A fruitful year for High-Luminosity-LHC magnets

Scientists, engineers and technicians gather around the first short model magnet, MQXFS1, for the High-Luminosity LHC at the Fermilab Technical Campus. Photo: Al Johnson

2016 has seen the celebration of several milestones for the development of the large-aperture, high-field quadrupole magnets that will be cornerstones of the High-Luminosity LHC at CERN. These quadrupoles, fabricated with superconducting niobium tin technology, have been developed by the U.S. LHC Accelerator Research Program (US-LARP) and CERN.

Our collaboration is developing both short, 1.5-meter magnets and long, 4.2-meter magnets for the HiLumi-LHC. Last spring the first short model quadrupole magnet, called MQXFS1, reached the ultimate operation current of 17.9 kiloamperes and demonstrated excellent training memory during the first test. This memory is a very important feature because it measures the capacity of the magnet to be warmed up and cooled down while maintaining its ability to reach operating current without issue. (It is often necessary to warm up sections of the accelerator for repair or maintenance.)

The first long MQXF coil in a mirror structure is attached to the head of a vertical test stand at Brookhaven National Laboratory. Photo: Ray Ceruti

We subsequently increased the MQXFS1 structural pre-compression, which allows the magnet to avoid the counterproductive effects of its electromagnetic forces (such as quenches due to conductor displacement), and this fall the slightly altered magnet, which we call MQXFS1b, reached 19 kA at 1.9 Kelvin, demonstrating a large margin above the 16.5-kA operation current. It also demonstrated again excellent memory and large temperature margin by achieving 18.5 kA at 4.5 K (the magnets will operate at 1.9 K in the LHC). During a period when the magnet was being trained at currents higher than its ultimate operation current, MQXFS1b experienced a few detraining quenches.

A quench is an undesirable transition from superconductivity to normal conductivity, which is unavoidable during magnet training (when the quench current increases from one current ramp to the next one). A detraining quench occurs at a current lower than previously reached, which may indicate a problem if it recurs. Scientists, engineers and technicians assembled both MQXFS1 and MQXFS1b at Berkeley Lab, and Fermilab members performed the tests at its Vertical Magnet Test Facility.

A second short model, named MQXFS3, has been recently assembled and tested at CERN. MQXFS3, as MQXFS1, was assembled with coils fabricated by both US-LARP and CERN. After exceeding operation current, MQXFS3 showed some detraining quenches. The axial pre-compression was increased during a short warm-up, and in the subsequent test, MQXFS3b was on its way to reaching ultimate operation current, showing a good temperature margin by reaching 17.8 kA at 4.5 K. The test run had to be stopped to allow other magnet tests before the end of the year.

A Brookhaven team tested the 4-meter-long LARP coil at their Vertical Test Stand Facility. Photo: Brookhaven National Laboratory

Meanwhile the test of the first long MQXF coil made by LARP is in progress in a newly refurbished vertical test facility at Brookhaven. The coil is in a magnetic-mirror structure designed and assembled at Fermilab. The training of this long coil is reproducing quite well that of the first short MQXF coil, reaching 18.4 kA with 13 quenches.

In 2018 and 2019 the High-Luminosity LHC Accelerator Upgrade Project will take over final prototyping and will start production in the United States. Our latest results are increasing confidence that the project is on the right track for CD-1 and next milestones, including the test of the first 4.2-meter-long prototype.

Giorgio Ambrosio is a Fermilab scientist and leader of the US-LARP magnet effort. Giorgio Apollinari is a Fermilab scientist and the head of US-LARP. Paolo Ferracin is a CERN engineer and leader of the MQXF effort at CERN. Soren Prestemon is a Berkeley Lab scientist and coordinator of Berkeley’s US-LARP effort. Ezio Todesco is a CERN scientist and leader of HL-LHC interaction region magnets. Peter Wanderer is a Brookhaven National Laboratory  scientist coordinating the US-LARP effort at and head of Brookhaven’s Superconducting Magnet Division.