Assembly disassembly and mechanical tests of the consolidated

Assembly, disassembly and mechanical tests of the consolidated insulation system Florian Meuter First Internal LHC Dipole Diode Insulation Consolidation Review, 10 October 2017 1

Outline • Assembly and disassembly of insulation pieces • Mechanical load cases of insulation insert • Set-up for mechanical tests of insulation insert • Conclusion 2

Assembly of insulation plates • Installation of the insulation plates on about 85% of all dipole diode half-moon splices where they are at present missing is essential for the insulation consolidation. • During LHC installation the insulation plates could be installed on top of the half-moon splices before mounting the T-tube and diode container. • In the present situation, due to the space constraints in the T-tube the mounting of the insulation plates is more difficult. • Installation of the consolidated insulation system must not degrade the existing insulation. • Goal is the consolidation of an average of 50 dipole diode insulation systems per week. From: Diode container sequence 3 assembly. LHCMB__S 0006

Mock-up for insulation plate assembly tests Mock-up of diode busbar assembly (a) without insulation insert and (b) with insulation insert. 4

Insulation plate installation sequence • The confined space inside the T-tube, requires the insulation plate to be moved along the busbar to its final position. • Deformed busbars and misalignment may not allow for this procedure with the original geometry of the insulation plates LHCMB__E 0077 and _0078. • Therefore, insulation plates with increased free space between busbars will be used for the consolidation. Insulation plate positions during installation inside the T-tube 5

The modified insulation plate geometry CAD model of original insulation plate, and modified insulation plate with increased free space to ease installation in case of deformed or misaligned busbars. See presentation of T. Sahner. 6

Alternative insulation plate geometries that can be mounted in the presence of severely deformed busbars • A smaller number of insulation plates with modified busbar cutout will be produced, to be mounted in case the busbars are so severely deformed that standard pieces cannot be installed. Severely deformed busbar in a mock-up Possible insulation plate geometrical modifications 7

Electrical insulation of the gaps between insulation pieces and busbars • The increased busbar cutout leaves gaps between busbars and insulation plates. • Therefore, pre-formed Polyimide foil will be systematically placed over the splice underneath the G 11 insulation plate to prevent metal chips reaching the half moon splice. • Epoxy adhesive is used to insulate the metal screw head. In exceptional cases an epoxy may also be used to fill gaps between insulation plates and busbars. Bolt heads insulated with epoxy (Araldite 2012). CAD model of preformed Polyimide foil (T. Sahner) First mounting tests with Polyimide foil installed on the half moon splice. It will be held in place with the G 11 half moon insulation plate mounted on top. 8

Disassembly of the insulation system • It is assumed that the insulation plates never need to be removed after the consolidation. Therefore, the screw heads can be electrically insulated using epoxy adhesive. • The insulation tubes need to be disassembled in few cases to disconnect the half-moon splices for diode and magnet exchange. • In exceptional cases large gaps (width >1. 5 mm) between the insulation plates and insulation tube will be closed using epoxy adhesive. This will make disassembly of the insulation tubes more time consuming. • The locking of the metallic screws of the insulation insert remains to be studied. 9

Visual inspection of the insulation plates • The consolidation sequence must be preceded by a visual control of the existing insulation. • For the visual inspection of the existing and consolidated insulation system an endoscope is needed. • Repair procedures to remove damaged insulation pieces and to repair adjacent busbar insulation need to be developed. • Installation and quality control procedures need to be developed. • An epoxy adhesive (e. g. Araldite 2012), that may be used to close larger gaps needs the be validated. Endoscope inspection setup. 10

Mechanical testing of insulation insert • Two main load cases: • Effect of thermal expansion mismatch between the insulation material and the stainless steel diode cover from RT to 1. 9 K. • Action of He gas pressure difference in case of a quench • A conservative pressure difference estimate is 5 bar, and a maximum hydrostatic pressure of 20 bar is assumed [i]. • Such a pressure difference acting on the diode insert surface can cause substantial mechanical loads on the connecting screws and the insulation. • A test setup has been developed to perform mechanical tests of the diode insulation at ambient temperature and in liquid nitrogen. • The effect of thermal expansion mismatch between insulation stainless steel diode pressure plate will be verified by repeated quenching of the assembly in liquid nitrogen. [i] LHC-DQD-ES-0003 -0 -1, EDMS No. 1852741 Insulation insert prototype. Insulation insert mount on steel plate 11 for quenching in liquid nitrogen.

Setup for mechanical tests of the insulation insert • The set-up shall simulate a static load corresponding with a pressure difference of up to 5 bar. • The test load is applied with a screw and will be monitored with a load cell (Burster 8402) with a load range up to 50 k. N. • The static load can be applied in ambient air or in liquid nitrogen. • Mechanical test results will be compared with Finite Element simulation results. During the test the load will be applied on the insert in the marked area. 12

Conclusion • The assembly of the insulation plates in the present configuration requires an adaptation of the plate geometry, and needs to be carefully prepared and trained at mock-ups. • An additional Polyimide insulation will be systematically added to the about 85% of half-moon splices where the modified insulation plates with larger busbar cutout will be used. • A set-up for mechanical testing of the insulation insert prototype pieces has been developed and is in production. • Mechanical test results will be complemented by FE simulation results, and shall lead to an optimisation of the insert design. 13

Back-up slides • Insulation installation sequence during first LHC installation • Drawing of insulation tube 14

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