TQS Quench Analysis

TQS Quench Analysis Shlomo Caspi LARP Video Meeting September 22, 2008

Technology Quadrupole Shell - TQS • Aluminum shell over iron yoke • Assembly with bladders and keys Low pre-stress during assembly High pre-stress with cool-down Reusable structural components 2 CERN, WAMSDO May 2008

Magnet Tests Virgin coils are listed in bold

TQS01 Training • ~10 Q to plateau • TQS01c - 1.9 K • Slow training • ~10% gain

TQS02a Training • TQS02 • 5 Q to plateau • No gain at 1.9 K • Erratic Similar coils - different limiting quenches

Short-Sample Performance – 4.4 K 6

Measured TQS Structure Stress • Low assembly stress • Gain during cool-down • Reversible during warm-up

TQS01 – Bronze Poles TQS02 – Titanium Poles Change of Pole Material in TQS02 • Titanium Poles remain in longitudinal compression at all stages • Eliminated stress concentration at pole cuts while reducing axial load • Coil fabrication improvements: - No gaps needed between segments • - Better coil parts fit after reaction • Titanium poles were also adopted for the HD2 and CARE dipoles

Quench Locations 9 TQS01 • Layer 1, straight section, pole turn, near ramp and island gaps • Limit to a single coil same location TQS02 • Layers 1 & 2 pole turn and multi-turns, straight section

4.5K SSL 1.9K SSL TQS01c @ 1.9K 1.9K4.5K (4.5K) TQS01c @ 4.5K Quench current (A) Post-test inspection of pole gaps Quench locations Epoxy tearing TQS01, 01b, 01c Test Results • For all magnets, training started above 70% of the short sample limit • Plateau quenches occur near gaps of pole parts; only one end quench • Plateau quenches in TQS01c follow temperature dependence of Jc

Coil 7 VT B6 VT A8 Coil 6 87% SS Fe FILLER POLE GAP Plateau Quenches in TQS01a, b, c • TQS01 plateau quenches are very repeatable (all segment dV/dt are overlays) • Quench propagation velocity along pole turn can be correlated with local Ic • Calculated “gap” Ic in coil 6 consistent with ~87% quench level (already in Q#4) • TQS01b & TQS01c limit also consistent with Ic degradation (in different coils) SQ02 Measured Quench Velocities Iq/Iss

Calculated bronze pole (TQS01/b/c) Spikes in coil axial strain (cool-down & excitation) Pole gaps Pole gaps Calculated titanium pole (TQS02) Spikes in coil axial strain are reduced/eliminated Coil Stress near Pole Gaps • 3D ANSYS calculations and TQS01b measurements • indicate high longitudinal tension in coil across gaps, • possibly leading to conductor degradation Differential measurements of coil axial strain in TQS01b 3. Training 4. Warm-up 2. Cool-down 1. Assembly

All plateau quenches in coil 21 (coil 20 & 21 participate in the initial training) • Quenches start in the pole turn and the multi-turn segments of the outer layer • Quenches in each of the two plateaus (before/after 1.9K)repeat almost exactly • 1st plateau (21-25): • 2nd plateau (49-54): • Pole turn starts 0.7 ms after multi-turn • Quench fronts also in the inner coil (next to pole & wedges) • pole turn & multi-turn start at the same time • no inner coil quench fronts Quench 25 4.5K Plateau (before 1.9K) Coil 21 Pole Around Lead end Ramp B6A10 Pole turn A10A9 Quenching Sequence ■ 1st ■ 2nd ■ 3rd ■ others Turn 2 A6/7 A5 TQS02a Plateau Quenches (4.5 K)

R&D Issues 14 R&D issues: • Short-sample plateau at 4.4K of 80-90% • Short-sample plateau at 1.9K of 77-84% • Is it only stability at 1.9 K ? • Why different limiting quench currents in similar coils? • Why same quench locations at 4.4K and 1.9K. and why erratic behavior does not move quench location? • We may have lower stability at 1.9K than 4.4K – however could local flaws during coil manufacturing and over-stressing be the main cause of performance limitations both at 4.4K and 1.9K? • Layer 2 quenches in TQS02

Summary • 6 tests – using TQS technology • LARP 200 T/m target – reached 220 T/m • Plans for next 2 tests using TQS02c: • Stability and protection heater studies now underway • Impact of axial pre-stress on magnet performance • Future plan - TQS03: • Improved QA on new coils using 108/127 conductor 15

kA T/m Ramp Rate 1.9 K 2.2K 4.5 K First training cycle at 4.5 K Plateau #1 Plateau #2 200T/m TQS02a Quench Performance TQS02 Test Results • Performed well above 200 T/m at both 4.5 K & 1.9 K; max gradient 224 T/m • First quench >175 T/m; Achieved 200 T/m after two training quenches • Delivered stable performance at 215 T/m(4.5K) after training • Demonstrated RRP 54/61 performance above target gradient (4.5K & 1.9K) • Confirmed the analysis of the cause of the TQS01 limitation and its cure • Training was limited to an average of ~215 T/m at both 4.5 K and 1.9 K • Some scatter/fall backs in the first ~20 quenches at 4.5 K, and at 1.9 K

First 4.5 K plateau (5 quenches) Second 4.5 K plateau (6 quenches) dV/dt (V/s) dV/dt (V/s) OL multi-turn half slope (training) 0.7 ms delay No delay Heater fired OL multi-turn OL pole-turn OL pole-turn (same as 1st plateau) (ms) Time (ms) TQS02 Quench Analysis (4.5K & 1.9K) • Quench origins cannot be precisely located: • However, voltage signal overlays indicate same origin and evolution • Comparison of 1st and 2nd plateau shows further training occurred at 1.9K • At 1.9 K, same limiting coil (#6) and same quench onsets/sequence as 4.5K • Some differences in quench evolution at 1.9K - four identical overlays identified • Some correlation between quench current and dV/dt signatures of each group • Too short extraction delays • Too few V-taps (multi-turn)

TQS02b Training Quench Location • All quenches (4.5K and 1.9K) started in coil 29 at same location (pole turn) • At 1.9K, 20A/s ramps resulted in lower quench current than at 4.5K • At 1.9K, higher ramp rates resulted in higher quench currents • Quench location correlates with cable “kinks” after un-winding/re-winding

TQS02 cool-down Titanium pole Iron filler 200 MPa TQS02 Evaluation and Next Steps • Ti poles removed TQS01 limitation at inner • pole gaps (but increased outer layer stress) • 4.5K plateau: • Quench area is mechanically complex • Different longitudinal strain condition • Possible slipping during unloading • High transverse stress at cool-down • Possible damage in a single coil • 1.9 K behavior: some features may suggest a conductor instability. However: • Slow gain and fall-backs also occurred in the first part of the 4.5K training • Two different mechanisms resulting in same coil, area, dynamics & current? • Overlays of voltage signals would require a very repeatable instability • Short sample measurements show dip, but at ~1.8 times higher current • The same mechanical issues are likely affecting both 4.5K & 1.9K performance • Next step: replace coil 20-21 & (if possible) reduce peak stress in outer layer

TQS02c Test Goals • 1. Improve quench performance by replacing the limiting coil of TQS02b (#29) with coil 20 • Coil 20 was considered a “weak” coil since it participated in the TQS02a quench training; however, it did not limit the magnet (the TQS02a plateau quenches were all in coil 21) • 2. Carry out an extended test in order to perform a deeper analysis of the magnet: • Using quench antennas to longitudinally localize the quenches • Analyzing voltage taps signals, in particular possible quench precursors • Using magnetic measurements to understand the structure behavior during assembly, cool down and powering, and possible modifications of the structure after thermal cycles • Extending magnetic measurements to measure the decay and its dependence on the pre-cycle parameters • 3. Transfer to CERN the knowledge for disassembling and assembling a Nb3Sn magnet in a bladder and key structure. • Disassembly of TQS02b and assembly of TQS02c were carried out at CERN with LBNL participation

TQS02c Quench Origin • All Quenches (4.5K and 1.9K) are in coil 23 B6A10 (ramp between inner and outer layer) • Quench start at 4.5K is at about 110 mm from the V tap A10 with ramp rate of 20A/s • Quench start at 1.9K is at about 210 mm from the V tap A10 with ramp rate of 20A/s • All confirmed by the QA signals • Exceptions: • the beginning of the training for q1-q2 : quenches are in coil 28 • ramp rate >20A/s (4.2K) and ramp rate >140A/s (1.9K): quenches are in coil 23 A2A4 • ramp rate <20A/s (4.2K) when quenches are in coil 23 B4B3 21

TQS Quench Analysis Summary • TQS01 (a,b,c): • Quenches originated at pole gaps, where high axial tension occurred • 3D FEA+SG data guided the change from Bronze to Titanium poles • TQS02 (a,b,c): • New Titanium poles eliminated pole-gap quenches • All models used the same structure and loading conditions • Performance limits in each model are in specific coils/locations: • TQS02a: limited by coil 21 at outer layer pole (both 4.4K & 1.9K) • TQS02b: limited by coil 29 at pole, near end (both 4.4K & 1.9K) • TQS02c: limited by coil 23 at inter-layer ramp (both 4.4K & 1.9K) • All models used the same conductor and heat treat • For TQS02b, weakness could be traced back to coil winding phase • Ramp area limiting TQS02c is also problematic (geometry, handling)

TQS Test Summary • Demonstrated accurate, repeatable control of warm and cold pre-load • Delivered safe, fast assembly and disassembly for all 6 models • Training starts high and improves rapidly to maximum • Reliable structure performance allows to identify conductor/coil issues • Selectively replaced coils to understand limits and improve coil quality • S02 models consistently surpassed the 200 T/m target at 4.4K & 1.9K • Limiting quenches originate at same locations in each model (4.4K & 1.9K) • Limiting quenches originate at different locations for different models • 1.9K limiting quench patterns are not consistent with an intrinsic wire instability • 1.9K limiting quenches are consistent with instability driven by local degradation • TQS02c never quenched below 200 T/m during 4.4K and 1.9K training

TQS Quench Analysis