resistor

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Issues in qxf protection

Frascati, 15th November 2012

QXF session

ISSUES IN QXF PROTECTION

E. Todesco

With contributions from

H. Bajas, H. Felice, T. Salmi, M. Sorbi


Qxf dump resistor
QXF: DUMP RESISTOR

  • Short magnets have been alwaystestedwith extraction throughdump resistor

    • Non negligible fraction of energyextracted

    • For long magnets situation canbedifferent

  • Estimate for the QXF

    • 800 V as maximal voltage on the magnet, current of 17 kA, 50 mW dump resistor

    • 1-m-long → half of energyextracted

    • 8-m-long negligibleeffect

  • We must work in the hypothesis of no (negligible) dump resistor


Qxf hotspot temperature
QXF: HOTSPOT TEMPERATURE

  • Time margin for protection: how long wecanstayat nominal

    • Beforehaving all magnetquenched

    • And beforereachingTmax=300 K at I(t)=0

    • Time is~30 ms: improved situation w.r.t. HQ and TQ, similar to 11T


Qxf hotspot temperature1
QXF: HOTSPOT TEMPERATURE

  • We have ~33 ms to quench all magnet

    • Quenchdetection (time to reach100 mV): typically 1-2 ms in HQ

      • [but up to 7 ms in one case at CERN]

      • With 30% largercable cross-section, this time shouldincrease by 30%

    • Validationwindow: 10 ms in LHC, possibly to bereducedat 5 ms

    • Switchopening: 2 ms (hardware)

    • Delay betweenfiringheaters

      and quenchonset: ~7 ms (HQ data)

  • So ~15 ms to startquenchouterlayer

  • Another~15 ms available to quench the inner layer

    • Data analysis of HQ needed

  • Westill plan to avoid the inner layer quenchheater

Measureddelay[H. Felice, T. Salmi, et al.]


Qxf hotspot temperature2
QXF: HOTSPOT TEMPERATURE

  • High MIITS test in HQ01e showedthat in absence of dump resistorwe are below 300 K

    • But thismagnet has strongquenchback(quenchinduced by heatcreated by cableeddycurrents due to dI/dt)

    • So this test is not conclusive

    • Test withcoredcablewillbe conclusive

18.3 MIITs

16.9 MIITs

13.2 MIITs

High MIITs test [H. Bajas, M. Bajko, et al.]

Evidence of quenchback[H. Bajas, M. Bajko, et al.]


Qxf voltage
QXF: VOLTAGE

  • Voltage scalewithmagnetlength

    • So wecould have effectsthatwe do not see on 3.4-m-long but are a killer at 8 m

    • Analysis of an extreme case: outer layer totallyquench, no quench on inner – for 8-m-long QXF we are stillsafe in this case

      • Anywayinner layer must quenchwithin 20 ms, wherewe are at 200 V


Conclusions
CONCLUSIONS

  • Protection is a verycriticalaspect for QXF

    • Scheme: littleenergycanbeextracted – we have to work in the scenario of negligible dump resistor

      • Important to test magnetswithout dump resistor!

    • Hotspottemperature: ~30 ms allowed to quench all magnetto staybelow 300 K

      • Main issues:

        • Analysis of time to getabovethreshold and quenchvelocity

        • Analysis of propagation fromouter to inner

        • Only data for magnetwithcoredcablewillbe conclusive

    • Voltage: estimated in a worse case with 8-m-long magnetseem to pose no problem (wellwithin 1kV)

      • Additionalverificationworkisneeded to reallyfind the worst case