Production Solenoid Research Articles

Fabrication and installation of the Mu2e cryogenic distribution system

The muon-to-electron conversion (Mu2e) experiment at Fermilab will be used to search for the charged lepton flavor-violating conversion of muons to electrons in the field of an atomic nucleus. The Mu2e experiment is currently in the construction stage. The scope of this paper is the cryogenic distribution system and superconducting power leads for four superconducting solenoid magnets: Production Solenoid (PS), an Upstream and Downstream Transport Solenoids (TSu and TSd) and Detector Solenoid (DS). The design of the cryogenic distribution system and the fabrication of several sub-systems was reported previously. This paper reports on additional fabrication and installation progress that has been performed over the past two years. Lessons learned during fabrication and testing of the cryogenic distribution system components are described. In particular, the challenges and solutions implemented for aluminum welding are reported.A description of the process used to qualify the welding procedure and welders for welding the aluminium stabilized NbTi superconducting power leads is provided. Additionally, the progress made with regards to installing the power leads into the cryogenic Feedboxes is covered.

Status of Performance Testing of the Mu2e Transport Solenoid Coils

The magnet system of the Muon to electron (Mu2e) experiment at Fermilab consists of three solenoid magnets: the Production Solenoid (PS), the Transport Solenoid (TS), and the Detector Solenoid (DS). The S-shaped TS contains 52 coils grouped into modules, which are typically 2 coils shrink fitted into Al shells. These modules are further grouped into units made of 1-3 modules. As part of the acceptance process for these units, the magnetic center of all coils and critical dimensions of the Al shells are measured. The magnetic model is updated with these as-built values to ensure the magnetic requirements for the experiment are met. In addition, units are tested to 120% of nominal current at liquid helium temperatures to study quench performance and splice resistance. Results from the first units will be presented.

Design and fabrication of the Mu2e cryogenic distribution system

The muon-to-electron conversion (Mu2e) experiment at Fermilab will be used to search for the charged lepton flavor-violating conversion of muons to electrons in the field of an atomic nucleus. The Mu2e experiment is currently in the design and construction stage and is expected to begin operations in 2022. The Mu2e experiment uses four large superconducting solenoid magnets including a Production Solenoid (PS), an Upstream and Downstream Transport Solenoid (TSu and TSd) and a Detector Solenoid (DS).This paper will focus on the cryogenic distribution system for these four solenoid magnets. Liquid helium will be supplied from two re-purposed Tevatron satellite refrigerators. A large cryogenic distribution box (DB) is located in the Mu2e building to distribute the required cryogens to each of the four solenoid magnets. Each solenoid magnet will have a dedicated transfer line and cryogenic feed box (FB). The solenoid magnets each require two liquid helium circuits and two liquid nitrogen circuits.The most unique feature about this cryogenic system is that the assemblies for the start of the superconducting portion of the power leads are mounted in feed boxes that are in the range of 23 m to 31 m away from the solenoid magnets. The cryogenic feed boxes are located remotely to provide protection from radiation damage and high magnetic fields. The power leads are NbTi superconducting cable stabilized with high conductivity aluminum. The 6061-T6 aluminum grade was selected for the transfer line piping so that the piping would thermally contract at the same rate as the power lead. A major concern for this transfer line is that a small helium leak could create an electric discharge arc due to the Paschen effect. This paper includes a description of the design features and testing done to ensure that the power leads are protected from the Paschen effect while still being adequately cooled to liquid helium temperatures.

Influence of the injector setup on digital and continuous injection rate-shaping performance in diesel engine passenger cars

Injection continuous rate-shaping strategies, realized by means of state-of-the-art Common rail solenoid and direct acting piezoelectric injectors, have been tested at a dynamometer cell. NOx, soot, combustion noise and heat release rate data, pertaining to the two injector types, have been compared, based on a pilot-main injection calibration. The performance of the solenoid injectors resulted to be in line with that of the direct acting piezoelectric injectors.Digital and continuous rate-shaping strategies have then been investigated at a hydraulic rig in solenoid injectors. The cycle-to-cycle dispersion in the injected mass increases significantly in the closely-coupled injection regime, where the overall injected quantity raises up as the dwell time progressively reduces. However, as the dwell time is diminished to values well within the injection fusion zone, the cycle-to-cycle dispersion of the injected mass again improves and this confirms that is possible to implement effective continuous injection rate-shaping schedules also for the solenoid injectors.A previously developed one-dimensional model of a solenoid fuel injection system has been applied to perform parametric analyses on the solenoid injector setup: mechanical, electromagnetic and hydraulic parameters have been changed in order to investigate their effect on the closely-coupled injections. The objective is to provide design keys for realizing more efficient injection rate-shaping schedules in order to improve engine emissions, fuel consumption and combustion noise.Finally, the performance of two production solenoid injectors, which feature a different internal layout, has been compared in the short dwell time range and the experimental results have been successfully interpreted on the basis of the injector parametric analyses.

Production of Aluminum Stabilized Superconducting Cable for the Mu2e Transport Solenoid

The Fermilab Mu2e experiment [1] , [2] , currently under construction at Fermilab, has the goal of measuring the rare process of direct muon to electron conversion in the field of a nucleus. The experiment features three large superconducting solenoids: the production solenoid (PS), the transport solenoid (TS), and the detector solenoid (DS). The TS is an “S-shaped” solenoid that sits in between the PS and the DS producing a magnetic field ranging between 2.5 and 2.0 T. This paper describes the various steps that led to the successful procurement of over 740 km of superconducting wire and 44 km of Al-stabilized Rutherford cable needed to build the 52 coils that constitute the Mu2e TS cold mass. The main cable properties and results of electrical and mechanical test campaigns are summarized and discussed. Critical current measurements of the Al-stabilized cables are presented and compared to expected critical current values as measured on extracted strands from the final cables after chemical etching of the aluminum stabilizer. A robust and reliable approach to cable welding is presented, and the effect of cable bending on the transport current is also investigated and presented.

Mu2e Transport Solenoid Cold-Mass Alignment Issues

The muon-to-electron conversion experiment (Mu2e) at Fermilab is designed to explore charged lepton flavor violation. It is composed of three large superconducting solenoids: the production solenoid, the transport solenoid (TS), and the detector solenoid. The TS is formed by two magnets: TS upstream and TS downstream. Each has its own cryostat and power supply. Tolerance sensitivity studies of the position and angular alignment of each coil in this magnet system were performed in the past with the objective to demonstrate that the magnet design meets all the field requirements. The alignment of the cold masses is critical to maximize the transmission of muons and to avoid possible backgrounds that would reduce the sensitivity of the experiment. Each TS magnet cold mass can be individually aligned. In this paper, we discuss the implications of the alignment of the TS cold masses in terms of the displacement of the magnetic center. Consideration of the practical mechanical limits is also presented.

An analytical approach to designing a thermosiphon cooling system for large scale superconducting magnets

A Thermosiphon cooling scheme is a productive way of cooling large scale superconducting magnets. The absence of active pumping and the availability of the higher heat capacity parameter “latent heat” make this an attractive cooling method. Nevertheless, the design of such a system demands a well-organized study of the effect of various flow parameters, such as, mass flow rates, flow quality, etc., and also a robust mechanical design of the various components of the system. This paper presents an analytical approach to designing a thermosiphon cooling scheme based on homogeneous flow conditions as well as separated flow conditions. The design of the mechanical components such as the piping is also discussed. The design approach presented here has been applied to the reference design of two large superconducting solenoids, the Production Solenoid and the Detector Solenoid of the Mu2e experiment at Fermilab.

Preliminary Design of the Production Solenoid Feedbox for the Mu2e Project at Fermilab

Preliminary Design of the Production Solenoid Feedbox for the Mu2e Project at Fermilab

Aluminum Stabilized Superconducting Prototype Cable Development for the Mu2e Transport Solenoid

The Fermilab Mu2e experiment seeks to measure the rare process of direct muon to electron conversion in the field of a nucleus. The experiment makes use of three large superconducting solenoids: the production solenoid (PS), the transport solenoid (TS), and the detector solenoid (DS). The TS is an “S-shaped” solenoid with a warm-bore aperture of half a meter and field between 2.5 and 2.0 T. The three solenoids are based on four different types of Al stabilized NbTi conductors. All the conductors are composed of a Rutherford cable embedded in an aluminum matrix through a conforming process. This paper describes the various steps that led to the successful procurement of 3 km of Al-stabilized prototype cable for the Mu2e TS. The main cable properties and results of electrical and mechanical tests are presented and discussed for each stage of the cable development process. Results are compared to design values to show how the prototype cable lengths satisfied all the design criteria starting from the NbTi wires all the way to the Al-stabilized cables. Following the successful completion of this initial phase, the TS prototype cable is currently being used to manufacture a prototype TS coil in industry. The cable production phase has recently been launched, with the goal of producing 700 km of superconducting wire for a total of 44 km of TS Al-stabilized cable needed to build the entire Transport Solenoid system.

Tolerance Studies of the Mu2e Solenoid System

The muon-to-electron conversion experiment at Fermilab is designed to explore charged lepton flavor violation. It is composed of three large superconducting solenoids, namely, the production solenoid, the transport solenoid, and the detector solenoid. Each subsystem has a set of field requirements. Tolerance sensitivity studies of the magnet system were performed with the objective of demonstrating that the present magnet design meets all the field requirements. Systematic and random errors were considered on the position and alignment of the coils. The study helps to identify the critical sources of errors and which are translated to coil manufacturing and mechanical support tolerances.

Optimization of the Mu2e Production Solenoid Heat and Radiation Shield

The Mu2e experiment at Fermilab is designed to study the conversion of a negative muon to electron in the field of a nucleus without emission of neutrinos. Observation of this process would provide unambiguous evidence for physics beyond the Standard Model, and can point to new physics beyond the reach of the LHC. The main parts of the Mu2e apparatus are its superconducting solenoids: Production Solenoid (PS), Transport Solenoid (TS), and Detector Solenoid (DS).Being in the vicinity of the beam, PS magnets are most subjected to the radiation damage. In order for the PS superconducting magnet to operate reliably, the peak neutron flux in the PS coils must be reduced by 3 orders of magnitude by means of sophisticatedly designed massive Heat and Radiation Shield (HRS), optimized for the performance and cost. An issue with radiation damage is related to large residual electrical resistivity degradation in the superconducting coils, especially its Al stabilizer.A detailed MARS15 analysis and optimization of the HRS has been carried out both to satisfy the Mu2e requirements to the radiation quantities (such as displacements per atom, peak temperature and power density in the coils, absorbed dose in the insulation, and dynamic heat load) and cost. Results of MARS15 simulations of these radiation quantities are reported and optimized HRS models are presented; it is shown that design levels satisfy all requirements.

Challenges and Design of the Transport Solenoid for the Mu2e Experiment at Fermilab

The Fermilab Mu2e experiment seeks to measure the rare process of direct muon to electron conversion in the field of a nucleus. The magnet system for this experiment is made of three warm-bore solenoids: the Production Solenoid (PS), the Transport Solenoid (TS), and the Detector Solenoid (DS). The TS is an “S-shaped” solenoid set between the other bigger solenoids. The Transport Solenoid has a warm-bore aperture of 0.5 m and field between 2.5 and 2.0 T. The PS and DS have, respectively warm-bore aperture of 1.5 m and 1.9 m, and peak field of 4.6 T and 2 T. In order to meet the field specifications, the TS starts inside the PS and ends inside the DS. The strong coupling with the adjacent solenoids poses several challenges to the design and operation of the Transport Solenoid. The coil layout has to compensate for the fringe field of the adjacent solenoids. The quench protection system should handle all possible quench and failure scenarios in all three solenoids. The support system has to be able to withstand very different forces depending on the powering status of the adjacent solenoids. In this paper, the conceptual design of the Transport Solenoid is presented and discussed focusing on these coupling issues and the proposed solutions.

Solenoid Magnet System for the Fermilab Mu2e Experiment

The Fermilab Mu2e experiment seeks to measure the rare process of direct muon to electron conversion in the field of a nucleus. Key to the design of the experiment is a system of three superconducting solenoids; a muon production solenoid (PS) which is a 1.8 m aperture axially graded solenoid with a peak field of 5 T used to focus secondary pions and muons from a production target located in the solenoid aperture; an “S shaped” transport solenoid (TS) which selects and transports the subsequent muons towards a stopping target; a detector solenoid (DS) which is an axially graded solenoid at the upstream end to focus transported muons to a stopping target, and a spectrometer solenoid at the downstream end to accurately measure the momentum of the outgoing conversion electrons. The magnetic field requirements, the significant magnetic coupling between the solenoids, the curved muon transport geometry and the large beam induced energy deposition into the superconducting coils pose significant challenges to the magnetic, mechanical, and thermal design of this system. In this paper a conceptual design for the magnetic system which meets the Mu2e experiment requirements is presented.

Superconducting magnet systems for the Muon-electron conversion experiment

The Muon-to-Electron Conversion Experiment (MECO) seeks to detect muon to electron conversion, providing evidence that the conservation of muon and electron type lepton number can be violated. Observation of this violation would suggest physics beyond the Standard Model. The experiment is to be installed at Brookhaven National Laboratory (BNL). A high energy proton beam produces pions upon hitting a heavy target inside the 1.5 m diameter by 5 m long Production Solenoid (PS). A fraction of the muons from pion decay are captured in the 0.5 m diameter bore by the 13 m long, S-shaped Transport Solenoid (TS), which contains collimators, providing sign and momentum selection. The muons are stopped in a target inside a 1.9 m bore by 10 m long Detector Solenoid (DS) that houses detectors to measure the energy of the conversion electrons. Magnetic field is controlled to 5 T /spl plusmn/5% at the high-field end of the PS and to 1 T /spl plusmn/0.2% in the detector region of the DS. The conceptual design for the magnets is summarized, including conductor, coil, structure and cryogenic design.