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We study, by optical spectroscopy, the properties of high-current electric arcs that form between opening Cu contacts. The presence of a current that increases linearly with a rate of about 14 kA/ms leads to the separation of the contacts and to the formation of a bridge of molten metal that eventually ruptures. We show that after the molten bridge rupture, it takes about 40 $\mu \text{s}$ for the initial arc to be at local thermal equilibrium. This long thermalization time suggests that the plasma density during that time range is low, which we confirm using a simple modeling of the energy transfer between electrons and heavy particles. We explain these low densities by the fact that the molten bridge rupture leads to the formation of a shock wave. The initial dense plasma rapidly expands and a region with a pressure below the background pressure forms between the two contacts, leading to low plasma densities and long thermalization times. [ABSTRACT FROM AUTHOR]

Arrays of superconducting transition-edge sensor (TES) microcalorimeters are attractive for some X-ray experiments where the combination of higher collection efficiency than crystal spectrometers and much better energy resolution than semiconductor detectors is enabling. For hard X-ray (>2 keV) applications, a TES is often integrated with an extra absorber to extend its dynamic range, quantum efficiency and collecting area. For >100 keV applications, millimeter size absorbers have been manually attached to TES pixels after fabrication. At lower energies, the absorber size needs to be much smaller, because a large heat capacity degrades energy resolution. In that case, the absorber is directly electroplated or evaporated on the TES during the fabrication process. In this work, we present TES microcalorimeters optimized for the intermediate hard X-ray energy region (20 keV ∼ 100 keV) that have thick absorbers directly deposited during the TES fabrication process. This microcalorimeter is designed to measure high-resolution muonic atom transition X-ray spectra as a method to study quantum electrodynamics (QED) effects. The absorber is comprised of evaporated gold and electroplated bismuth layers and is designed to optimize dynamic range, collecting efficiency, and energy resolution in the 20 keV to 45 keV energy range. A prototype with pure gold absorbers has been fabricated and characterized, in order to obtain a first experimental reference in the detector development process. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

KEK is currently constructing a long series of superconducting solenoid beamline for the COMET Phase-I experiment at the Hadron facility of J-PARC. The magnet system consists of a 5-T pion capture solenoid, a curved muon transport solenoid, and a large bore detector solenoid. The pion capture solenoid system consists of a large cold mass including four coils with an inner diameter of 1340 mm and a small cold mass including six small coils with an inner diameter of 500 mm. The peak magnetic field on the conductor reaches to 5.4 T at an operation current of 2700 A. This paper presents the design and structural details of a magnet, radiation-resistant coil, cold mass and vacuum vessel, apart from the results of the electromagnetic analysis in two-dimensional (2-D) and 3-D. [ABSTRACT FROM PUBLISHER]

We are developing a new technique to apply transition-edge sensors (TESs) to X-ray spectroscopy of exotic atoms, especially of kaonic atoms. To demonstrate the feasibility of this pioneering project, performance of a TES-based X-ray detector was evaluated in pion- and kaon-beam environments at particle accelerators. We successfully observed X-rays from pionic-carbon atoms with a resolution as good as 7 eV FWHM at 6 keV. Also at a kaon beamline, we confirmed that the TES spectrometer will be able to achieve our resolution goal, 6 eV, in our first scientific campaign to measure X-rays from kaonic-helium atoms. [ABSTRACT FROM AUTHOR]

The iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) will be used to measure neutrino mass hierarchy. The magnet in the ICAL detector will be used to distinguish the \mu ^- and \mu ^+ events induced by \nu \mu and anti- \nu \mu , respectively. Due to the importance of the magnet in ICAL, an electromagnetic simulation has been carried out to study the $B$ -field distribution in iron using various designs. The simulation shows better uniformity in the portion of the iron layer between the coils, which is bounded by regions that have lesser field strength as we move to the periphery of the iron layer. The ICAL magnet was configured to have a tiling structure that gave the minimum reluctance path, while keeping a reasonably uniform field pattern. This translates into less ampere-turns needed for generation of the required magnetic field. At low ampere-turns, a larger fractional area with $|B|\ge 1$ T can be obtained using a soft magnetic material. A study of the effect of the magnetic field on muon trajectories has been carried out using GEANT4. For muons up to 20 GeV, the energy resolution improves as the magnetic field increases from 1.1 to 1.8 T. The charge identification efficiency for muons was found to be >90% except for large zenith angles. [ABSTRACT FROM PUBLISHER]

The Mu2e experiment at Fermilab is designed to explore charged lepton flavor violation by searching for muon-to-electron conversion. The magnetic field generated by a system of solenoids is a crucial component of Mu2e and requires accurate characterization to detect any potential flaws and to produce a detailed field map. In order to design and build a precise field mapping system consisting of Hall and NMR probes, tolerances and precision for such a system need to be evaluated. To generate a final magnetic field map of the Mu2e solenoids, a continuous field has to be extracted from a discrete set of measurement points. A design for the Mu2e field mapping hardware, and results from simulations to specify parameters for Hall and NMR probes are presented. A fitting procedure for the analytical treatment of our expected magnetic measurements is introduced. [ABSTRACT FROM PUBLISHER]

The Mu2e experiment at Fermilab has been approved by the Department of Energy to proceed with the development of the preliminary design. Integral to the success of Mu2e is the superconducting solenoid system. One of the three major solenoids is the detector solenoid that houses the stopping target and the detectors. The goal of the detector solenoid team is to produce detailed design specifications that are sufficient for vendors to produce the final design drawings, tooling and fabrication procedures and proceed to production. In this paper we summarize the reference design of the detector solenoid. [ABSTRACT FROM PUBLISHER]

The definition of the magnetic center in the Mu2e solenoid system is not trivial given the S-shaped nature of the transport solenoid. Moreover, due to the fringe field of the larger bore adjacent magnets—production solenoid and the detector solenoid—the magnetic center does not coincide with the geometric center of the system. The reference magnetic center can be obtained by tracking a low-momentum charged particle through the whole system. This paper will discuss this method and will evaluate the deviations from the nominal magnetic center given the tolerances in the manufacturing and the alignment of the coils. Methods for the correction of the magnetic center will also be presented. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

A program to develop model magnets for a helical cooling channel is under way at Fermilab. In the first steps of a planned sequence of magnets, two four-coil helical solenoid models with 300 mm aperture have been fabricated and tested. These two models, HSM01 and HSM02, used insulated NbTi Rutherford cable wound onto stainless steel rings with spliceless transitions between coils. Strip heaters were included for quench protection of each coil, and the coils were epoxy-impregnated after winding inside the support structures. Based on the results of the first model the second model was made using a cable with optimized cross-section, improved winding and epoxy-impregnation procedures, enhanced ground insulation, and included heat exchange tubing for a test of conduction cooling. We report on the results and lessons learned from fabrication and tests of these two models. [ABSTRACT FROM PUBLISHER]

In this work we present the design, the construction and the measurements of the magnet for a so-called spin-rotator (Wien filter), a beam line device used to rotate the spin direction (and the associated magnetic moment) of muons in a beam used for condensed matter research at the Swiss Muon Source at the Paul Scherrer Institute. The design parameters—originating both from the properties of the preferred particle beam as well as the technological constraints for the high-voltage components generating the necessary electric field—were optimized for device compactness, cost and high beam transmission. [ABSTRACT FROM PUBLISHER]

A quench protection system for superconducting curved segmented solenoids has been experimentally studied. The curved solenoids consist of short straight solenoids aligned along a curved beamline axis. The quench propagation between the short solenoids may not naturally occur because of the separation between the solenoids, and an artificial quench need to be induced by a protection heater for each short solenoid to boost the quench propagation. A protection heater driven by the coil self current was tested with a model coil. [ABSTRACT FROM AUTHOR]

The construction of the 1st phase Japan Proton Accelerator Research Complex (J-PARC) was completed. Three major experimental facilities, which have been utilized by users, are instrumented with the superconducting magnet systems; a muon transport solenoid in Materials and Life Science Experimental Facility, a superconducting spectrometer in Hadron Experimental Facility, and a 150 m superconducting beam line in Neutrino Experimental Facility. There are also several superconducting magnet systems proposed as part of future experiments at J-PARC. The paper briefly summarizes the current status of the superconducting magnet systems currently in operation, and introduces the superconducting magnet systems associated with the new proposals. [ABSTRACT FROM AUTHOR]

A 3-GeV (333 \muA, 1.0 MW) proton beam from the J-PARC Rapid Cycle Synchrotron passes through a graphite target producing muons in the Materials and Life Science Facility. Muons of various momenta of up to 50 MeV/c and of both electric charges are captured and transported to an experimental area by using an axial magnetic field in the bore of solenoid magnets. This beam line, named Super Omega, is composed of a normal conducting MIC (Mineral Insulation Cable) magnet for capture, a curved superconducting solenoid system for transportation, and an axial focusing magnet system. Once in the experimental area, the muon beam is focused onto an experimental target for various purposes. The superconducting solenoid system is composed of one 6-m long straight section and two 45-degree segmented curved sections at both ends of the straight section. A magnetic field of about 2 T is applied in the transportation channel of 300 mm in diameter. The conceptual design of this solenoid system is reported. [ABSTRACT FROM AUTHOR]

The new muon beamline, MuSIC, is being constructed at the Research Center for Nuclear Physics (RCNP) at Osaka University in Japan. The project utilizes superconducting solenoid magnets to collect pions and to transport muons with the ultimate efficiency by putting pion-production target inside the solenoid magnet. This is the first of such a novel method to produce intense muon beams. All the superconducting coils are cooled with conduction cooling using Gifford-McMahon cryocoolers. A large superconducting coil with the diameter of 90 cm encloses the pion-production target and thick shielding to protect the coil against severe radiation from the target, so that energy deposit by particles on the coil should be less than 1 W. Pions are captured in a 3.5 T magnetic field and are injected into the subsequent toroidal magnets with the magnetic field of 2 T. Superconducting dipole coils are equipped on each solenoid coil of the transport solenoid to correct the particle trajectory in the toroidal field. The design and construction status of the solenoid channel are described in this paper. [ABSTRACT FROM AUTHOR]

Basic R&Ds of a superconducting solenoid for a new g-2 experiment at J-PARC are on going. High uniformity of magnetic field below 0.1 ppm is required for the g-2 experiment within a storage region of 33.3 \pm5 cm in radius and \pm10 cm in height. Two R&Ds have been started to develop the magnet with such high uniformity; a development of a precise field monitoring system and a study of seismic ground vibration. The prototype monitoring system using continuous wave type NMR probe for horizontal MRI solenoid has been built and tested. Cross-check between NMR and Hall probe has been also carried out. The seismic ground vibration has been measured at Materials and Life science Facility, MLF, in J-PARC. Based on the measured results, the spectrum analysis of the iron yoke has been performed using ANSYS. [ABSTRACT FROM AUTHOR]

An intense muon beam is mandatory for next-generation experiments to search for lepton flavor violating processes in the muon sector. The COMET experiment, J-PARC E21, aims to search for muon to electron conversion with an unprecedented sensitivity. All the components of the experiment, such as the pion production target, the muon stopping target and the tracker are embedded in superconducting solenoids, resulting in a total length longer than 30 m. The pions are captured in a 5 T solenoid magnet with a diameter of 1.3 m, and decay to muons in the subsequent 3 T toroidal magnets over a length of 10 m. The pion capture solenoid is designed to be as small as possible, however, thick shielding is necessary within the solenoid to avoid severe radiation from the target. Aluminum-stabilized NbTi superconducting wire is employed to reduce the cold mass and energy deposited in it. The damage of the conductor of the coils should be estimated carefully, since the expected neutron fluence reaches 10^22\ neutrons/m^2. This paper describes the design of the solenoid magnets and R&D programs. [ABSTRACT FROM AUTHOR]

An international collaboration plans to measure the lifetime of the muon to a precision of 1 part per million [1]. The "MuLan" experiment wilt take place at the Paul Scherrer Institut (PSI) in Northern Switzerland. The MuLan experiment requires a fast beam line kicker, which can turn the beam on and off, to invoke an artificial time structure on the continuous beam which has a 50.6-MHz time microstructure. The kicker needs to run with a standard "on-off time cycle" or in a "Muon on Request" mode. The MuLan kicker consists of two pairs of deflector plates mechanically in series, driven by four modulators. Each modulator consists of two stacks of MOSFETs operating in push-pull mode. The specifications for the kicker demand that the rise and fall times of the deflector plate voltage do not exceed 45 ns. There is a requirement for an adjustable output voltage from 0 V to ± 12.5 kV per deflector plate, a minimum pulse duration of 200 ns, and adjustable repetition rate up to a maximum of 50 kHz, continuous. Short turn-on and turn-off delays are required for the "Muon on Request" mode; the measured propagation delay is 200 ns. The specifications also require that the polarity of the pulses on the plates be selectable, although not on a pulse-by-pulse basis. This paper describes the novel design of the kicker and presents both predictions and measurements. [ABSTRACT FROM AUTHOR]