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ISSUES IN QXF PROTECTION

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

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  1. Frascati, 15th November 2012 QXF session ISSUES IN QXF PROTECTION E. Todesco With contributions from H. Bajas, H. Felice, T. Salmi, M. Sorbi

  2. 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

  3. 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

  4. 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.]

  5. 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.]

  6. 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

  7. 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

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