Low-budget muon source

MuSIC is a project to provide the world's highest-intensity muon beam with continuous time structure at Research Center of Nuclear Physics (RCNP) of Osaka University, Japan. A pion capture system using a superconducting solenoid magnet and a part of superconducting muon transport solenoid channel have been build in 2010. The highest muon production efficiency was demonstrated by the beam test carried out in February 2011. The result concludes that the MuSIC can provide more than 109 muons/sec using a 400W proton beam. The pion capture system is one of very important technologies for future muon programs such as moon to electron conversion searches, neutrino factories, and a muon collider. The MuSIC built the first pion capture system and demonstrate its potential to provide an intense muon beam. The construction on the entire beam channel of the MuSIC will be finished in five years. We plan to carry out not only an experiment to search the lepton flavor violating process but also other experiments for muon science and their applications using the intense muon beam at RCNP. The design performance has been confirmed by results of muon yield estimations from several beam tests.

We report recent progress of slow muon beam line constructed at the RIKEN‐RAL muon facility. The slow muons are muons which are re‐accelerated from the one at thermal velocity. This beam is expected to have very small emittance compared with conventional muon beam, where muons are obtained from decays of pions at rest or on move. Especially, its smallness of energy spread will make it possible to apply μSR technique to the studies of thin films, multilayered systems, nanomaterials, and other objects of restricted dimensionality. Intense slow muon beams which can be realized at future neutrino factories will be a valuable tool for material science.

Muon beams of low emittance provide the basis for the intense, well-characterised neutrino beams necessary to elucidate the physics of flavour at the Neutrino Factory and to provide lepton-antilepton collisions at energies of up to several TeV at the Muon Collider. The International Muon Ionization Cooling Experiment (MICE) will demonstrate ionization cooling, the technique by which it is proposed to reduce the phase-space volume occupied by the muon beam at such facilities. In an ionization-cooling channel, the muon beam passes through a material (the absorber) in which it loses energy. The energy lost is then replaced using RF cavities. The combined effect of energy loss and re-acceleration is to reduce the transverse emittance of the beam (transverse cooling). A major revision of the scope of the project was carried out over the summer of 2014. The revised project plan, which has received the formal endorsement of the international MICE Project Board and the international MICE Funding Agency Committee, will deliver a demonstration of ionization cooling by September 2017. In the revised configuration a central lithium-hydride absorber provides the cooling effect. The magnetic lattice is provided by the two superconducting focus coils and acceleration is provided by two 201 MHz single-cavity modules. The phase space of the muons entering and leaving the cooling cell will be measured by two solenoidal spectrometers. All the superconducting magnets for the ionization cooling demonstration are available at the Rutherford Appleton Laboratory and the first single-cavity prototype is under test in the MuCool Test Area at Fermilab. The design of the cooling demonstration experiment will be described together with a summary of the performance of each of its components. The cooling performance of the revised configuration will also be presented.

High-gradient, pressurized RF cavities are investigated as a means to improve the capture efficiency, to effect phase rotation to reduce momentum spread, and to reduce the angular divergence of a muon beam. Starting close to the pion production target to take advantage of the short incident proton bunch, a series of pressurized RF cavities imbedded in a strong solenoidal field is used to capture, cool, and bunch the muon beam. We discuss the anticipated improvements from this approach to the first stage of a muon cooling channel as well as the requirements of the RF cavities needed to provide high gradients while operating in intense magnetic and radiation fields.

The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb3Sn-based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb3Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb3Sn solenoid as originally planned. Instead, a complementary project was approved by the DOE Technical Topic Manager to develop magnets for the Mu2e experiment that fit well into the Fermilab Technical Division availability. The difference between the MCC helical solenoid and the Mu2e bent solenoid described in Appendix I is that the helical solenoid is made of coils that are in parallel planes with offset centers, while the coils in the bent solenoid follow the central particle trajectory and look much like a “slinky” toy. The muon-beam cooling-channel technologies developed in this project will enable a muon collider, the next step toward the energy frontier, Higgs/neutrino/Z-factories, and rare muon decay experiments. Commercial uses of the beams made possible by the cooling techniques developed in this project include scanning for nuclear contraband, studies of material properties with spin resonance techniques, and muon-catalyzed fusion.

High intensity muon beam source for neutrino beam experiments

Muon beams of low emittance provide the basis for the intense, well-characterised neutrino beams necessary to elucidate the physics of flavour at the Neutrino Factory and to provide multi-TeV lepton-antilepton collisions at the Muon Collider. The international Muon Ionization Cooling Experiment (MICE) will demonstrate muon ionization cooling, the technique proposed to reduce the phase-space volume occupied by the muon beam at such facilities. In an ionization-cooling channel, the muon beam traverses a material (the absorber) losing energy, which is replaced using RF cavities. The combined effect is to reduce the transverse emittance of the beam (transverse cooling). The configuration of MICE required to deliver the demonstration of ionization cooling was prepared in parallel to the execution of a programme designed to measure the cooling properties of liquid-hydrogen and lithium hydride (Step IV). The design will be presented together with a summary of the projected performance of the experiment.

Modifications have been made to the LAMPF biomedical channel that allow the delivery of intense muon beams for physics experiments while retaining the design high-flux pion capability. Two types of muon beams have been developed: first, muons from the backward decay of pions and second, cloud muons, from the target region, momentum-degraded in the channel to reduce the pion component. Muons are collected from a region between the second and third bending magnets in the channel which can contain a Be degrader. A momentum-dispersed image is formed at a new downstream slit which is used to determine the momentum spread of both types of muon beams. The decay beam provides good polarization and low electron contamination. The degraded beam has higher intensity but about 40% electron contamination. Both beams have a pion contamination of about 3%.

Within the framework of the Fermilab Muon Collider Task Force, the possibility of developing a dedicated muon test beam for cooling experiments has been investigated. Cooling experiments can be performed in a very low intensity muon beam by tracking single particles through the cooling device. With sufficient muon intensity and large enough cooling decrement, a cooling demonstration experiment may also be performed without resolving single particle trajectories, but rather by measuring the average size and position of the beam. This allows simpler, and thus cheaper, detectors and readout electronics to be used. This paper discusses muon production using 400MeV protons from the Linac, decay channel and beamline design, as well as the instrumentation required for such an experiment, in particular as applied to testing the Helical Cooling Channel (HCC) proposed by Muons Inc.

The provision of intense stored muon beams would allow the properties of neutrinos to be measured precisely and provide a route to multi-TeV lepton-anti-lepton collisions. The short muon lifetime makes it impossible to employ traditional cooling techniques while maintaining the muon-beam intensity. Ionisation cooling, a process in which the muon beam is passed through a series of liquid hydrogen absorbers followed by accelerating RF-cavities, is the proposed cooling technique. The international Muon Ionisation Cooling Experiment (MICE) collaboration has been approved at the Rutherford Appleton Laboratory and proposes to perform an engineering demonstration of ionisation cooling. The MICE experiment will require the measurement of the momentum and position of muons entering and leaving a section of ionisation cooling channel with high precision and purity in the presence of a large background. The technology chosen to meet this challenge is scintillating fibres readout with Visible Light Photon Detectors. The design, construction and operation of a prototype detector is described, as well as a summary of ongoing research and development activities in preparation for supplying the trackers needed for the MICE experiment.

Current muon collider schemes call for significant six dimensional (6D) cooling of the muon beam before it is accelerated [1]. One cooling scheme, the Helical Cooling Channel (HCC), employs RF cavities filled with high pressure hydrogen gas [2]. The gas acts both as an energy loss mechanism to allow for ionization cooling [3, 4], and as a buffer in order to prevent RF breakdown [5]. When a beam of particles passes through a HPRF cavity, it will ionize the gas. The amount of plasma generated is dependent on the beam energy, the stopping power of the gas, and the density of the gas. The resulting plasma will gain energy from the RF electric field and transfer it through collisions to the gas. This effect is called plasma loading. An experiment performed at theMuCool Test Area at Fermilab studied the formation of plasma created by a proton beam and its evolution over the course of many 805 MHz RF cycles [6].

The accelerators must take the muon beams from -100 MeV to 2 TeV energies within the muon lifetime for a 4 TeV energy muon collider. These constraints plus the muon decay heating seriously challenge the designs of the superconducting RF (SRF) cavities and magnets in the accelerators and collider ring. The multiple superconducting recirculation linac and the very rapid-cycling superconducting synchrotron approach are both studied. We briefly introduce the technical considerations and preliminary designs of the SRF systems and magnets.KeywordsMuon DecayMuon BeamMagnet DesignCoil RadiusMuon LifetimeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The Muon Ionization Cooling Experiment (MICE) at the Rutherford Appleton Laboratory aims to demonstrate 10% ionization cooling of a muon beam by its interaction with low-Z absorber materials followed by restoration of longitudinal momentum in RF linacs. MICE Step IV, including the rst LH 2 or LiH absorber cell sandwiched between two particle tracking spectrometers, is the collaboration's near-term goal. Two large superconducting spectrometer solenoids and one focus coil solenoid will provide a magnetic eld of 4 T in the tracker and absorber-cell volumes. The status of these components is described, as well as progress towards Steps V and VI, including the eight RF cavities to provide the required 8 MV/m gradient in a strong magnetic eld; this entails an RF drive system to deliver 2 MW, 1 ms pulses of 201 MHz frequency at 1 Hz repetition rate, the distribution network to deliver 1 MW to each cavity with correct RF phasing, diagnostics to determine the gradient and the muon transit phase, and development of the large-diameter magnets required for the linacs.

The muon collider requires intense, cooled muon bunches to reach the required luminosity. Due to the limited lifetime of the muon, the cooling process must take place very rapidly. Ionization cooling seems to be our only option, given the large emittances of the muon beam from pion decay. However, this ionization cooling method has been found quite difficult to implement in practice. We describe a scheme based on the use of liquid hydrogen absorbers followed by RF cavities (pillbox or open iris type), embedded in a transport lattice based on high field solenoids. These solenoidal fields are reversed periodically in order to suppress the growth of the canonical angular momentum. This channel has been simulated in detail with independent codes, featuring conventional tracking in e.m. fields and detailed simulation of multiple scattering and straggling in the the absorbers and windows. These calculations show that the 15 Tesla lattice cools in 6D phase space by a factor /spl ap/2 over a distance of 20 m.

The High Intensity Muon Beams (HIMB) project at the Paul Scherrer Institute (PSI) will deliver muon beams with unprecedented intensities of up to 1010muons/s for next-generation particle physics and material science experiments. This represents a hundredfold increase over the current state-of-the-art muon intensities, also provided by PSI. We performed beam dynamics optimisations and studies for the design of the HIMB beamlines MUH2 and MUH3 using Graphics Transport, Graphics Turtle, and G4beamline, the latter incorporating PSI’s own measured π+ cross-sections and variance reduction. We initially performed large-scale beamline optimisations using asynchronous Bayesian optimisation with DeepHyper. We are now developing an island-based evolutionary optimisation code glyfada based on the Paradiseo framework, where we implemented Message Passing Interface (MPI) islands with OpenMP parallelisation within each island. Furthermore, we implemented an island model that is also suitable for high-throughput computing (HTC) environments with asynchronous communication via a Redis database. The code interfaces with the codes COSY INFINITY and G4beamline. The code glyfada will provide heterogeneous island model optimisation using evolutionary optimisation and local search methods, as well as part-wise optimisation of the beamline with automatic advancement through stages. We will use the glyfada for a future large-scale optimisation of the HIMB beamlines.