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US LHC Accelerator Research Program bnl - fnal- lbnl - slac TQC 01 Mechanical

US LHC Accelerator Research Program bnl - fnal- lbnl - slac TQC 01 Mechanical Structure, Design, Modeling and Construction R. Bossert LARP Internal Review Nov 29 - Dec 1, 2006 TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction

Introduction TQC 01 Design Goal: Achieve 200 T/m after training. After reaching 9000 A

Introduction TQC 01 Design Goal: Achieve 200 T/m after training. After reaching 9000 A at 4. 5 K, TQC 01 reached 200 T/m (12000 amps) at 1. 9 K, about 85% of short sample. SSL at 4. 5 K = 12. 7 - 12. 9 k. A at 1. 9 K = 14 k. A TQC 01 is the first of the TQC short model series to be built. It was constructed at Fermilab between May and July of 2006 and tested at Fermilab in August 2006 at both 4. 5 K and 1. 9 K. TQC 01 has been disassembled, and mechanical measurements as well as strain gauge readings have been taken during disassembly. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 2

TQC 01 Mechanical Structure TQ Internal Review Nov 29 -Dec 1, 2006 • Based

TQC 01 Mechanical Structure TQ Internal Review Nov 29 -Dec 1, 2006 • Based on structural analysis, specific features of the LHCIR quadrupole have been modified, and features have been added to allow this system to meet the requirements of the higher field Nb 3 Sn magnets. • Shims are added between collar and yoke at each midplane to allow preload to be shared between skin and collars and control collar-yoke interference. • Outer layer poles, originally retained for coil alignment, have been replaced with bronze poles impregnated into coil, as are the inner poles. TQ Mech Structure Design Modeling & Construction 3

TQC 01 Mechanical Structure TQ Internal Review Nov 29 -Dec 1, 2006 • A

TQC 01 Mechanical Structure TQ Internal Review Nov 29 -Dec 1, 2006 • A radial cut is made in each yoke quadrant to provide symmetrical loading to the collars. • Control spacers are introduced for collared coil alignment and yoke motion control. • 12 mm thick stainless steel skin, increased from 8 mm used for MQXB. • Mechanical structure and coil pre-stress was studied and optimized using a series of mechanical models. TQ Mech Structure Design Modeling & Construction 4

TQC 01 Mechanical Structure – End Loading End load in TQC 01 used the

TQC 01 Mechanical Structure – End Loading End load in TQC 01 used the “minimal” axial end loading system. Load is applied by a combination of radial force through the collars by the skin, and end force applied by four preload screws, or “bullets” through 50 mm thick stainless steel end plates. A total force of 14000 N (3000 lbs. ) is applied to each end. This system is identical to that which has been proven effective on Nb 3 Sn dipoles at Fermilab. It is designed to ensure that the magnet ends are in contact with the bullets during all phases of cool-down and operation. TQC 01 was tested with this system and remained preloaded during all phases of operation, as did the HFM dipoles. 14000 N TQ Internal Review Nov 29 -Dec 1, 2006 14000 N TQ Mech Structure Design Modeling & Construction 5

TQC 01 2 D Mechanical Analysis All values in MPa TQ Internal Review Nov

TQC 01 2 D Mechanical Analysis All values in MPa TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 6

TQC 01 3 D Mechanical Analysis 3 D FEA of structures was completed at

TQC 01 3 D Mechanical Analysis 3 D FEA of structures was completed at both LBNL and FNAL. Analysis indicates that, depending on input parameters and end loading, separation between end parts and first turn of coils of between 20 um and 200 um can take place when the magnet is powered if the design end load of 14 k. N is applied. Axial Lorentz forces Parts Separation TQ Internal Review Nov 29 -Dec 1, 2006 Effect of this separation on training behavior is not clear. There is evidence from racetracks at LBNL that a correlation exists between gaps and training. Many magnets built and tested at Fermilab, both Nb 3 Sn and Nb. Ti, with minimal and no end loading, do not have excessive training quenches in the ends. Total load per end from Lorenz forces at 12000 amps is estimated to be 280 k. N. Total load increase on bullets in TQC 01 from 0 -12000 amps was about 50 k. N, or 15 -20% of the total force. TQ Mech Structure Design Modeling & Construction 7

TQC 01 Instrumentation – Strain Gauges Resistive strain gauges were placed on various components

TQC 01 Instrumentation – Strain Gauges Resistive strain gauges were placed on various components within the cold mass. • Azimuthal gauges on coil inner surfaces near pole • Axial gauges at two positions on inner coil surface • Gauges on the control spacers. • Gauges on the exterior surface of the skin. • Gauges on the end preload bolts. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 8

TQC 01 Instrumentation-Strain Gauges • Strain gauges on the control spacers. • Strain gauges

TQC 01 Instrumentation-Strain Gauges • Strain gauges on the control spacers. • Strain gauges on skin. • 2 temperature sensors, one near each end in yoke. TQ Internal Review Nov 29 -Dec 1, 2006 • Strain gauges on end preload screws (bullets). TQ Mech Structure Design Modeling & Construction 9

TQC 01 Instrumentation - Traces • Voltage taps applied to coils through traces, as

TQC 01 Instrumentation - Traces • Voltage taps applied to coils through traces, as in TQS design. Outer coil positions identical to TQS. Inner coil positions identical to the TQS positions, with 2 taps added. • 1 strain gauge on inner surface of each pole, on lead end key/island, measuring longitudinal stress, identical to gauge position on TQS 01. • Strip heaters embedded into outer coil traces (identical to TQS 01). TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 10

TQC 01 Mechanical Models Mechanical Model #1 - A preliminary model using an aluminum

TQC 01 Mechanical Models Mechanical Model #1 - A preliminary model using an aluminum tube with collar structure was used to confirm analysis of collared coil assembly. Strain in the aluminum tube was measured while the collaring keys were inserted, incrementally, in small steps until they were fully inserted. Demonstrated that the incremental stress between keyed sections can be controlled to within 15 MPa. Also showed that the “full round” collars can apply preloads in excess of 100 MPa. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 11

TQC 01 Mechanical Models Mechanical Model #2 – Used practice coils #1 and #3,

TQC 01 Mechanical Models Mechanical Model #2 – Used practice coils #1 and #3, with lead ends and return ends opposing each other. One coil had pole slot and one without. End areas and some body were collared with “full round” collars using coil midplane shim of 250 um. Stress read from collar deflections was 130 MPa peak, 90 MPa average. Strain from azimuthal gauges was 5500 µs in coils without slots and 3000 us in coils with slots. Conclusion: Midplane shim should be smaller than 250 µm and pole slot decreases peak stress significantly. Yoke welding was done using 8 mm skin in automatic welding press using 75 um collar/yoke interference and finished by hand to achieve contact on control spacers. Design skin stress of 150 -200 MPa was obtained. Strain from azimuthal gauges after yoking was 9000 µs in coils without slots and 6000 µs in coils with slots. Welding procedure still needs further optimization. Mechanical Model #2 TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 12

TQC 01 Mechanical Models Mechanical Model #3 - Intended to understand collaring process over

TQC 01 Mechanical Models Mechanical Model #3 - Intended to understand collaring process over straight section with “tabbed” collars and differences between inner and outer layer preload. Capacitor gauges were placed at all inner and outer midplanes and resistive gauges on collar laminations at poles. Collar deflections and collar gauge readings after keying showed large differences in size and preload between quadrants, suggesting side-toside variations between coils. Capacitor gauge readings were erratic and were disregarded. As a result, the collar tabs were eliminated and a “full round” configuration was chosen for the body of TQC 01. Subsequent measurements of coil cross sections showed that the cross sections of coils were uniform and symmetrical. Large preload differences between quadrants are therefore attributed to size variations between molded coils and other parts (collars, collaring shims, etc. ) Full round collars will continue to be used in TQC 02 TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 13

TQC 01 Mechanical Models Mechanical Model #4 – Collared using practice coils #2 and

TQC 01 Mechanical Models Mechanical Model #4 – Collared using practice coils #2 and #4 (TQS style with glued outer poles) and full round collars. Purpose was to determine midplane preload shims. Midplane shims of 0, 100 and 125 microns were used, with Fuji film placed at the midplane in the 100 µm case. Results showed that large variations in collar deflections were eliminated, as expected, and that preload at midplane was uniform between the inner and outer coils. A moderate shim of 125 um placed at each midplane yielded acceptable collar deflections, comparing with the FEA prediction of 150 µm. Mechanical Model #5 – Consisted of MM#3 with yoke welded around it. Used to again verify yoke welding processes in the straight section. Established the number of weld passes to achieve proper contact on control spacers, although with 8 mm skin. Collar/yoke interference of 75 um. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 14

TQC 01 Mechanical Model Summary of Mechanical model results: • Collars can achieve coil

TQC 01 Mechanical Model Summary of Mechanical model results: • Collars can achieve coil prestress in excess of 100 MPa • Incremental stress between collar sections can be controlled to within 15 MPa. • Large variations in coil size between quadrants make full round collars the desirable option. • Collaring shim of 125 -150 um and 425 um (75 um interference) achieves desired preload in coils. • Collaring and yoke welding processes established. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 15

TQC 01 Assembly - Collaring • • • Impregnated coils are assembled and surrounded

TQC 01 Assembly - Collaring • • • Impregnated coils are assembled and surrounded by layers of Kapton ground wrap. Collars are incrementally keyed, in 8 cm. longitudinal sections, applying azimuthal preload to the coils of 70 MPa after keying is complete. Initial pressure is applied by the main cylinders, then key cylinders are energized. Multiple passes are applied, with key depth controlled and incrementally increased with each pass. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 16

TQC 01 Assembly - Collaring Coil was collared using a 75µm mid-plane shim, slightly

TQC 01 Assembly - Collaring Coil was collared using a 75µm mid-plane shim, slightly smaller than was originally anticipated, using “full round” collars over both straight section and ends. Full Round Collars TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 17

TQC 01 Assembly – Cold Iron • • • Control spacers, 425 um preload

TQC 01 Assembly – Cold Iron • • • Control spacers, 425 um preload shims, yoke packs and skin were assembled in the yoke press. Hydraulic pressure is applied and skin was welded in several passes, while monitoring all strain gauges. Preload to coils from yoke/skin is limited by the control spacers. Readings of azimuthal coil gauges during collar and yoke processes TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 18

TQC 01 Assembly – Splices and End Load End plates are welded, and torque

TQC 01 Assembly – Splices and End Load End plates are welded, and torque is applied to end preload bolts. TQ Internal Review Nov 29 -Dec 1, 2006 Nb. Ti midplane leads are formed into appropriate shapes, and leads are spliced. TQ Mech Structure Design Modeling & Construction 19

TQC 01 Strain Gauge Readings Baseline and measured stresses within TQC 01 during all

TQC 01 Strain Gauge Readings Baseline and measured stresses within TQC 01 during all phases of operation. Actual Bmax values are at 12000 A. *Note: Peak stresses are estimated from readings at gauges. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 20

TQC 01 Disassembly - Inner Coil Traces Picture of inside of bore of TQC

TQC 01 Disassembly - Inner Coil Traces Picture of inside of bore of TQC 01 after 1. 9 K test showing de-bonding of inner trace. Traces “bubbled” in many (≈ 120) places throughout the bore during testing from super-fluid helium during quenches. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 21

TQC 01 Disassembly – Observation of Coils Evidence of stress between turns and end

TQC 01 Disassembly – Observation of Coils Evidence of stress between turns and end parts in TQC 01, indicated by observation of coils after disassembly. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 22

TQC 01 disassembly – Bore measurements TQC 01 Bore Diameter Measurements with assumed bore

TQC 01 disassembly – Bore measurements TQC 01 Bore Diameter Measurements with assumed bore shape added Bore radius is smaller at mid-planes than at poles by about 50 microns. Measurements indicate slightly larger horizontal than vertical diameter, but only by about 50 microns. Measurements show place where “flash” on coil 10 was not removed. Looking from Lead End TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 23

TQC 01 disassembly – Skin Dia Measurements Looking from Lead End Measurements show yoke

TQC 01 disassembly – Skin Dia Measurements Looking from Lead End Measurements show yoke to be slightly wider at horizontal axis, in agreement with bore measurements, with no significant change within measurement errors. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 24

TQC 01 disassembly – Collar Measurements Before testing, measurements show average prestress to be

TQC 01 disassembly – Collar Measurements Before testing, measurements show average prestress to be about 50 MPa, but a decrease in prestress as measured during disassembly. In addition, an asymmetry occurs near the lead end, with position 7 increasing with respect to position 2. Peak stress at area in which midplane quenches occurred. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 25

TQC 01 disassembly – Collaring “shoes” are made of. 75 mm thick stainless steel,

TQC 01 disassembly – Collaring “shoes” are made of. 75 mm thick stainless steel, formed to the coil diameter. TQ Internal Review Nov 29 -Dec 1, 2006 Imprints on shoes in coils #9 and #13 are aligned with areas near lead end where degradation is believed to have occurred. TQ Mech Structure Design Modeling & Construction 26

Conclusions Based on construction data, test results, observations and measurements during disassembly. • Preload

Conclusions Based on construction data, test results, observations and measurements during disassembly. • Preload after construction was lower than desired, for the reasons listed below: 1. 2. 3. A deliberate attempt during construction to stay near the low end of the “acceptable preload window”, due to fears of over-compression causing cable degradation. A very conservative shim system was therefore used. MOE of coils not actually linear at 40 GPa, as assumed. Material used inside inner pole slot was epoxy instead of G-10. • Outer pole pieces in much of the straight section were not bonded to the coil, allowing motion by the pole block and more severe bending in this area, with the result that all straight section quenches were in the “non-glued” area. • Low collar-to-yoke preload ratio also contributed to the additional bending. These items have contributed to the inability to reach short sample at 4. 5 or 1. 9 K. • There are indications that the cable has been degraded at the mid-planes, particularly near the lead end, primarily due to excessive pressure applied at these areas during the yoke process. This item is the root cause of the quenches at the outer midplane area. TQ Internal Review Nov 29 -Dec 1, 2006 TQ Mech Structure Design Modeling & Construction 27