1. QXF protection heater design : Overview and status Tiina Salmi QXF quench protection meeting April 30, 2013

2. E. Todesco: Time margins in superconducting magnets (WAMSDO 2013) Protection heater design for QXF GOAL: Quench all the turns fast enough (ideally in ~ 35 ms, including detection time!) CONSTRAINS: 1.Heater voltage ≤ 400 V (t.b.d.) 2.Heater temperature ≤ 300 K 3.Heater strip length = 4 m 2

3. Concept of heating stations 3 HS Hotspot First quench after “Heater delay”, t d,PH Quench propagation (QP) All turn quenched, t d,Qturn = t d,PH + t d,QP Hotspot * L NS = Longitudinal heater coverage at the turn under HS L NS * Optimization: Minimize t d,Qturn LQ-style heater strip I PH stainless steel

4. Design trade-offs 4 Heating station power Several low-power heating stations  Longer t d,PH, Faster t d,QP vs. Fewer high-power heating stations  Faster t d,PH, Longer t d,QP Heater insulation thickness Thicker insulation  Better electrical integrity  Longer t d,PH What is the optimal geometry and power? Heater geometry Several short heating stations  Longer t d,PH, Faster t d,QP vs. Fewer long heating stations  Faster t d,PH, Longer t d,QP

5. QXF heater: First iteration HF: w wide = 25 mm, w NS = 8.3 mm LF: w wide = 32 mm, w NS = 10.7 mm Heater insulation: 0.050 mm Kapton (2 mils) NS lengths and heater power result of optimization* (taking into account magnetic field) LF and HF optimized separately Design margin of 0.2 Ω for connectors 5 QXF |B| [T] @ I NOM (17320 A) HF block, NZPV = 20 m/s NS1, B = 9.3 T NS2, B = 7.8 T NS3, B = 6.9 T LF block, NZPV = 10 m/s NS1, B = 6.5 T NS2, B = 6.0 T NS3, B = 5.7 T Only outer layer heater: 4 strips per coil 3 NS for HF and LF block * More information in the appendix Heating station: 3 tunable Narrow Segments (NS)

6. Preliminary result 6 L NS1 L NS2 L NS3 w NS Narrow segment lengths and periodSimulated delays L NS1 (mm)L NS2 (mm)L NS3 (mm)L wide (mm)L Period (mm)t d,PH (ms)*t d,Qturn (ms)** HF strip102550681612125 LF strip253550902112536 Delay to quench all block (does not include detection time!) “Heater delay” The time margin was 35 ms… We cannot conclude that the magnet is safe with only heaters on the outer layer. Heater power = 75 W/cm 2

7. Next steps Improved modeling for heater design: Simulate quench propagation velocity (now maybe too optimistic) Simulate quench propagation from outer layer to inner layer Iteration with heating stations shape Simulation of hotspot temperature: Input heater geometry and delays in QLASA and/or ROXIE Experimental data from HQ02: Measurement of heater delays and quench propagation velocity – Impact of magnet current and heater power – Inner and outer layer Important to experiment also with quench back since we are really at the limit of heater performance… – For example: Measuring MIITs after a provoked protection with only outer layer heaters (already tests at low current informational) 7

8. Appendix 8

9. Heater delay simulation Single turn with periodic PH coverage 2-D Heat conduction model No turn-to-turn propagation Thermal network method Quench when cable reach T cs (I,B) *No free parameters* NS length / 2 (Kapton or G10) Cable width Imag HQ: Field and heater coverage (L NS ) vary  Delay depends on quench location… Simulation for 6 turns, shortest delay predicts the measurement HQM04 HQ01e Simulated delays in HQ coils are within 20% of measurement. Magnet current / short sample limit [%] Magnet current [A] Model Validation 9

10. Length of the heating station, L HS The heating stations mathematics 10 Schematic for demonstration purposes, not final drawing. HS dimensions to be optimized Narrow segment width, w NS is constant Stainless steel thickness, d ss is given Resistance of heating station, R HS : Resistance of wide part, R wide : Strip total length L strip and resistance R strip : NHS = Number of heating stations / strip

11. QXF heater design: Parameters 11 Conductor RRR150 Cu%53 Cu/SC1.13 # strands40 Cable width (bare)18.3mm Cable mid thickness (bare)1.557mm Strand diameter (before reaction)0.85mmG10 Voids fraction (estimation)0.15Epoxy Heater and insulation layers Cable insulation thickness0.15mmG10 Interlayer insulation0.5mmG10 PH Bottom ins. (interlayer + cable)0.65mmG10 PH Top ins. (ground ins.)0.5mmKapton Stainless steel thickness0.0254mmSs Heater strip length4.0m Magnet operation Transfer functionB peak = 0.0007044*Imag Bpeak – 12.2 T at I NOM I Nom 17320A Critical surface fit Bc2m = 28.46 T, C = 2105 TAGodeke

12. Symbols and abbreviations NotationExplanationUnit PHProtection heater HSHeating station- NHSNumber of periods / strip- P HS Dissipated HS power / AreaW/m 2 wwidthm LLength longitudinally along cablem RResistanceOhm V PH Heater strip voltageV I PH Heater strip currentI T PH Heater strip temperatureK t d,PH Delay time to quench after heater activations t d,QP Time to quench propagate btw HSs td, Qturn Time to quench all turn after heater activations t ss Stainless steel heater thicknessm ρStainless steel resistivityΩm BMagnetic field strengthB I ss Magnet current short sample limitA OL / ILCoil Outer Layer / Inner Layer- 12