[ Innovation ]
[ Innovation ]
Magnet components The LHC magnet cold bore is manufactured as a seamless 316LN tube . 316LN is also the grade of the shrinking cylinder of the dipole magnets . For the LHC , 2500 bent plates of 15.35 m length and 10 mm thick for a total weight of approximately 3000 tonnes were used , welded longitudinally by a special Surface Tension Transfer ( STT ) technique combined with traditional pulsed Metal Inert Gas ( MIG ) welding . For the HL-LHC magnets ( Fig . 2 ), similar 316LN plates in thicknesses up to 15 mm were produced by ArcelorMittal Industeel under the same specification , same manufacturing route and forming process . “ Some components required innovative and unprecedented solutions ”, argues Stefano . “ An example is the more than 2800 magnet end covers of complex shape and large diameter ( 570 mm ), including several nozzles that have been fabricated for the LHC , starting from HIPed 316LN powders and near net shaped into geometry close to the final form . They operate smoothly in the machine since decades at almost absolute zero temperature and are perfectly leak tight ”. Between the magnets , some 1600 interconnections are installed , consisting of several thousand of components for which leak tightness is also paramount , mainly working at cryogenic temperature . These interconnection components are also essentially based on austenitic stainless steels . For the convolutions of the several thousands of bellows involved in the machine and working under cyclic load at 1.9 K , a special ESR high alloy and highly formable 316L grade was used showing an extremely low inclusion content and improved
Figure 2 . Welding operations on the cold masses of superconducting HL-LHC magnets . Image courtesy of H . Prin , CERN .
austenite stability at the working temperature .
Stainless steel solutions High strength stainless steel solutions are also applied to structural components of the ITER magnet system . An example is the precompression structure of the Central Solenoid ( CS ) that consists of six independent coils kept together by a precompression support , providing a precompression load of 210 MN to ensure contact in between modules , by reacting vertical tensile loads and maintaining coil-to-coil contact when the solenoid is energized . The CS precompression system includes large open die forged components such as tie plates , lower and upper key blocks , load distribution and isolation plates and other attachment support and insulating hardware . The tie plates operating at 4 K are manufactured starting from forgings in a high-strength austenitic stainless steel ( FXM-19 ) with a stringent specification . FXM-19 ( also known through its proprietary version Nitronic ® 50 ) is a high N and Mn bearing austenitic stainless steel , featuring ready weldability and forgeability , high strength and toughness in a wide temperature range including at cryogenic temperatures . The 27 tie plates operating at 4 K are manufactured by the company Rolf Kind GmbH from single forgings involving blanks of more than 15 m length ( Fig . 3 ). Stefano reminds that in order to comply with the tight metallurgical requirements applicable to the final product ( inclusion cleanliness , fineness of microstructure , limited ferrite content and magnetic permeability , internal soundness - the products are 100 % ultrasonic checked ), the steelmaking process includes a mandatory ESR step despite the heavy gauge ingots needed as starting products for forging .
Figure 3 . Final forging operations of the 15 m length ITER CS tie plates . Image courtesy of Rolf Kind GmbH .
Upgrades for high luminosity operation The beams inside the LHC collide at four locations around the ring , corresponding to the positions of four experiments . The Compact Muon Solenoid ( CMS ) is one of two large particle detectors at the LHC that , together with ATLAS is one of two general-purpose experiments having observed the Higgs boson decays . CMS contain the largest superconducting solenoid magnet ever constructed in terms of stored energy , featuring a length of 12.5 m , an inner diameter of 6 m and delivering a maximum magnetic field of 4 T ( Fig . 4 ).
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