MQXFA Electrical Design Criteria Giorgio Ambrosio HLLHC AUP

MQXFA Electrical Design Criteria Giorgio Ambrosio HL-LHC AUP Magnets L 2 Manager, FNAL Structural and Electrical Design Criteria Review of the MQXFA Magnets Fermilab, April 23 -24, 2018

Outline § § § Review Charge HL-LHC Electrical Requirements MQXFA Electrical Design Criteria Insulation Design Criteria Electrical QC Appendix: § Electrical Issue during 1 st Prototype Test § Lessons learned § Conclusions Design Criteria Review of the MQXFA Magnets - April 2018 2

Review Charge “… demonstration that AUP can document and satisfy the Design Criteria used to develop the MQXFA Magnets. In particular, the HL-LHC AUP MQXFA Magnets can be considered as a stand-alone deliverable from the point of view of Structural Design, and therefore Structural Design Criteria for the MQXFA Magnets are developed by HL-LHC AUP. On the other hand, the MQXFA Magnets will operate within the larger HLLHC electrical system, and therefore the Electrical Requirements have been developed by CERN and are expected to be implemented in all in-kind contributions” Design Criteria Review of the MQXFA Magnets - April 2018 3

Review Charge 1. Are the Design Criteria appropriate to specify the design guidelines and develop a methodology to assess components for the MQXFA magnets 2. Do the Structural Design Criteria include an assessment of thermal and power cycles, and allow a determination of tolerable defect, specifically for brittle materials 3. Are safety factor levels appropriate for the MQXFA Magnets 4. Are data and/or sources of information properly documented in the definition of the Design Criteria. 5. Are the Electrical Design Criteria properly addressing the electrical requirements from CERN. Design Criteria Review of the MQXFA Magnets - April 2018 4

Electrical Requirements Charge 4 § Electrical Design Criteria for the HL-LHC Inner Triplet Magnets § Doc with criteria for different testing condition and explanation To be approved on EDMS this week § MQXFA Functional Requirements Specification § Main electrical requirements Design Criteria Review of the MQXFA Magnets - April 2018 5

Electrical Requirements & Safety Levels Charge 3 § Drivers are the max voltages at nominal operating condition (1. 9 K, 16. 47 k. A): § Computed taking into account conductor variations, different quench start locations and heater failures § Test voltages: Design Criteria Review of the MQXFA Magnets - April 2018 6

Electrical Requirements § Note: no margin is applied at ultimate current (HL-LHC rule) § Therefore, margins are set at nominal current § Test voltages at warm after test in helium are performed at reduced values: Test voltages at warm after test in helium are lower than 500 V, LARP did Hipot at warm after test in helium at 1 k. V with no issues Design Criteria Review of the MQXFA Magnets - April 2018 7

Electrical Requirements § Summary Table: Component V_max V_test @ 1. 9 K V_test @ warm after He Coil-Ground 670 V 1850 V 3700 V 380 V Coil-Heater 900 V 2300 V 460 V Table 3. MQXFA electrical test values Design Criteria Review of the MQXFA Magnets - April 2018 8

MQXFA Electrical Design Criteria § AUP document Design Criteria Review of the MQXFA Magnets - April 2018 9

MQXFA Electrical Design Criteria § Peak voltage estimates: Charge 4 § Baseline: Outer Layer Quench Heaters + CLIQ (Coupling Loss Induced Quench) system § Very thorough analysis including effect of: § Heater failure scenarios § Different quench start and different QH-failure locations E. Ravaioli, “Quench Protection Studies for the High-Luminosity LHC Inner Triplet Circuit” US-Hi. Lumi-doc-363. 10

Electrical Requirements Charge 5 § Electrical requirements in MQXFA Electrical Design Criteria are taken from the Electrical Design Criteria for the HL-LHC Inner Triplet Magnets Component V_max V_test @ 1. 9 K V_test @ warm after He Coil – Ground 670 V 1850 V 3700 V 380 V Coil – Heater 900 V 2300 V 460 V Design Criteria Review of the MQXFA Magnets - April 2018 11

Exploded views of the MQXFA magnet structure Design Criteria Review of the MQXFA Magnets - April 2018 12

Insulation Design Criteria: Charge 1 § The Insulation Design Criteria are based on standard practices for accelerator magnets and on LARP experience [5]. § The MQXFA Functional Requirements Specification [4] requires that “all MQXFA components must withstand a radiation dose of 35 MGy, or shall be approved by CERN for use in a specific location as shown in the MQXFA Material list (US Hi. Lumi Doc. DB # 96)”. Therefore, G 10 cannot be used in any location of MQXFA magnets, whereas polyimide can be used in any location. G 11 can be used in the locations listed in the MQXFA Material list, based on analysis of local dose and required material properties. For epoxy impregnation LARP has extensively used CTD-101 K [5, 6]. A dedicated test campaign performed under the Eu. CARD program [7] has demonstrated that CTD-101 K is suitable for use in the Inner Triplet magnets of High Luminosity LHC. 13

Insulation Design Criteria: Charge 1 Coil-Ground § The Coil-Ground insulation between coils and collars shall be made of polyimide layers. Each layer shall have a minimum thickness of 110 um. The minimum number of layers is 3, and seams shall not overlap in order to have everywhere at least 2 continuous layers between coil and ground. These polyimide layers are in addition to the G 11 layers set on collars inner surface, and to the polyimide layers that may be used for coil shimming. § Minimum creep path is 7 mm. This criterion is based on the helium voltage breakdown that is 3 k. V with 5 mm distance at 75 K and 1 bar [8]. § The pole keys shall be made of G 11 (or equivalent insulating material). The collar edges around the pole keys shall be covered by polyimide (7 mm minimum creep path). 14

Insulation Design Criteria: Charge 1 Coil-Ground § At magnet ends these polyimide layers shall extend beyond coil ends by at least 20 mm. § End pushers apply a significant load on coil ends. The ground insulation between coil saddles (or saddle extensions) and the end pushers shall be sufficiently strong to withstand the coil axial loads and sufficiently thick to separate coil to ground: minimum thickness is 10 mm. 15

Insulation Design Criteria: Charge 1 Coil-Coil Insulation § Coil to coil insulation is set on coil midplanes and around their edges. The minimum coil-coil insulation shall be made of a G 11 layer (minimum thickness is 125 um) potted on each coil midplane, and of a polyimide layer (minimum thickness is 125 um) extending at least 7 mm beyond the midplane edge, on each coil. Figure: MQXFS Coil cross section during Impregnation. Design Criteria Review of the MQXFA Magnets - April 2018 16

Insulation Design Criteria: Charge 1 Heater-Ground § The protection heaters are installed on coil outer surface before epoxy impregnation, and they become permanent part of each coil during the potting process. Therefore, they share the same insulation to ground of the coils. § Special care must be paid to the wiring of the leads around the end pushers in order to avoid the possibility of pinching the leads during magnet end pre-loading. Figure: Perforated Kapton with quench heaters Design Criteria Review of the MQXFA Magnets - April 2018 17

Insulation Design Criteria: Charge 1 Heater-Coil § The optimization of the heater-coil insulation is often the result of a difficult trade-off: on one side a too thick insulation may lead to excessive heater delays (the time between heater firing and the heater induced quench); on the other hand, a too thin insulation may lead to failing heater-coil hipot requirements. LARP has shown that the minimum acceptable heater-coil insulation is made of a 50 -um polyimide layer where heaters are glued (trace), in addition to the cable insulation. These traces shall be hipot-tested upon reception (for acceptance) and shall be carefully stored to assure that no damage to the insulation may occur during storage, shipment, or other operations. § Special care must be paid for the heaters-lead connections. These connections shall be embedded in pockets within the coil saddles (or saddle extensions) where additional polyimide insulation shall be added to the standard trace insulation. Epoxy or similar material shall be used to permanently secure the leads and provide stress-relief after soldering the connections. § Inner Layer Quench Heaters shall not be used unless a reliable solution to the “bubble issue” is found. Design Criteria Review of the MQXFA Magnets - April 2018 18

Insulation Design Criteria: Charge 1 Layer-Layer § The layer-layer insulation is applied on the wound-and-cured inner layer before winding the outer layer. Therefore, the layer-layer insulation shall be designed to withstand the coil heat treatment. LARP has demonstrated that S 2 -fiberglass cloth pre-shaped and cured with ceramic binder provides a smooth surface for outer layer winding, and sufficiently good electrical insulation if a limited amount of ceramic binder is used. The AUP project shall assess the correct amount of ceramic binder and set procedures for controlled and uniform application. The minimum thickness of the layer-layer insulation is 500 um. LARP has shown that saddle edges may compromise the layer-layer insulation if there is excessive compression caused by conductor expansion during heat treatment. Therefore, the cavity of the reaction fixture shall be computed using the conductor dimensions after heat treatment. Additional requirements for coil parts are presented in next section. Figure: MQXFS Coil cross section during Impregnation. Design Criteria Review of the MQXFA Magnets - April 2018 19

Insulation Design Criteria: Charge 1 Coil parts § All coil parts (pole parts, wedges, end parts, saddles and saddle extensions) will be installed before coil heat treatment. Therefore, all coil parts shall be able to withstand the heat treatment without damage nor excessive deformation. End parts, saddle and saddle extension shall be coated with insulation materials capable of withstanding the heat treatment, and subsequent cold shocks. Wedges and pole parts shall be insulated with S 2 -fiberglass. The wedges shall use an S 2 -sleeve with minimum thickness of 125 um. The coil pole shall be insulated with several turns of S 2 -glass tape for a minimum thickness of 400 um. The tape width shall be equal to the insulated cable width, and the tape shall be wound around the pole in order to provide thickness as uniform as possible. Figure: End Parts Identification. Design Criteria Review of the MQXFA Magnets - April 2018 20

Insulation Design Criteria: Charge 1 Turn-turn § The turn-turn insulation shall be continuous and as uniform as possible. LARP has demonstrated that S 2 -glass braided on the cable provides a continuous and uniform insulation, whose thickness can be fine-tuned during R&D and kept constant during production. The minimum recommended insulation thickness is 140 um, based on LARP experience. The S 2 -glass provides separation between the turns, which is filled by epoxy during the impregnation process. A thorough analysis of turn-turn voltages has demonstrated that they will be lower than 105 V in any quench condition including failure scenarios [2]. Therefore, this insulation scheme is adequate also in case of epoxy cracks since turn-turn voltages are lower than the Paschen minimum for helium (150 -160 V [8, 9]). It should also be noted that MQXFA magnets are operating at higher pressure·distance values (>28 Pa·m) than the Paschen minimum for helium (6 Pa·m), and that non-flat electrode geometry is expected to increase the minimum breakdown voltage [10, 11]. These factors provide a safety margin larger than 10. § Special care must be paid to prevent metallic inclusions, which may compromise the turn-turn electrical insulation. The methods to prevent metallic inclusions shall include: continuous electrical QC of insulated cable with low-voltage rollers, and high-voltage impulse tests of coils after epoxy impregnation. 2) E. Ravaioli, “Quench Protection Studies for the High-Luminosity LHC Inner Triplet Circuit” US-Hi. Lumi-doc-363. 8) P. Fessia, G. Kirby, J. C. Perez, and F. O. Pincot, “Guidelines for the insulation design and electrical test of superconducting accelerator magnets during design assembly and test phase” CERN EDMS# 1264529. 9) J. Knaster and R. Penco, “Paschen Tests in Superconducting Coils: Why and How” IEEE Trans. App. Supercond. , vol. 22, no. 3, 9002904, June 2012. Design Criteria Review of the MQXFA Magnets - April 2018 21

Electrical QC Charge 1 Coil and Magnet electrical QC shall include the following measurements, to be compared with min -max range for acceptance: § Coil RLQ § Resistance, Inductance, Quality factor § Voltage drop at Voltage Taps § With 1 amp current § Heaters resistance § Hipot tests § Coil to Ground, QH to Coil, QH to ground § Impulse tests § direct and revers. Design Criteria Review of the MQXFA Magnets - April 2018 22

References Charge 4 1) 2) “High-Luminosity Large Hadron Collider (HL-LHC) TDR” CERN-2017 -007 -M E. Ravaioli, “Quench Protection Studies for the High-Luminosity LHC Inner Triplet Circuit” USHi. Lumi-doc-363. 3) F. Menendez Camara, F. Rodriguez Mateos, “Electrical Design Criteria for the HL-LHC Inner Triplet Magnets” CERN EDMS No. 1963398; US-Hi. Lumi-doc-879. 4) “MQXFA Functional Requirements Specification”, US-Hi. Lumi-doc-36. 5) G. Sabbi. “Studies of Maximum Allowed Coil Stress in LARP Quadrupole Models”, LARP-doc-1230, available at : http: //larpdocs. fnal. gov/LARP-public/Doc. DB/Show. Document? docid=1230 6) Composite Technology Development, Inc. , “CTD-101 K Epoxy Resin System Datasheet”, available online at http: //www. ctd-materials. com/papers 7) J. Polinski, M. Chorowski, and P. Bogdan, “Certification of the Radiation Resistance of Coil Insulation Material” Eu. CARD-Del-D 7 -2 -1 -final-1 8) P. Fessia, G. Kirby, J. C. Perez, and F. O. Pincot, “Guidelines for the insulation design and electrical test of superconducting accelerator magnets during design assembly and test phase” CERN EDMS# 1264529. 9) J. Knaster and R. Penco, “Paschen Tests in Superconducting Coils: Why and How” IEEE Trans. App. Supercond. , vol. 22, no. 3, 9002904, June 2012. 10) an S. Uhm, Han S. Uhm, “Investigation of electrical breakdown properties in curved electrodes”, Physics of Plasmas, Vol. 7, No. 11, pp. 4748 -4754, Nov. 2000. 11) Shou-Zhe Li, and Han S. Uhm, “Investigation of electrical breakdown characteristics in the electrodes of cylindrical geometry”, Physics of Plasmas, Vol. 11, No. 6, pp. 3088 -3095, June 2004. Design Criteria Review of the MQXFA Magnets - April 2018 23

Appendix Design Criteria Review of the MQXFA Magnets - April 2018 24

Electrical Issue During Prototype Test § 2 thermal cycles during training § Caused by rupture of burst disk § Warm Hipot after each thermal cycle § 18 training quenches § Coil-Ground short after quench 18 Design Criteria Review of the MQXFA Magnets - April 2018 25

Electrical Issue During Prototype Test § MQXFAP 1 developed a short Coil-Ground § Coil 5 Outer Layer § Location of Coil-Ground short is very close to previous Heater-Coil short § Coil 5 Outer Layer Low-Field Heater § Measurements show that there may be two Heater. Coil shorts § Magnet autopsy is in progress Design Criteria Review of the MQXFA Magnets - April 2018 26

Analysis & Lessons Learned § Most probable cause: Hi-Pot at warm using original values after exposure to helium*: - Typical for LARP magnets and MQXFS short models (although Hi-Pot values increased from 1 k. V to 2. 5 k. V) - Shall not be done on production magnets according to HL-LHC Electrical Design Criteria (not available at time of test) § Lesson learned: HL-LHC Electrical Design Criteria will be applied also to short models and prototypes *V. Marinozzi, Analysis of MQXFAP 1 Short-to Ground, US-Hi. Lumi-doc-897 Design Criteria Review of the MQXFA Magnets - April 2018 27

Conclusions § MQXFA Electrical Design Criteria have been developed and documented § They meet HL-LHC requirements § They present design guidelines (insulation) and test methodology (QC) § The electrical issue during 1 st prototype testing has been analyzed: § Lessons learned are in the MQXFA Electrical Design Criteria Review of the MQXFA Magnets - April 2018 28

Back up Slides Design Criteria Review of the MQXFA Magnets - April 2018 29

Electrical scheme of the HL-LHC inner triplet circuit Design Criteria Review of the MQXFA Magnets - April 2018 30