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ISSUES IN QXF PROTECTION

This session discusses key issues in QXF magnet protection focusing on energy extraction via dump resistors and hotspot temperature management. It outlines the differences in energy extraction for short and long magnets, estimating a maximum voltage of 800 V and current of 17 kA, with significant implications for safety margins in quench detection. The session also highlights a time margin of approximately 30 ms to quench all magnets and carefully analyzes the risks associated with outer and inner magnet layers. The emphasis is on critical protection schemes and the need for further testing without dump resistors.

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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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