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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


E. Todesco

With contributions from

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

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

  • 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

  • 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

  • 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

  • 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


  • 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