Steven Hays

Mu2e Transport Solenoid Prototype Tests Results

The Fermilab Mu2e experiment has been developed to search for evidence of charged lepton flavor violation through the direct conversion of muons into electrons. The transport solenoid is an s-shaped magnet that guides the muons from the source to the stopping target. It consists of 52 superconducting coils arranged in 27 coil modules. A full-size prototype coil module, with all the features of a typical module of the full assembly, was successfully manufactured by a collaboration between INFN-Genoa and Fermilab. The prototype contains two coils that can be powered independently. To validate the design, the magnet went through an extensive test campaign. Warm tests included magnetic measurements with a vibrating stretched wire and electrical and dimensional checks. The cold performance was evaluated by a series of power tests and temperature dependence and minimum quench energy studies.

A Measurement of HTS Cable Power Loss in a Sweeping Magnetic Field

Short sample HTS power cable composed of multiple 344C-2G strands and designed to energize a fast-cycling dipole magnet was exposed to a sweeping magnetic field in the (2-20) T/s ramping rate. The B-field orientation toward the HTS strands wide surface was varied from to -4° to 8°, in steps of 10. The test arrangement allowed measurements of combined hysteresis and eddy current power losses of the cable assembly. For the validity of these measurements, the power losses of a short sample cable composed of multiple LTS wire strands were also performed and compared with the known data. The test arrangement of the power cable is described, and the test results are compared with the projections for the eddy and hysteresis power losses using fine details of the test cable structures.

Prototype Conduction Cooled Capture Solenoid Test Design and Plans

Large aperture superconducting solenoid magnets are needed for the production and capture of pions, which decay to create intense muon beams in future experiments to search for direct muon to electron conversion. The COMET experiment in Japan and the Mu2e experiment in the U.S. are jointly conducting research into the design of capture solenoid coils made from aluminum-stabilized NbTi superconductor that is cooled by conduction to a supply of liquid helium. A prototype coil of 1.3-m inner diameter, having four layers of eight turns each, has been wound with pure aluminum interlayer fins for the conduction cooling. The test coil includes two types of welded splices, two film heaters for quench studies, and extensive instrumentation to evaluate strain, temperature profiles, and coil voltages. Details of the cryogenic conduction cooling scheme, test systems design, and test program plans will be discussed.

Design, Construction, and Test Arrangement of a Fast-Cycling HTS Accelerator Magnet

Design, fabrication, and assembly of a novel fast-cycling accelerator magnet is presented. A short-sample magnet is powered with a single-turn HTS cable capable to carry 80-kA current up to a temperature of 20 K. This allows for a (13-15) K margin when using the operational temperature of (5-7) K. The availability of such a wide temperature margin for a fast cycling magnet constitutes the most necessary parameter for prevention and control of the fast-cycling magnet quench. Therefore, the HTS conductors have unsurpassed advantage over the LTS ones for which the maximum temperature margin is typically 2 K. The maximum possible generated field in the 40-mm test magnet gap is 1.75 T. The applied conventional leads and the power supply, however, allow only for the sin-wave 24-kA current of 20-Hz repetition rate, thus limiting magnet tests to the B-field of 0.5 T with a maximum cycling rate of 20 T/s. The critical aspects of cable construction and the splicing connection to the power leads are described. Tentative power losses of the proposed HTS-based accelerator magnet in possible applications for the proton and muon accelerators are presented.

Design Study and Test Arrangement of HTS Transmission Line Power Cable for Fast Cycling Accelerator Magnets

Designs of the HTS transmission line power cable and the matching magnetic core for a fast-cycling accelerator dipole magnet are presented. The hysteretic and eddy currents induced power losses of the proposed HTS cable operating under various sweeping magnetic fields are projected and compared to those of the LTS cable in similar applications. The engineering design of the HTS power cable for the fast cycling dipole magnet is presented, and the test arrangement of a short-sample cable operating under the sweeping magnetic field is described.

Improvements and Performance of the Fermilab Solenoid Test Facility

The solenoid test facility at Fermilab was built using a large vacuum vessel for testing of conduction-cooled superconducting solenoid magnets, and was first used to determine the performance of the MICE coupling coil. The facility was modified recently to enable the testing of solenoid magnets for the muon-to-electron (Mu2e) experiment, which operates at much higher current than the coupling coil. One pair of low-current conduction-cooled copper and NbTi leads was replaced with two pairs of 10-kA high-temperature superconducting leads cooled by heat exchange with liquid nitrogen and liquid helium. The new design, with additional control and monitoring capability, also provides helium cooling of the superconducting magnet leads by conduction. A high current power supply with energy extraction was added, and several improvements to the quench protection and characterization system were made. Here, we present details of these changes and report on performance results from a test of the Mu2e prototype transport solenoid (TS) module. Progress on additional improvements in preparation for production TS module testing will be presented.