Muon Beamline Research Articles

Delivering the world’s most intense muon beam

A new muon beamline, muon science innovative channel (MuSIC), was set up at the Research Centre for Nuclear Physics (RCNP), Osaka University, in Osaka, Japan, using the 392 MeV proton beam impinging on a target. The production of an intense muon beam relies on the efficient capture of pions, which subsequently decay to muons, using a novel superconducting solenoid magnet system. After the pion-capture solenoid the first $36^\circ$ of the curved muon transport line was commissioned and the muon flux was measured. In order to detect muons, a target of either copper or magnesium was placed to stop muons at the end of the muon beamline. Two stations of plastic scintillators located upstream and downstream from the muon target were used to reconstruct the decay spectrum of muons. In a complementary method to detect negatively-charged muons, the X-ray spectrum yielded by muonic atoms in the target were measured in a germanium detector. Measurements, at a proton beam current of 6 pA, yielded $(10.4 \pm 2.7) \times 10^5$ muons per Watt of proton beam power ($\mu^+$ and $\mu^-$), far in excess of other facilities. At full beam power (400 W), this implies a rate of muons of $(4.2 \pm 1.1) \times 10^8$ muons s$^{-1}$, amongst the highest in the world. The number of $\mu^-$ measured was about a factor of 10 lower, again by far the most efficient muon beam produced. The set up is a prototype for future experiments requiring a high-intensity muon beam, such as a muon collider or neutrino factory, or the search for rare muon decays which would be a signature for phenomena beyond the Standard Model of particle physics. Such a muon beam can also be used in other branches of physics, nuclear and condensed matter, as well as other areas of scientific research.

The full stereo drift chamber for the MEG II experiment

The MEG experiment, at the Paul Scherrer Institute (PSI) near Zurich in Switzerland, aims at searching for the charged-lepton-flavor-violating decay μ+arrow e+γ, prohibited in the Standard Model but allowed, at a measurable level, in many of its extensions. MEG has already determined the world best upper limit on the branching ratio: BR(μ+arrow e+γ)<4.2×10−13 at 90% CL with the full data set collected in the years 2009–2013. A further improvement of the MEG single event sensitivity requires a substantial upgrade of the detector performances and, in particular, the complete replacement of the positron tracker. The MEG upgrade experiment (MEG II) is currently under construction and it is conceived in order to further improve the sensitivity by one order of magnitude in three years of data taking. The new positron tracker is a high transparency single volume, full stereo cylindrical Drift Chamber, immersed in a non uniform longitudinal B-field, co-axial to the muon beam line. Due to the high wire density (12 wires/cm2), the use of the traditional feed-through technique as wire anchoring system could hardly be implemented and therefore it was necessary to develop new wiring strategies. The number of wires and the stringent requirements on the precision of their position and on the uniformity of the wire mechanical tension impose the use of an automatic system to operate the wiring procedures. The drift chamber is currently under construction at INFN Lecce and Pisa, and should be completed by the summer 2017 to be then delivered to PSI for commissioning. The upgraded detector, the new drift chamber and its construction technique, will be described.

A new muon-pion collection and transport system design using superconducting solenoids based on CSNS**Supported by National Natural Science Foundation of China (11527811)

A new muon and pion capture system is proposed for the China Spallation Neutron Source (CSNS), currently under construction. Using about 4% of the pulsed proton beam (1.6 GeV, 4 kW and 1 Hz) of CSNS to bombard a cylindrical graphite target inside a superconducting solenoid, both surface muons and pions can be acquired. The acceptance of this novel capture system - a graphite target wrapped up by a superconducting solenoid - is larger than the normal muon beam lines using quadrupoles at one side of the separated muon target. The muon and pion production at different capture magnetic fields was calculated using Geant4. The bending angle of the capture solenoid with respect to the proton beam was also optimized in simulation to achieve more muons and pions. Based on the layout of the muon experimental area reserved at the CSNS project, a preliminary muon beam line was designed with multi-purpose muon spin rotation areas (surface, decay and low-energy muons). Finally, high-flux surface muons (108/s) and decay muons (109/s) simulated by G4beamline will be available at the end of the decay solenoid based on the first phase of CSNS. This collection and transport system will be a very effective beam line at a proton current of 2.5 μA.

Cryogenic system for COMET experiment at J-PARC

Superconducting conductors and cryogenic refrigeration are key factors in the accelerator science because they enable the production of magnets needed to control and detect the particles under study. In Japan, a system for COMET (Coherent Muon to Electron Transition), which will produce muon beam lines, is under the construction at J-PARC (Japan Proton Accelerator Research Complex). The system consists of three superconducting magnets; the first is a pion-capture solenoid, the second is a muon-transport solenoid, and the third is a detector solenoid. It is necessary to cool down the magnets efficiently using two-phase helium and maintain them securely at 4.5K. For stable cryogenic refrigeration of the magnets, a suitable cooling method, structures, and the irradiation effect on materials should be investigated. In this paper, we focus on the development of an overall cryogenic system for cooling the capture and transport solenoids. A conduction-cooling method is considered for cooling the capture and transport solenoids because of the advantages such as the reduction of total heat load, fewer components, and simplified structure. To supply cryogenic fluids (4.5K liquid helium and 58K gas helium) and currents to the conduction-cooled magnets subjected to high irradiation, cryogenic components (cooling paths in the magnets, transfer tubes, and a current lead box) are developed. Based on the environment of high irradiation, the conditions (temperature and pressure) of helium in cooling paths are estimated, as well as the temperature of the capture magnet. We develop a dynamic model for quench simulation and estimate the maximum pressure in the cooling pipe when the capture magnet quenches. We conclude with a discussion of the next steps and estimated challenges for the cryogenic system.

The design of an optimized muon beamline

For the Heavy Ion Accelerator Project in South Korea we designed an optimized antimuon beamline by using a simulation with the G4beamline and the TRANSPORT software packages. This research suggests that the optimized muon beamline can transport 2.4×108 antimuons per second to a circle with a radius of 3 cm. In terms of the muon rate, this is competitive with world-leading muon beam facilities.

H line; a beam line for fundamental physics study

The muon facility, J-PARC (Muon Science Establishment; MUSE), has been operating since the first beam in 2008. Starting with a 200 kW proton beam, a beam intensity of 3 × 106 muons/s was reached in 2009 which was the most intense pulsed muon beam in the world. From the 2 cm thick graphite target, four secondary muon beam lines are designed to be extracted. Three beam lines currently exist, the first being operational and the other two undergoing commissioning. The fourth and the last beam line, the H line, is planned to be constructed. This new beam line is designed to have a large acceptance, provides the ability to tune the momentum, and use a kicker magnet and/or a Wien filter. The H line is designed to provide an intense beam of 108 surface muons/s for fundamental physics studies to observe new physics beyond the standard model. Such studies require high statistics and they need to occupy the experimental areas for a relatively long period.

Design and construction of the ultra-slow muon beamline at J-PARC/MUSE

At the J-PARC Muon Science Facility (MUSE), a new Ultra-Slow Muon beamline is being constructed to extend the μSR technique from bulk material to thin films, thus empowering a wide variety of surface and nano-science studies, and also a novel 3D imaging with the "ultra-slow muon microscope". Ultra-slow muons will be produced by the re-acceleration of thermal muons regenerated by the laser resonant ionization of muonium atoms evaporated from a hot tungsten foil, a method that originated from the Meson Science Laboratory at KEK. The design parameters, construction status and initial beam commissioning are reported.

Muon-to-Electron Conversion with COMET

The Coherent Muon-to-Electron Transition (COMET) experiment ispresented, focusing on the particle detection systems. COMET is currentlyunder construction as the first of two phases at the J-PARC protonaccelerator laboratory in Tokai, Japan. COMET will search formuon-to-electron conversion with a single-event sensitivity of 2.6 × 10−17, with Phase-I achievinga sensitivity of 3.1 × 10−15 and due to enter commissioning in 2016. Phase-I will also allow us to studythe novel pion and muon beamline and the rates of background processes.

Positron separators in Superomega muon beamline at J-PARC

A positron separator is one of the essential components of a muon beamline to eliminate contamination in the beam, mainly positrons that have the same momentum as muons and are transported together with the beam. In order to eliminate positrons efficiently, we selected a Wien filter type three-stage positron separator for the new muon beamline, called Superomega, that is under construction in the Materials and Life Science Experimental Facility (MLF) of the Japan Accelerator Research Complex (J-PARC). The Superomega muon beamline is the second muon beamline at MLF/J-PARC, and started operation in October of 2012. Here, we report on the features and the test results of the positron separators installed in the Superomega muon beamline.

Superconducting curved transport solenoid with dipole coils for charge selection of the muon beam

At the J-PARC Muon Science Facility (MUSE) the Super-Omega muon beamline is now under construction in the experimental hall No. 2 of the Materials and Life Science Facility building. Muons up to 45MeV/c will be extracted with a large acceptance solid angle to produce the world highest intensity pulsed muon beam. This beamline comprises three parts, a normal-conducting capture solenoid, a superconducting curved transport solenoid and an axial focusing solenoid. Since only solenoids are used, both surface μ+ and cloud μ− are extracted simultaneously. To accommodate future experiments that would only require either μ+ or μ− beam, two dipole coils located on the straight section of the curved solenoid provide the muon charge selection by directing one of the beam onto the solenoid inner-wall. The design parameters, the construction status and the initial beam commissioning are reported.

Ultra slow muon microscopy by laser resonant ionization at J-PARC, MUSE

As one of the principal muon beam line at the J-PARC muon facility (MUSE), we are now constructing a Muon beam line (U-Line), which consists of a large acceptance solenoid made of mineral insulation cables (MIC), a superconducting curved transport solenoid and superconducting axial focusing magnets. There, we can extract 2 × 108/s surface muons towards a hot tungsten target. At the U-Line, we are now establishing a new type of muon microscopy; a new technique with use of the intense ultra-slow muon source generated by resonant ionization of thermal Muonium (designated as Mu; consisting of a μ + and an e − ) atoms generated from the surface of the tungsten target. In this contribution, the latest status of the Ultra Slow Muon Microscopy project, fully funded, is reported.

The Mu2e experiment at fermilab: [formula omitted

Mu2e will search for coherent, neutrino-less conversion of muons into electrons in the field of a nucleus to a few parts in 10−17, a sensitivity improvement of a factor of 10,000 over existing limits. Muon-Electron conversion provides unique windows into new physics inaccessible to other lepton flavor violation searches and probes up to mass scales ∼104TeV, far beyond the reach of present or planned high energy colliders. We present the design of the muon beamline and spectrometer, how the experiment fits in the current Fermilab complex, and discusses potential upgrades at Fermilab's Project X.

J-PARC Muon Facility, MUSE

Abstract The muon science facility (MUSE) is located in the Materials and Life Science Facility (MLF), which is a building integrated to include both neutron and muon science programs. For Phase 1, we succeeded in installing one super conducting decay/surface muon beamline, so called D-line, with a modest-acceptance pion injector of about 45 mSr in the summer of 2008. In November 2009, by iterative beam tuning and developing new beamline elements such as a larger separator, the surface muons (μ +) extraction rate was significantly increased up to 1.8 × 106/s with the use of a 120 kW proton beam from the RCS. The achieved intensity is equivalent or even larger than that at the RIKEN-RAL muon facility, and would correspond to 1.5 × 107/s surface muons when in the future the proton beam will reach a power of 1MW. Recently, the Superomega muon beamline, so called U-line, with a large acceptance of 400 mSr was funded for construction, delivering 4 × 108/s surface muons to the experimental area, aiming at creating a new type of muon source; an intense ultra-slow muon source of 1 × 105-6/s for the study of thin film magnetism, etc.

Status of the Superomega Muon Beam Line at J-PARC

Abstract Superomega muon beamline is currently under construction at Experimental hall No. 2 of Materials and Life Science Facility at J-PARC in Tokai, Japan. The beamline has a large solid angle acceptance, and will produce the highest intensity pulsed muon beam in the world. The beamline is designed to capture both surface positive and cloud negative muons for simultaneous use in a variety of experiments. The expected rate of surface muons for this beamline is 4×108 μ+/s, and that for cloud muons is 107 μ−/s. The beamline consists of the normal-conducting capture solenoid, the superconducting curved transport solenoid and axial focusing solenoid. The construction of the capture solenoid has been completed and installed in March 2009, and the transport solenoid is now fabricated, and will be installed by the end of 2011. The conceptual design of the axial focusing solenoid is completed, and the mechanical design is underway.

New Muon Kicker System for the Decay Muon Beamline at J-PARC

Abstract At J-PARC Muon Science Facility a conventional superconducting decay muon beamline (D-Line) was constructed that can extract surface (positive) muons and decay positive/negative muons up to 120 MeV/c. This beamline will be used for various kinds of muon experiments like μSR, muon catalyzed fusion and nondestructive elements analysis. Similarly to the ISIS facility at RAL, the muon beam produced at J-PARC has a double-pulsed structure. To utilize the muon beam more efficiently, a muon kicker system will be installed to separate the double-pulsed beam and send the two pulses to two experimental areas simultaneously, allowing μSR experiments with single-pulsed muons. A muon kicker system, comprising two magnetic kicker magnets, two switchyard magnets and a septum magnet, is now been constructed. Single-pulsed muon beam up to 60 MeV/c can be transported. New state-of-the-art power supplies are also been fabricated. The installation in the beamline is planned in summer 2011.

The Fermilab muon [formula omitted] project

A proposal to Fermilab, P989, has the goal to improve on the precision of the muon anomalous magnetic moment, a μ = ( g μ − 2 ) / 2 by at least a factor of 4 beyond the 0.54 ppm relative precision obtained in E821 at Brookhaven. The precision storage ring will be moved to Fermilab and installed in a new building. A new 8 GeV/c proton beamline and 3.1 GeV/c muon beamline will be built. The unique capabilities of Fermilab to produce a proton beam with pulses containing ≃ 1 × 10 12 protons at an advantageous duty factor will provide the necessary increase of statistics in a reasonable running time. This new experiment should clarify the apparent difference between the experimental and Standard-Model values of a μ .

Superconducting Solenoid Magnets for the MuSIC Project

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.

Conceptual Design of a Superconducting Solenoid System for the Super Omega Muon Beam Line at J-PARC

A 3-GeV (333 μA, 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.

Quench Protection of Curved Solenoids for High Intensity Muon Beamlines

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.

Study of Superconducting Curved Solenoids for a High Intensity Muon Beam Line

A study of superconducting curved solenoids have been carried out for a high intensity muon beamline at JPARC project at KEK. The curved solenoid is designed with 6 segmented short solenoids combined with tapered spacers in series. A pair of model coils were successfully developed and assembled with the tapered spacer to demonstrate the technical concept and the practical assembly. The cool down and excitation tests were successfully carried out. The design and test results are discussed.