H. Felice

Mechanical Performance of Short Models for MQXF, the Nb3Sn Low-β Quadrupole for the Hi-Lumi LHC

In the framework of the Hi-Lumi LHC Project, CERN and U.S. LARP are jointly developing MQXF, a 150-mm aperture high-field Nb3Sn quadrupole for the upgrade of the inner triplet of the low-beta interaction regions. The magnet is supported by a shell-based structure, providing the preload by means of bladder-key technology and differential thermal contraction of the various components. Two short models have been produced using the same cross section currently considered for the final magnet. The structures were preliminarily tested replacing the superconducting coils with blocks of aluminum. This procedure allows for model validation and calibration, and also to set performance goals for the real magnet. Strain gauges were used to monitor the behavior of the structure during assembly, cool down and also excitation in the case of the magnets. The various structures differ for the shell partitioning strategies adopted and for the presence of thick or thin laminations. This paper presents the results obtained and discusses the mechanical performance of all the short models produced up to now.

Assembly Tests of the First Nb 3 Sn Low-Beta Quadrupole Short Model for the Hi-Lumi LHC

In preparation for the high-luminosity upgrade of the Large Hadron Collider (LHC), the LHC Accelerator Research Program (LARP) in collaboration with CERN is pursuing the development of MQXF: a 150-mm-aperture high-field Nb3Sn quadrupole magnet. The development phase starts with the fabrication and test of several short models (1.2-m magnetic length) and will continue with the development of several long prototypes. All of them are mechanically supported using a shell-based support structure, which has been extensively demonstrated on several R&D models within LARP. The first short model MQXFS-AT has been assembled at LBNL with coils fabricated by LARP and CERN. In this paper, we summarize the assembly process and show how it relies strongly on experience acquired during the LARP 120-mm-aperture HQ magnet series. We present comparison between strain gauges data and finite-element model analysis. Finally, we present the implication of the MQXFS-AT experience on the design of the long prototype support structure.

Quench protection challenges in long nb3sn accelerator magnets

The quench protection of the several meter long, large aperture high-field Nb3Sn quadrupoles that the LARP collaboration is developing for the LHC interaction region upgrade, requires efficient protection heaters to quickly generate large resistive segments across the windings. To support the protection design, experiments in the recently tested LARP R&D magnets are aimed to characterize the coil response to different protection schemes. In particular, the delay to quench and the final hotspot temperatures are evaluated after firing the heaters at different powering regimes and coverage. Also, the contribution of external energy extraction is investigated. Based on the performed studies and computer simulations, it seems that if the same protection efficiency per unit length that is measured in a 1 m long model magnet can be scaled to a 3.6 m long magnet, and the heater coverage can be improved, about 1 MJ/m of stored energy can be absorbed in the magnet after a quench. However, significant technology dev...

Modeling heat transfer from quench protection heaters to superconducting cables in Nb3Sn magnets

We use a recently developed quench protection heater modeling tool for an analysis of heater delays in superconducting high-field Nb3Sn accelerator magnets. The results suggest that the calculated delays are consistent with experimental data, and show how the heater delay depends on the main heater design parameters.

Test of the High-Field Nb

We report test results for the one meter long dipole HD3b, a block-type accelerator quality Nb3Sn magnet built at LBNL with operational bore fields in the range of 13-15 T. The magnet is an upgrade of the previously reported HD2 and HD3a versions, with several modifications implemented to improve conductor positioning, reduce cable “hard-way” bending radius, and strengthen electrical insulation between cables and coil parts. The magnet exhibited long training behavior, but showed a good “memory” of the trained state upon thermal cycling. Ramp-rate dependence of the quench current, field quality performance characteristics, and protection heater studies were conducted. Quench propagation velocity and quench locations were determined based on the voltage signals; quench localization was further improved using inductive quench antenna and acoustic emission sensors. Short- and long-term acoustic precursors to quenching were observed.

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New low-β quadrupole magnets are being developed within the scope of the High Luminosity LHC (HL-LHC) project in collaboration with the US LARP program. The aim of the HL-LHC project is to study and implement machine upgrades necessary for increasing the luminosity of the LHC. The new quadrupoles, which are based on the Nb3Sn superconducting technology, will be installed in the LHC Interaction Regions and will have to generate a gradient of 140 T/m in a coil aperture of 150 mm. In this paper, we describe the design of the short model magnet support structure and discuss results of the detailed 3D numerical analysis performed in preparation for the first short model test.

Sn Dipole Magnet HD3b

Large-aperture, high-field, Nb3Sn quadrupoles are being developed by the U.S. LHC accelerator research program (LARP) for the High luminosity upgrade of the Large Hadron Collider (HiLumi-LHC). The first 1 m long, 120 mm aperture prototype, HQ01, was assembled with various sets of coils and tested at LBNL and CERN. Based on these results, several design modifications have been introduced to improve the performance for HQ02, the latest model. From the field quality perspective, the most relevant improvements are a cored cable for reduction of eddy current effects, and more uniform coil components and fabrication processes. This paper reports on the magnetic measurements of HQ02 during recent testing at the Vertical Magnet Test Facility at Fermilab. Results of baseline measurements performed with a new multilayer circuit board probe are compared with the earlier magnet. An analysis of probe and measurement system performance is also presented.

Support Structure Design of the Quadrupole for the High Luminosity LHC

In order to continue supporting the development of accelerator magnets for the next generation of particle colliders, the LBNL Superconducting Magnet Program has started the design and fabrication of the Large-aperture Dipole LD1. The goal of the magnet is to generate a dipole field of 13 T to 15 T in a clear aperture of 144 mm × 94 mm, enabling high-field tests of Rutherford cables and insert coils made of or high temperature superconductors (HTS), like Bi-2212, YBCO, and Bi-2223. The bore size will also accommodate large Cable-In-Conduit Conductors (CICCs), including ITER cables. We describe in this paper the design of LD1, in particular cable geometry, coil lay-out and support structure. Operational conditions based on strand measurements will be discussed, focusing on coil peak fields in straight section and end region, bore field homogeneity, and stress on the conductor during assembly, cool-down and excitation.