Flux jumps in HQ Hugo BAJAS H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN

Background The flux jump (FJ) occurred at low current (low field instability) during the current ramp. The occurrence of FJ depends on: the filament size the current the operating temperature the ramp rate The FJ are an issue because they imply a change in the quench detection threshold for the magnet protection system. The FJ are an issue because they can affect significantly the field quality. What did we learn from HQ test campaign? (though the FJ were not intended to be studied.) H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN

HQ design 70 mm filaments for C8 and C9 50 mm filaments for C5 and C7 HQ cross-section 2 kinds of OST RRP Nb3Sn conductor [P. Wanderer 2009] [H. Felice 2010] The 4 coils are grouped by pair: 70 mm filaments for C8 and C9 50 mm filaments for C5 and C7 H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN

Comparison of the coils’ behavior More FJ are occurring in C8 & C9 (larger filaments) but the effect is not ‘spectacular’. Inductive response of the diametrically opposed coils. H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN

Effect of the Operating Temperature RR= 50 A/s FJ amplitudes higher @ 4.2 K than @ 1.9 K FJ frequency lower @ 4.2 K than @ 1.9K Need to change our Quench Detection threshold after 10 kA... H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN

50 A/s 10 A/s The higher ramp rate, the lower the flux jump frequency. Effect of the Ramp Rate @ 4.2 A/s Voltage 10 A/s 50 A/s Voltage The higher ramp rate, the lower the flux jump frequency. H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN

Effect on the Field Quality The FJ perturb the field quality, with relaxation of the spike of about 1min. The Nb3Sn cable used in HQ does not seem relevant for accelerator so far… H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN

Conclusion The HQ campaign test has allowed showing the importance of flux jump in magnet configuration with observed classical effects in terms of filament size, temperature, current, ramp rate, etc… The effect on the field quality is dramatic at 4.2K but much limited at 1.9K. In the Operational standpoint, the FJ should be ignored from the Quench detection. For coming magnet in SM18 vertical bench station (March 2013), the FJ will be automatically analysed by dedicated software and the PotAim cards will be adapted to have threshold depending on the current. For future Nb3Sn magnet to come, the FJ should be more carefully analysed since these are now playing big role. H. BAJAS | Flux Jump in HQ01-e , December 2012, CERN