Impact of Coil Compaction on ${\hbox {Nb}}_{3}{\hbox {Sn}}$ LARP HQ Magnet

Abstract

In the past two years the US LARP program carried out five tests on a quadrupole magnet aimed at the high luminosity upgrade of Large Hadron Collider (HiLumi-LHC). The 1-meter long, 120 mm bore Nb Sn IR quadrupole magnet (HQ) with a short sample gradient of 219 T/m at 1.9 K and a conductor peak field of 15 T is part of the US LHC Accelerator Research Program (LARP). In a series of tests, carried out at 4.4 K, the magnet reached a maximum "short-sample" performance of 86%. The tests exposed several shortcomings that are now being addressed in a Research & Development program. This paper summarizes the magnet test results, reveals findings, R&D actions and future improvements.

Analysis of Field Errors for LARP Nb$_3$ Sn HQ03 Quadrupole Magnet

“…The tolerance of HQ02 and HQ03 magnets are consistent with earlier TQ quadrupole magnets developed by LARP [23]. They are higher than the positioning tolerance for the LHC NbTi magnets, typically 30 µm, because the size of Nb 3 Sn coils changes during the heat treatment [8], [25]. fabrication for HQ03 gave 10% lower positioning tolerance with respect to HQ02.…”

“…The alignment features at all stages of coil fabrication, magnet assembly and cold powering were incorporated first in HQ01 magnets. While the magnet reached 170 T/m, 86% of short-sample limit (SSL) at 4.4 K [6] and 184 T/m, 85% of SSL at 1.9 K [7], HQ01 magnets also revealed several issues related to the conductor damage due to coil compaction and insulation failures [8]. To address these issues, HQ02 used smaller Nb 3 Sn strands (diameter decreased from 0.8 mm to 0.778 mm) to reduce the coil compaction without significant change of the magnet fabrication tooling [8], [9].…”

Fabrication and Analysis of 150 mm Aperture Nb<sub>3</sub>Sn LARP MQXF Coils

“…All S2 Glass insulation is qualified by measurement at 5 MPa rather than accepting the generally oversized nominal manufacturer thickness. More extensive reductions to assumed growth increase the risk of electrical shorts during heat treatment and reduced quench performance [5], [30].…”

Test Results of the LARP Nb3Sn Quadrupole HQ03a

“…These models, while demonstrating operation well above the HQ target gradient of 170 T/m, were affected by stress degradation, electrical insulation failures, and large dynamic field errors [7][8][9][10]. Detailed analysis [11] led to critical revisions of the coil parameters and components which were validated through dedicated tests in a mirror structure [12][13] and gradually implemented in the HQ02 series [14]. The HQ02a model confirmed that the previous performance issues had been resolved, but its gradient was limited to 182 T/m due to the choice of a conservative pre-load level [15][16][17].…”