Possibility to apply a coverlay on existing HL-LHC quench heaters C. Scheuerlein with a lot of help from R. De Oliveira and PCB lab team

The HL-LHC quench heaters The HL-LHC quench heaters (QH) are large flexible circuits that are produced in a photolithographic process. In order to reduce the overall heater resistance the steel circuits are partially Cu coated. The base material of the heaters is a commercially available lamination (GTS laminate L960461), consisting of a 50 µm-thick polyimide film (Kaneka Apical AV) and a 25‑µm thick austenitic stainless steel EN 1.4307 (304L) hard temper foil. The steel foil is glued onto the film with a 15 µm-thick epoxy adhesive (GTS AS1084). The steel surface of the laminate is electrolytically coated with an approximately 10 µm-thick Cu layer.

HL-LHC quench heater production status The series production of the quench heaters for the 11 T dipole and MQXF quadrupole has started in the beginning of 2018 by the company Trackwise. 11 T dipole QH production is completed (32 heaters in total). 27 out of 105 MQXFA and 36 out of 66 MQXFB heaters have been received, see Table I. Table I: Number of 11 T dipole and MQXF quench heaters to be produced per delivery year. Delivery year 11 T dipole MQXFA MQXFB 2018 32 27 22 2019 - 42 29 2020 36 15 Total 105 66

11 T dipole quench heaters with coverlay Flexible heater circuits are commonly encapsulated with a polyimide coverlay (like for instance the LHC quench heaters). On the already completed 11 T dipole quench heaters, a coverlay (Krempel AKAFLEX KDF 0 50 25-50 µm polyimide + 25 µm) glue is systematically applied at CERN PCB lab with a static laminator. The coverlays applied at PCB lab are of very good quality (no inclusions or bubbles) Production rate is one, or maximum two heaters per week. Cost depends on heater length (600 CHF per 11 T dipole heater coverlay). 11 T dipole heater with coverlay 11 T dipole heater without coverlay

Options to apply a coverlay onto the MQXF quench heaters Application of a coverlay on the already existing MQXF heaters at PCB lab is possible too. If coverlays have to be applied on a larger quantity of heaters, the production rate can be increased (and cost reduced) using a new tooling (feasibility still needs to be demonstrated). If future quench heaters are to be produced systematically with coverlay it should be envisaged to have the coverlay applied directly by the quench heater manufacturer. For applying coverlays on quench heaters Trackwise uses a modified hot roll laminator. Trackwise has successfully applied a coverlay Dupont LF0120, consisting of 25 µm adhesive and 50 µm polyimide film, on the quench heaters for the D1 short models at KEK. The same coverlay is applied on the MQ quench heaters (with some issues in part of the first production, that are now hopefully solved). Trackwise also produced an inner MQXFB heater with coverlay Dupont LF0120, which was ok, apart from some geometrical imperfections.

Conclusion Application of a coverlay on the already existing MQXF heaters at PCB lab is possible. Production rate is at present one or maximum two heaters per week, which can probably be increased when using a dedicated tooling. Application of a coverlay on new MQXF heaters by the manufacturer should be possible to.